• I have set up a circuit for remote temperature reading using the Xbee on the zigby mesh. The batteries went dead multiple times faster than I calculated it
Message 1 of 19 , Jul 19, 2013
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I have set up a circuit for remote temperature reading using the Xbee on the zigby mesh.  The batteries went dead multiple times faster than I calculated it would.  I expected it to be good for 1+year but it was more like weeks.

Facts:

XBee series 2

Setup as an endpoint

Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms

Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in other units

Uses MCP1700 voltage regulator

Using the eevblog micro current reader http://www.adafruit.com/products/882#Learn going into digit scope to see the voltage and duration

When XBee is in sleep mode is uses about 120 micro amps continuously

When XBee is awake it uses 1.2 ma for about 38ms.  Which is strange it is supposed to use 40ma.  I have taken current readings right off the batteries and right off the module and get the same current reading.

Either way the batteries to several units died in a matter of weeks not 1+ year as calculated.

120 micro amp continuos

+ 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average

221 micro amps average use

1,200,000 micro ah/221 = 5430 hours = 226 days

(note over a year by the measurement of 1.2ma instead of 40ma.)

But I only got weeks.

Anybody with a clue or experience in these areas?

Doug

• From the evidence you ve got, you ought to be getting 1 year but you re not. So the evidence must be in error. ... I presume their shelf life is years not
Message 2 of 19 , Jul 20, 2013
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From the evidence you've got, you ought to be getting 1 year but you're not.
So the evidence must be in error.

> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries
> in
> other units

I presume their shelf life is years not weeks. Hmmm - allegedly "Shelf Life:
10 years at 21°C".

> Uses MCP1700 voltage regulator

1.6 µA of quiescent current - fine.

> Uses TMP36 to read temperature

50 µA Quiescent Current. Shutdown Current 0.5 µA max. Do you shut it down?

> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the
> batteries
> and right off the module and get the same current reading.

Using a digital meter? Some digital meters have trouble with pulsing
current - maybe try an analogue meter. (I don't really believe that's the
problem but one is grasping at straws.)

> Anybody with a clue or experience in these areas?

Do the batteries _really_ give 1200mAh? Well, we all know that an advertised
"1200mAh" is probably half that (when taking large currents - not 200uA!).
But that would still be 16 weeks.

Let's say it's 1200mAh at 2mA - that would last 3.6 weeks. 2mA average is
40mA 5% of the time. You _ought_ to be able to measure that. If it were me,
I'd distrust my digital meter and use an analogue one. Or put a 4R7 resistor
in the battery line and watch the voltage across it with an oscilloscope.

Peter
• Peter thank you for your input and for taking the time. You must be right one of those evidences is incorrect. BTW I am using a very low current reader that
Message 3 of 19 , Jul 20, 2013
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Peter thank you for your input and for taking the time.

You must be right one of those evidences is incorrect.

BTW I am using a very low current reader that has low load on circuit (eevblog micro current reader http://www.adafruit.com/products/882#Learn).  It converts the current into a voltage which can be read which I read using a digital oscilloscope not a volt meter, the pulse goes by too fast to be read by a volt meter.  I can see the current drainage pulse very nicely on the scope.

Looking at more data it looks like they may have died in about 6-8 weeks, problem I was gone on a trip when they died.  If the pulse is 40ma rather than 1.2ma and if the batteries only lasted ¼ of advertised time then they would have died.  But all this is guessing.

I do not shut down the TMP36 therefore a large reason for the 110 µA steady drainage.  Maybe in the future version I will shut the tmp36 down.  The version of the tmp36 I have does not have a pin for that.

The specs on the battery shows at 25ma continuous discharge lasts for 1200ma dropping to .8 V.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Peter Balch
Sent: Saturday, July 20, 2013 6:06 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Xbee battery drainage

From the evidence you've got, you ought to be getting 1 year but you're not.
So the evidence must be in error.

> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries
> in
> other units

I presume their shelf life is years not weeks. Hmmm - allegedly "Shelf Life:
10 years at 21°C".

> Uses MCP1700 voltage regulator

1.6 µA of quiescent current - fine.

> Uses TMP36 to read temperature

50 µA Quiescent Current. Shutdown Current 0.5 µA max. Do you shut it down?

> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the
> batteries
> and right off the module and get the same current reading.

