Re: Testing an HP41CX - yet more info Message #4 Posted by Randy Sloyer on 2 Aug 2003, 10:01 a.m., in response to message #3 by Vieira, Luiz C. (Brazil)
Yes, there is circuitry inside the pack, a basic rectifier with current and voltage limiting devices.
The charger input to the pack is 8 VAC, 3VA max. I would recommend charging the pack outside the calculator so you can monitor battery voltage to see if the pack is any good. Connect the AC source to the two side pins and watch what happens on the battery terminals. Voltage that never rises is a shorted pack, voltage that immediately rises to 4 volts and above is an open pack.
While Ernie's suggestion of using alkaline N cells is good, you'll find it an almost impossible task to locate a battery holder. The best method is to buy the cheapest dead 41C you can find on eBay with a holder. You'll still pay at least $40 though. Average price these days is $50 to $60 for a decent shape unit. You can resell the remaining bits and recover maybe $20-$30.
All my rechargeable 82120A packs have been rebuilt with Gold Peak 160 mah 1/3 AAA nickel-metal-hydride cells. They run forever since they have almost three times the capacity of the original ni-cads. http://www.tnrtechnical.com/ in Florida will rebuild your pack for $15 plus shipping. I buy replacement cells from them welded up in the proper orientation and rebuild my own. Takes some patience to split the case open, but it can be done very cleanly with a single-edge razor blade.
Beware of using alligator clips on the gold battery terminals (actually, don't do it), it is a flexible film and will tear. Clip onto a ball of crumpled tin foil and tape in place for testing. There is no current draw to speak of (< 100 ua) so the contact force need not be very high. Only when using accessories does the power go up.
Edited: 2 Aug 2003, 10:07 a.m.
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