## bottom balancing WAS Re: CALB 100's first drive

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• A few words about balancing. And I am no expert... Consider, for simplicity, a pack of only two cells. If the two cells are at the same voltage at SOME point
Message 1 of 59 , Oct 31 12:19 PM
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A few words about balancing. And I am no expert...

Consider, for simplicity, a pack of only two cells. If the two cells are at the same voltage at SOME point in the charge/discharge cycle, we call the pack "balanced". A bottom balanced pack is at uniform voltage near the end of discharge. A top balanced pack is at uniform voltage near the top of charge. You can, of course, define balancing in the middle of the charge curve, but for LiFePO4 chemistry, the flatness of the charge curve makes this difficult to achieve in practice (the cells can be at very different SOC's with only a few millivolts difference in terminal voltage).

Now, given that the cells have differing individual capacities, it's obvious that you cannot, in general BOTH top- and bottom- balance a pack.

This has a corollary, and that is, if you choose to top-balance the pack, then during discharge, some cells will drop to the bottom of their discharge curve before others. Conversely, in a bottom-balanced pack, some cells will reach the top of their discharge curve before others.

Therefore, if you bottom balance, you need to be careful about not overcharging some cells. If you top balance, you need to be careful about not over-discharging some cells.

The flip side of this is that in a bottom-balanced pack, you can tell when the cells are at bottom of cycle by simply looking at the overall pack voltage. Conversely, in a top-balanced pack, you can tell when the cells are at top of cycle by looking at pack voltage. This is why Mike chose to bottom balance -- his cells are all discharged at the same time, and he knows when that is, by looking at pack voltage. The flip side of that is, he needs to be careful not to overcharge ANY cells. Since Mike is only taking the cells up to about 3.4V each, there is no risk that any of them will be overcharged.

I think the reason most in-car active balancing systems for EVs top-balance is that the current is *consistent* during charging, whereas it is *inconsistent* during discharging. So, the internal resistance of the cells makes it very hard to measure the resting terminal voltage during driving, whereas it's pretty easy with a constant current charge.