Using a digital meter? Some digital meters have trouble with pulsing
current - maybe try an analogue meter. (I don't really believe that's the
problem but one is grasping at straws.)

> Anybody with a clue or experience in these areas?

Do the batteries _really_ give 1200mAh? Well, we all know that an advertised
"1200mAh" is probably half that (when taking large currents - not 200uA!).
But that would still be 16 weeks.

Let's say it's 1200mAh at 2mA - that would last 3.6 weeks. 2mA average is
40mA 5% of the time. You _ought_ to be able to measure that. If it were me,
I'd distrust my digital meter and use an analogue one. Or put a 4R7 resistor
in the battery line and watch the voltage across it with an oscilloscope.

Peter

• Reading your data i have idea that might out whats wrong remove the xbee circuit and put a 40 ma load and 3 fresh new batteries and see how long it lasts (LDO
Message 4 of 19 , Jul 20, 2013
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remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>
• I like trying what you suggested, at least gives me something to do. I have set it up with a constant current of 35ma, according to energizer specs that is
Message 5 of 19 , Jul 20, 2013
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I like trying what you suggested, at least gives me something to do.

I have set it up with a constant current of 35ma, according to energizer specs that is about 30 hours.

I am assuming what you mean by LDO is low-dropout regulator.

Let you know what happens.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• Getting closer to what I did wrong. First in reading using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading. Sure
Message 6 of 19 , Jul 20, 2013
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Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• You might also want to monitor how often and how long it is awake. It could be that it is actually transmitting more often than every 15 minutes. Or it may be
Message 7 of 19 , Jul 21, 2013
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You might also want to monitor how often and how long it is awake. It could be that it is actually transmitting more often than every 15 minutes. Or it may be staying awake longer than what you think. Possibly due to interference causing retransmits.

- Jeff Sampson

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> Getting closer to what I did wrong.
>
>
>
> scale and therefore it was a wrong reading. Sure enough XBee is about 36ma
> for about 38ms which is what the documentation said it should be.
>
>
>
> Second issue is that AAA Alkaline batteries last about 30 hours at 35ma. If
> the current is less they average better but what the battery sees is a 36ma
> pulse therefore it must be calculated using the higher current.
>
>
>
> I am running one of the circuits with a resister to see how long it will
> last. That will tell me more precisely how long it should last.
>
>
>
> Good news I can "fix" it in software. I believe I can shorten the time the
> XBee is awake. Also instead of taking readings every 15 seconds do it 2
> minutes or more which will be ok for my application. I will play with the
> parameters until I reach the year goal.
>
>
>
> Doug
• Thanks all for your input. I ran the circuit with a resistor load to emulate the XBee with drain of 36ma which the specs says it does. The AAA batteries go
Message 8 of 19 , Jul 22, 2013
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Thanks all for your input.  I ran the circuit with a resistor load to emulate the XBee with drain of 36ma which the specs says it does.  The AAA batteries go 25+ hours at that drainage.  Which is what the specs say it should go for that current drain.

Confirmed the following:

·         Circuit is firing every 15 seconds

·         XBee on for about 38ms on average

·         There is a constant drain of about 120 µA

Therefore they should have lasted at least 200+ days.  But it was closer to 60 days.  So am going to put batteries back in them again and watch them closer maybe it was bad batch maybe something else.

Spent too much time on this at this point.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jws8675309
Sent: Sunday, July 21, 2013 2:30 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

You might also want to monitor how often and how long it is awake. It could be that it is actually transmitting more often than every 15 minutes. Or it may be staying awake longer than what you think. Possibly due to interference causing retransmits.

- Jeff Sampson

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> Getting closer to what I did wrong.
>
>
>
> scale and therefore it was a wrong reading. Sure enough XBee is about 36ma
> for about 38ms which is what the documentation said it should be.
>
>
>
> Second issue is that AAA Alkaline batteries last about 30 hours at 35ma. If
> the current is less they average better but what the battery sees is a 36ma
> pulse therefore it must be calculated using the higher current.
>
>
>
> I am running one of the circuits with a resister to see how long it will
> last. That will tell me more precisely how long it should last.
>
>
>
> Good news I can "fix" it in software. I believe I can shorten the time the
> XBee is awake. Also instead of taking readings every 15 seconds do it 2
> minutes or more which will be ok for my application. I will play with the
> parameters until I reach the year goal.
>
>
>
> Doug

• A little late to the game, but another tool you might consider using when you want to hunt down power draws is a DAQ (http://www.ni.com/data-acquisition/). You
Message 9 of 19 , Jul 22, 2013
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A little late to the game, but another tool you might consider using when you want to hunt down power draws is a DAQ (http://www.ni.com/data-acquisition/). You could use it to record the output from your uCurrent device so you can see those transients easier.

