hp classic calculator charger without battery pack

[Jeff_Birt]

(01-08-2023 10:34 PM)teenix Wrote:  Assuming the charger components have not degraded over time, and it is supplying the correct power to the calculator, this is probably a warning about mains spikes and surges which will probably pass through the charger and into the calculator circuits and damage them.

The warning is not related to any spikes or noise on the AC line.

The chargers/wall-warts are unregulated power supplies (a transformer, rectifier and filtering cap). There is no voltage regulation. A 6V adapter might output ~8V when not loaded. As you approach the rated current capability of the adapter you get closer to the rated voltage.

When you plug the adapter in the load of the battery pack helps loads the adapter and lowers the voltage applied to the rest of the system. With our example of a 6V adapter that outputs ~8V unloaded, the load of the battery back would drop it down to ~6V. Without the load of the battery pack too high a voltage is applied to the rest of the electronics.

If, IIF, you understand what voltage would be applied with the original adapter loaded by the battery pack, to the machine you can substitute a well-regulated adapter of the proper voltage. If you do this wrong though you chance blowing things up.

I did a video on this very subject recently. https://youtu.be/f2ShjK9uq9Y