//Geo

--- In solectria_ev@yahoogroups.com, Frank John <biker_ev@...> wrote:
>
> I'll jump in with other consideration about the bottom-balancing question.Â  If all the cells are at equal SOC at the bottom and you accidentally take the pack to depletion all the cells will hit bottom at the same time.Â  This has been demonstrated on EVTV: the car just stops and the cells all recovered.Â  If you top balance and use the pack up, at least one cell will certainly hit bottom first; you'll most likely ruin the cell (or worse) because you're forcing 100, 150, 200A through it from the other cells.Â  By choosing a conservative charge voltage (ex. 3.5VPC for LiFePO4) you probably won't overcharge a single cell but even if you did, it's at charge current levels (low) and not driving current (high) and the risk of damage is greatly reduced.Â  Also, it's a way of using the pack without BMS although most folks who do this monitor their cells.
>
> Frank
>
>
> Â
> Frank John
> NEDRA NE Regional Director &Loring Timing Association Liaison
>
>
>
>
> >________________________________
> > From: Tom Hudson <tdhudson@...>
> >To: solectria_ev@yahoogroups.com
> >Sent: Monday, October 29, 2012 12:03 PM
> >Subject: Re: [solectria_ev] Re: CALB 100's first drive
> >
> >
> >Â
> >Actually, I revised my approach to take them down to 2.75V on the bottom balancing since
> >I'm seeing them wanting to spring back to 2.75V, which is what Mike Rydjord did (IIRC, he
> >ended up using 2.8V but using the 2.75V with the CCCV setting on the Powerlab 6, I'm
> >getting uniform results). Mike has had good results with this approach so I'm following suit.
> >
> >My understanding is that by starting out with all the cells at a uniform voltage near the
> >bottom end, then charging to ~80% (3.39V per module) they will tend to stay in balance and
> >you're not hammering them with 100% charges. Mike was also looking at not exceeding the
> >voltage limits on his DC/DC and Air conditioner controller so he wanted to keep that
> >top-end voltage down; I don't have that issue since my components are set up for the
> >higher voltage NiCD range of the NiCDs I had in there, but if only charging the cells to
> >80-85% routinely will extend their life, that's good enough for me.
> >
> >Maybe Mike can chime in with his input as well.
> >
> >-Tom
> >
> >On 10/28/2012 10:55 PM, Charles Bliss wrote:
> >>
> >> It is my understanding that taking them to 2.5 is into the damage zone.
> >> On my new pack, using a BMS, the batteries are all taken up to max 3.9,
> >> then balanced down to 3.75. From there, they settle to 3.52.
> >> On the very first charge, I had to bring up some low cells with a power
> >> supply but those cells are now balancing to within +/- .01 volts on
> >> regular charging.
> >>
> >> I am not clear on why you would bottom charge. Please explain.
> >> We never do it and the race bikes packs have never lost a cell. The
> >> only cells I have seen damaged are ones taken below 2.5.
> >>
> >> On 10/28/2012 7:31 PM, Tom Hudson wrote:
> >> >
> >> > A little status update on my CALB upgrade...
> >> >
> >> > I'm working on battery module 36 now (out of 56) -- I'm expecting to
> >> > have my Force back up
> >> > and running with the CALBs by Thursday of this week.
> >> >
> >> > I've been totally amazed over the fact that the regenerative discharge
> >> > isn't overcharging
> >> > the source batteries! Must be some inefficiency in the regenerative
> >> > discharge mechanism.
> >> > It turns out to be a great thing -- what I'm doing is individually
> >> > charging the modules to
> >> > 3.555 volts, then setting them aside. Each charge takes about 2.5
> >> > hours from the factory
> >> > charge level of around 50%.
> >> >
> >> > Right before I go to bed at night, I strap together 4 modules in
> >> > parallel and connect them
> >> > to a Powerlab 6 and start a 40A discharge into the source batteries
> >> > with a target voltage
> >> > of 2.5V -- this process bleeds off about 400Ah of energy (at 3V) which
> >> > at 40A should take
> >> > about 10 hours (in reality, since the batteries actually contain more
> >> > energy than they are
> >> > spec'd to, it takes about 10:30-10:50). In this way, I'm using my time
> >> > very efficiently,
> >> > with no idle time for the chargers with nothing going on. The
> >> > batteries are sitting at
> >> > about 2.7V when I get up in the morning after this discharge due to
> >> > the voltage recovery.
> >> >
> >> > My plan is to process all batteries using this individual
> >> > charge/parallel discharge
> >> > method, and when all are done, do another discharge cycle to 2.5V on
> >> > each battery module
> >> > individually, making sure the batteries are all bottom-balanced to the
> >> > same voltage before
> >> > assembling them to a pack in the car.
> >> >
> >> > So far I've been very impressed with the Powerlab 6's and the CALB
> >> > 100Ah modules, which
> >> > have been remarkably consistent.
> >> >
> >> > I really can't wait to get everything back in the car and take a test
> >> > drive!
> >> >
> >> > -Tom
> >> >
> >> > On 10/25/2012 3:36 PM, Wade Perry wrote:
> >> > > Hi Geo-
> >> > > I noticed! But didn't have time to look into what you said.
> >> > > I'm assuming you'd need a set of monitoring leads for each cell, but how
> >> > > does it take more power from one cell and less from another?
> >> > >
> >> > > On Thu, Oct 25, 2012 at 12:29 PM, geo_homsy2 <geo.homsy@...
> >> <mailto:geo.homsy%40gmail.com>
> >> > <mailto:geo.homsy%40gmail.com>> wrote:
> >> > >
> >> > >> **
> >> > >>
> >> > >>
> >> > >> Tom-
> >> > >>
> >> > >> two things. I've mentioned it before here, but maybe no one
> >> > noticed: The
> >> > >> Powerlab can perfectly well balance several cells during discharge. You
> >> > >> have to install the windows utility and alter your profile to
> >> > include the
> >> > >> "balance while discharging" check box.
> >> > >>
> >> > >> The powerlab will indeed stop regenerative discharging when it sees the
> >> > >> "source" battery (i.e. not the target battery) go above a certain
> >> > voltage.
> >> > >> This voltage is also configurable with the utility program. It may