-Max

From: Doug Leppard <doug.leppard.list@...>
To: SeattleRobotics@yahoogroups.com
Sent: Monday, July 22, 2013 1:04 PM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Thanks all for your input.  I ran the circuit with a resistor load to emulate the XBee with drain of 36ma which the specs says it does.  The AAA batteries go 25+ hours at that drainage.  Which is what the specs say it should go for that current drain.

Confirmed the following:
·         Circuit is firing every 15 seconds
·         XBee on for about 38ms on average
·         There is a constant drain of about 120 µA

Therefore they should have lasted at least 200+ days.  But it was closer to 60 days.  So am going to put batteries back in them again and watch them closer maybe it was bad batch maybe something else.

Spent too much time on this at this point.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jws8675309
Sent: Sunday, July 21, 2013 2:30 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

You might also want to monitor how often and how long it is awake. It could be that it is actually transmitting more often than every 15 minutes. Or it may be staying awake longer than what you think. Possibly due to interference causing retransmits.

- Jeff Sampson

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> Getting closer to what I did wrong.
>
>
>
> scale and therefore it was a wrong reading. Sure enough XBee is about 36ma
> for about 38ms which is what the documentation said it should be.
>
>
>
> Second issue is that AAA Alkaline batteries last about 30 hours at 35ma. If
> the current is less they average better but what the battery sees is a 36ma
> pulse therefore it must be calculated using the higher current.
>
>
>
> I am running one of the circuits with a resister to see how long it will
> last. That will tell me more precisely how long it should last.
>
>
>
> Good news I can "fix" it in software. I believe I can shorten the time the
> XBee is awake. Also instead of taking readings every 15 seconds do it 2
> minutes or more which will be ok for my application. I will play with the
> parameters until I reach the year goal.
>
>
>
> Doug

• A couple quick thoughts Doug. Looks like the XBee wants to see 3.3v. The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum. When
Message 10 of 19 , Jul 22, 2013
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A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.

On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• Thanks tony, The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v. So I considered It dead once
Message 11 of 19 , Jul 23, 2013
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Thanks tony,

The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v.  So I considered It dead once it falls below the 3.3v.  I watch the current drain coming off the batteries with a scope I see some spiking.  I expected to see variations with transmit but all I saw was it turn on and off with pretty much a square wave for the right period of time.

It has been an interesting journey.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Tony Mactutis
Sent: Tuesday, July 23, 2013 1:51 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.

On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• Wondering what the result of low level current pulses might be on AAA cells I asked Google, nothing in the first three pages but I did come across this
Message 12 of 19 , Jul 23, 2013
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Wondering what the result of low level current pulses might be on AAA cells I asked Google, nothing in the first three pages but I did come across this
It might be .co.uk but the English in places leaves me mystified!
However it does talk about adding SuperCaps in parallel with the cells so the SCs handle the current pulses and the cells just trickle out current.
It may help, at least doing that you can eliminate the 36mA current pulses from the AAA cells and set their maximum current and thus check for bad cells or bad Data sheets.
DAvid

----- Original Message -----
Sent: Saturday, July 20, 2013 9:55 PM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can fix it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

•   Hi Doug,   It sounds like 3qty 1.5v alkaline cells are being used in series to present a nominal (under load) voltage of 4.5V to the input of the LDO.  At
Message 13 of 19 , Jul 24, 2013
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• 0 Attachment

Hi Doug,

It sounds like 3qty 1.5v alkaline cells are being used in series to present a nominal (under load) voltage of 4.5V to the input of the LDO.  At the same time the LDO is being asked to  produce a regulated 3.3V based on the part number selected.  The LDO requires a differential of input to output of an absolute minimum (from the data sheet) of 178mV.  This means the each battery can only discharge 341mV before the LDO will begin to become unstable and  start shunting current through the ground terminal as it struggles to maintain regulation during transients. [ 4.5 - (3.3 + 178) ] / 3 ~ 0.341   It is also important  to notice that although the 178mV differential is a gauranteed parameter, it is a MIMUMUM, which means that current rushes through the system return lines will change this potential as the battery discharges due to switching noise in the returns. (as the XBEE turns on / off the transmitter)  This will force the unit to shunt current in pulses as the differential input voltage is approached but still above the 178mV differential, draining the batteries significantly faster.

