Different cell ratings in a 2 cell mod

Hi everyone.

I was wondering, is it possible to have two different rated cells ion a dual cell mod?? For example, my bit has it's stock 80mah cell and I've purchased a 120mah cell. I'm wondering whether I can link the two for extra voltage together ?? Or do the cells HAVE to be identically rated ?? Help much appreiciated.

[funkymonkey]

Different capacity cells is a BAD idea. You end up with something called reverse charging. Confused? Yeah its ok so was I.

Say you have one 100ma and one 50ma. The 50ma will lose its capacity first. Once its empty, current will still be coming from the 100ma one, and because the 50ma is in the circuit, the 50ma actually starts to charge in reverse. This really kills the battery.

From the Ni-Cad FAQ


"Now, as discharge continues, the current through the dead cell is becomes a charging current, except that it is reversed. So, now reduction is occurring at the positive terminal. As there is no more nickelic hydroxide, it reduces the water, and produces hydrogen. Cell pressure builds, and it vents. The cell has lost water and the life of the cell has been shortened

Hope that helps.

Flip. Well, that was close. Cheers for clearing that up for me! Looks like I'm gonna have to go and buy another 120mah cell !! By the way, where abouts you from in England ??

[funkymonkey]

Im from Darwen in the Northwest

And you?

Couldn't be further!!
I'm in Kent in the south east!

What type of Char-g do you have ?? Any mods to it ??

[funkymonkey]

Just a Bensu Bullet clone. Only got into the hobby a couple of weeks ago. I soldered the motor because the heatsink wasn't holding it in properly, and ive changed the bit aerial for a solid core one.

Probably gonna do the rare-earth magnet steering mod and might do a two cell mod on it with the button cells i have.

Gonna buy a couple of 'the real thing' this month though, and maybe buy a few Bensu's cheap for spares and guniea pigs.

I was wondering.
After you do the controller mod (the one that makes the charge bypass the timing circuit and gives your car the full 3volts of charge) it will charge both cells (of a 2 cell mod) very well. But If you had this same controller mod and only one cell (say, a 50mAh) would this 3v charge from the controller ruin the lone cell ??

[funkymonkey]

Ideally you should charge the battery at the same voltage, in reality the controller charges the battery at a higher rate. Its probably not so healthy for the battery but with the short charge times of the controller, it shouldnt be a real worry.

So, no, I wouldnt worry about it too much.

Ok. It's just I was thinking of doing the dual cell mod, but with the second cell as removable. Thanks for your input mate! Just need to find another 120mAh cell now ...