> >> > also be
> >> > >> configurable from the front panel -- I don't remember.
> >> > >>
> >> > >> //Geo
> >> > >>
> >> > >>
> >> > >> --- In solectria_ev@yahoogroups.com <mailto:solectria_ev%40yahoogroups.com>
> >> > <mailto:solectria_ev%40yahoogroups.com>, Tom Hudson <tdhudson@> wrote:
> >> > >>> Thanks for the info, Wade.
> >> > >>>
> >> > >>> Well, I'm finally starting to prep my CALB 100Ah pack for my '97
> >> > Force.
> >> > >> Had the batteries
> >> > >>> for several weeks, but have been doing a lot of traveling and haven't
> >> > >> had a window
> >> > >>> sufficient to bottom-balance my entire pack at one go. Just got back
> >> > >> from (hopefully) my
> >> > >>> last trip and set up a couple of new group 24 SLA's wired in parallel
> >> > >> for a power supply
> >> > >>> for my two Powerlab 6's and am in the process of getting the CALBs all
> >> > >> balanced.
> >> > >>> Batteries 3 and 4 are on there now (got a ways to go).
> >> > >>>
> >> > >>> I was wondering what I was going to see as far as excess power going
> >> > >> back into the supply
> >> > >>> batteries when I do the discharge phase -- I mean, since I'm only
> >> > >> putting ~50Ah (@3V) , or
> >> > >>> 150Wh into each battery to initially top them off, but pulling out
> >> > more
> >> > >> Wh to bring them
> >> > >>> down to the ~2.5V and trying to stuff that back into the supply
> >> > >> batteries, I was worried
> >> > >>> that it may cause the Powerlabs to stop the discharge prematurely,
> >> > since
> >> > >> the supply
> >> > >>> batteries might get fully charged. Mike Rydjord indicated that he had
> >> > >> this issue, but it
> >> > >>> sounds like you didn't. Interesting. We'll see what happens here.
> >> > >>>
> >> > >>> I'm really excited to get this car back up and running again on the
> >> > >> CALBs.
> >> > >>> -Tom
> >> > >>>
> >> > >>>
> >> > >>> On 10/9/2012 10:38 PM, Wade Perry wrote:
> >> > >>>> Hi Charles-
> >> > >>>> I'm using a pretty cool tool, borrowed from my friend Robin. Like I
> >> > >> said
> >> > >>>> earlier in this thread:
> >> > >>>>
> >> > >>>> My fourth-last pair is being balanced "on the bench" as I type this.
> >> > >> By a
> >> > >>>> pair of Revolectrix Powerlab 6s. Using a 2S2P arrangement of 4 gel
> >> > >> cells
> >> > >>>> as a nominal 24v DC power source for the PL6s. One full cycle- charge
> >> > >> to
> >> > >>>> the top and discharge all the way to the bottom (regenerative
> >> > discharge
> >> > >>>> back into the gels). 2.0v cutoff. Cells spring back to around 2.92 or
> >> > >> so.
> >> > >>>> Noting the capacity of each cell. I may bring them all down a bit
> >> > >> further
> >> > >>>> to balance them evenly a bit lower down.
> >> > >>>>
> >> > >>>> The Powerlab 6
> >> > http://www.revolectrix.com/pl6_description_tab.htm(PL6) is
> >> > >>>> targeted to the remote-controlled plane/helicopter/boat industry (or
> >> > >> "RC").
> >> > >>>> Which is actually a big business (unlike the EV industry so far). So
> >> > >> this
> >> > >>>> gear has really matured because of its economy of scale. With the PL6
> >> > >> you
> >> > >>>> can use any DC power source between 10 (8?) and 32 Volts DC. So what
> >> > >> these
> >> > >>>> RC guys do is pack up all their gear on a Saturday morning, including
> >> > >> some
> >> > >>>> fully charged large capacity deep cycle batteries, and head to the RC
> >> > >>>> airstrip to fly their stuff. They use the PL6 or a device like it to
> >> > >> hook
> >> > >>>> up to their DC battery bank to draw power and recharge their tiny
> >> > Li-Po
> >> > >>>> packs they put into their helicopters. The PL6 is very programmable,
> >> > >> you
> >> > >>>> can hook it up to a windows computer for control and programming and
> >> > >>>> generating cool graphs too. You can do full discharges, full charges,
> >> > >> full
> >> > >>>> cycles, even multiple cycles, and graph the whole thing. You set what
> >> > >> the
> >> > >>>> "fully charged" voltage is at the top and what the cutoff voltage is
> >> > >> at the
> >> > >>>> bottom. Then you set it running and walk away. It takes perhaps 2 1/2
> >> > >>>> hours in my case to run one cycle. It's very precise and does
> >> > Constant
> >> > >>>> Current Constant Voltage charging, meaning it charges at full power
> >> > >>>> "Constant Current" (~40A is the max for the PL6) until it reaches the
> >> > >>>> charge voltage, in this case 3.65v, then it gradually decreases the
> >> > >> current
> >> > >>>> while maintaining the voltage precisely at 3.65volts. It does
> >> > this very
> >> > >>>> well, I've watched it more than a few times. When the current
> >> > decreases
> >> > >>>> down to say 1 amp (this part is also adjustable but I'm fuzzy on the
> >> > >>>> details) it cuts off and the charge is complete. I used 4 of the gel
> >> > >> cells
> >> > >>>> from my car's previous pack ("yes, this used to be a lead-acid
> >> > battery
> >> > >>>> powered car", he said modestly) as a power source: 2S2P = 2 Serial, 2
> >> > >>>> Parallel. So the 4 gels together form a 24 volt pack that I can
> >> > charge
> >> > >> 1/2
> >> > >>>> at a time with a standard 12 volt car battery charger when necessary.
> >> > >> Even
> >> > >>>> while the PL6 is doing its thing.
> >> > >>>> After charging, the PL6 sits for a minute, and begins the discharge.
> >> > >> It's
> >> > >>>> actually a REGENERATIVE discharge. Very cool because the energy
> >> > the PL6
> >> > >>>> takes from the CALBs it puts back into the "source" pack. (sounds
> >> > >> familiar
> >> > >>>> don't it- This is one of the cool reasons why I wanted to own a
> >> > >> Solectria
> >> > >>>> in the first place) The CALBs come at ~50% S.O.C. (state of charge,
> >> > >> trying
> >> > >>>> to maintain coolness here even though I don't really know what I'm
> >> > >> talking
> >> > >>>> about), get charged up to full by taking energy from the source pack,
> >> > >> then
> >> > >>>> discharged down to empty by putting energy back into the source
> >> > pack. I
> >> > >>>> thought for sure I'd have extra energy because the CALBs are
> >> > giving me
> >> > >>>> electricity manufactured in China, shipped across the ocean and
> >> > >> imported,
