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[ohhaidere]

I have a spare monolith that I'd like to use for a project. Unfortunately after measuring the voltage at the contactor its only reading 12V

what do I have for options? I've heard revival from as low as 24v but wasnt sure if I could go much lower.

any ideas?

[Auriga]

If it's actually 12V that monolith is permanently damaged and should not be recovered 

[Doug S]

Not gonna hurt anything to try. Set up a power supply for the nominal pack voltage (or as high as the power supply can go -- even 40VDC or so might be enough to get it off the floor), but set the current limit very low, say no more than 100mA. Unless I miss my guess, you should be able to charge very slowly through the equalization resistor string, until the circuitry comes alive and can start managing things. At that point, the regular charger should be able to take over.

You might want to charge very gently at first, charging slowly and maybe even stopping for a while every time the pack voltage rises 10 volts or so. A monolith that's at 12VDC is obviously very depleted, if it's even functional any more, and very gentle revival might be the best thing for it.

[Biff]

Not gonna hurt anything to try. Set up a power supply for the nominal pack voltage (or as high as the power supply can go -- even 40VDC or so might be enough to get it off the floor), but set the current limit very low, say no more than 100mA. Unless I miss my guess, you should be able to charge very slowly through the equalization resistor string, until the circuitry comes alive and can start managing things. At that point, the regular charger should be able to take over.

You might want to charge very gently at first, charging slowly and maybe even stopping for a while every time the pack voltage rises 10 volts or so. A monolith that's at 12VDC is obviously very depleted, if it's even functional any more, and very gentle revival might be the best thing for it.

I can think of a number of things that could get hurt by following that advice.  If you are very certain that the battery total voltage is below 70V (actually if you know that any cell went below 2.5V resting voltage which can happen at any total battery voltage in an un-balanced battery) that battery (or cells if you can safely remove just the cells from the battery) should be properly recycled, no question.  If it is used for anything, it will not only not work well, it could suffer a sudden and serious failure.  The usefulness of an  Li-Ion NCM cell that has sat at below 3.0V for any period of time is questionable, to try and use something that sat at below 2.5V is foolish.

-ryan

[Doug S]

Since you specifically said you wanted to use it "for a project", and not to ride with, I say give it a shot. I wouldn't use it in any critical applications, and I wouldn't want it in a go-kart inches from my head, but if it's nothing like that, what have you got to lose? Modern Li-ion battery packs are pretty resilient, and have safeguards (thermal fuses, BMS's, etc.) to keep them from incinerating.

Yes, I'm aware that a few Teslas and other EVs have had battery fires. But it's extremely infrequent (nothing's perfectly safe, boys and girls!), and the ones I'm aware of had been punctured by shrapnel or actually been in a collision...physically violated in some way.

[NoMoreIdeas]

If it's really 12V, those are 28S batteries, so that means each cell is on average under .5v! Anything under 3v isnt a great idea but down to 2.5v/cell is considered salvageable. Voltages that low will cause trouble mainly during the initial charge. If you do decide to charge it anyway, do it outside and carefully watch the battery temp. You'll have a decent chance the battery will heat up enough to go into thermal run-away and catch fire, but the slower you charge the better you can hedge against that. I'd charge the pack extremely slow (under half an amp if you can) until the battery voltage gets up to 90ish volts, which should happen fairly quickly.