The description of the circuit above (put together from the various  e-mails in this chain) appear to show that the design is attempting to take advantage of only a fraction of the discharge range of the battery.   In  practice, in many comercial  applications, alkaline batteries are typically drawn down to 800mV and agressive applications will go all the way down to 600mV.  In the application above, the useful range of the battery is only being drawn down to 1.16V, wasting a significant chunk of stored energy.  Combine this with operating the LDO right down to the bottom of the differential range with current swings in the return line and even more energy is being thrown away.  These two steps when  combined are throwing away nearly 60% of the energy in the batteries.

Another issue is the choice to use a linear regulator.  The raw calculation (Vin - Vout) * current delivered = [ ( 4.5 - 3.3 ) * 36mA ] = 43mW are being disipated by the regulator while  the transmitter is active.  Consider that at that same  time 3.3V * 36mV = 118mW is being delivered to the load.  This shows that the choice of linear regulator is throwing away 36% of your battery life right off the top.  Said another way, although they are extremely simple to use and require almost no design expierence, if at all possible linear regulators should not be used in battery driven applications because they are horribly inefficent.  It is worth noting that the 36% mentioned here is best  case and is likely much worse if you have not provided a good amount of copper area to get the  heat flowing out of the die.  It is also  worth noting that the 36% loss mentioned here is compounded on top of the 60% loss mentioned above.

Just something to chew on, but those three pieces, when combined are throwing away most of the energy from the batteries by design.  Hope that  helps take you a bit further down the road in your investigation and suggests a few further aspects to  research....

-Kenneth

From: Doug Leppard <doug.leppard.list@...>
To: SeattleRobotics@yahoogroups.com
Sent: Tuesday, July 23, 2013 5:50 AM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Thanks tony,

The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v.  So I considered It dead once it falls below the 3.3v.  I watch the current drain coming off the batteries with a scope I see some spiking.  I expected to see variations with transmit but all I saw was it turn on and off with pretty much a square wave for the right period of time.

It has been an interesting journey.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Tony Mactutis
Sent: Tuesday, July 23, 2013 1:51 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.
On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In mailto:SeattleRobotics%40yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• Kenneth, Great response, as usual. Although not the original poster, you gave me great pause for thought. If it were you, would you instead go with a switching
Message 14 of 19 , Jul 24, 2013
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• 0 Attachment
Kenneth,

Great response, as usual. Although not the original poster, you gave me great pause for thought. If it were you, would you instead go with a switching regulator, or would you go for something else entirely?

Doug, one other thing you might consider: I know you're doing the design in house, and there's no reason you shouldn't. However, have you considered using the "off the shelf" low power "motes" out there? We used some of these in a wireless sensor nodes class that I took in college. http://bullseye.xbow.com:81/Products/Product_pdf_files/Wireless_pdf/MICAz_Datasheet.pdf

-Max

From: K Maxon <k_maxon23@...>
To: "SeattleRobotics@yahoogroups.com" <SeattleRobotics@yahoogroups.com>
Sent: Wednesday, July 24, 2013 4:57 PM
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Hi Doug,

It sounds like 3qty 1.5v alkaline cells are being used in series to present a nominal (under load) voltage of 4.5V to the input of the LDO.  At the same time the LDO is being asked to  produce a regulated 3.3V based on the part number selected.  The LDO requires a differential of input to output of an absolute minimum (from the data sheet) of 178mV.  This means the each battery can only discharge 341mV before the LDO will begin to become unstable and  start shunting current through the ground terminal as it struggles to maintain regulation during transients. [ 4.5 - (3.3 + 178) ] / 3 ~ 0.341   It is also important  to notice that although the 178mV differential is a gauranteed parameter, it is a MIMUMUM, which means that current rushes through the system return lines will change this potential as the battery discharges due to switching noise in the returns. (as the XBEE turns on / off the transmitter)  This will force the unit to shunt current in pulses as the differential input voltage is approached but still above the 178mV differential, draining the batteries significantly faster.

