question

knownot avatar image
knownot asked

using swollen lipo batteries

I know the surgeon general recommends against it but I got a deal on some us2000 that had been allowed to sit discharged for some time. Cell voltage had dropped to about 1.2. I gently recharged them (c/20) to about 3.2 then hooked them up to the easysolar to finish them off. Early indications look good - no crazy self discharge, some capacity even though only half charged. Anyone else here used swollen lipo's? One pack I may no be able to put the cover back on due to the swelling - although it behaved similar to the other less swollen ones.

Pylontech
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2 Answers
wkirby avatar image
wkirby answered ·

Once the cells have been deeply discharged they will be permanently damaged. The swelling indicates severe damage and they will be almost useless because the separator is damaged.
A better option is to remove the cells and have them re-cycled and then strip the rest of the unit down for spare parts and scrap metal.

Using damaged components is kind of like driving around in a car with partially inflated tyres with no treads remaining. It will drive, but it will be dangerous and unpredictable.

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marekp avatar image marekp commented ·
@WKirby

Why scrap the boxes when you can use them after replacing just the cells. Case and internal BMS has value.

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wkirby avatar image wkirby ♦♦ marekp commented ·
Even better idea assuming you can find some replacement cells for reasonable cost. If the cost for replacement cells + effort is more than a new module then maybe not.
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knownot avatar image knownot commented ·
@WKirby @MarekP So I have 3 us2000 that were connected to the same failed inverter (I think fully discharged) then left for a year. In each module the 3 cell packs are very similar. One all look normal, one all slightly swelled, one all very swelled. All 9 cell packs behaved similarly electrically. For my own interest I'll bring these packs back to working voltage (supervised) and test their capacity. I know the usual outcome should be that all these batteries have very low capacity(ie. useless), but I doubt it is the case here. I'll post my findings.
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snoobler avatar image snoobler knownot commented ·

Lithium, including LFP, suffers substantially when deeply discharged, especially if they remain their for an extended period. I have 80+ 40Ah CALB cells. All but 5 of them were deeply discharged to 0.6V and held there for a very long time. The battery monitoring boards attached to each cell drained them @ microA currents even after they were supposed to shut off.


All recovered to 60-80% of their rated capacity with ONE big difference. All those that discharged to 0.6V had much higher internal resistance, 3-4mΩ, where those that held at about 3.30V over the same period are in the 0.8-1.0mΩ.


Higher IR means more heat, less efficiency and shorter life.


Do yourself a favor and buy a YR-1035 IR tester and test 100% of the cells individually. Don't use any outlier cells.

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marekp avatar image marekp knownot commented ·
@knownot

I am with @snoobler on this.

I also have a bunch of calls that were deeeeeply discharged and they came back with a proper voltage and even capacity is close to 90%. Problem is that this capacity can only be achieved by veeery low charge and discharge rate (0.01C).

If I start charging and discharging them with even 0.1C, their capacity drop quick because energy is converted to heat.

The only application I found for them is in flashlight and emergency lighting. :)



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knownot avatar image knownot marekp commented ·
@MarekP @snoobler all of what you are saying agrees with conventional experience - although some have shared my experience. At BMS controlled charge rate and approx 1000w discharge I appear to have 2.3 kwhrs on the intermediately swollen pack. I will take the advice about monitoring cell temp more accurately (I'll be doing a few cycles to test and monitor) although a regular feel detects no warmth whatsoever. The most swollen pack looks too scary so won't be returned to unattended use.
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marekp avatar image marekp knownot commented ·
@knownot

Be extra caution.

If you want to be even more "hard-core", you can use a needle to puncture the outer shell of the pouch and let the gas out. Than cover the hole with the tape.

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snoobler avatar image snoobler knownot commented ·

Buy a YR-1035. check internal resistance.

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kevgermany avatar image
kevgermany answered ·

Hope your insurance will cover the fire this is likely to cause.

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