HP-35 and HP-65 Current Requirements - Printable Version +- HP Forums (https://archived.hpcalc.org/museumforum) +-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html) +--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html) +--- Thread: HP-35 and HP-65 Current Requirements (/thread-240034.html) HP-35 and HP-65 Current Requirements - Dan Lewis - 03-05-2013 Hello all, I got bored in the lab today, and I was thinking of the wikipedia article on the HP-35. It says that users would press the decimal point key to save the battery (and the on/off switch). I got to thinking just how much battery this would really save, so I figured I'd do some current measuring and share the results with you. -------------------------HP-35------------------ Display----------Current in DC milliamperes .--------------------79 0.-------------------84 88.------------------88 888.-----------------91 8888.---------------95 88888.--------------98 888888.------------102 8888888.-----------106 88888888.----------109 888888888.---------113 8888888888.-------116 -8888888888.-88--125 So, assuming you have a 1000 mAh battery, 1000 mAh ÷ 84 mA = 11.90 hours If you press the decimal point, 1000 mAh ÷ 79 mA = 12.66 hours Now for the HP-65, ----------------------HP-65-------------------- Display----------Current in DC milliamperes .-------------------133 0.00----------------142 8.------------------137 88.-----------------141 888.---------------144 8888.--------------148 88888.-------------152 888888.------------155 8888888.----------159 88888888.---------163 888888888.--------167 8888888888.-------171 -8888888888.-88--179 I knew the deciding factor on run time was how many cards I passed through the machine, so I decided to try that next. I fed a card in (with the ammeter set to capture and hold the biggest value it encountered) 4 times. Trial-----Current in DC milliamperes 1---------258 2---------302 3---------307 4---------392 It should be noted that these trials were done in quick succession. This means I put the card back through immediately after it came out the other side. I'm unsure if this has anything to do with the results, however. I took the meter off its MAX function and fed the card a couple more times, averaging about 295 mA. So, if we were to (somehow) run the motor constantly (probably not a good idea): 2000 mAh ÷ 295 mA = 8.51 hours which is significantly shorter than illuminating just the decimal point: 2000 mAh ÷ 133 mA = 15.04 hours. I hope you learned something from the results and I encourage you to come up with your own. -Dan