The description of the circuit above (put together from the various  e-mails in this chain) appear to show that the design is attempting to take advantage of only a fraction of the discharge range of the battery.   In  practice, in many comercial  applications, alkaline batteries are typically drawn down to 800mV and agressive applications will go all the way down to 600mV.  In the application above, the useful range of the battery is only being drawn down to 1.16V, wasting a significant chunk of stored energy.  Combine this with operating the LDO right down to the bottom of the differential range with current swings in the return line and even more energy is being thrown away.  These two steps when  combined are throwing away nearly 60% of the energy in the batteries.

Another issue is the choice to use a linear regulator.  The raw calculation (Vin - Vout) * current delivered = [ ( 4.5 - 3.3 ) * 36mA ] = 43mW are being disipated by the regulator while  the transmitter is active.  Consider that at that same  time 3.3V * 36mV = 118mW is being delivered to the load.  This shows that the choice of linear regulator is throwing away 36% of your battery life right off the top.  Said another way, although they are extremely simple to use and require almost no design expierence, if at all possible linear regulators should not be used in battery driven applications because they are horribly inefficent.  It is worth noting that the 36% mentioned here is best  case and is likely much worse if you have not provided a good amount of copper area to get the  heat flowing out of the die.  It is also  worth noting that the 36% loss mentioned here is compounded on top of the 60% loss mentioned above.

Just something to chew on, but those three pieces, when combined are throwing away most of the energy from the batteries by design.  Hope that  helps take you a bit further down the road in your investigation and suggests a few further aspects to  research....

-Kenneth

From: Doug Leppard <doug.leppard.list@...>
To: SeattleRobotics@yahoogroups.com
Sent: Tuesday, July 23, 2013 5:50 AM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Thanks tony,

The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v.  So I considered It dead once it falls below the 3.3v.  I watch the current drain coming off the batteries with a scope I see some spiking.  I expected to see variations with transmit but all I saw was it turn on and off with pretty much a square wave for the right period of time.

It has been an interesting journey.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Tony Mactutis
Sent: Tuesday, July 23, 2013 1:51 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.
On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In mailto:SeattleRobotics%40yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

•   Hi Max,   Yes, likely a sepic  configured regulator, with an anlog interrupted operation  controller so  that  it  is  only  operating
Message 15 of 19 , Jul 25, 2013
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• 0 Attachment

Hi Max,

Yes, likely a sepic  configured regulator, with an anlog interrupted operation  controller so  that  it  is  only  operating intermittently for  a fraction of the  needed time.  This would also allow  for different types / configurations of cells.  I did not make  the recomendation in the original post as high efficency implementations of this type are going to need to be tuned at the  hardware level to the  particular implemenation and are not a buy it and drop it  in sort of implementation.  One of the easiest thing that could be done in Doug's case without taking on the challenge of the afore mentioned implementation would be to simply change out the LDO for one  with a wider input  range and then add one additional cell, allowing each individual cell to be drawn down further.

There are a handful of other options to apply here, but I don't  have visibility on all of the design constraints so it likely isn't a good idea to try and second guess what Doug was trying to  do.

-Kenneth

From: Max Cato <maxsthekat@...>
To: "SeattleRobotics@yahoogroups.com" <SeattleRobotics@yahoogroups.com>
Sent: Wednesday, July 24, 2013 9:30 PM
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Kenneth,

Great response, as usual. Although not the original poster, you gave me great pause for thought. If it were you, would you instead go with a switching regulator, or would you go for something else entirely?

Doug, one other thing you might consider: I know you're doing the design in house, and there's no reason you shouldn't. However, have you considered using the "off the shelf" low power "motes" out there? We used some of these in a wireless sensor nodes class that I took in college. http://bullseye.xbow.com:81/Products/Product_pdf_files/Wireless_pdf/MICAz_Datasheet.pdf

-Max

From: K Maxon <k_maxon23@...>
To: "SeattleRobotics@yahoogroups.com" <SeattleRobotics@yahoogroups.com>
Sent: Wednesday, July 24, 2013 4:57 PM
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Hi Doug,

It sounds like 3qty 1.5v alkaline cells are being used in series to present a nominal (under load) voltage of 4.5V to the input of the LDO.  At the same time the LDO is being asked to  produce a regulated 3.3V based on the part number selected.  The LDO requires a differential of input to output of an absolute minimum (from the data sheet) of 178mV.  This means the each battery can only discharge 341mV before the LDO will begin to become unstable and  start shunting current through the ground terminal as it struggles to maintain regulation during transients. [ 4.5 - (3.3 + 178) ] / 3 ~ 0.341   It is also important  to notice that although the 178mV differential is a gauranteed parameter, it is a MIMUMUM, which means that current rushes through the system return lines will change this potential as the battery discharges due to switching noise in the returns. (as the XBEE turns on / off the transmitter)  This will force the unit to shunt current in pulses as the differential input voltage is approached but still above the 178mV differential, draining the batteries significantly faster.