> >> > >>>> then the cells are leaving the process empty, having contributed all
> >> > >> their
> >> > >>>> power to the source pack. ("All" is of course relative, it can indeed
> >> > >> go
> >> > >>>> lower and it will go lower if asked to, but according to spec it's
> >> > >> close
> >> > >>>> enough to fully discharged when the PL6 is done with it.) But I don't
> >> > >> seem
> >> > >>>> to end up with extra energy, I guess there's enough losses in the
> >> > >>>> back-and-forth (the PL6 has a fan, after all) and in the resistance?
> >> > >> of the
> >> > >>>> Lead Acid batteries, that I do need to periodically charge the Pb
> >> > >> pack. I
> >> > >>>> have two 12v car battery chargers on a timer and I just let that run
> >> > >> for an
> >> > >>>> hour or so during the charging phase of the full cycle, to keep
> >> > the Pb
> >> > >>>> voltage up. You want the source pack to stay somewhere in the middle,
> >> > >> not
> >> > >>>> fully charged, because you want room for the regenerative
> >> > discharge to
> >> > >> get
> >> > >>>> stored. Probably not being charged up isn't great for the gels... But
> >> > >> at
> >> > >>>> least they're being useful!
> >> > >>>> The PL6s can be connected together and run as a set- I'm running two,
> >> > >> so I
> >> > >>>> can cycle two cells at a time. The one that finished the charge first
> >> > >>>> waits for the 2nd one before it begins the "cool down period" of one
> >> > >>>> minute, then they start down again. For 56 cells that means I have to
> >> > >> do
> >> > >>>> this 28 times. I only have one more pair left to do, and I've already
> >> > >>>> re-done my lowest pair...
> >> > >>>> I'd said I was using
> >> > >>>> 2.0v cutoff. Cells spring back to around 2.92 or so.
> >> > >>>> Which was true until yesterday? I dunno, it's a blur. Perhaps it
> >> > >>>> shouldn't be a blur when you're balancing your expensive batteries...
> >> > >>>> But I changed it recently because I wanted the bottom-balanced
> >> > resting
> >> > >>>> voltage to be lower than 2.92- I'd messed around with a resistor
> >> > >> trying to
> >> > >>>> bring it down that last bit and the resistor got HOT man hot. :) I'm
> >> > >> new
> >> > >>>> at this and learning tons.
> >> > >>>> So I changed the settings to a CCCV discharge also, with target
> >> > voltage
> >> > >>>> 2.5v.
> >> > >>>> So instead of just discharging at constant current of ~40A until the
> >> > >>>> voltage drops to 2.0v and then shutting off suddenly (and when the
> >> > >> load is
> >> > >>>> removed the voltage on the CALB springs back up quite quickly,
> >> > >> eventually
> >> > >>>> resting at ~2.92), for the last few batches I've had it discharge at
> >> > >>>> constant current until the voltage falls to 2.5v, then the discharge
> >> > >>>> current drops off gradually while holding the voltage down to 2.5v.
> >> > >>>> Eventually the discharge current required to hold the cell's
> >> > voltage at
> >> > >>>> 2.5v is very small (details), and the PL6 stops. The resulting spring
> >> > >> back
> >> > >>>> in voltage is also smaller, and the cells are coming back to rest
> >> > >> at... I
> >> > >>>> dunno that was last night and I haven't looked at them yet but I'm
> >> > >> hoping
> >> > >>>> somewhere around 2.60, where I'll bottom-balance the whole pack as
> >> > >>>> precisely as I can- holding a resistor on a cell for a second or so,
> >> > >> then
> >> > >>>> leaving it and measuring the next cell, etc.
> >> > >>>> So I'm testing capacity in the sense that the PL6s measure how many
> >> > >> Ahr was
> >> > >>>> put into the cell during the charge phase, and how many Ahr were
> >> > taken
> >> > >> out
> >> > >>>> of the cell during the discharge phase.
> >> > >>>> I think it's safe and I'm not stressed letting the PL6s run in my
> >> > >> basement
> >> > >>>> and going to bed.
> >> > >>>>
> >> > >>>>
> >> > >>>> On Tue, Oct 9, 2012 at 12:21 AM, Charles Bliss <cbliss@> wrote:
> >> > >>>>
> >> > >>>>> **
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> How are you testing the capacity without risking cell damage?
> >> > >>>>> I have yet to determine what is a conservative / safe range for
> >> > my 93
> >> > >>>>> Solectria Hatchback.
> >> > >>>>> I installed 46 Thundersky 100ah. I keep them charged and balanced.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> On 10/8/2012 10:26 PM, Wade Perry wrote:
> >> > >>>>>> Thanks Bouty, I certainly hope so.
> >> > >>>>>> My lowest cell so far is 61.743 Ahr. Highest is 64.208.
> >> > >>>>>> Or ~3% to ~7% above rated capacity.
> >> > >>>>>> So it appears for these smaller CALB cells the "overrating"
> >> > factor is
> >> > >>>>> also
> >> > >>>>>> smaller.
> >> > >>>>>>
> >> > >>>>>>
> >> > >>>>>
> >> > >>>> [Non-text portions of this message have been removed]
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>> ------------------------------------
> >> > >>>>
> >> > >>>> Yahoo! Groups Links
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>> --
> >> > >>> Thomas Hudson
> >> > >>> http://portev.org -- Electric Vehicles, Solar Power & More
> >> > >>> http://klanky.com -- Animation Projects
> >> > >>>
> >> > >>
> >> > >>
> >> > >
> >> > > [Non-text portions of this message have been removed]
> >> > >
> >> > >
> >> > >
> >> > > ------------------------------------
> >> > >
> >> > > Yahoo! Groups Links
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> >
> >> > --
> >> > Thomas Hudson
> >> > http://portev.org -- Electric Vehicles, Solar Power & More
> >> > http://klanky.com -- Animation Projects
> >> >
> >> >
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >>
> >
> >--
> >Thomas Hudson
> >http://portev.org -- Electric Vehicles, Solar Power & More
> >http://klanky.com -- Animation Projects
> >
> >[Non-text portions of this message have been removed]
> >
> >
> >
> >
> >
>
> [Non-text portions of this message have been removed]
>
• A few words about balancing. And I am no expert... Consider, for simplicity, a pack of only two cells. If the two cells are at the same voltage at SOME point
Message 59 of 59 , Oct 31 12:19 PM
• 0 Attachment
A few words about balancing. And I am no expert...

