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Re: question

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  • Kerim F
    Hi Larry, Thank you for replying. It looks a compact good tester and also economical but... I am afraid you missed my last paragraph ;) Thank you anyway, some
    Message 1 of 64 , Jul 2, 2012
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      Hi Larry,

      Thank you for replying.
      It looks a compact good tester and also economical but...
      I am afraid you missed my last paragraph ;)

      Thank you anyway, some others may be interested to get it.

      Kerim

      --- In Electronics_101@yahoogroups.com, "Larry Beaty" <lbeaty@...> wrote:
      >
      > Kerim, I used this battery tester to test wet cells with:
      >
      >
      >
      >
      > <http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-906
      > 36.html>
      > http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-9063
      > 6.html
      >
      > Larry
      >
      > From: Electronics_101@yahoogroups.com
      > [mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
      > Sent: Monday, July 02, 2012 4:08 AM
      > To: Electronics_101@yahoogroups.com
      > Subject: [Electronics_101] Re: question
      >
      > Hi Rick,
      >
      > I guess soon I will need to work on it since I sell lately many DC to AC
      > inverter/charger sets for house usage. I had to include in their design all
      > possible protections and regulations since only foreign products don't have
      > to be guaranteed while mine are supposed being 100% reliable for life and
      > stand all conditions :)
      >
      > The main problem my assistants have is convincing a consumer that his
      > battery is weak. Even a car battery having relatively high internal
      > impedance gives 12V but cannot be charged properly even at C/10 current or
      > provide its expected load power. The consumer sees only the good looking of
      > his battery and is proud that he has a voltmeter to prove it is working. I
      > hope with this simple measuring tool, the few LEDs will be enough for
      > showing the internal difference between two batteries; fresh and old for
      > example.
      >
      > If I will finish it, it will be my pleasure to present it here (hardware and
      > firmware). I am afraid that I usually include on my boards my favorite small
      > MCU from ATMEL, AT89C2051. Obviously LM324 will take care of the analogue
      > part. The trick is doing the measurement at a 'constant' current (likely not
      > low) in a voltage range say 8 to 13V (battery in standby) and for a period
      > of time which is long enough to stabilize the drop and short enough to
      > minimize the load dissipation. But perhaps it is better replacing the load
      > current regulation by measuring both maximum and minimum voltages of the
      > battery and by calculating (software) its internal resistance based on the
      > known load resistance.
      >
      > I envy people who have time to design what they like and are also allowed
      > getting any component they heard of and know it suits their application. On
      > the other hand, sanctions push one's mind to work much harder hence to have
      > more fun ;)
      >
      > Best wishes,
      >
      > Kerim
      >
      > --- In Electronics_101@yahoogroups.com
      > <mailto:Electronics_101%40yahoogroups.com> , "Rick Sparber" <rgsparber@>
      > wrote:
      > >
      > > Kerim,
      > >
      > > I think the circuit could be modified to do what you want. Rather than use
      > > comparator "C", you would need an amplifier with sample and hold
      > > capabilities. The monitor should work with any reasonable load on the
      > > battery so could run continuously. I played with this idea back in 1973
      > when
      > > I developed an in-circuit ohm meter.
      > >
      > > Rick
      > >
      > > -----Original Message-----
      > > From: Electronics_101@yahoogroups.com
      > <mailto:Electronics_101%40yahoogroups.com>
      > > [mailto:Electronics_101@yahoogroups.com
      > <mailto:Electronics_101%40yahoogroups.com> ] On Behalf Of Kerim F
      > > Sent: Saturday, June 30, 2012 1:31 AM
      > > To: Electronics_101@yahoogroups.com
      > <mailto:Electronics_101%40yahoogroups.com>
      > > Subject: [Electronics_101] Re: question
      > >
      > > --- In Electronics_101@yahoogroups.com
      > <mailto:Electronics_101%40yahoogroups.com> , "Rick Sparber" <rgsparber@>
      > > wrote:
      > > >
      > > > I have posted two articles in the last few weeks that deal with analog
      > > > circuits. The response has been underwhelming. Not a single comment.
      > > > Are there any analog circuit designers left on this BBS?
      > > >
      > > >
      > > >
      > > > Rick
      > > >
      > > > rgsparber@
      > > >
      > > > rick.sparber.org
      > > >
      > >
      > > Your work reminds me an old small project I was working on but I didn't
      > > finish it. I liked to measure approximately the DC internal resistance of
      > a
      > > car acid battery by measuring the small voltage drop on its terminals for
      > a
      > > known load (DC current).
      > > Let us assume the battery voltage is 12V and its internal DC resistance is
      > > about 5mR. If the load current (actually a current pulse with a proper
      > short
      > > period) is 10A (via MOSFET and current regulator) the voltage drop would
      > be
      > > 50mV. In this case, the ratio of the high side voltage is 11.95/12=0.996.
      > > This ratio depends on the battery size and its age, for a few.
      > > I didn't have time yet analyzing attentively your interesting circuit so I
      > > am not sure how much it may be related to the high side voltage
      > measurement
      > > that has a very small difference to be measured even approximately. After
      > > all, the project is just to build a tool for comparing the strength of
      > some
      > > big batteries under test. I am afraid it will need a few LEDs (instead of
      > a
      > > display for simplicity).
      > >
      > > Kerim
      > >
      >
    • Rick Sparber
      Kerim, It is funny what consumers latch onto for importance. You work hard to get the circuit board down by 0.1 and then have to bolt it to a block of steel
      Message 64 of 64 , Jul 8, 2012
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        Kerim,

        It is funny what consumers latch onto for importance. You work hard to get
        the circuit board down by 0.1" and then have to bolt it to a block of steel
        to get any credibility. Going with a simple resistive load current should
        work fine since delta Vbattery is small.

        I look forward to hearing more.

        Rick

        -----Original Message-----
        From: Electronics_101@yahoogroups.com
        [mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
        Sent: Thursday, July 05, 2012 7:10 PM
        To: Electronics_101@yahoogroups.com
        Subject: [Electronics_101] Re: question

        Rick,

        In my free time (since I work on other projects), I started designing its
        analogue part on LTspice. I will include the digital part using voltage
        sources having each a proper timing list. Since AT89C2051 is an old and
        simple MCU (20-pin), it doesn't have an ADC feature. Instead, it has an
        internal comparator and its two inputs are P1.0 and P1.1 (its output is
        P3.6, an internal flag). So when I need measuring a voltage, I measure for
        example the charging time of a capacitor till its voltage reaches the
        measured voltage. Obviously an external opamp or comparator can also be
        used.

        You are right about the display; a number looks more professional. After
        all, implementing either one is done mainly by software. The irony is that I
        noticed most consumers are impressed more by the size (if not the weight
        too) if it is larger ;)

        To reduce the circuit, I removed the load current regulation. So the current
        will be I_load = V_batt / R_load when R_load is on.

        Measuring V_open (I_load=0) will give
        R_batt = (V_open - V_batt) / I_load
        R_batt = R_load (V_open - V_batt) / V_batt

        The circuit on LTspice is almost finished. When it will be ready, I will
        upload all its necessary files in case some members have LTspice and like to
        play with it :) The software will be next. For instance, since I cannot get
        windows C51 compiler, assembler, debugger and/or emulator, I used (for 30
        years) writing my MCU (or CPU in the past) programs using a text editor and
        DOS assembler (via command line) ;)

        Kerim
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