Hacking li-ion charger

[jumpjack]

Does it exist any tutorial on these widespread li-ion chargers about how to tune voltage and current?
They look all similar, maybe they just differ for... some turns of the interal trimmers!

I'd like to reduce current of my 67.2V/3A li-ion charger to reduce heating.

 

[dnmun]

3A is about as low as you can go and still get the battery to charge. most people wanna hack to 30A.

 

[peters]

Here are the schematics of a similar one, reverse engineered by a guy:
http://www.avdweb.nl/solar-bike/electronics/portable-lightweight-lifepo4-ebike-battery-charger-800g.html

They are usually similar, there are 3 potmeters (or perhaps there were 4 in mine, I dont remember), one for voltage, one for charge current, and one for current threshold (i.e. indication of low current/end of charge).
If the controller IC is TL494, then this schematic is usable.
I adjusted the voltage and current, need to measure the current during charging to see the change.
Need to be careful with voltage, too, not to exceed the the voltage limit of the output components. For example if the output capacitor is rated to 63V, then the voltage must be kept below this, with a few volts margin. Also need to take care of the power limit, if voltage is increased then current should be reduced.

 

[jumpjack]

3A is about as low as you can go and still get the battery to charge. most people wanna hack to 30A.

I know, but my charger is experiencing kind of a thermal runaway; as all DOZEN of previous ones (same model) I had, after 5 months from purchase it starts getting very hot rather than just warm; it usually ends by blowing up the capacitors close to the overheating coil... and I'd like to prevent it this time.

I think for some reasons an overcurrent starts flowing in the coil after some months. Which other reasons could cause coil overheating?
http://jumpjack.files.wordpress.com/2012/03/25032012167-cap.jpg
http://jumpjack.wordpress.com/2012/03/26/diario-elettrico-41-ancora-sul-caricabatterie/
http://jumpjack.wordpress.com/2012/03/20/diario-elettrico-36-viaggio-nel-caricabatterie/


Could the undersized 35V capcitors in a 60V charger be the cause?

 

[dnmun]

it is not clear why the choke gets so hot on them. you should try using a different charger if this has happened a dozen times. a larger size maybe?

the 35V capacitors are on a 20V circuit.

 

[melodious]

Curious here. Is there an average +/- voltage range on, say, 1/2 a turn. And is it linear

Example: Say I want to charge my 36v battery using my 48v charger. Would it be as easy as 1 1/2 counterclockwise turns on the trim (this is a guess, I don't know how many turns it takes)? Of course, I'd verify this by using a DMM on the output. Don't want to cause a big disturbance (i.e. overvolting) in the pack.

 

[jumpjack]

it is not clear why the choke gets so hot on them. you should try using a different charger if this has happened a dozen times. a larger size maybe?
.

I was never able in years to find a li-ion (LiCoO2) 60V charger sold in Europe!
Any suggestion?