Electronically identifying between NiMH and Alkaline batteries...

I know a number of battery chargers (and devices with built-in charging capability) include an IC allowing the device to identify when a set of alkalines has been inserted instead of NiMH, thereby disabling the charging circuit... (I don't believe my Logitech mouse is such a product, but my Maha charger is and I've also read of various CD players with this ability)

Anyone come across any documentation for implementing such a design? Or come across suppliers of ICs that already handle this (perhaps with charge management capabilities as well)? Obviously for integrating into a device that takes batteries, to allow charging without removing the batteries and to prevent some doofus from charging it while populated with alkalines.

Bruno

Tony, this is not part of my world-domination plot. Simply an aside.

The Rio Volt CD player I bought my sister came missing the rechargable batteries. I put some NiMH in, and found it wouldn't charge them. With some help here, I found that the supplied batteries expose the bottom metal of the battery for a second contact to sense. Scraping the label off the bottom of the rechargable batteries worked as a substite to the missing ones.

Not sure how her newer one does it. The Volt eventually broke, so she got a new one under the protection plan at Best Buy. She is rough on electronics, and is bound to break anything given time. The Volt still outlasted any other CD players she had, so it was worth the money.

Interesting... That would require batteries that have been pre-modified (or having to modify them). Much simpler (low tech) than trying to sense the chemistry of the battery though. A simple continuity check could then test to see if the bottom is exposed. Of course if someone were to do this to an alkaline we're back into the original problem - chance for explosion/rupture of the cell.

I managed to find a few links to manufacturers of charge management ICs but I haven't looked closely enough at the various datasheets to find out if they can detect between the different battery chemistries.

Bruno

So I started looking more closely at batteries and found out that NiMH cells are negative around their casing while alkaline cells are positive. That's likely what the Rio Volt was counting on above. But since not all brands are made to exact (the same) specs there's likely to be variation causing some incompatibility.

The NiMH cells I have all expose a lot more of the bottom of the battery (negative) than regular cells. However, they all expose exactly the same amount of positive surface (just the center tip) - unlike regular cells which expose nearly the entire top (usually about the same as the bottom).

I'll find out which is the most fool-proof way of checking, but right now I'd lean toward testing the top (positive side).

Bruno