Found my old HP-34C from high school

[jebem]

(09-21-2014 07:43 PM)Graan Wrote:  I charged the batteries for a while and it seems to work. I think I replaced them , but a long time ago (198X)
Seems not to be original batteries. Has a Mitshubishi logo (or equal) and "Made in Japan"
So how do I charge them? Outside the calculator in a charger?

/Andreas

Hi, Andreas,

The HP charger was designed to work with the NiCd battery pack installed in the calculator.
(Edit: Charger technical details - The charger adapter is just a transformer supplying 10VAC, so the charger circuit is located inside the calculator and contains a rectifier diode and a current limiter resistor).


However if the battery contacts shows oxidation and/or the battery pack life has reached its end, there is a risk of damaging the calculator electronics if it is operated while plugged to the charger, due to a potential over voltage situation (the batteries works like a voltage regulator).

To minimize the risks, I would not power on the calculator while the charger is connected to the calculator.
Charge the batteries for 8 hours, then unplug the charger and use the calculator.

If you find that the battery autonomy is too short, replace them by the same NiCd types.
More info here.