Re: [EVDL] Battery Pack drained completely

[Matt via EV]

Both the miniBMS and the cell logs draw current from every cell continuously
It’s only a few mA, but, given enough time it will take the whole battery to 
0v, if not charged



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From: Alan Arrison via EV
Sent: Monday, 17 August 2020 7:57 AM
To: ev@lists.evdl.org
Cc: Alan Arrison
Subject: Re: [EVDL] Battery Pack drained completely

Ouch! Your whole ex$pensive pack destroyed? What did you do about the 
alarm that was sounding. I'm hoping that the pack isn't really dead and 
there is another problem like the 12V house battery went dead.

Al

On 8/16/2020 1:27 PM, Denis Boutet via EV wrote:
> Hello everyone,
>
> RE: Ranger EV 2000, LiFePO4 pack 104x3.65V China HiPower, 104 Mini BMS 
> + head board, CellLog8 x 13
>
> I need help figuring out what is wrong and how to proceed with this 
> problem.  Any help, suggestion will be greatly appreciated.
>
> The pack seams to have been drained completely by the mini BMS system, 
> or another cause.  In the fall, the head board alarm went off 
> permanently as I was winterizing my truck.  This spring I found the 
> pack was dead.  Find listed here the codes from the NGS:
>
> BAT_PV     0.00V
>
> BCM_OP      2
>
> PREV_OS      7
>
> CCNT   4
>
> ENG_PO    DISABL
>
> LOWVOLT    0
>
> MAINSEN 2,5v
>
> SOC    49.99%
>
> WKDFBMF    NO
>
> BTM_1FT - BTM_39FT YES  (ALL)
>
> LEAK  NO  (9 Ohm)
>
> Next step I beleive is to drop the pack and try and find the faulty 
> mini BMS.  I guess I won't see any green lights, since the pack is dead.
>
> Many thanks for your interest
>
> Denis B
>
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Re: [EVDL] Battery Pack drained completely

[Willie via EV]

I see online that the MiniBMS idle current is 2.2ma.  If your DC:DC
converter was connected and supplying power to the truck's 12v system, that
probably uses yet more current to maintain the body computer, radio presets,
and so on.  On modern vehicles something close to 100ma of parasitic loads
on the 12v bus is not that uncommon.


I believe old miniBMS modules would eventually pull a cell all the way 
down to zero.  Newer versions, I think, would stop vampire draw at about 2v.


MrSharkey (or others) can probably give a more definitive answer.

My experience is that a small fraction of LFP cells discharged to zero 
can be resurrected by charging.  At least some of the cells that appear 
to take a charge may not hold it.

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Re: [EVDL] Battery Pack drained completely

[Mr. Sharkey via EV]

> I see online that the MiniBMS idle current is 2.2ma.

Depends on the version of the MiniBMS. The early "analog" models 
(original and v.2) that use the LM239/339 comparitor chips typically 
have a quiescent current of about 6.5mA. Individual modules can have 
a current draw of up to 9mA. These older modules are more than happy 
to draw the battery down until its empty, as they have no low cell 
voltage shutdown.


The v.3 modules, with the ATTiny 85 AVR processors have low battery 
"sleep" programming, but it would only come into play when the cell 
it is connected to is nearly empty. The point is that this gives a 
limited grace period to find and correct problems before reaching 0% SOC.


Denis mentions "seeing green lights", so his MiniBMS system is the 
early analog version, the v.3 modules have a single blinky red LED 
for indication of all functions.


> 4.5 amp hours per month, which doesn't seem like
> it'd be enough to run the battery flat over a winter

I did similar calculations, and if the pack was adequately charged 
when put into storage, the BMS modules shouldn't have drawn it down 
to completely discharged.


> I think that the first step is to see where you stand

Agreed. Having to "drop the pack" for maintenance and 
troubleshooting, even as little attention as Lithium requires, makes 
keeping up with things like this difficult, with the result being ... 
well, things happen.


All of which reminds me that I need to go out and pull the cover off 
my pack and do a balancing charge on my Thunderskys. Full manual 
control comes with responsibilities.


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Re: [EVDL] Battery Pack drained completely

[EVDL Administrator via EV]

Hi Denis.  I'm not an expert on these matters, so if I say something wrong 
here, I trust that someone else will correct me.  