Consider, for simplicity, a pack of only two cells. If the two cells are at the same voltage at SOME point in the charge/discharge cycle, we call the pack "balanced". A bottom balanced pack is at uniform voltage near the end of discharge. A top balanced pack is at uniform voltage near the top of charge. You can, of course, define balancing in the middle of the charge curve, but for LiFePO4 chemistry, the flatness of the charge curve makes this difficult to achieve in practice (the cells can be at very different SOC's with only a few millivolts difference in terminal voltage).

Now, given that the cells have differing individual capacities, it's obvious that you cannot, in general BOTH top- and bottom- balance a pack.

This has a corollary, and that is, if you choose to top-balance the pack, then during discharge, some cells will drop to the bottom of their discharge curve before others. Conversely, in a bottom-balanced pack, some cells will reach the top of their discharge curve before others.

Therefore, if you bottom balance, you need to be careful about not overcharging some cells. If you top balance, you need to be careful about not over-discharging some cells.

The flip side of this is that in a bottom-balanced pack, you can tell when the cells are at bottom of cycle by simply looking at the overall pack voltage. Conversely, in a top-balanced pack, you can tell when the cells are at top of cycle by looking at pack voltage. This is why Mike chose to bottom balance -- his cells are all discharged at the same time, and he knows when that is, by looking at pack voltage. The flip side of that is, he needs to be careful not to overcharge ANY cells. Since Mike is only taking the cells up to about 3.4V each, there is no risk that any of them will be overcharged.

I think the reason most in-car active balancing systems for EVs top-balance is that the current is *consistent* during charging, whereas it is *inconsistent* during discharging. So, the internal resistance of the cells makes it very hard to measure the resting terminal voltage during driving, whereas it's pretty easy with a constant current charge.

