Revive a dewalt cell.. Is it possible?

[steveo]

I'm obtaining a free dewalt pack from a local service centre with probably a bad cell problem; is there any possibility of bringing the bad cell back to life?
How would i go about doing so?

thanks
-Steve

 

[Ypedal]

Might be able to use a " bad " cell for other applications like powering a headlight etc....

But for the powersource of a motor, built into a pack, it's best to have all good and matching cells.

 

[Malcolm]

I think I read somewhere that the BMS won't charge a cell if its voltage drops below 2.5V. Some of the RC folks have had success reviving cells by charging them with other single cells to raise their voltage high enough so that the BMS will start charging them. You could possibly do this without disconnecting the BMS, but it's extremely sensitive and very easy to kill.

 

[Jozzer]

Ideed, if the cell isn't actually damaged but has a low cell voltage the charger wont kick in. If you take the cell block out of the packaging to get at the cell ends, find the weak cell and parralell it with another 3.3v battery for a few seconds it may recover enough to charge, but be aware you may need to rebalance the pack by hand, or test it over many cycles charging with the dewalt charger before the weak cell gets a full charge and stops being the "weak" one.

 

[fechter]

If you tear down the pack so you can individually charge and discharge each cell separately, you could test them that way.

Once a cell actually fails, I don't know if there's any hope for it. I haven't heard of any tricks for reviving Li cells, but i suppose it depends on the failure mode. I don't even know what the failure modes are for Li batteries.

 

[Q-Bike]

The first time I used my dewalt pack, I forgot it connected to the controler for a few days. When tried to charge, the dewalt charger would say that battery is defective. Measured the voltage after each trial (the charger takes about 40 seconds trying to charge) the voltage increased by about 0.1 V. After many trials (maybe 30-80) the voltage was high enough to the charger stop to give the defective warning and start to charge normally. After this episode, I have not found this pack being worse than another pack I have. :lol:

 

[steveo]

I think i will go with placing another cell in perrall with the bad cell; could i use a lipo cell say at 3.3v to use instead of one of the other a123 cells?; i really don't wana tear apart the pack unless the cell doesn't funtion properly after reviving it.

the second method i might wana try is putting the battery in and out of the charger 30-80 times; i've seen this long method work on reviving a cell phone battery lithim ion.

I'll pop open the cell tonite or tommorw and let you know whats the issue is..

thanks the quick responses

 

[Jozzer]

Yes you can use any battery thats around 3v to 3.7v. (I used 3 NiMh). If the voltage is any higher than this, alot of current could flow, which would be bad considering you don't know the state of the cell...be carefull when making connections.
The problem with the second method is that its not one cell like a mobile, its 10 in series. All cells need to have the same state of charge, or else the very next time you discharge it you will run out on that same cell before the others. As Fetcher says, best to discharge each cell seperatly, or at least discharge the whole pack (with a bulb or somesuch) paying close attention to the cell voltages...especially the one that is low now. When its voltage starts dropping below 3v, probably the others will still be well over 3.2v, showing that the cell still isn't recieving full charge.

Without a method for charging individual cells it can be very difficult to balance a pack correctly, the best method being to charge each one to the 3.6v, and ten testing to make sure each has full capacity..

Good luck

 

[Doctorbass]

The first time I used my dewalt pack, I forgot it connected to the controler for a few days. When tried to charge, the dewalt charger would say that battery is defective. Measured the voltage after each trial (the charger takes about 40 seconds trying to charge) the voltage increased by about 0.1 V. After many trials (maybe 30-80) the voltage was high enough to the charger stop to give the defective warning and start to charge normally. After this episode, I have not found this pack being worse than another pack I have. :lol:

Welcome here Q-bike!

 

[steveo]

So... As i promised

Got my Free Dewalt dc9360; opened up the pack and tested the cell voltages

cell 1 3.28v
cell 2 3.29v
cell 3 3.28v
cell 4 3.28v
cell 5 3.28v
cell 6 3.28v
cell 7 3.28v
cell 8 3.28v
cell 9 3.28v
cell 10 3.28v

NO DEAD CELLS!!

seems like a perfect pack to me :lol: ; i ordered a charger of ebay.. so i'm waiting on that to come in, i think the bms went on this pack, but i don't know, i'm unable to test it at this point .

-steve

 

[Q-Bike]

Welcome here Q-bike!

Merci docteur!

 

[OneEye]

magudaman sold a BMS and case on ebay a few months ago and the final price was less than $7. You might be able to find an RC hobbyist or someone who is tearing the packs apart for the cells and offer $10 for the BMS out of it. Or just skip the whole BMS and run the cells raw with a compatible charger.