Recovering a dead cell

[Charles_Snyder]

I purchased this battery from BatterySpace back in January.

http://www.batteryspace.com/customizelifepo4battery64v10ah64wh10aratewithpcb.aspx

Since then, it has done a fine job of powering my running lights and horn for my Quest velomobile.

Just the other day, it seemed to have died on me. I took off the cover and tested the batteries with a multimeter, one shows 3.5 volts and the other none. Now, I know I have several choices, throw it away, replace the dead battery or possibly charge the lone battery. Currently, I am using this charger:

http://www.batteryspace.com/smartfastcharger12aforany64v2cells76vcut-offlifepo4batterypack.aspx

I also understand that I need to ensure both are balanced, but what I need to know and I'm guessing no, can I use this charger to charge up the other "dead" battery? I have nothing to lose right? It already has charged up one, so what would be the difference if I charged up the other, assuming I could. If I do, should I remove the dead battery from the pack and pcm, or leave and soldier charging leads to that battery? I suppose I'm also asking what's the worst that could happen if I tried charging the dead battery using the default charger.

 

[dnmun]

how did the cell end up totally discharged? if you were using it under load as it dropped below 2V then it is not likely to ever function again. you will need a single cell charger to charge it up. you will need to buy another pair of cells if you wish to use the 2 cell charger and it will also end up ruining the next pair since there is no BMS to balance and protect it. you would be better off having a regular battery with BMS, and then use a DC/DC converter to power the lights.

 

[marty]

Dnmun is right, the cell with 0 voltage is probably done. Miracles do happen. Try charging the dead cell. RC charger is the best tool to charge just about any type of battery. Or go looking at your collection of old cell phone chargers.

Copy from:
http://www.batteryspace.com/ProductImages/pdf/IFR42120e1000.pdf
2.1 Description
Lithium ion rechargeable battery cell

Nominal Voltage 3.2V

7.1 Standard Charge
The "Standard Charge" means charging the Cell with initial charge current 2000 mA and with constant voltage 3.65 V ,then constant voltage(3.65V)with floating current taper to 500mA cut-off (Charger for exclusive use lithium ion rechargeable battery, with an accuracy 3.65+/-0.1V) at 20 °C for 7.5 hours.

Good source of information on low voltage lighting batteries is here:
http://www.candlepowerforums.com/vb/forum.php

 

[pdf]

The PCM should have kept the cell from going dead so I'd be curious about that (bad PCM or bad cell maybe). If the voltage is truly 0, it is finished for sure. Even if you manage to charge it, at best, the capacity will be very much reduced.

All I can say about the dangers of trying to resurrect a dead cell would only apply to RC LiCo oxide and in that case, the worst that can happen is a fire. This is not generalizable to all battery chemistries and not even to all batteries with the same chemistry so is of little general value. In my opinion, I'd get rid of the cell. It is done for anyway. If you want to experiment with it (which I hardily encourage), do so where any untoward behavior (i.e., fire) will not result in any problems. I would not expect any if you charge only the bad cell and keep the voltage under the LiFePO4 limit, but on the other hand, why bother? Your cycle looks like it could be worth close to $10k. I'd guess so not a good place to try to save a few bucks.

Since the cell went dead when the PCM should have (I think) cut the drain from that cell when it went below LVC, you might check the performance of the PCM. It looks like the PCM does not have balancing capabilities and as dnmum suggests, that would be beneficial if you are looking to replace it anyway. If your ride is electrified, going with a DC/DC converter off the main pack would be the way to go and you won't have to mess with a separate battery.

Sweet velo by the way.
Edit: You will need a single cell charger to charge the cell that is currently dead, not the one you have.
Edit 2: if the link http://www.batteryspace.com/pcbprotectioncircuitmodulefor2cells60vlifepo4batterypackat10alimited.aspx is to an actual PCM that comes with the pack, it looks like from the text that it only measures overall voltage not cell voltages, so if somehow (how?) one cell went low while the other was not discharged at all then the PCM would not cut the drain until the overall pack voltage was below the LVC for the pack which is around 4 v. At any rate, the one at 0 v is history. I agree with dnmum below; it looks like two headways. Way overpriced.

 

[dnmun]

just looked at his battery picture in the ad. there is no pcm to monitor the voltage or to cut off the current. that is so bogus to claim otherwise.

looks like two headway knockoffs, 42120s, for $100?

i think battery space should be on that list of non believers and others who should be shunned religously.

 

[circuit]

DO NOT "recover" a cell that has been overdischarged. When the cell is overdischarged, copper plating occurs inside the cell. This can go until cell shorts out internally. This is why overdischarged cells typically have higher self-discharge, also they can spontaneously burst into flames or explode. This is the main reason for most "it was all okay, I charged it and left it to rest" explanations.

 

[Charles_Snyder]

Thank you gentlemen for your concise help. I will leave that dead battery alone and I have another smaller version on order. Perhaps in the near future I might get around to replacing the dead battery. Thanks again for helping out a newbie. Gratz.

 

[davec]

DO NOT "recover" a cell that has been overdischarged. When the cell is overdischarged, copper plating occurs inside the cell. This can go until cell shorts out internally. This is why overdischarged cells typically have higher self-discharge, also they can spontaneously burst into flames or explode. This is the main reason for most "it was all okay, I charged it and left it to rest" explanations.

@circuit- interesting i was not aware of this
when i had my lifepo4 calbs 40ah cells ....18 of em... i had a bms issue and 2 of my calbs were indeed overdischarged to 0.6v and 0.1v respectively
anyways

here is what i observed...
the capacity on the cell that was overdischarged to 0 was lower by 3ah- so it pushed out 37ah
the capacity for the cell that was down to 0.6 v was a full 40ah
both cells delivered good capacity & had ok IR- however the bleeding aka self discharge was high on both cells- and that's permanent

i fully charged both cells and put them away into storage
the 0.6v cell was down to 3 volts after 3 months and the 0v cell was down to about 2v
after another 3 months the 0v was back at 0v and the 0.6v cell sitting at around 1v

so i used a small single cell lifepo4 charger and brought both back to life charging @ 2a
i also noticed that a few %100 dod cycles helped to improve the responsiveness
using both in my pack for month- both are usable... i can live with the high self discharge..but if it can flame up on me i might need to think twice about using these....also.... i was never able to balance my 18s pack properly as these 2 cells were basically weak...

others on this forum have brought lifepo4 back as well- but again if the chemistry is unsafe ... that's something to note