//Geo

--- In solectria_ev@yahoogroups.com, Frank John <biker_ev@...> wrote:
>
> I'll jump in with other consideration about the bottom-balancing question.Â  If all the cells are at equal SOC at the bottom and you accidentally take the pack to depletion all the cells will hit bottom at the same time.Â  This has been demonstrated on EVTV: the car just stops and the cells all recovered.Â  If you top balance and use the pack up, at least one cell will certainly hit bottom first; you'll most likely ruin the cell (or worse) because you're forcing 100, 150, 200A through it from the other cells.Â  By choosing a conservative charge voltage (ex. 3.5VPC for LiFePO4) you probably won't overcharge a single cell but even if you did, it's at charge current levels (low) and not driving current (high) and the risk of damage is greatly reduced.Â  Also, it's a way of using the pack without BMS although most folks who do this monitor their cells.
>
> Frank
>
>
> Â
> Frank John
> NEDRA NE Regional Director &Loring Timing Association Liaison
>
>
>
>
> >________________________________
> > From: Tom Hudson <tdhudson@...>
> >To: solectria_ev@yahoogroups.com
> >Sent: Monday, October 29, 2012 12:03 PM
> >Subject: Re: [solectria_ev] Re: CALB 100's first drive
> >
> >
> >Â
> >Actually, I revised my approach to take them down to 2.75V on the bottom balancing since
> >I'm seeing them wanting to spring back to 2.75V, which is what Mike Rydjord did (IIRC, he
> >ended up using 2.8V but using the 2.75V with the CCCV setting on the Powerlab 6, I'm
> >getting uniform results). Mike has had good results with this approach so I'm following suit.
> >
> >My understanding is that by starting out with all the cells at a uniform voltage near the
> >bottom end, then charging to ~80% (3.39V per module) they will tend to stay in balance and
> >you're not hammering them with 100% charges. Mike was also looking at not exceeding the
> >voltage limits on his DC/DC and Air conditioner controller so he wanted to keep that
> >top-end voltage down; I don't have that issue since my components are set up for the
> >higher voltage NiCD range of the NiCDs I had in there, but if only charging the cells to
> >80-85% routinely will extend their life, that's good enough for me.
> >
> >Maybe Mike can chime in with his input as well.
> >
> >-Tom
> >
> >On 10/28/2012 10:55 PM, Charles Bliss wrote:
> >>
> >> It is my understanding that taking them to 2.5 is into the damage zone.
> >> On my new pack, using a BMS, the batteries are all taken up to max 3.9,
> >> then balanced down to 3.75. From there, they settle to 3.52.
> >> On the very first charge, I had to bring up some low cells with a power
> >> supply but those cells are now balancing to within +/- .01 volts on
> >> regular charging.
> >>
> >> I am not clear on why you would bottom charge. Please explain.
> >> We never do it and the race bikes packs have never lost a cell. The
> >> only cells I have seen damaged are ones taken below 2.5.
> >>
> >> On 10/28/2012 7:31 PM, Tom Hudson wrote:
> >> >
> >> > A little status update on my CALB upgrade...
> >> >
> >> > I'm working on battery module 36 now (out of 56) -- I'm expecting to
> >> > have my Force back up
> >> > and running with the CALBs by Thursday of this week.
> >> >
> >> > I've been totally amazed over the fact that the regenerative discharge
> >> > isn't overcharging
> >> > the source batteries! Must be some inefficiency in the regenerative
> >> > discharge mechanism.
> >> > It turns out to be a great thing -- what I'm doing is individually
> >> > charging the modules to
> >> > 3.555 volts, then setting them aside. Each charge takes about 2.5
> >> > hours from the factory
> >> > charge level of around 50%.
> >> >
> >> > Right before I go to bed at night, I strap together 4 modules in
> >> > parallel and connect them
> >> > to a Powerlab 6 and start a 40A discharge into the source batteries
> >> > with a target voltage
> >> > of 2.5V -- this process bleeds off about 400Ah of energy (at 3V) which
> >> > at 40A should take
> >> > about 10 hours (in reality, since the batteries actually contain more
> >> > energy than they are
> >> > spec'd to, it takes about 10:30-10:50). In this way, I'm using my time
> >> > very efficiently,
> >> > with no idle time for the chargers with nothing going on. The
> >> > batteries are sitting at
> >> > about 2.7V when I get up in the morning after this discharge due to
> >> > the voltage recovery.
> >> >
> >> > My plan is to process all batteries using this individual
> >> > charge/parallel discharge
> >> > method, and when all are done, do another discharge cycle to 2.5V on
> >> > each battery module
> >> > individually, making sure the batteries are all bottom-balanced to the
> >> > same voltage before
> >> > assembling them to a pack in the car.
> >> >
> >> > So far I've been very impressed with the Powerlab 6's and the CALB
> >> > 100Ah modules, which
> >> > have been remarkably consistent.
> >> >
> >> > I really can't wait to get everything back in the car and take a test
> >> > drive!
> >> >
> >> > -Tom
> >> >
> >> > On 10/25/2012 3:36 PM, Wade Perry wrote:
> >> > > Hi Geo-
> >> > > I noticed! But didn't have time to look into what you said.
> >> > > I'm assuming you'd need a set of monitoring leads for each cell, but how
> >> > > does it take more power from one cell and less from another?
> >> > >
> >> > > On Thu, Oct 25, 2012 at 12:29 PM, geo_homsy2 <geo.homsy@...
> >> <mailto:geo.homsy%40gmail.com>
> >> > <mailto:geo.homsy%40gmail.com>> wrote:
> >> > >
> >> > >> **
> >> > >>
> >> > >>
> >> > >> Tom-
> >> > >>
> >> > >> two things. I've mentioned it before here, but maybe no one
> >> > noticed: The
> >> > >> Powerlab can perfectly well balance several cells during discharge. You
> >> > >> have to install the windows utility and alter your profile to
> >> > include the
> >> > >> "balance while discharging" check box.
> >> > >>
> >> > >> The powerlab will indeed stop regenerative discharging when it sees the
> >> > >> "source" battery (i.e. not the target battery) go above a certain
> >> > voltage.
