4 dead cells. options? 18650

[oobagooba]

10s4p samsung 26f bottle battery has 1 string of 4 dead cells. The bms was crushed in one corner and quit feeding that group of 4. I replaced the bms, it now charges the 4 cells up to .74v then cuts off when the remaining 36 cells hit 4.2. When the charger cuts out the 4 bad cells drop to 0 and stay there.

The vendor (gbk) sent me the new bms. Now they are telling me to charge the dead cells individually so it can balance the pack. I read on a flashlight forum that charging a 0 volt 18650 can start a fire.

What are my options? I don't have a spot welder or a 4.2 charger. The vendor is in china so i'm on on my own with the pack. Should i look for a 4.2 charger? Is there someone in the states who spot welds cells? I can solder wires and cut strips, could i remove some cells (10?) to keep 36v but with less range?

 

[oobagooba]

Here are some pics

Samsung 26f

Bad bms

New bms charging the pack

4 dead cells are above the blue exacto knife. Easy to get to at the end of the pack.

View from the other side. The main discharge leads are connected to the dead string, fwiw.

 

[joss]

Any cells that have been discharged to <1V are possibly damaged and present a future risk of total failure (possibly catastrophically). However, you may want to get a charger to see if you can 'lift' the voltage back to usable levels. There are many reports out on the web of people doing this and have some useful life from the batteries. A point to note that many 4.2v chargers will not start the charging process if the battery voltage is under about 2.7v. In this case you need to manually 'lift' the voltage using something like a bench top power supply. This should only take a few minutes to bring the battery(s) to a voltage that the 'proper' charger will start/engage.

For the cost of 4 replacement cells the pack could be repaired properly but, yes, getting them welded in is the tricky part. Good luck!

 

[redilast]

The general rule of thumb is any Li-ions that have spent potentially more than 1 week under 2 volts are dead and you should not try to recharge them. They can develop copper shunts and internally short out. The above poster is correct that most IC controlled LI-ion chargers will not initiate a charge if the cells voltage is too low (UVL under voltage lockout at 2.5 - 2.7v or so). The only way then is to use a bench power supply to lift up the voltage slightly to allow for charging. Or to parallel the cell with another good cell to trick the charger into thinking its ok then remove the paralleled cell after a couple minutes. I don't recommend this unless like I said the cell has been <2 volts for less than a week. The other thing is when trying to recover a cell that has a resting voltage <3v you want to charge it about as slowly as reasonably possible until the voltage increases a bit. This will reduce damage to the cell and many Li-ion charging IC's actually have a soft start feature built in.

If the cells have been <2v for potentially more than a week those 4 cells are dead and should not try to be revived. At that point its a bit of a tricky situation because you do not generally want to mix brand new cells with old used ones. If the pack only has like <50 cycles on it throwing a new one in the mix may be fine, but otherwise you'd probably want to try to look for the same model used samsung cells out of a laptop battery pack like on ebay or something. And you would want to capacity test them as well as other cells to find ones that are similar in capacity (within 10% or so). Then spot welding is by far the preferred solution, as soldering can damage the cell and the PTC. The heat increases the resistance on the PTC. If you do end up soldering, probably the preferred method would be to use several tabs or short wires as opposed to one large tab / wire that way less heat for less time is applied to the cell.

 

[999zip999]

2.5v - 2.7v is zero capacity or empty, very close.

 

[oobagooba]

Here is what i got from the vendor. "Could you please use a cell phone charger to charge each cell to 3.7V then the bms can balance them."

Here is what i found at bu. "Do not boost lithium-based batteries back to life that have dwelled below 1.5V/cell for a week or longer. Copper shunts may have formed inside the cells" http://batteryuniversity.com/learn/article/low_voltage_cut_off

It took a few weeks of back-and-forth with the vendor to get the new bms. Sounds like it is too late to try "boost charging" the cells...?

Sounds like a hazard to try boosting them in place still welded up to the other 36...? Sounds like they should be boosted individually inside my wood stove...? If so I would need a spot welder anyway to reassemble.

Anybody ever boost 18650's back from 0 volts? Still connected to a pack? Anybody know of someone in the states who can weld in new cells through mail order? thanks for the help so far

 

[999zip999]

Hard to mess with cells below 2.5 volt.

 

[999zip999]

Hard to believe zero volts.

 

[Grizzl-E]

Don't charge them. Or do, no one can stop you from doing something stupid.

Or buy 4 new cells.
http://m.gearbest.com/batteries/pp_190732.html

And take them and the pack to any tool battery repair shop for spot welding. Look for cordless drill repair shops locally, many will have a battery spot welder.


Sent from my iPhone using Tapatalk

 

[999zip999]

Make sure all cells of same voltage before assembly. All cells, it's easier on the bms ect. Plus start out balanced.

 

[friendly1uk]

Tell them you have tried to charge them. They charged up a bit but the charge just went away.


Don't confuse them with how you did this. You have done it is all that matters. If it makes things easier then tell them you used a phone charger, but I would just tell them what they need to hear. No lies.

 

[oobagooba]

So i've given up on the idea of boosting them back from 0. They've been asleep too long and i'd have to cut them out of the pack for safety. I was trying to avoid cutting the pack open because I don't have a spot welder.

Has anyone repaired a bottle battery before? It looks like the cells are welded up inside the plastic holders... in which case i'd need a spot welder with leads. Can someone recommend a good cheap spot welder with handheald leads? From a vendor that takes paypal? thanks...

 

[docw009]

How would 4 18650's with tabs work out? They look to cost run $6 to $8 on ebay and amazon. I don't know how they would solder.

 

[oobagooba]

thanks i will look into that. cheaper than buying a spot welder and i'd be adding 4 new cells either way, so maybe the same results....

 

[999zip999]

Don't solder on cells. You can solder on tabs with big 80watt fat tip iron. Not a solder gun. With a a sponge to cool. Making sure all cells are of same voltage to start with. A dremel with a diamond wheel from harbor freight to cut it apart. Be Careful it's alive. Very much alive.