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Old Jul 31, 2009, 03:17 PM
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Question
Can you revive a dead LiPo cell?

Title of this thread was changed from

[Can LiPo battery be slow charged at 1/10C for 10 hours without harm]
using non-LiPo charger?

One dead cell in 3S LiPo was successfully revived using non-LiPo variable current charger at 1/10C for 10 hours. Cell termperature stayed within warm range. Only one dead cell was separately charged, not whole pack. Voltage was monitored during charge.

This method was used because LiPo balance charger rejected the dead cell and refused to charge, indicating too low voltage.

Now the LiPo balance charger has taken it over and charging it regular way.

During the experimental charge, the battery was placed in the mug for precaution.

If you have a dead cell, try it and report your result here so that we can judge whether it is acceptable method.
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Old Jul 31, 2009, 03:42 PM
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Letchworth, Great Britain (UK)
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No need to slow charge it. If one or more cells are below the threshold recongnised by your LiPo charger, they can often be brought above that threshold (somewhere around 3 volts, I think) by charging them at about 1C with a non-LiPo charger whilst constantly monitoring the voltage.

They should be switched to a LiPo charger as soon as the low cells are up to a voltage that the charger will accept. I think that leaving them for 10 hours -- even at 1/10C -- is asking for trouble.

By the way, what voltage were your dead cells showing?
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Old Jul 31, 2009, 06:00 PM
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Haralson County GA. USA
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hall whoo used to use a voltage clamp to charge his race ready LiPoly packs at 1/10 C all of the time. He no longer seems to be a member here but I believe Robynflyer knows how to get in touch with him.

Charles
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Old Jul 31, 2009, 08:52 PM
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United States, WA, Puyallup
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Quote:
Originally Posted by John Kim
Can LiPo battery be slow charged at 1/10C for 10 hours without harm using non-LiPo charger?

One dead cell in 3S LiPo was successfully revived using non-LiPo variable current charger at 1/10C for 10 hours. Cell termperature stayed within warm range. Only one dead cell was separately charged, not whole pack.

This method was used because LiPo balance charger rejected the dead cell and refused to charge, indicating too low voltage.

Now the LiPo balance charger has taken it over and charging it regular way.

During the experimental charge, the battery was placed in the mug for precaution.

If you have a dead cell, try it and report your result here so that we can judge whether it is acceptable method.
Charging LiPos at any rate for 10 hours without a voltage cut-off is not a safe practice. Suggesting that others do so is irresponsible.

If you want to resurrect an over discharged cell or pack, follow the procedure in post #2.

Bill
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Old Aug 02, 2009, 04:19 AM
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Quote:
Originally Posted by abenn
No need to slow charge it. If one or more cells are below the threshold recongnised by your LiPo charger, they can often be brought above that threshold (somewhere around 3 volts, I think) by charging them at about 1C with a non-LiPo charger whilst constantly monitoring the voltage.

They should be switched to a LiPo charger as soon as the low cells are up to a voltage that the charger will accept. I think that leaving them for 10 hours -- even at 1/10C -- is asking for trouble.

By the way, what voltage were your dead cells showing?
I had this problem with my 14.8V 2200mAh battery. It would only recognize 3 cells. I went ahead with a balance charge at 2.2 amps. This has brought the battery back up to voltage and the battery charger now recognizes (Turnigy 3e) 4 cells.

What damage could I have caused?
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Old Aug 02, 2009, 04:23 AM
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Any Lithium Polymer (LiPo) battery with more than two cells should be balanced. A LiPo battery is composed of individual cells, and each cell can charge and discharge at different rates. Eventually, the difference will increase until it can harm the entire pack. When charging the pack, a balancer will set all the cells to the same voltage. By not having certain cells charged and discharged beyond their limits, the life of the entire LiPo pack is increased.

you can read more about Lipo battery here.
http://www.cuongnp.com
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Old Aug 03, 2009, 10:58 AM
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I think I caused unncessary commotion.

The dead cell I thought I revived did not hold charge.

My conclusion. When a cell in the pack shows 0 voltage, just discard it. Don't try to revive it. It is dead.

NiCd batteries revive after completely discharged. LiPo seems different.
Once discharged to zero, it does not revive. Finished.
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Old Aug 03, 2009, 11:56 AM
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Quote:
Originally Posted by John Kim

My conclusion. When a cell in the pack shows 0 voltage, just discard it. Don't try to revive it. It is dead.

NiCd batteries revive after completely discharged. LiPo seems different.
Once discharged to zero, it does not revive. Finished.
I agree with the cautions stated above.

That stated permanent death depends on a number of factors, not an unimportant one being YOUR willingness to take some risk. I have had cells discharge, and that was the end of it. No recovery possible.

I have a Hextronic 2S, almost new, I unfortunately was doing a discharge with light bulbs I forgot about and sent to zero. My fault completely.

I did the NiXX boost to 3v, then balance charged normally at 1/2C. It charged, balanced, puffed a little, and continues to function about as well as an identical mate. BUT, it ONLY has maybe 10-12 cycles since the incident and it is NOT a flogged lipo. I fully expect it to die early. I DO NOT advocate this behavior but am personally willing to accept the risk and watch that lipo very carefully.
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Old Aug 03, 2009, 01:56 PM
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Quote:
Originally Posted by nguyencuongaa
Any Lithium Polymer (LiPo) battery with more than two cells should be balanced. A LiPo battery is composed of individual cells, and each cell can charge and discharge at different rates. Eventually, the difference will increase until it can harm the entire pack. When charging the pack, a balancer will set all the cells to the same voltage. By not having certain cells charged and discharged beyond their limits, the life of the entire LiPo pack is increased.

you can read more about Lipo battery here.
http://www.cuongnp.com
Thanks man, thats really helpful. I worked out how to check on my balancer the voltage of each cell and all are holding a rather healthy voltage. The reason I was so concerned about this is that it's a second hand battery out of a 70mm F16 EDF I bought second hand, which when I took for it's maiden didn't have any power to fly.

I guess the cells had dropped to such a low voltage, one of them was just below the sensor threshold.
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Old Aug 03, 2009, 04:39 PM
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After the flight, I left my FMA 18C 2100 4S pack connected in
my EDF jet for about a week . Voltage got so low.
The TP 425 could not recharge the pack. My early version
cellpro 4S recognized only 2 cells and could not
charge it. I thought of throwing that dead pack
away. Then....

A friend of my brought life back to the pack
with his Cellpro 10S. Now The pack works fine.


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Old Aug 05, 2009, 03:00 AM
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I have found that if I accidentally render a cell or two on my 4s2200mAh lipos, then all I do is set it up on my triton 2 at 11.1V or 7.4 instead of the usual 14.4. I also attach a blinky balancer to it. Usually after about 5 minutes I'm able to get the cell revived. I then switch the charger back to 14.4V and charge normally.
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