A question about alternative power supply for hp41 series

[Dieter]

(02-24-2016 06:09 PM)wojtek Wrote:  But just count, on average 1800 mAh for a single nimh accu...

What battery size do you want to use? Typical AA NiMHs have 2000...2500 mAh, some even more (well, at least the label says so), while AAAs are typically 700...800 mAh.

(02-24-2016 06:09 PM)wojtek Wrote:  ...would give 1mA for some 500 hours till the voltage drops to some 1V from 1.2V. With 100uA the accu would last for 5000 hours or 200 days.

Let's say a running HP41 draws 10 mA at 6 Volts. That's 60 mW. Even with a 100% efficient voltage converter these 60 mW would translate to 60 mA at 1 V input voltage. Using a 800 mAh NiMH battery this means 13 hours. Or roughly one sixth of what you get ouf of a set of four regular Alkaline N-cells, resp. a quarter if N-size NiMHs are used. Unrealistically assuming 100% efficiency, that is. At 25% it's only 1/4 of these figures, i.e. in total roughly 5% of an N-size battery set.

Please correct me if I'm wrong here.

Dieter