Bottom balancing batteries

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Bottom balancing batteries

Electric Vehicle Discussion List mailing list
Hello all: I am a newby so, bear with me . I have converted my 1965 Ford
Falcon  to an all electric vehicle with an HPEVS AC51  motor with a Curtis
1239e controller,
an Orion2 BMS . I've fitted 48- 271 Ah  3.2 volt batteries and am
experiencing
battery balance problems . I am in the process of bottom balancing the
batteries but, I'm not sure how critical the bottom voltage should be after
discharging. Do they all need to be exactly 2.5 volts ?The battery voltage
keeps jumping up to about 2.51 to 2.54 volts after numerous  discharging.
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Re: Bottom balancing batteries

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Hi John,

     Your very nice Orion BMS will balance your batteries in standard
manner ("top" balancing, so to speak.)  Orion makes an outstanding (and
a bit pricey) battery management system, with all the bells and whistles
if you wish to use those features.

     Attempting to perform some sort of manual "bottom" balancing will
simply confuse the Orion. It will see the "bottom" balanced pack as
completely unbalanced, and wok diligently to correct the situation. This
might take the system awhile to correct, perhaps several days. It will,
eventually, bring the pack into perfect balance. This is what the
battery companies all recommend, as do the OEMs.

  >>>> "Bottom" "balancing" explained  <<<<

     The folks that advocate bottom balancing  are trying to get by
without a BMS at all. It really only "works" for a short while, perhaps
only a few cycles. The batteries get out of "bottom" balance inevitably.

     Think of a herd of cats. They might go in the same direction and
same speed for a short time. They will not march in sync because it is
simply not in their nature.Expecting them to stay in sync is foolish.

     If you drive your car regularly, then you will ruin batteries with
some regularity, and are taking a very big chance on a battery pack
fire. I personally know several "anti-BMS" folks that drive their EVs
regularly, and ruin several batteries every year. They attribute their
ruined batteries to flawed manufacturing. A few anti-BMS folks have had
spectacular fires, often more than one spectacular fire. Some have lost
a garage.

     If you ignore self-discharge (or actively dis-believe in self
discharge) then bottom balancing sounds enticing. Folks don't understand
why you really need a BMS. You _want_ to believe that you can get by
without a BMS, so this is what you convince yourself. It is very much
like the flat earth folks, or the climate change deniers, or cigarettes
are not addictive, or any other conspiracy theory that you might name
that is contrary to the mountain of scientific research that shows
otherwise.

     Trust the science. Trust that the OEMs would not spend an extra
penny on a BMS if they did not have to. Believe that you will have a
fire that could very well burn down your house if you forgo a BMS.

     Bill D.

On 3/13/2021 5:30 PM, John Titman via EV wrote:

> Hello all: I am a newby so, bear with me . I have converted my 1965 Ford
> Falcon  to an all electric vehicle with an HPEVS AC51  motor with a Curtis
> 1239e controller,
> an Orion2 BMS . I've fitted 48- 271 Ah  3.2 volt batteries and am
> experiencing
> battery balance problems . I am in the process of bottom balancing the
> batteries but, I'm not sure how critical the bottom voltage should be after
> discharging. Do they all need to be exactly 2.5 volts ?The battery voltage
> keeps jumping up to about 2.51 to 2.54 volts after numerous  discharging.
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Re: Bottom balancing batteries

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On 3/13/21 4:00 AM, Bill Dube via EV wrote:

>      Trust the science. Trust that the OEMs would not spend an extra
> penny on a BMS if they did not have to. Believe that you will have a
> fire that could very well burn down your house if you forgo a BMS.

A very good support; I had intended to respond but it was too late when
I noticed.  You did a FAR better than I would have.  We've had quite a
few here advocating bottom balancing.  Most seem to have silently
disappeared without reporting what ever problems they may have encountered.

I was going to suggest that putting all cells in parallel before
discharging down to minimum voltage was a very easy and effective way to
precisely bottom balance.

I have not had patience to wait out most of Jack Rickard's videos but do
remember a very early one touting bottom balancing.  His primary point
was that bottom balanced voltage would drop off so perspicaciously as
the battery neared full discharge that there was little risk of ignoring
a few low cells as might be the case with top balancing.

