# Any ideas on reviving over discharged Lifepo4?



## gregdugas (Nov 14, 2012)

Setup: 2005 GEM eS; converted to (24) HiPower 3.2V 100AH Lifepo4; miniBMS system.

Issue: Shortly after making conversion to Lifepo4, I left out-of-country for 3 months. Upon returning battery pack registered a total of 5.8V caused by a parasitic short.

Goal: To determine if any cells are still good.

Approach: Connected 24 cells in parallel and charged with single output power supply set at 3.57V. After 24 hours charge was measured at .25V. After 48 hours charge went down to .20v then .18V. Voltage for individual cells ranged from a low of 0.0 to a high of .71V.
Reduced number of charging cells FROM 24 to 6. The voltage reading then reached max of .4V. Reduced to a single cell being charged noting max of .6V charge.

Q1: Any other suggestions on how to attempt to possibly revive cells? 
Q2: I have two spare cells which have never been used - and owned for 9 months. In contemplating buying new 100AH HiPower cells to replace the damaged ones, any problem to incorporate these 2 spare cells as part of the new group thereby saving the expense of 2 cells. I will top-balance entire pack.
Q3: Any problem in combining these 2 spare HiPower cells with another manufacturer - like Calb?
Thanks in advance for your input!


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## Ziggythewiz (May 16, 2010)

Sounds like they're all toast. To be sure you should charge each of them individually and see if any will hold a charge.

I have cells (CALB SEs and CAs) of varying ages/use that get along just fine top balanced, but I wouldn't bother for just 2 different cells.


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## dougingraham (Jul 26, 2011)

Charge them individually at a C/20 rate until they come back to about 3 volts. Once they reach 3 volts charge them at your normal rate. If you parallel them like you did a single failed cell will drag the rest down. They need to be done separately.

When they are unrecoverable you see the behavior you have mentioned. A single bad one will mask all the survivors when you parallel them.

Good luck!


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## mora (Nov 11, 2009)

Sorry about this happening. Not all is lost though.


gregdugas said:


> Q1: Any other suggestions on how to attempt to possibly revive cells?


This is what I've done and still most of cells that were at 0.01V are going strong (2.5 years of use since revival):

charge at low amps one cell at time. Use adjustable power supply or put them in string of 4 (~12V nominal) and use 12V lead acid charger found cheaply on almost any store. 1-6 amps should do fine. Any higher power and you might heat cells way too fast if they are really bad. Watch cells carefully all the time and stop when cells are close to 3.0V. If any cell heats noticeably during charge you should stop immediately. In my experience cells that are resting at 0.01V might survive and cells above that will survive. 0.00V resting voltage equals lost cell. These cells only heat during charge and charge voltage is something like you mentioned. Voltage drops immediately when you disconnect charger. You can feel the heat directly from terminals. Just watch not to short them via rings or any other objects. One terminal at a time.

Let cells rest overnight after charging them to 3.0V or somewhere close to that reading. If voltage drops significantly cell is likely to go bad soon. Restore good cells to desired charge voltage and cycle them few times if possible (discharge & charge). This will tell you if there is significant capacity loss between them. Or just top balance and use as is with existing miniBMS. You'll find weakest cells soon during drive. Hehe.


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## Roy Von Rogers (Mar 21, 2009)

And what is the moral of that story....


Roy


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## gregdugas (Nov 14, 2012)

Don't go on vacation for 3 months??


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