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+--- 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