The description of the circuit above (put together from the various  e-mails in this chain) appear to show that the design is attempting to take advantage of only a fraction of the discharge range of the battery.   In  practice, in many comercial  applications, alkaline batteries are typically drawn down to 800mV and agressive applications will go all the way down to 600mV.  In the application above, the useful range of the battery is only being drawn down to 1.16V, wasting a significant chunk of stored energy.  Combine this with operating the LDO right down to the bottom of the differential range with current swings in the return line and even more energy is being thrown away.  These two steps when  combined are throwing away nearly 60% of the energy in the batteries.

Another issue is the choice to use a linear regulator.  The raw calculation (Vin - Vout) * current delivered = [ ( 4.5 - 3.3 ) * 36mA ] = 43mW are being disipated by the regulator while  the transmitter is active.  Consider that at that same  time 3.3V * 36mV = 118mW is being delivered to the load.  This shows that the choice of linear regulator is throwing away 36% of your battery life right off the top.  Said another way, although they are extremely simple to use and require almost no design expierence, if at all possible linear regulators should not be used in battery driven applications because they are horribly inefficent.  It is worth noting that the 36% mentioned here is best  case and is likely much worse if you have not provided a good amount of copper area to get the  heat flowing out of the die.  It is also  worth noting that the 36% loss mentioned here is compounded on top of the 60% loss mentioned above.

Just something to chew on, but those three pieces, when combined are throwing away most of the energy from the batteries by design.  Hope that  helps take you a bit further down the road in your investigation and suggests a few further aspects to  research....

-Kenneth

From: Doug Leppard <doug.leppard.list@...>
To: SeattleRobotics@yahoogroups.com
Sent: Tuesday, July 23, 2013 5:50 AM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Thanks tony,

The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v.  So I considered It dead once it falls below the 3.3v.  I watch the current drain coming off the batteries with a scope I see some spiking.  I expected to see variations with transmit but all I saw was it turn on and off with pretty much a square wave for the right period of time.

It has been an interesting journey.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Tony Mactutis
Sent: Tuesday, July 23, 2013 1:51 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.
On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In mailto:SeattleRobotics%40yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• David, I do like the thought of using Supercaps. From the specs on the batteries they do better when in low current mode, even pulsing brings down their
Message 16 of 19 , Jul 29, 2013
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David,

I do like the thought of using Supercaps.  From the specs on the batteries they do better when in low current mode, even pulsing brings down their ability to deliver.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of David Buckley
Sent: Tuesday, July 23, 2013 3:57 PM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Wondering what the result of low level current pulses might be on AAA cells I asked Google, nothing in the first three pages but I did come across this

It might be .co.uk but the English in places leaves me mystified!

However it does talk about adding SuperCaps in parallel with the cells so the SCs handle the current pulses and the cells just trickle out current.

It may help, at least doing that you can eliminate the 36mA current pulses from the AAA cells and set their maximum current and thus check for bad cells or bad Data sheets.

DAvid

----- Original Message -----

From:

Sent: Saturday, July 20, 2013 9:55 PM

Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In SeattleRobotics@yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

• Max and Kenneth, Thank you so much for your input. I had to work on other projects and had ignored this list until now. On the motes idea. I am using the
Message 17 of 19 , Jul 29, 2013
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Max and Kenneth,

Thank you so much for your input.  I had to work on other projects and had ignored this list until now.

On the "motes" idea.  I am using the XBees because they are low power and cost effective.  I like the zigbee mesh network is working well for the most part for my project.

Kenneth your summary of what I said was right on.  Yes you are right I am not using a portion of the battery abilities by only allowing the voltage to go to 1.1 instead or .8 or even lower.

In future releases I might go with the four battery idea or change regulator.  I like the regulator I use because of its low power drain and cost.

