Locked 4200's HELP!!!

[philly]

Hello.
I have 3 packs of matched 4200's. 2 of them have some how stopped holding charge. I charged them the night before the York regional and topped before they went in the car, and they lasted till the second corner!

The packs are about 3 months old and have been used maybe 6 times?

I'm hoping it will be a case of fully discharging and then starting again, but what is the best way to go about this?

[Lee]

Sounds to me like they are already discharged (too much)

The cells have probably false peaked when you have charged them, the only thing you can do is charge them till they are warm, to stop it false peaking put a high delta peak on the charger but dont let them get above 45 degrees, then discharge them and try it again. if they false peak bang them back on till they are warm

[jimmy]

Equalize them and cycle them a couple of times - see if that brings them back. Someone with some more 'cell knowlege' might be able to offer some better advice or even help you with it.

I had the same thing at the last n.west regional - I did one lap before it began to dump on a fully charged pack.
I have some almost new 4200 cells also which both packs had one cell that had discharged before the rest - a quick equalize on priceys novak tray has brought them back to life though.

[_sleigh_]

You need to discharge each cell individually.
Then "force" charge them individually to a set voltage (1v)
Once done, discharge the whole pack on a normal discharger down to 6v.
After that stick them on a discharge tray (The LRP one is good, oh or Nosram ).

Now... stick them on a charger to fully charge and monitor each cell voltage periodically during charge.


Obviously between each stage let the cells cool down...


This is the method I used on some 3700's a few season back, and it rescued them quite happily. Used them of several months after.

[JCJC]

Put a volt meter across each cell, possibly only one cell giving you grief, you will spot any that are different. plus check the volts on the whole pack, compare with your good packs. Of course could be a duff solder joint.

[Chequered Flag Racing]

Originally Posted by JCJC

Put a volt meter across each cell,

if you haven't got a Pro-Trak or access to one whilst you charge the pack @ say 10 anps for 1 minute.

See Pack Test on Pro-Trak site for more info.

[Richard Lowe]

Originally Posted by philly

I charged them the night before the York regional and topped before they went in the car

If thats what you've been doing with them that explains why you're having problems, re-peaking IB's after a while kills them.

From the Demon website...
"Do not precharge the night before and repeak on day of race. This may cause the vent to fail, and subsequent loss of fluid. If you repeak after a long wait, the peak voltage will remain flat and the cell may overcharge, especially if they were already fully charged."

Also...
"If you get a cell that has flat lined to 0.0volts and will not charge, it can be bump started back to life by flashing it with 12volts. Use a couple of wires and spark the +ve 12volt to the +ve of the cell."

I have no idea if this works, I'm guessing you won't have to give them 12v for more than a second unless you want a melted puddle on the floor

[Lee]

Rich,

I have seen a pack of cells charged directly from a 12v battery, it didnt take long and the speed of the car was awesome, but they only lasted a few more charges after that

Those were the days of 1700 scrc`s though

[_sleigh_]

Originally Posted by Richard Lowe

Also...
"If you get a cell that has flat lined to 0.0volts and will not charge, it can be bump started back to life by flashing it with 12volts. Use a couple of wires and spark the +ve 12volt to the +ve of the cell."

I have no idea if this works, I'm guessing you won't have to give them 12v for more than a second unless you want a melted puddle on the floor

That's the method I used to "force" charge mine.

Be sure you make the connection quickly and don't let it arc to much, as it might arc weld to the cell.

[Richard Lowe]

Originally Posted by Lee

I have seen a pack of cells charged directly from a 12v battery, it didnt take long and the speed of the car was awesome, but they only lasted a few more charges after that

I don't think it means to 'charge' the cell straight from 12v, just to give it a bit of a wake up by touching the contact to the cell momentarily. Connecting the cell across a 12v won't so much charge it as just heat it up and kill it

[philly]

Sounds like fun!
Thanks for the help. I guess I'm in for a boring weekend!