HP 67: charging of battery pack

[rprosperi]

(04-25-2017 12:34 PM)PANAMATIK Wrote:  I have to disagree. The HP-67 is not susceptible to this problem. When calling it a "Woodstock" calculator, this belongs only to the chip set but not to the charger. This will become clear when you have a look to the charger slot. Like the "Classic" calculators, it has three contacts. If you insert the charger plug pins 1 and 3 will be interrupted and the battery plus will become completely disconnected from the circuit, the high charging voltage is applied only to the battery, thus it is irrelevant to have a battery pack inside while charging and working with it while charging.

Because the HP-67 was a more expensive model, the charger was designed more costly to deliver two voltages, one regulated voltage for the circuit and one unregulated for charging. Only the cheaper "Woodstocks" used a charger with only two contacts and only one voltage for working and charging, this design requires the batteries inserted while charging and having switched on the calculator.

The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80.

Bernhard

Thank you for clarifying this Bernhard. I have read several past threads on this exact topic, and each time there seem to be folks arguing for each view. Your simple explanation is convincing, but if someone else can explain the damage mechanism given the '67 design, please do so. I prefer to simply charge my '67 battery in the machine, and have done so for many years, but don't want to risk it if there is some confirmed failure mode that has not yet been explained.