shiftynick avatar image
shiftynick asked

Can I revive a "Deeply Discharged" 200Ah 12V Smart Lithium Battery?

I have the 200Ah LiFePO4 as the house battery on my bus conversion. It is connected to a BMS 12/200. I was out of the country for 5 weeks. After a couple of weeks it was clear that the location was not getting enough solar to keep up with the charge on the system, so I had someone go into the bus and turn off all of my main disconnects for the battery itself, the MultiPlus inverter/charger, the BlueSolar MPPT charger, and the connection to the starter battery for alternator charging. It only had about a 13.5V charge on it when I had them cut everything, or so I thought, they didn't fully disconnect everything as I had asked.

I came back to find the battery at 8.73V, with the cells at 2.29V, 1.84V, 2.14V, and 2.46V.

I thought the BMS would protect from over-discharging... but that's a different question.

Is this battery a lost cause, or would it be possible to revive?

Lithium Batterydischarge level
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Not an answer to the revive question, but more on the BMS and over-discharge. The BMS itself consumes power. In case of BMS 12/200, the spec sheet says current consumption after cut-off due to low cell voltage is 3mA. This 3mA is not subject to cut-off by the BMS and can flatten battery given enough time if its not offset by a supply.

Three options -

1) disconnect the BMS and loads completely from the battery for long term non-usage

2) use the remote switch to disable BMS (= using BMS's LB path to cut out loads) and rely on your solar to supply the 5mA BMS operating current (the spec sheet says it draws 5mA when "off" but still connected).

3) disconnect all loads but leave BMS + solar active.

Don't forget to test before relying on whatever scheme you decide to go with!

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Ok, that all makes sense. I was able to get the battery stabilized starting with a slow 2A charge before moving back up to normal charge. I have a better solar location for storage now, but if that doesn't cut it I suspect I will go with option 1 and disconnect everything from the battery. Thanks!

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I looked at the data sheet for a bms12/200. Am I reading this right?

As I see it the "BMS" 12/200 is really nothing more than a fancy 12V isolator with a voltage tripped on/off relay. And knows nothing, let alone manages the balance, of the state of individual cells of a battery?

Or is there some special "magic" that happens specifically with Victron batteries? (Which it kinda looks like there is).

As such, a BMS 12/200 (or similar Victron device) is pretty much just for managing Victron batteries only?

-I can move this to a different thread if this is becoming a thread hijack :)

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The Victron smart lifepo4 + victron bms combo splits the (traditional?) BMS functions. Balancing and status detection is on the smart battery, and cut out actions are on the BMS.

edit: BMS functions are defined by vendor. Need to read fine print as you noted.

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3 Answers
boekel avatar image
boekel answered ·

Use a very small current to charge, like 100mA until all the cells are above 2.5V then continue charging slowly (5-10 A) and make sure the battery doesn't get warm. If the battery bulges...stop.

read the BMS manual about how to disconnect.

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The lowest I could go with what I had was 2A, but that worked great and the cells all balanced on the way up to about 2.6V before I went up to 10A. At about 3.1V I moved up to 60A. All good now. Temp never got very high at all.

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glad to hear, thanks for reporting.

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geomz avatar image
geomz answered ·

I am curious how the BMS allowed this deep of a discharge?

Is the BMS awake? Accessible? Can it see the cells individually?

Do you have access to the cells individually yourself? Or only collectively through the BMS?

I agree with @boekel, go VERY slowly. But you may not have the ability to do so if the BMS is horked.

Take the battery completely physically out of circuit and attach as small of a trickle charger as you can find to it. Or you can fashion one from an old 12V "wall-wart" plug, just check the plate voltage and output power on the faceplate. I'd stay under 1A.

Depending on cell chemistry/config (pouch, sleeve, cylinder) it may be beyond hope or significantly reduced in capacity. Also keep in mind, if one cell is indeed significantly reduced in capacity, it might cause aberrant behavior from the other cells. That can cause unbalanced discharge or worse, charge/heat/fire.

So even if you revive it, continue watching it very closely.

Good luck.

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Thanks for the feedback, I was able to get it back up with a slow 2A charge before giving it some real juice. Seems back to normal now, but keeping an eye on it.

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adev avatar image
adev answered ·

@shiftynick you said you managed to get these charged up and balanced again. How have they been in use since? I have a similar situation with some secondhand victron batteries I recently got on ebay and am wondering the chances of getting them usable again...

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I was able to bring it back to a safe level with a low current trickle charger, and then completed a normal charge after that. Everything seems to be fine now.

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Have you noticed any reduced capacity or does it all seem as normal?

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