If you have other ideas let me know.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of K Maxon
Sent: Thursday, July 25, 2013 9:42 PM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Hi Max,

Yes, likely a sepic  configured regulator, with an anlog interrupted operation  controller so  that  it  is  only  operating intermittently for  a fraction of the  needed time.  This would also allow  for different types / configurations of cells.  I did not make  the recomendation in the original post as high efficency implementations of this type are going to need to be tuned at the  hardware level to the  particular implemenation and are not a buy it and drop it  in sort of implementation.  One of the easiest thing that could be done in Doug's case without taking on the challenge of the afore mentioned implementation would be to simply change out the LDO for one  with a wider input  range and then add one additional cell, allowing each individual cell to be drawn down further.

There are a handful of other options to apply here, but I don't  have visibility on all of the design constraints so it likely isn't a good idea to try and second guess what Doug was trying to  do.

-Kenneth

From: Max Cato <maxsthekat@...>
To: "SeattleRobotics@yahoogroups.com" <SeattleRobotics@yahoogroups.com>
Sent: Wednesday, July 24, 2013 9:30 PM
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Kenneth,

Great response, as usual. Although not the original poster, you gave me great pause for thought. If it were you, would you instead go with a switching regulator, or would you go for something else entirely?

Doug, one other thing you might consider: I know you're doing the design in house, and there's no reason you shouldn't. However, have you considered using the "off the shelf" low power "motes" out there? We used some of these in a wireless sensor nodes class that I took in college. http://bullseye.xbow.com:81/Products/Product_pdf_files/Wireless_pdf/MICAz_Datasheet.pdf

-Max

From: K Maxon <k_maxon23@...>
To: "SeattleRobotics@yahoogroups.com" <SeattleRobotics@yahoogroups.com>
Sent: Wednesday, July 24, 2013 4:57 PM
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

Hi Doug,

It sounds like 3qty 1.5v alkaline cells are being used in series to present a nominal (under load) voltage of 4.5V to the input of the LDO.  At the same time the LDO is being asked to  produce a regulated 3.3V based on the part number selected.  The LDO requires a differential of input to output of an absolute minimum (from the data sheet) of 178mV.  This means the each battery can only discharge 341mV before the LDO will begin to become unstable and  start shunting current through the ground terminal as it struggles to maintain regulation during transients. [ 4.5 - (3.3 + 178) ] / 3 ~ 0.341   It is also important  to notice that although the 178mV differential is a gauranteed parameter, it is a MIMUMUM, which means that current rushes through the system return lines will change this potential as the battery discharges due to switching noise in the returns. (as the XBEE turns on / off the transmitter)  This will force the unit to shunt current in pulses as the differential input voltage is approached but still above the 178mV differential, draining the batteries significantly faster.

The description of the circuit above (put together from the various  e-mails in this chain) appear to show that the design is attempting to take advantage of only a fraction of the discharge range of the battery.   In  practice, in many comercial  applications, alkaline batteries are typically drawn down to 800mV and agressive applications will go all the way down to 600mV.  In the application above, the useful range of the battery is only being drawn down to 1.16V, wasting a significant chunk of stored energy.  Combine this with operating the LDO right down to the bottom of the differential range with current swings in the return line and even more energy is being thrown away.  These two steps when  combined are throwing away nearly 60% of the energy in the batteries.

Another issue is the choice to use a linear regulator.  The raw calculation (Vin - Vout) * current delivered = [ ( 4.5 - 3.3 ) * 36mA ] = 43mW are being disipated by the regulator while  the transmitter is active.  Consider that at that same  time 3.3V * 36mV = 118mW is being delivered to the load.  This shows that the choice of linear regulator is throwing away 36% of your battery life right off the top.  Said another way, although they are extremely simple to use and require almost no design expierence, if at all possible linear regulators should not be used in battery driven applications because they are horribly inefficent.  It is worth noting that the 36% mentioned here is best  case and is likely much worse if you have not provided a good amount of copper area to get the  heat flowing out of the die.  It is also  worth noting that the 36% loss mentioned here is compounded on top of the 60% loss mentioned above.

Just something to chew on, but those three pieces, when combined are throwing away most of the energy from the batteries by design.  Hope that  helps take you a bit further down the road in your investigation and suggests a few further aspects to  research....

