NiMH Charge Controller

Other Hardware General Electronics
1

I have a couple projects that I want to keep running through a utility power outage, I'm thinking that 3x or 4xAA NiMH cells would make a good supply and would be considerably less expensive than Lithium battery technology. I'm looking for either a charge controller IC, or perhaps a pre-assembled module, that would keep the cells topped off while they are connected to the load, so that they could run it for some time if utility power is lost.

I found the MAX712, and it looks pretty good, but is obsolete. The recommended replacements don't seem to be all that close. I'd rather have a current part, one that can operate without a lot of external components, and not cost half again as much as the project it's powering (~$35).

Wondering if anyone has done anything similar.

2

One of my cheap solutions (disclaimer: Use at your batteries own risk) is just set a constant voltage that supplies the correct current.

Example: I have a 9V, 300mah (from ebay) battery embedded in a project. It requires 17ma over 14 hrs to charge. I charge it with 10.38V which gives it the 17ma that it needs. Initially it will charge over 50ma but will soon decrease to 17ma where it will remain for hours. I know it's not the proper way to charge NiMhs, but it seems to work in my case. I wouldn't do it with expensive or high capacity batteries.