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Re: Bottom balancing batteries

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I like Bill's "trust the science" analogies, too :) And I know someone
who thinks the moon landing was simulated (with amazing graphics
software we had back in the '60s) and that he can prove that the earth
is not round.

As for bottom vs top, it just seems that the logistics for bottom
balancing would be very difficult. It's easy to carefully charge to max
voltage, but it's very hard to discharge to the bottom voltage. You
would have to start with a nearly empty pack and then discharge it
before recharging, I think.

Peri

<< Annoyed by leaf blowers ? https://quietcleanseattle.org/ >>

------ Original Message ------
From: "Willie via EV" <[hidden email]>
To: [hidden email]
Cc: "Willie" <[hidden email]>
Sent: 13-Mar-21 8:18:13 AM
Subject: Re: [EVDL] Bottom balancing batteries

>
>
>On 3/13/21 4:00 AM, Bill Dube via EV wrote:
>
>>      Trust the science. Trust that the OEMs would not spend an extra penny on a BMS if they did not have to. Believe that you will have a fire that could very well burn down your house if you forgo a BMS.
>
>A very good support; I had intended to respond but it was too late when I noticed.  You did a FAR better than I would have.  We've had quite a few here advocating bottom balancing.  Most seem to have silently disappeared without reporting what ever problems they may have encountered.
>
>I was going to suggest that putting all cells in parallel before discharging down to minimum voltage was a very easy and effective way to precisely bottom balance.
>
>I have not had patience to wait out most of Jack Rickard's videos but do remember a very early one touting bottom balancing.  His primary point was that bottom balanced voltage would drop off so perspicaciously as the battery neared full discharge that there was little risk of ignoring a few low cells as might be the case with top balancing.
>
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Re: Bottom balancing batteries

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In reply to this post by Electric Vehicle Discussion List mailing list


On 3/13/21 11:18 AM, Willie via EV wrote:
> Jack Rickard's... primary point
> was that bottom balanced voltage would drop off so perspicaciously as
> the battery neared full discharge that there was little risk of ignoring
> a few low cells as might be the case with top balancing.


I can see the point that IF you are going to drive your lithium battery
pack without a BMS, it's better if all cells get down to zero capacity
as close to the same time as possible so that no cell will hit full zero
and get reversed by current flow (which is VERY likely to cause a fire...)


But as others have said, I believe you should have at a minimum a per
cell low voltage alarm when driving, and an automatic per-cell high
voltage charger cutoff when charging.  [Perhaps you don't need a
balancing BMS....but the alarm & cutoff functions are critical....]

Jay
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Re: Bottom balancing batteries

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In reply to this post by Electric Vehicle Discussion List mailing list
John, first of all, a '65 Falcon conversion is a SUPER COOL idea.  I'm
jealous. Well done!

Second, I'm far from a lithium battery expert, but I'm having trouble seeing
why you're concerned with "bottom balancing."  I don't see why it would be
necessary or even desirable.

As I understand it, the BMS's job is to

(1) Limit and eventually shut down the discharge when any cell is flat

(2) Limit the charge rate when any cell is full

(3) Balance - that is bring up the other cells to full charge without
overcharging the already-full cells

This is how you get the optimum capacity from your battery without damaging
it.

It seems to me that if the BMS can't bring all the cells up to full charge
even with a very long balancing session, then one short term solution is to
individually charge each cell until it's full.  

Then see if the BMS can keep the cells properly balanced over a period of
cycling.  If it can't, it seems likely that the cells are inconsistent in
usable capacity.  

This can be from several causes including

(1) Cells aging at different rates

(2) Some cells newer than others (replaced for premature failure?)

(3) Careless manufacturing quality control which causes inconsistent
capacity and/or varying self-discharge levels

(4) Inconsistent temperature across cells in the battery, which can easlly
happen in coversions where the cells are distributed around the car with
multiple boxes and simple/passive air cooling

(5) Tapping the battery for various loads at different voltages

As I say I'm not an expert and those here who are can probably add to this
list.

I hope that I haven't given you any incorrect information, and welcome
corrections if I have.

