Re: Low loss/dissipation xistor or ...

Tim Wescott wrote:
Something doesn't jibe here. You're using a cordless drill pack, which should deliver about 1A-hour, and you say a 1W load lasts about an hour. But that 1W load should consume about 110mA (only slightly more at 11V), which means that you should have a good 8-9 hours from a 1A-hour battery.

Even the wimpiest imaginable electric screwdriver pack should be at least 500mA-hour, so we're still not down to one hour.

Are you sure you weren't running 10W (1A)?

You're right - good "catch". I wrote about the battery from memory & had it wrong. I was just using a 10 ohm load - 1A. And fully charged was 10v, not 11 - just to get all the facts righted.

A low battery _shutdown_ is, IMHO, a Very Good Thing. The references I have on the care and feeding of NiCd batteries claim that you can run a single NiCd cell down to nothing with little damage, but charging it in reverse is Very Bad Juju. With a pack, there will always be some mismatch in the cells, so when you get down to 0.9V/cell or so you can pretty much count on some cells being well above 0.9V and at least one poor *** that's at 0V and getting charge rammed through the wrong way.
....

I've read that too, but had forgotten it. My plans for a low battery detector was motivated by a desire to keep the heater going & my toes warm <G>. Thanks for the reminder.

Bob
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