> >> > >> This voltage is also configurable with the utility program. It may
> >> > also be
> >> > >> configurable from the front panel -- I don't remember.
> >> > >>
> >> > >> //Geo
> >> > >>
> >> > >>
> >> > >> --- In solectria_ev@yahoogroups.com <mailto:solectria_ev%40yahoogroups.com>
> >> > <mailto:solectria_ev%40yahoogroups.com>, Tom Hudson <tdhudson@> wrote:
> >> > >>> Thanks for the info, Wade.
> >> > >>>
> >> > >>> Well, I'm finally starting to prep my CALB 100Ah pack for my '97
> >> > Force.
> >> > >> Had the batteries
> >> > >>> for several weeks, but have been doing a lot of traveling and haven't
> >> > >> had a window
> >> > >>> sufficient to bottom-balance my entire pack at one go. Just got back
> >> > >> from (hopefully) my
> >> > >>> last trip and set up a couple of new group 24 SLA's wired in parallel
> >> > >> for a power supply
> >> > >>> for my two Powerlab 6's and am in the process of getting the CALBs all
> >> > >> balanced.
> >> > >>> Batteries 3 and 4 are on there now (got a ways to go).
> >> > >>>
> >> > >>> I was wondering what I was going to see as far as excess power going
> >> > >> back into the supply
> >> > >>> batteries when I do the discharge phase -- I mean, since I'm only
> >> > >> putting ~50Ah (@3V) , or
> >> > >>> 150Wh into each battery to initially top them off, but pulling out
> >> > more
> >> > >> Wh to bring them
> >> > >>> down to the ~2.5V and trying to stuff that back into the supply
> >> > >> batteries, I was worried
> >> > >>> that it may cause the Powerlabs to stop the discharge prematurely,
> >> > since
> >> > >> the supply
> >> > >>> batteries might get fully charged. Mike Rydjord indicated that he had
> >> > >> this issue, but it
> >> > >>> sounds like you didn't. Interesting. We'll see what happens here.
> >> > >>>
> >> > >>> I'm really excited to get this car back up and running again on the
> >> > >> CALBs.
> >> > >>> -Tom
> >> > >>>
> >> > >>>
> >> > >>> On 10/9/2012 10:38 PM, Wade Perry wrote:
> >> > >>>> Hi Charles-
> >> > >>>> I'm using a pretty cool tool, borrowed from my friend Robin. Like I
> >> > >> said
> >> > >>>> earlier in this thread:
> >> > >>>>
> >> > >>>> My fourth-last pair is being balanced "on the bench" as I type this.
> >> > >> By a
> >> > >>>> pair of Revolectrix Powerlab 6s. Using a 2S2P arrangement of 4 gel
> >> > >> cells
> >> > >>>> as a nominal 24v DC power source for the PL6s. One full cycle- charge
> >> > >> to
> >> > >>>> the top and discharge all the way to the bottom (regenerative
> >> > discharge
> >> > >>>> back into the gels). 2.0v cutoff. Cells spring back to around 2.92 or
> >> > >> so.
> >> > >>>> Noting the capacity of each cell. I may bring them all down a bit
> >> > >> further
> >> > >>>> to balance them evenly a bit lower down.
> >> > >>>>
> >> > >>>> The Powerlab 6
> >> > http://www.revolectrix.com/pl6_description_tab.htm(PL6) is
> >> > >>>> targeted to the remote-controlled plane/helicopter/boat industry (or
> >> > >> "RC").
> >> > >>>> Which is actually a big business (unlike the EV industry so far). So
> >> > >> this
> >> > >>>> gear has really matured because of its economy of scale. With the PL6
> >> > >> you
> >> > >>>> can use any DC power source between 10 (8?) and 32 Volts DC. So what
> >> > >> these
> >> > >>>> RC guys do is pack up all their gear on a Saturday morning, including
> >> > >> some
> >> > >>>> fully charged large capacity deep cycle batteries, and head to the RC
> >> > >>>> airstrip to fly their stuff. They use the PL6 or a device like it to
> >> > >> hook
> >> > >>>> up to their DC battery bank to draw power and recharge their tiny
> >> > Li-Po
> >> > >>>> packs they put into their helicopters. The PL6 is very programmable,
> >> > >> you
> >> > >>>> can hook it up to a windows computer for control and programming and
> >> > >>>> generating cool graphs too. You can do full discharges, full charges,
> >> > >> full
> >> > >>>> cycles, even multiple cycles, and graph the whole thing. You set what
> >> > >> the
> >> > >>>> "fully charged" voltage is at the top and what the cutoff voltage is
> >> > >> at the
> >> > >>>> bottom. Then you set it running and walk away. It takes perhaps 2 1/2
> >> > >>>> hours in my case to run one cycle. It's very precise and does
> >> > Constant
> >> > >>>> Current Constant Voltage charging, meaning it charges at full power
> >> > >>>> "Constant Current" (~40A is the max for the PL6) until it reaches the
> >> > >>>> charge voltage, in this case 3.65v, then it gradually decreases the
> >> > >> current
> >> > >>>> while maintaining the voltage precisely at 3.65volts. It does
> >> > this very
> >> > >>>> well, I've watched it more than a few times. When the current
> >> > decreases
> >> > >>>> down to say 1 amp (this part is also adjustable but I'm fuzzy on the
> >> > >>>> details) it cuts off and the charge is complete. I used 4 of the gel
> >> > >> cells
> >> > >>>> from my car's previous pack ("yes, this used to be a lead-acid
> >> > battery
> >> > >>>> powered car", he said modestly) as a power source: 2S2P = 2 Serial, 2
> >> > >>>> Parallel. So the 4 gels together form a 24 volt pack that I can
> >> > charge
> >> > >> 1/2
> >> > >>>> at a time with a standard 12 volt car battery charger when necessary.
> >> > >> Even
> >> > >>>> while the PL6 is doing its thing.
> >> > >>>> After charging, the PL6 sits for a minute, and begins the discharge.
> >> > >> It's
> >> > >>>> actually a REGENERATIVE discharge. Very cool because the energy
> >> > the PL6
> >> > >>>> takes from the CALBs it puts back into the "source" pack. (sounds
> >> > >> familiar
> >> > >>>> don't it- This is one of the cool reasons why I wanted to own a
> >> > >> Solectria
> >> > >>>> in the first place) The CALBs come at ~50% S.O.C. (state of charge,
> >> > >> trying
> >> > >>>> to maintain coolness here even though I don't really know what I'm
> >> > >> talking
> >> > >>>> about), get charged up to full by taking energy from the source pack,
> >> > >> then
> >> > >>>> discharged down to empty by putting energy back into the source
> >> > pack. I
> >> > >>>> thought for sure I'd have extra energy because the CALBs are
