Power.....

Javalin

Hi,

Anybody know any way of monitoring voltage/battery capacity?· Ideally something like an IC that returns a voltage would be ideal!

Thanks

james

Jonathan H

James,

Batteries are rated in amp-hours (i.e. 100 Ah) and both their voltage and current delivering capacity drops as the battery is discharged. Some (like alkalines) drop continuously over the life of the battery while others (like NICads) drop precipitously just before the battery is fully exhausted. Ideally, you should measure current delivering capacity, but this is hard (I believe) and is subject to fluctuation as the load on the battery varies. A capacity rating like 100Ah is usually relative to what is called a "C20" discharge, meaning that the battery will deliver its full charge (the C, or 100A) when smoothly discharged over 20 hr (which would be 5A/hr).

As far as I know, the usual way of measuring when a battery is going dead is to use a comparitor and a voltage reference. You can construct these from a couple transistors and a zener, or buy a chip that collects it all in one nice package. Lots of people make these, but check out the Maxim Max8211 / 8212 chips, available in a DIP package (if desired). These are programmable and use an external voltage divider to set their trigger voltages.

Hope this helps!

Javalin

Hi Jonathan,

Thanks for the info - I will look into it!

james