Custom Li Ion battery pack

[Packhorse]

Im about to build a Li Ion 18650 battery pack with 2S4P cells

I cant find any protection PCBs with balance feature in the 7.4 volt range.
Is balancing important for this set up or just prefered?

The Cells I am using are the Ultrafire 2500 protected with the PCBs removed. Can I just use 2 PCBs for the protection of the pack? From what I have seen the Fets on the PCB are rated at 6amps each (2 FETs per board) so current is OK for my load.

Thanks

 

[steve6690]

Hi packhorse,
I can't answer your question but I found these :

http://stores.ebay.co.uk/All-Batter...W0QQcolZ4QQdirZ1QQfsubZ11120517QQftidZ2QQtZkm

pcb's at the bottom of the page.

I've used the seller before and the transaction went fine..

hth

steve

 

[MatajumotorS]

I made balancing circuit for my 2s5p li-ion pack by my self, but i used protected cells for this pack, to be shure not to drain them too mutch.

I used balincing circuit because, if using only protected cells or pack with pcbs from them, the overall available pack capacity will drop after each charge discharge cycle when not in balance (little different paraneters of cells). That wold be like this - on cell lets say charged to 4,15V, other to 4,25V and protection cuted in. First did not reach full, and when discharging protection of first will cut earlier than of the second. The difference will increase further.

But if you have perfectly matched cells what i wrote will not happen.

Ofcourse you can take out cells after some 10 cycles, and charge them individualy to make them balanced.

Added sch. Use one peace for each series cell.

used more resistors for higer balancig current