> >> > giving me
> >> > >>>> electricity manufactured in China, shipped across the ocean and
> >> > >> imported,
> >> > >>>> then the cells are leaving the process empty, having contributed all
> >> > >> their
> >> > >>>> power to the source pack. ("All" is of course relative, it can indeed
> >> > >> go
> >> > >>>> lower and it will go lower if asked to, but according to spec it's
> >> > >> close
> >> > >>>> enough to fully discharged when the PL6 is done with it.) But I don't
> >> > >> seem
> >> > >>>> to end up with extra energy, I guess there's enough losses in the
> >> > >>>> back-and-forth (the PL6 has a fan, after all) and in the resistance?
> >> > >> of the
> >> > >>>> Lead Acid batteries, that I do need to periodically charge the Pb
> >> > >> pack. I
> >> > >>>> have two 12v car battery chargers on a timer and I just let that run
> >> > >> for an
> >> > >>>> hour or so during the charging phase of the full cycle, to keep
> >> > the Pb
> >> > >>>> voltage up. You want the source pack to stay somewhere in the middle,
> >> > >> not
> >> > >>>> fully charged, because you want room for the regenerative
> >> > discharge to
> >> > >> get
> >> > >>>> stored. Probably not being charged up isn't great for the gels... But
> >> > >> at
> >> > >>>> least they're being useful!
> >> > >>>> The PL6s can be connected together and run as a set- I'm running two,
> >> > >> so I
> >> > >>>> can cycle two cells at a time. The one that finished the charge first
> >> > >>>> waits for the 2nd one before it begins the "cool down period" of one
> >> > >>>> minute, then they start down again. For 56 cells that means I have to
> >> > >> do
> >> > >>>> this 28 times. I only have one more pair left to do, and I've already
> >> > >>>> re-done my lowest pair...
> >> > >>>> I'd said I was using
> >> > >>>> 2.0v cutoff. Cells spring back to around 2.92 or so.
> >> > >>>> Which was true until yesterday? I dunno, it's a blur. Perhaps it
> >> > >>>> shouldn't be a blur when you're balancing your expensive batteries...
> >> > >>>> But I changed it recently because I wanted the bottom-balanced
> >> > resting
> >> > >>>> voltage to be lower than 2.92- I'd messed around with a resistor
> >> > >> trying to
> >> > >>>> bring it down that last bit and the resistor got HOT man hot. :) I'm
> >> > >> new
> >> > >>>> at this and learning tons.
> >> > >>>> So I changed the settings to a CCCV discharge also, with target
> >> > voltage
> >> > >>>> 2.5v.
> >> > >>>> So instead of just discharging at constant current of ~40A until the
> >> > >>>> voltage drops to 2.0v and then shutting off suddenly (and when the
> >> > >> load is
> >> > >>>> removed the voltage on the CALB springs back up quite quickly,
> >> > >> eventually
> >> > >>>> resting at ~2.92), for the last few batches I've had it discharge at
> >> > >>>> constant current until the voltage falls to 2.5v, then the discharge
> >> > >>>> current drops off gradually while holding the voltage down to 2.5v.
> >> > >>>> Eventually the discharge current required to hold the cell's
> >> > voltage at
> >> > >>>> 2.5v is very small (details), and the PL6 stops. The resulting spring
> >> > >> back
> >> > >>>> in voltage is also smaller, and the cells are coming back to rest
> >> > >> at... I
> >> > >>>> dunno that was last night and I haven't looked at them yet but I'm
> >> > >> hoping
> >> > >>>> somewhere around 2.60, where I'll bottom-balance the whole pack as
> >> > >>>> precisely as I can- holding a resistor on a cell for a second or so,
> >> > >> then
> >> > >>>> leaving it and measuring the next cell, etc.
> >> > >>>> So I'm testing capacity in the sense that the PL6s measure how many
> >> > >> Ahr was
> >> > >>>> put into the cell during the charge phase, and how many Ahr were
> >> > taken
> >> > >> out
> >> > >>>> of the cell during the discharge phase.
> >> > >>>> I think it's safe and I'm not stressed letting the PL6s run in my
> >> > >> basement
> >> > >>>> and going to bed.
> >> > >>>>
> >> > >>>>
> >> > >>>> On Tue, Oct 9, 2012 at 12:21 AM, Charles Bliss <cbliss@> wrote:
> >> > >>>>
> >> > >>>>> **
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> How are you testing the capacity without risking cell damage?
> >> > >>>>> I have yet to determine what is a conservative / safe range for
> >> > my 93
> >> > >>>>> Solectria Hatchback.
> >> > >>>>> I installed 46 Thundersky 100ah. I keep them charged and balanced.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> On 10/8/2012 10:26 PM, Wade Perry wrote:
> >> > >>>>>> Thanks Bouty, I certainly hope so.
> >> > >>>>>> My lowest cell so far is 61.743 Ahr. Highest is 64.208.
> >> > >>>>>> Or ~3% to ~7% above rated capacity.
> >> > >>>>>> So it appears for these smaller CALB cells the "overrating"
> >> > factor is
> >> > >>>>> also
> >> > >>>>>> smaller.
> >> > >>>>>>
> >> > >>>>>>
> >> > >>>>>
> >> > >>>> [Non-text portions of this message have been removed]
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>> ------------------------------------
> >> > >>>>
> >> > >>>> Yahoo! Groups Links
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>> --
> >> > >>> Thomas Hudson
> >> > >>> http://portev.org -- Electric Vehicles, Solar Power & More
> >> > >>> http://klanky.com -- Animation Projects
> >> > >>>
> >> > >>
> >> > >>
> >> > >
> >> > > [Non-text portions of this message have been removed]
> >> > >
> >> > >
> >> > >
> >> > > ------------------------------------
> >> > >
> >> > > Yahoo! Groups Links
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> > >
> >> >
> >> > --
> >> > Thomas Hudson
> >> > http://portev.org -- Electric Vehicles, Solar Power & More
> >> > http://klanky.com -- Animation Projects
> >> >
> >> >
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >>
> >
> >--
> >Thomas Hudson
> >http://portev.org -- Electric Vehicles, Solar Power & More
> >http://klanky.com -- Animation Projects
> >
> >[Non-text portions of this message have been removed]
> >
> >
> >
> >
> >
>
> [Non-text portions of this message have been removed]
>
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