HP34C AC input

[gwanghoops]

Hi,

Just got my first Spice calculator, a HP34C, and it works fine from a DC supply to the battery terminals (I never a rechargeable calculator from AC only).

Just wondering if I can provide DC input to the 9VAC charger port to power this calculator without a battery pack. I do this on TI-58/59 calculators when the battery pack leads are broken. Very curious.

Geoffrey

[teenix]

It depends on whether you intend to keep the battery in circuit or not when on the DC supply.

The battery is acting as a regulator (of sorts) for the charger input, which is fed via a series diode giving half wave rectification from the AC charger. The charge circuit is dependent on the power switch position so that when turned OFF the battery is charged through an 8.2 ohm resistor and when turned ON the resistor is shorted so the charger can charge the battery and also supply current to the calculator.

You would have to check that the DC voltage is compatible with the voltage that is supplied by the charger while it is under load just charging the battery, or charging the battery and running the calculator. I don't know what the battery charge specifications are.

If you omit the battery, then a regulated 3V DC supply should be sufficient, which will be around 2.4V after the diode. I would make sure this voltage is not exceeded by much during normal operation. The charger input will be reverse polarity protected because of the diode.

cheers

Tony

[gwanghoops]

Thanks!

And for those who have poor google search capabilities, such as me,

HPCC Schematics

HP-38E Power Supply Circuit

[John Garza (3665)]

If you intend to run it 'wired' all the time anyway, why not just connect alligator clips to the battery terminals and run it without the battery door? Simpler, and no modifications required.

Unlike the TI-58/59, the battery door is open to the top of the machine and you can route wires out there without the machine resting (and wobbling!) on the exposed wires.

Either use a 3VDC power supply, wall wart or 'real' power supply, or build a little 3V external battery box.

-J

[gwanghoops]

(03-11-2024 07:18 PM)John Garza (3665) Wrote:  If you intend to run it 'wired' all the time anyway, why not just connect alligator clips to the battery terminals and run it without the battery door? Simpler, and no modifications required.

Unlike the TI-58/59, the battery door is open to the top of the machine and you can route wires out there without the machine resting (and wobbling!) on the exposed wires.

Either use a 3VDC power supply, wall wart or 'real' power supply, or build a little 3V external battery box.

-J

It's a matter of convenience and curiosity right now. I have multiple TI-58/59s and other nicad powered calculators and it's easier to run a AC plug with DC input.

If I ever get some more Spice calculators...