In my admittedly limited experience I have found that BMSes always use a 
little current from the cells they're monitoring. 
 
I see online that the MiniBMS idle current is 2.2ma.  If your DC:DC 
converter was connected and supplying power to the truck's 12v system, that 
probably uses yet more current to maintain the body computer, radio presets, 
and so on.  On modern vehicles something close to 100ma of parasitic loads 
on the 12v bus is not that uncommon.

Accounting for DC:DC losses, that would be about 4ma on a 312v traction 
battery.  Add the BMS self-load and you get about 4.5 amp hours per month, 
which doesn't seem like it'd be enough to run the battery flat over a 
winter.  But you may have had other energy thieves.  

The MiniBMS manual also says that "After shutdown due to low cell voltage, a 
capacity reserve of approximately 1Ah per 100Ah battery capacity is left in 
the battery."  The BMS draw drops to 1.2ma at low cell voltage.  That is 864 
mah (.864 ah) per month, so if indeed the truck did run the traction battery 
down to its BMS cutoff voltage, another month would just about do it in.

I think that the first step is to see where you stand. You'll need to get to 
the individual cells by whatever means, and take a voltage reading from 
each.
 
The vast improvements in range and utility of EVs in just the last few years 
have pretty well crushed the value of older used EVs.  This is especially 
true of conversions, and yours is really a factory conversion, aka "Electric 
Powertrain Option" or EPTO.  OTOH there does seem to be a devoted community 
of followers from this vehicle.

My opinion is that if the range and utility still suit your needs, even if 
you end up having to replace the battery, you may be better off to try to 
fix it.  You could look into replacing the cells with used or new Leaf or 
Volt modules.  

But before you panic, I suggest that you get to those cells with a voltmeter 
and a small parallel load (don't just use a high impedance DMM), and see 
what's really going on.  

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: [EVDL] Battery Pack drained completely

[Alan Arrison via EV]

Ouch! Your whole ex$pensive pack destroyed? What did you do about the 
alarm that was sounding. I'm hoping that the pack isn't really dead and 
there is another problem like the 12V house battery went dead.


Al

On 8/16/2020 1:27 PM, Denis Boutet via EV wrote:

Hello everyone,

RE: Ranger EV 2000, LiFePO4 pack 104x3.65V China HiPower, 104 Mini BMS 
+ head board, CellLog8 x 13


I need help figuring out what is wrong and how to proceed with this 
problem.  Any help, suggestion will be greatly appreciated.


The pack seams to have been drained completely by the mini BMS system, 
or another cause.  In the fall, the head board alarm went off 
permanently as I was winterizing my truck.  This spring I found the 
pack was dead.  Find listed here the codes from the NGS:


BAT_PV     0.00V

BCM_OP      2

PREV_OS      7

CCNT   4

ENG_PO    DISABL

LOWVOLT    0

MAINSEN 2,5v

SOC    49.99%

WKDFBMF    NO

BTM_1FT - BTM_39FT YES  (ALL)

LEAK  NO  (9 Ohm)

Next step I beleive is to drop the pack and try and find the faulty 
mini BMS.  I guess I won't see any green lights, since the pack is dead.


Many thanks for your interest

Denis B

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[EVDL] Battery Pack drained completely

[Denis Boutet via EV]

Hello everyone,

RE: Ranger EV 2000, LiFePO4 pack 104x3.65V China HiPower, 104 Mini BMS + 
head board, CellLog8 x 13


I need help figuring out what is wrong and how to proceed with this 
problem.  Any help, suggestion will be greatly appreciated.


The pack seams to have been drained completely by the mini BMS system, 
or another cause.  In the fall, the head board alarm went off 
permanently as I was winterizing my truck.  This spring I found the pack 
was dead.  Find listed here the codes from the NGS:


BAT_PV     0.00V

BCM_OP      2

PREV_OS      7

CCNT   4

ENG_PO    DISABL

LOWVOLT    0

MAINSEN 2,5v

SOC    49.99%

WKDFBMF    NO

BTM_1FT - BTM_39FT YES  (ALL)

LEAK  NO  (9 Ohm)

Next step I beleive is to drop the pack and try and find the faulty mini 
BMS.  I guess I won't see any green lights, since the pack is dead.


Many thanks for your interest

Denis B

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