HP-19C Charger Output

[teenix]

Hi all,

I don't have one of these, does anyone know or can measure the AC output voltage unloaded direct from the connector plug. I would imagine around 9-12VAC.

cheers

Tony

[AndiGer]

Hi Tony,

Measured at 3 different chargers, all HP82066B.
Unloaded between 11.1 and 11.5 VAC

EDIT: One is HP82066A - the one with 11.1 VAC. The two other tend to be a bit higher, 11.3 to 11.5 VAC

Andi

[teenix]

Hi Andi,

Thanks for that, much appreciated.

Due to one component in my 19C CPU board I have to try and clamp it to 6.5V if the battery disconnects during charging. Under normal charge operation I would think the battery voltage is <6V, so a zener should do if I tap into the 15 ohm Hi charge resistor. The AC output should drop with a load on it so probably around 1W.

The processor monitors the battery voltage so I can display a flashing message if it is too high.

Even so, I think external charging is still the best approach, especially if things warm up with a fault.

cheers

Tony

[AndiGer]

Tony,

The charger has a nominal voltage of 8VAC.
Maybe you have to consider ….

Andi

[teenix]

Thanks Andi,

I was thinking with reference to the 97 charger setup which would be similar although with larger batteries than the 19C, the output may be a bit stiffer. The 97 has an overvoltage circuit that limits the battery voltage to 6.25V, most likely by loading the charge adaptor to reduce its voltage, whereas the 19C does not appear to have anything. Maybe there just wasn't enough room to fit such a circuit. I'm assuming the charge voltages are similar even though the 97 NiCads are C size and the 19C are AA. Both supply the same 5V to run the calculator. I am assuming then that while on charge under normal circumstances the battery voltage is going to less than 6V.

cheers

Tony