This is really valuable info, Bob! I'm thinking of just pasting a dallas 1-wire temperature sensor on my battery pack, and another on the circuit board, which will be remote. That will get me a measure of the battery vs ambient temperature. I'm going to have a 7.2 volt stack, several in parrallel, so I'll stay away from using the peak voltage method, as you said. How well does the voltage into a charging NiMH need to be regulated? I am planning on using an unregulated 12V supply only regulating the current , not the voltage. The rated amp-hour capacity of my battery stack will be about 5-6 amp-hours. I understand that is also the maximum quick-charge current. Then I'll have a pass transistor that can turn off the power either briefly ( to measure actual battery voltage) or for good. Won't need trickle charging, this device will be charged, then taken to the field, then brought back for charging. I could also charge off some solar cells. These will have a max. capacity of only an amp at best. I'm not sure how this lower-current charger would work, though. Would the temperature method still work at 1/6th the battery's mAH rating? Or do I also need to use the voltage method? Seems like if you pump in some current, and deltaV is less than zero, zero, or just a little above zero, then you can't add any more juice. If you could hit the flat spot just before it peaked, by stopping at a certain minimum slope of voltage, that might save the battery from early death?? Lawrence Lile Lile's Integrated 'Lectronic Engineering Services ----- Original Message ----- From: "Bob Blick" To: "Lawrence Lile" Cc: Sent: Thursday, April 26, 2001 5:16 PM Subject: Re: [PIC]: NiMH battery chargers > Hi Lawrence, > > Only chargers that do fast or quick charging need this. > > Both nicad and nimh batteries show a peak in the voltage at full charge, > then drop. In nimh it is about half as noticeable. If you have just a few > cells and they are well matched, you can detect the peak and use that as > your indicator, because it will come before temperature rise. You > absolutely must measure temperature because the peak method is not > infallible. And temperature is the biggest killer of nicad and nimh > batteries. > > I didn't have much luck doing peak detection on a 10 cell nimh pack. One > thing that I did recently was measure the battery and also the ambient > temperature, quit charging when the difference was greater than 6 deg C. > > If you do the peak detection, you should probably switch to trickle, if > you use temperature, they're definitely full and probably don't want any > more charge. > > Keep them as cool as possible, if your charger itself produces heat, try > to prevent it getting transmitted to the battery. > > Cheerful regards, > > Bob > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads