HP 97 AC Adapter/Recharger Replacement

[zixingcheche]

(07-27-2023 06:22 PM)Jeff_Birt Wrote:  This sort of adapter is a small transformer in a box. There is no voltage regulation to it so voltage out is a factor of voltage in plus the load on the output. The more it is loaded down the lower the voltage. Conversely when measured open circuit the output voltage will be higher.

Typically, the output rating on unregulated adapters is voltage at rated load. Looking at the label on an original 120V adapter the input voltage range is 90-120VAC. Quite a broad range of input voltage. Output is rates as your 220V adapter 8V @ 3W which is 0.375A. I'm not sure if one of the calculators these adapters was used for would draw that much current while charging. I would guess that this AC output rating is RMS but perhaps it is average.

Looking at modern wall adapters about this size the smallest 6VAC adapter I quicky found has 1A rated output. Its open circuit voltage would be similar to the HP adapter. The smallest 9VAC adapter I found was rated at 500ma output. This is about 4.5W so the loaded voltage might be a bit higher.

It does not look like the exact output voltage was terribly important based on the wide input range. If you have an original adapter, you can measure its open circuit voltage and loaded voltage and compare that against a 6VAC adapter with the same load applied.

Thanks! My HP adaptor in un-loaded status is around 11VAC. maybe I need a similar one around it. I will have a try.