David Roden, EVDL moderator & general lackey

To reach me, don't reply to this message; I won't get it.  Use my
offlist address here : http://evdl.org/help/index.html#supt

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     a smaller boy. I expostulated, but he replied: "The bigs hit
     me, so I hit the babies; that's fair." In these words he
     epitomized the history of the human race.

            -- Bertrand Russell, "Education and the Social Order"
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

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Re: Bottom balancing batteries

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On 3/14/2021 5:18 AM, Willie via EV wrote:
>
>   His primary point was that bottom balanced voltage would drop off so
> perspicaciously as the battery neared full discharge that there was
> little risk of ignoring a few low cells as might be the case with top
> balancing.

By "solving" the issue of torturing cells during full discharge, you
ignore another, far more serious problem of torturing cells during charge.

     Cells in a pack, _never_ have equal capacity. What happens to the
one or two, grossly overly full, over-voltage cells, when you recharge
this "bottom balanced" pack?  Typically, charging occurs on an
unattended car, perhaps while you are asleep in your bedroom over the
garage.

     This also assumes that the "bottom balanced" cells will stay in
this "bottom balanced" condition, which has been shown countless times
to be incorrect. Batteries are never perfect in any respect.

     A quote from The Breakfast Club: "Screws fall out. The world is an
imperfect place."

Bill D.


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Re: Bottom balancing batteries

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In reply to this post by Electric Vehicle Discussion List mailing list
I recommend the iCharger 306B for charging individual cells, it can do
up to 30 amps.

Jay

On 3/13/21 3:29 PM, EVDL Administrator via EV wrote:

> John, first of all, a '65 Falcon conversion is a SUPER COOL idea.  I'm
> jealous. Well done!
>
> Second, I'm far from a lithium battery expert, but I'm having trouble seeing
> why you're concerned with "bottom balancing."  I don't see why it would be
> necessary or even desirable.
>
> As I understand it, the BMS's job is to
>
> (1) Limit and eventually shut down the discharge when any cell is flat
>
> (2) Limit the charge rate when any cell is full
>
> (3) Balance - that is bring up the other cells to full charge without
> overcharging the already-full cells
>
> This is how you get the optimum capacity from your battery without damaging
> it.
>
> It seems to me that if the BMS can't bring all the cells up to full charge
> even with a very long balancing session, then one short term solution is to
> individually charge each cell until it's full.
>
> Then see if the BMS can keep the cells properly balanced over a period of
> cycling.  If it can't, it seems likely that the cells are inconsistent in
> usable capacity.
>
> This can be from several causes including
>
> (1) Cells aging at different rates
>
> (2) Some cells newer than others (replaced for premature failure?)
>
> (3) Careless manufacturing quality control which causes inconsistent
> capacity and/or varying self-discharge levels
>
> (4) Inconsistent temperature across cells in the battery, which can easlly
> happen in coversions where the cells are distributed around the car with
> multiple boxes and simple/passive air cooling
>
> (5) Tapping the battery for various loads at different voltages
>
> As I say I'm not an expert and those here who are can probably add to this
> list.
>
> I hope that I haven't given you any incorrect information, and welcome
> corrections if I have.
>
> David Roden, EVDL moderator & general lackey
>
> To reach me, don't reply to this message; I won't get it.  Use my
> offlist address here : http://evdl.org/help/index.html#supt
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>       I found one day in school a boy of medium size ill-treating
>       a smaller boy. I expostulated, but he replied: "The bigs hit
>       me, so I hit the babies; that's fair." In these words he
>       epitomized the history of the human race.
>
>              -- Bertrand Russell, "Education and the Social Order"
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
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Re: Bottom balancing batteries

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In reply to this post by Electric Vehicle Discussion List mailing list


On 3/13/21 3:47 PM, Bill Dube via EV wrote:
> On 3/14/2021 5:18 AM, Willie via EV wrote:
>>
>>   His primary point was that bottom balanced voltage would drop off so
>> perspicaciously as the battery neared full discharge that there was
>> little risk of ignoring a few low cells as might be the case with top
>> balancing.
>
> By "solving" the issue of torturing cells during full discharge, you
> ignore another, far more serious problem of torturing cells during charge.

I was NOT advocating bottom balancing.  Only recounting reasoning that
has been used by others.