-Kenneth

From: Doug Leppard <doug.leppard.list@...>
To: SeattleRobotics@yahoogroups.com
Sent: Tuesday, July 23, 2013 5:50 AM
Subject: RE: [SeattleRobotics] Re: Xbee battery drainage

Thanks tony,

The XBee works down to 2.1V but I am not sure if it will read the temperature IC correctly once it falls below 3.3v.  So I considered It dead once it falls below the 3.3v.  I watch the current drain coming off the batteries with a scope I see some spiking.  I expected to see variations with transmit but all I saw was it turn on and off with pretty much a square wave for the right period of time.

It has been an interesting journey.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of Tony Mactutis
Sent: Tuesday, July 23, 2013 1:51 AM
To: SeattleRobotics@yahoogroups.com
Subject: Re: [SeattleRobotics] Re: Xbee battery drainage

A couple quick thoughts Doug.  Looks like the XBee wants to see 3.3v.  The regulator will need the input voltage to be a bit higher, maybe 3.5v minimum.  When your batteries fall below that, the circuit will at some point stop working even though they are not dead by the manufacturer's definition.

Also, that 40 mA figure is probably an average.  The load from a digital circuit is not steady; it spikes as the transistors switch.  Your circuit will have decoupling capacitors to supply a transient current, but there may still be times (such as on startup) when the circuit demands a much higher current from the power supply.  Also, with a radio the current will be much higher when it is transmitting and much lower when it is receiving.

If you try to draw a large current from a partially depleted battery, the voltage will droop and the circuit may malfunction, even though it seems ok when you check it with your meter.

On 7/20/2013 1:55 PM, Doug Leppard wrote:

Getting closer to what I did wrong.

First in reading  using the micro current reader, I had it on the wrong scale and therefore it was a wrong reading.  Sure enough XBee is about 36ma for about 38ms which is what the documentation said it should be.

Second issue is that AAA Alkaline batteries last about 30 hours at 35ma.  If the current is less they average better but what the battery sees is a 36ma pulse therefore it must be calculated using the higher current.

I am running one of the circuits with a resister to see how long it will last.  That will tell me more precisely how long it should last.

Good news I can “fix” it in software.  I believe I can shorten the time the XBee is awake.  Also instead of taking readings every 15 seconds do it 2 minutes or more which will be ok for my application.  I will play with the parameters until I reach the year goal.

Doug

From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of jamericanfreddy
Sent: Saturday, July 20, 2013 12:56 PM
To: SeattleRobotics@yahoogroups.com
Subject: [SeattleRobotics] Re: Xbee battery drainage

remove the xbee circuit and put a 40 ma load and 3 fresh new batteries
and see how long it lasts (LDO and batteries)
it seems thats it the LDO is the problem,

SOMEHOW its a internal resistance of the LDO since XBEE is constant.

ANOTHER idea try a different type of battery like NI-CADS at the same current output.

--- In mailto:SeattleRobotics%40yahoogroups.com, "Doug Leppard" <doug.leppard.list@...> wrote:
>
> I have set up a circuit for remote temperature reading using the Xbee on the
> zigby mesh. The batteries went dead multiple times faster than I calculated
> it would. I expected it to be good for 1+year but it was more like weeks.
>
>
>
> Facts:
>
>
>
> XBee series 2
>
> Setup as an endpoint
>
> Sleeps for 15 seconds awakes and reads and transmits for 35-40 ms
>
> Uses 3 AAA batteries 1200 mah alkaline energizer E92, had other batteries in
> other units
>
> Uses MCP1700 voltage regulator
>
> Uses TMP36 to read temperature
>
>
>
> Using the eevblog micro current reader
> http://www.adafruit.com/products/882#Learn going into digit scope to see the
> voltage and duration
>
>
>
> When XBee is in sleep mode is uses about 120 micro amps continuously
>
>
>
> When XBee is awake it uses 1.2 ma for about 38ms. Which is strange it is
> supposed to use 40ma. I have taken current readings right off the batteries
> and right off the module and get the same current reading.
>
>
>
> Either way the batteries to several units died in a matter of weeks not 1+
> year as calculated.
>
>
>
> 120 micro amp continuos
>
> + 40ma @ 38ms/(15 sec * 1000ms) = 101 micro amps average
>
> 221 micro amps average use
>
>
>
> 1,200,000 micro ah/221 = 5430 hours = 226 days
>
> (note over a year by the measurement of 1.2ma instead of 40ma.)
>
>
>
> But I only got weeks.
>
>
>
> Anybody with a clue or experience in these areas?
>
>
>
> Doug
>

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