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AC Charger for HP-21
11-15-2015, 10:22 PM (This post was last modified: 11-15-2015 10:28 PM by Harald.)
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RE: AC Charger for HP-21
(11-15-2015 09:11 PM)smp Wrote:  Hello all,

I just won a nice looking HP-21 with the manual and applications guide on eBay. No AC charger, though.

Can anyone please tell me what the correct part number for the AC charger for an HP-21 is?

Also, is it possible to mod the battery pack to accept AA Alkaline batteries? If it is possible, is it advisable?

Your thoughts are requested and welcome.


It is very much advisable to modify the battery pack to accept alkalines and not bother with the charger. If you have bad batteries or a bad contact while charging and the calculator is turned on, the supply voltage can become far to high and damage the calculator.
All you need to do is cut open the thin plastic strip at the end where the opening for the battery contacts is. Now you can push it up and to one side and slide out one battery. You will have to bend the plastic of the holder, so it is easiest to use a screwdriver do pry the battery out. The second battery will come out much easier.

Edit: Here is a picture of the strip cut away completely, but it is sufficient to cut it only on the left side.
[Image: Woodstock_bat_5.jpg]
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Messages In This Thread
AC Charger for HP-21 - smp - 11-15-2015, 09:11 PM
RE: AC Charger for HP-21 - smp - 11-15-2015, 10:17 PM
RE: AC Charger for HP-21 - Harald - 11-15-2015 10:22 PM
RE: AC Charger for HP-21 - smp - 11-15-2015, 10:25 PM

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