I don't recall what Jack recommended about stopping the charge.  Perhaps
depending on one or more cells reaching the upper single cell limit.

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Re: Bottom balancing batteries

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If you regularly run your cells to 2.5 volts, you'll be replacing them soon.

3.00 volts with no load is considered dead. 2.5 volts is deader than dead.

Al

On 3/12/2021 11:30 PM, John Titman via EV wrote:

> Hello all: I am a newby so, bear with me . I have converted my 1965 Ford
> Falcon  to an all electric vehicle with an HPEVS AC51  motor with a Curtis
> 1239e controller,
> an Orion2 BMS . I've fitted 48- 271 Ah  3.2 volt batteries and am
> experiencing
> battery balance problems . I am in the process of bottom balancing the
> batteries but, I'm not sure how critical the bottom voltage should be after
> discharging. Do they all need to be exactly 2.5 volts ?The battery voltage
> keeps jumping up to about 2.51 to 2.54 volts after numerous  discharging.
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Re: Bottom balancing batteries

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On 13 Mar 2021 at 19:17, Alan Arrison via EV wrote:

> If you regularly run your cells to 2.5 volts, you'll be replacing them soon.
>
> 3.00 volts with no load is considered dead. 2.5 volts is deader than dead.

Thanks Alan.  Is that true for LiFePO4?  In the original post, John gave the
nominal cell voltage as 3.2v, so they just about have to be LiFePO4.  

Again, I'm not a lithium expert, but with the few hobbyist LiFePO4 batteries
I have, I usually stop the discharge at between 2.6 and 2.7 volts per cell.  
For a 4-cell 12v battery that's 10.4v to 10.8v, conveniently close to the
usual 10.5v "stop here" value for lead batteries.  

From what I've seen, there seems to be a negligible amount of additional
usable AH capacity between 2.7 and 2.5 volts per cell.  So I don't see much
point in going below around 2.6vpc.

John, what brand and type are your cells?

Also, what charger are you using?

David Roden, EVDL moderator & general lackey

To reach me, don't reply to this message; I won't get it.  Use my
offlist address here : http://evdl.org/help/index.html#supt

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Re: Bottom Balancing Batteries

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Sorry if this message is not in the flow - I am a digest-only subscriber.

I have been helping John through this via direct email for maybe a couple
of weeks, and it was Willie who said it most accurately.

John's pack has probably never been properly balanced and an fire early on
due to improper mounting of the cells didn't help.  Instead of the usual
thick plastic case on these prismatic LFP cells there was (by this
particular manufacturer) a relatively thin transparent plastic film around
the metal case (apparently an electrode) of the cells according to his
description.  The cells must have been mounted in a sheet metal battery box.

Very likely the replacements for the burnt cells were not matched in
voltage when installed.  And I think the BMS was only configured via CAN to
the charger to prevent overcharging.  As far as I know the BMS was *not*
configured to shut down the motor inverter either via CAN or using the
(active low) Discharge Enable line on the Orion BMS.

It seemed logical to suggest a one-time bottom balance as this mix of old,
new and perhaps damaged cells might never top balance within a reasonable
timeframe and I didn't want to hear of the car being test-driven with an
unbalanced pack.  I suggested 2.8v as a reasonably safe bottom but the
manufacturer spec sheet apparently stated 2.5v.

My idea was to expedite the balancing process by starting at a low SOC and
let the BMS stop the charge when the lower capacity cells came up to 3.6
something or whatever the BMS was set to.

Then short drives would rout out rather quickly any cells that were still
significantly lower in capacity.  And I emphasized before going much
further to enable that very important *other* function of the BMS, the one
which should at least alert the driver if not outright stop the motor
inverter.  I believe that this oversight reverse-charged some of the
cells.

For individual cell charging I suggested  a commonly available  bench power
supply and John did take delivery of a (5A or 10A?) unit but apparently it
failed before very long.

