Battery run competition, category 41

[emece67]

(12-16-2016 06:01 PM)MeindertKuipers Wrote:  The setup stopped this afternoon. Total run time 66 hrs (plus or minus 2 minutes), on 2* 1000 mAH AAA batteries, see picture.
This was a bare HP41CX with only the PPC ROM plugged, running a small user program generating primes with the NP routine.
Boost converter used is one from Polulu https://www.pololu.com/product/2560, set at an output voltage of 5.2V.

Being the converter regulable, perhaps you can get a little more run time slightly lowering the output voltage, say to 4.3 V or so (slightly above the low bat indicator). The internal voltage converter inside my 41 seems to have better efficiency around such voltage. On the other side, the efficiency of the Boost converter you use (it seems to be a TI TPS61200) may be slightly less at lower voltages, in part compensating the better efficiency of the 41's converter, but according to my measures/calculations such lower input voltage can give you around 3 hours more.

As a side effect, the battery life with the machine turned off will also rise, as the current consumption when off (in my 41) at 4.3 V is half of that at 5.5 V. The TPS61200 has a much greater quiescent current, though, so the overall effect is not such high.