backup battery charger

[PhilBot]

Originally Posted by Tom Line

Yep. We built the circuit last year, and then chucked it out. You're much better off going to a hobby store and spending $25 on a high capacity 7.2 volt pack for RC cars and a nice charger actually comes with it. Once we did so, we never once had a backup battery issue, even when running with the same battery all day (with camera).

Even with a better battery, there's still the issue of someone remembering to change it periodically. The longer it lasts, the longer between changes... so kids tend to forget.

Having it charged on-board means never having to remember to change it. Granted, without the camera this year, the batteries should last longer....

We built a PCB for the charge circuit and got 3 boards made (just the boards) for $60.

I attached the ExpressPCB scematic and PCB files on this post: http://www.chiefdelphi.com/forums/sh...6&postcount=27

We'll be building a new one this year....

[eeeeweeezeee]

Originally Posted by Al Skierkiewicz

NiCad battery technology requires some method of limiting charge current to prevent battery failure.

you're right, and I forgot to mention it but I also have a very large 300ohm variable resistor just for this. we already have plenty of backup battery packs and chargers, but every year I am disappointed by the chargers given out in the kit of parts. with at least two of them, their internal components have failed catastrophically. the exact description is the charging indicator turned a color its not supposed to, and there was a muffled THUD! and the light went out. I don't quite trust the ones provided by IFI so if I can make one myself and it fails, at least it is part of my learning experience as a high school student.