- Gordon Wong

PS John is a member of the Vancouver EV Association as am I.  He is some 80
miles to the east.  I haven't seen Roger Stockton for a couple of years.
He's running a Leaf now and I think he is still part of Delta-Q.  All are
welcome to come visit VEVA via Zoom (Tuesdays 7-9 Pacific and Saturdays
10-12) - register at veva.ca.
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Re: Bottom Balancing Batteries

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Gordon,

We use a "CellPro" PowerLab 8 to initially balance, and cycle our
LiFePO4 packs in groups of eight cells (or less.)
http://www.store.revolectrix.com/Products/Cellpro-PowerLab-8-EC5-version/Cellpro-PowerLab-8_3299

About $250 and you will realize that you have been sleeping under a
rock. Amazing device. 1300 watt

Get the USB interface module ($22)  so you can easily collect and plot
the data while you are testing and cycling the cells. Get the CPBP9P-10
battery pigtail so you can easily wire up the individual cell taps.
(Tough to wiring it up to the cells without the proper connector, so for
$3, get a pigtail.)

We use a deep cycle 12 volt battery with the CellPro to provide the
input charging energy, (plus a modest 12 volt charger,) and to also
provide a reservoir for the CellPro to dump the energy from the Li-Ion
cells under test.

 >>>> Charging, balancing, and using a pack with used/mixed cells <<<<

     You have what you can afford, so sometimes you build a pack out of
cells that aren't well matched. First, put them on the CellPro and cycle
them in groups to find any defective or low capacity cells. Cycle all
the cells, and then cycle them once again to gauge what the self
discharge is for each cell. Toss any that have large self discharge as
that is a sign that they have internal damage, and will prove impossible
to keep in balance in the car.

     Get all the cells fully charged. Then assemble the ones that proved
good on the CellPro into a pack.

 >>>> "Foil covered cells" <<<<

     These cells with a thin metal, plastic covered, outside are "pouch"
type cells and need to be constrained before they are used. They
basically are a hermit crab without its shell. _You_ need to provide the
shell. If you try to use them without a proper case, they will have low
performance, and a very short life. They require a case that presses
them into a giant sandwich at a very specific pressure range. It can be
done, but it is tricky stuff to build the proper case.

     Bill D.

On 3/14/2021 6:47 PM, Gordon Wong via EV wrote:

> Sorry if this message is not in the flow - I am a digest-only subscriber.
>
> I have been helping John through this via direct email for maybe a couple
> of weeks, and it was Willie who said it most accurately.
>
> John's pack has probably never been properly balanced and an fire early on
> due to improper mounting of the cells didn't help.  Instead of the usual
> thick plastic case on these prismatic LFP cells there was (by this
> particular manufacturer) a relatively thin transparent plastic film around
> the metal case (apparently an electrode) of the cells according to his
> description.  The cells must have been mounted in a sheet metal battery box.
>
> Very likely the replacements for the burnt cells were not matched in
> voltage when installed.  And I think the BMS was only configured via CAN to
> the charger to prevent overcharging.  As far as I know the BMS was *not*
> configured to shut down the motor inverter either via CAN or using the
> (active low) Discharge Enable line on the Orion BMS.
>
> It seemed logical to suggest a one-time bottom balance as this mix of old,
> new and perhaps damaged cells might never top balance within a reasonable
> timeframe and I didn't want to hear of the car being test-driven with an
> unbalanced pack.  I suggested 2.8v as a reasonably safe bottom but the
> manufacturer spec sheet apparently stated 2.5v.
>
> My idea was to expedite the balancing process by starting at a low SOC and
> let the BMS stop the charge when the lower capacity cells came up to 3.6
> something or whatever the BMS was set to.
>
> Then short drives would rout out rather quickly any cells that were still
> significantly lower in capacity.  And I emphasized before going much
> further to enable that very important *other* function of the BMS, the one
> which should at least alert the driver if not outright stop the motor
> inverter.  I believe that this oversight reverse-charged some of the
> cells.
>
> For individual cell charging I suggested  a commonly available  bench power
> supply and John did take delivery of a (5A or 10A?) unit but apparently it
> failed before very long.
>
> - Gordon Wong
>
> PS John is a member of the Vancouver EV Association as am I.  He is some 80
> miles to the east.  I haven't seen Roger Stockton for a couple of years.
> He's running a Leaf now and I think he is still part of Delta-Q.  All are
> welcome to come visit VEVA via Zoom (Tuesdays 7-9 Pacific and Saturdays
> 10-12) - register at veva.ca.
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Re: Bottom Balancing Batteries

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On 3/13/21 11:47 PM, Gordon Wong via EV wrote:

>
> My idea was to expedite the balancing process by starting at a low SOC and
> let the BMS stop the charge when the lower capacity cells came up to 3.6
> something or whatever the BMS was set to.

