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

[dmh]

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

[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

[Paul Dale]

I do this all the time.

Pauli

[dmh]

(02-28-2021 11:31 PM)Steve Simpkin Wrote:  

(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 on AC power without a battery pack is safe. The AC power supply on these models has a separate regulated power source for the calculator logic.
There was some concern about doing this on the HP-67 (which is not really a "Classic") but it appears safe on those as well. More information here.

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

Regarding the 55, thanks!

Regarding the 67, I read that thread you shared (thank you) and am still confused about the 67. Towards the end it seems to go back to saying don't run the 67 without a battery.

[Steve Simpkin]

(02-28-2021 11:44 PM)dmh Wrote:  

(02-28-2021 11:31 PM)Steve Simpkin Wrote:  Yes. Running the Classics on AC power without a battery pack is safe. The AC power supply on these models has a separate regulated power source for the calculator logic.
There was some concern about doing this on the HP-67 (which is not really a "Classic") but it appears safe on those as well. More information here.

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

Regarding the 55, thanks!

Regarding the 67, I read that thread you shared (thank you) and am still confused about the 67. Towards the end it seems to go back to saying don't run the 67 without a battery.

Yes I read that too and edited my post. As per the manual, do *not* use the AC charger on the HP-65, HP-67 or HP-97 without the battery pack installed. Of course this is also true for any of the Woodstock or Spice models. Sorry for the confusion.

[teenix]

I think the 97 can be used on charger only but the calculator will not function properly and the printer, card reader will not work.

The owners manual mentions to have the batteries in with the charger, but only for improper display etc.

The service manual states that the 97 won't be damaged on charger only, but won't work properly.

The 97 has a voltage regulator setup on the main circuit board. However, it only regulates over voltage from the charger and stops this voltage exceeding 6V. The charger itself is only capable of supplying a reasonably small current (150mA or so I think) and the output voltage will drop as more current is dragged from it. This is the principle that the voltage regulator relies on which basicly shorts the recharger with a 47 ohm resistor. An external supply should not exceed 5.5V or so if it can supply a large current or this resistor will turn to smoke.

The other question is that the AC adaptor is just that, it outputs only AC and the main circuit does not have much in the way of a smoothing capacitor so the power supply will be fed with a DC ripple voltage from the full wave rectifiers. The battery probably substitutes for a suitable filter capacitor.

Either way, I'd prefer a regulated 5V external power supply without batteries, or keep the battery in whilst in use.

cheers

Tony

[teenix]

(02-28-2021 11:31 PM)Steve Simpkin Wrote:  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.

All good advice. Bear in mind that the chargers are as old as the calculators and the internal logic supply may be faulty. Just a thought :-)

cheers

Tony

[Steve Simpkin]

(03-01-2021 01:18 AM)teenix Wrote:  I think the 97 can be used on charger only but the calculator will not function properly and the printer, card reader will not work.

The owners manual mentions to have the batteries in with the charger, but only for improper display etc.

The service manual states that the 97 won't be damaged on charger only, but won't work properly.

The 97 has a voltage regulator setup on the main circuit board. However, it only regulates over voltage from the charger and stops this voltage exceeding 6V. The charger itself is only capable of supplying a reasonably small current (150mA or so I think) and the output voltage will drop as more current is dragged from it. This is the principle that the voltage regulator relies on which basicly shorts the recharger with a 47 ohm resistor. An external supply should not exceed 5.5V or so if it can supply a large current or this resistor will turn to smoke.

The other question is that the AC adaptor is just that, it outputs only AC and the main circuit does not have much in the way of a smoothing capacitor so the power supply will be fed with a DC ripple voltage from the full wave rectifiers. The battery probably substitutes for a suitable filter capacitor.

Either way, I'd prefer a regulated 5V external power supply without batteries, or keep the battery in whilst in use.

cheers

Tony

Hi Tony, There is a nice thread with good information about trying to use the HP-97 on AC power without batteries installed. Someone mentioned they thought doing that and trying to use the printer had damaged a nylon gear. In any event the HP-97 does not seem to operate reliably without batteries installed. I can't quite remember who started the thread but the name sounds vaguely familiar...
https://www.hpmuseum.org/forum/thread-14...tteries%22

[teenix]

(03-01-2021 01:34 AM)Steve Simpkin Wrote:  Hi Tony, There is a nice thread with good information about trying to use the HP-97 on AC power without batteries installed. Someone mentioned they thought doing that and trying to use the printer had damaged a nylon gear. In any event the HP-97 does not seem to operate reliably without batteries installed. I can't quite remember who started the thread but the name sounds vaguely familiar...
https://www.hpmuseum.org/forum/thread-14...tteries%22

Ahh yes, I remember the fellow - nice chap ;-)

I still think a Maintenance/Repair Forum would be a good idea these days, it might be easier to look up such things. Maybe while the Forum is getting an upgrade....hint hint :-)


cheers

Tony

[ThomasF]

Hi,

From own experience, I can say that running the 67 with a bad connection between the calculator and battery can fry the ACT when running on the AC-charger, so nowadays I'm very cautious when using the charger!