Battery balancer/charger

I have lots of rechargeable AA betteries (around 30) - a mixture of 1700mAh and 2000mAh, all Ni-Mh.

However, due to self discharge, I find that there is never a charged one when I want it.

I'm planning to make a battery balancer/charger, which keeps all the batteries at the same voltage, at a charged level.

By thought was to connect all of the batteries together to ensure they are all at the same voltage. I would connect them via resistors to ensure that only a low current flows if a dead cell is inserted into the bank. This solves the problem of ensuring they are all charged to the same level.

I would then connect a power source to this (possibly a solar pannel), which would continuously trickle charge the batteries at a VERY low level - possibly ~2mA per cell. They would be charging at this level permanantly.

Can anyone see any obvious faults with this setup?

Thanks

Andrew

Edit - schematic added - ignore the resistor values - I just guessed them.

It should work. You should be able to trickle-charge NiMh batteries at 0.01 of their rated AH rating (17-20mA for your batteries) indefinitely without harm.

I don't see any reason for R15.

I find the new low self-discharge NiMh batteries much better in that respect. They are the ones that come already charged. They only lose about 10-20% of their charge in a year.

I will agree on low self-discharge NiMHs. I've been using **broken link removed** for a while now and they work great, especially in devices that have low drain like TV remotes, cordless keyboards/mice, WII controllers, etc where normal NiMH cells discharge themselves before the device would.

Hi,

Couldnt help but comment here a little too...

I have purchased several low self discharge NiMH cells in the past years and actually tested some of them over a period of 6 months just to see if they work the way they are supposed to work. I found that they really do work as advertised (low self discharge) and am turning to the use of these cells for all of my NiMH needs.
The nice thing about them is that you can charge them in December, leave them sit until the following November, pick them up and put them in something, turn it on, and it works! With regular NiMH cells that would not work because they would have self discharged to a very very low state by then. This means we dont have to keep them under constant trickle charge like the old style NiMH's (and NiCd's) need.

Thanks for the comments - look like I need to buy some of those LSD batteries.

Andrew