can you run the HP 55 on AC adaptor without batteries?

[Steve Simpkin]

(02-28-2021 10:41 PM)dmh Wrote:  I know this should never be done for the Woodstock and Spice series and for the 67 but what about the 55? Is there any risk of causing damage?

Can someone advise definitively regarding the 55 with the technical details to confirm if so and why?

TIA, dmh

Yes. Running the Classics (HP-35, 45, 55, 70 and 80) on AC power without a battery pack is perfectly safe. The AC power supply on these models has a separate regulated power source for the calculator logic.

There is some concern about doing this on the HP-65 and HP-67 (which is not really a "Classic"). It appears the card reader circuitry is connected directly to the battery pack on those models. The manual for these two models warns against using the AC supply without batteries installed so I would not do it on the HP-65 or HP-67 (or HP-97).

More information here.

https://www.hpmuseum.org/forum/thread-82...l#pid72353