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HP Forum Archive 08

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"plug in" power for HP 41
Message #1 Posted by aruid on 21 Apr 2002, 3:55 p.m.


I recently found an HP 41, but it only has the rechargable battery pack (very corroded) and not the akaline battery holder. My question is can I make the calculator run by modifying the rechargable battery pack and having it constantly plugged in?

Is their another quick way of providing power to it so I can test the calculator?



Re: "plug in" power for HP 41
Message #2 Posted by Ellis Easley on 21 Apr 2002, 9:31 p.m.,
in response to message #1 by aruid

Tony Duell said there are two versions of the rechargable pack - one has a voltage regulator that applies no more than 6 volts to the NiCads, the other just has a limiting resistor and would produce a higher voltage if the NiCads opened up. Since the NiCads are soldered in, there isn't the same risk of an open circuit as in the Spice and Woodstocks. But what I have considerd doing (haven't done it yet), since my rechargable pack, which I got in non-working order, has the voltage regulator, is to use the pack without NiCads just to run the calculator from the line, as you suggest. My pack has a rectifier, filter cap, a TO-92 12 volt (I think) regulator, a resistor, and a 6 volt zener diode. Adding some large electrolytic caps, maybe some approximately 1 farad "supercaps", in place of the NiCads might even keep the memory without AC for some time (if you are very careful not to turn on the calculator!)

Re: "plug in" power for HP 41 - additional
Message #3 Posted by Ellis Easley on 24 Apr 2002, 10:22 a.m.,
in response to message #2 by Ellis Easley

I should have mentioned that I would not expect to be able to operate the card reader and maybe some other peripherals that need extra power (HPIL?) using the regulated version of the rechargable pac without NiCads.

Re: "plug in" power for HP 41 - additional
Message #4 Posted by aruid on 24 Apr 2002, 11:22 p.m.,
in response to message #3 by Ellis Easley

You are partly correct, But I was unable to use the calculator at all with the nicads removed. The power supply only charges the batteries and will not run the calculator the output was only 4.75 volts. To fix the problem I just "gutted" the nicad pack and ran wire directly to the connectors, the calulator now operates on 4 "AA" size batteries in a seperate pack.


41's Power Pack? - Some questions
Message #5 Posted by Vieira, Luiz C. (Brazil) on 22 Apr 2002, 3:21 p.m.,
in response to message #1 by aruid


I have a full-nut that came with the golden-spheres contacts (say, a pair of golden-plated spheres with one golden-plated spring each,built with a rubber "holder" (?); these are built in the two little holes inside the charger tunnel). I read that these allow the 41 to be powered by an AC/DC converter. I also noticed that the holes are available in the newer half-nut's, but they are dummy (say, no contacts for the AC/DC converter available at the mainboard).

Getting Aruid's requests, I would like to know if anyone have already used these contacts. I remember (sometime ago, in the past 80's) I connected an external battery pack (four 1.5 A-size batteries) to read a bunch of cards. Successfull. But I don't remember the polarity...

Maybe this is more usefull.


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