Nominal power supply for an HP-75D and question about batteries

[Tomás (España)]

Hello all.

I am new here, and also new at the HP calculators world (I've been using for 25 years Casio's ones)

I have got an used HP-75D but it came without cable cord nor power supply. I guess my friend had it retired for several years, probably since he left the USA.

My questions are:

1) Which power supply does this unit need to work? (there is no signal nor label indicating it) (I have dismounted the calc from the pod too, to check) I am in Spain now, and here we have AC 220V@50Hz, moving towards 230~240V@50Hz. Also, don't know if there was a power transformer and then the unit needs DC at, let's say, 12V or so.

Reading http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=910 it seems it is 110V@60Hz minimum 2A, but would like to be sure to avoid damaging the HP-75D.

2) At the back of the pod there are 2 empty slots. Inside both, one can read: "PROPER OPERATION REQUIRES BATTERY IN THIS LOCATION". My doubts are:

a) are they really needed to work, or they are only needed if you don't want to lose your programs/data stored in the RAM if you un-plug the power cord?

b) if they are needed, could you give me the technical details or model of that batteries to look for them?

I find rare there is no written indication of these data in the calculator.

Excuse my poor english, and nice meeting you in this nice site!

Tomás.

[Michael de Estrada]

Tomas,

I copied the following from this site:

Computers HP-75/D
Battery HP 82001B, Chargers HP 82059B/C/D - not A, (82066B, 82068B 240 VAC only)

You should be able to use any classic series (e.g. HP-35) battery. There are several vendors of replicas on ebay. You will want to use one of the 240 Vac model chargers.

Regards,

Michael

[Tomás (España)]

Thank you very much, Michael.

Your comment has guided me in the correct way, and I will look at eBay for those replacements. Yes, I have to go for the 82066B (EUR) or 82068B (AUS) 240 VAC chargers.

But a doubt still remains...

Are the batteries pack mandatory to 'test' the unit? I am not going to use in day-to-day basis, but only to 'play around', try programming and so on, few hours/days. What happens if there are no batteries but the power supply is pluged? Does it works but when turning off or disconnecting from the AC power it loses the memory and data? Or it just doesn't work?

Regards,

Tomás

[Tomás (España)]

Hello again.

I think I have found the answer to my last doubt here: HP Battery Information

It says:

"Warning! Most models can be damaged if run from the charger without good batteries installed. Only the manuals for the HP 35 and 45 models say that it's OK to run without batteries, but many collectors feel that even those should have batteries installed for maximum protection and long life."

So I understand I should never try to run the HP-75D whithout the 2 batteries HP 82001B, using only the charge adaptor 82066B or 82068B. Rigth?

Thank you very much for the help.

Tomás

[Nigel J Dowrick]

Tomas,

I also have a used HP-75 without battery packs or charger. I have managed to run it by wiring a 4.5V dc (regulated) power source directly to the terminals in one of the battery compartments. I used photographs of the battery packs on this website to decide which terminal was positive and which was negative. It worked fine; it was only necessary to power one of the two compartments.

Depending on your needs, this might be an easier way to go than obtaining a charger and battery pack. My plan is to obtain a triple AAA battery holder: this will provide the 4.5V needed, and the AAA cells in their holder should be small enough to fit inside one of the battery compartments. I intend to solder the leads from the holder direct to the battery compartment terminals.

Hope this helps,

Nigel

[Tomás (España)]

Hello Nigel,

Thank you for your suggestion. But when I read it, I had already done something similar: I have connected 2 x 3R12C. The 3R12C is a 4.5V Zinc Chloride, I think they are the same or equivalent to those 3R12 shown on List of battery sizes

With that, the system seems to work nicely. I have not try to connect just one battery slot as you did. Nevertheless, I have just try to store a short BASIC program and run it.

Anyway, I will try to get an adaptor and 2 battery sets. What I wonder is how yours can work. I expected the two slots were connected in serial, so to give (in my case) an overall voltage of 2x4.5=9V (and crossing my fingers that it didn't harm the unit, as the charger is 8V DC)

If your setup works with only 4.5V then why does the unit needs an 8V charger? I am not good on electrics ;)

Tomás

Edited: 28 June 2009, 11:30 a.m.

[Nigel J Dowrick]

Dear Tomas,

On my machine the two battery holders are wired in parallel, so even with a battery in each only 4.5V would be provided! This arrangement doubles battery life, and allows the packs to be changed one at a time without total loss of power, I suppose.

Incidentally, according to this link (www.rskey.org) the power pack for the HP-75C/D supplies 8VAC, not 8VDC! I haven't got the power pack so I don't know whether this is correct.

Good luck!

Nigel

[Tomás (España)]

Nigel, thank you for your comments.

Yes, I didn't noticed, but you are rigth pointing out the charger supplies 8VAC... I will try to buy a pair of battery packs, and eventually, an original charger.

Tomás