That bottom balancing confused everyone.  As Bill well explained, that
may only worsen the problem when a BMS is dedicated to top balancing.

We don't know the details of the pack.  The number of cells, the
capacity of the cells, the manufacturer, the recommended voltages.  We
don't know what the BMS is supposed to do.

I hope the BMS is set up to top balance with resistor bypass.  I hope
the BMS is set up to terminate charging when a single cell goes high.
If so, the BMS can eventually bring the pack into balance. If badly out
of balance as your pack sounds, it may take a very many cycles.  The
process can be hastened by both charging only the low cells and
discharging only the high cells.  Something like an incandescent light
bulb can be used for a single cell load.  Or some other resistor.

I again recommend putting all cells in parallel and charging with a
single cell charger up to around 3.45v.

I recognize that paralleling may not be feasible.  The magic multi-cell
charger/cycler/balancer Bill mentioned sounds wonderful but he mentioned
using only with higher voltage LiPo cells rather than your lower voltage
LFP.  Likely, it will handle both.
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Re: Bottom Balancing Batteries

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Hi Gordon,

I'm still around, and still at Delta-q, which is now part of Zapi Group.

The Leaf is my wife's car, but she does let me drive it from time to time.  I've still got my conversion, and a lithium pack for it, but health issues in recent years are making it quite challenging to do much physical work anymore (heart valve and pacemaker in '18, and I celebrated the arrival of covid this past march with removal of a brain tumor).  Reaching 50 is harder on some of us than other... ;^>

Maybe I will see you at one of the VEVA Zoom meetings.

Roger.

Gordon Wong wrote:

> PS John is a member of the Vancouver EV Association as am I.  He is some
> 80 miles to the east.  I haven't seen Roger Stockton for a couple of
> years.
> He's running a Leaf now and I think he is still part of Delta-Q.  All
> are welcome to come visit VEVA via Zoom (Tuesdays 7-9 Pacific and
> Saturdays
> 10-12) - register at veva.ca.

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Re: Bottom balancing batteries

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On Sat, Mar 13, 2021 at 9:30 PM Willie via EV <[hidden email]> wrote:
> I don't recall what Jack recommended about stopping the charge.  Perhaps
> depending on one or more cells reaching the upper single cell limit.
>
Basically it was to charge to 3.65Vpc and stop when the current
dropped to 0.05C. That is what the specs sheet said which came with my
made in November 2009 Thundersky LFP100AHA cells. Too many would miss,
over and over again, that "stop at 0.05C" figure and over charge their
cells. For my non-BMS 12V trolling batteries I bottom balance and set
my charger to stop at 3.55Vpc and current has dropped to about 0.03C
(I can't adjust the cutoff current so I adjust the max voltage). The
resting open circuit voltage at 100%SOC of a LiFePO4 cell at room
temperature is 3.38V so I just test the individual cells after resting
for a while. In one of my 12V batteries, one cell gets to 3.78V just
as the charge cuts off and it rests at 3.36V a couple of hours later
so I know I'm not over charging them.

FWIW, in the Gizmo I had with buddy-paired 100AH LiFePO4 Thunderskys
and 20 in series I top balanced them because my Zivan charger would
not cut off at a current setpoint. I ran over 8 years without a cell
level BMS installed and only a half-pack voltage monitor. When I sold
the Gizmo I reinstalled the BMS boards since I didn't trust the new
owner to be part of the BMS. After I sold it, there was one cell pair
which started sagging below the rest so that one will either need to
be removed or replaced. The new owner didn't understand the importance
of the half-pack voltage difference needing to be close to zero. The
BMS showed the issue. Unfortunately the owner rolled it on its side
and hasn't driven it much for a while.

If you don't know exactly what you are doing and understand the
ramifications of it, then definitely get a quality robust BMS.

--
David D. Nelson
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