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AC Charger for HP-21
11-15-2015, 09:11 PM
Post: #1
AC Charger for HP-21
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.

smp
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11-15-2015, 10:17 PM
Post: #2
RE: AC Charger for HP-21
OK, so I've (now) done some looking around, and it appears that the HP-82026A charger would be the one that I want.

As far as the battery pack goes, I would appreciate hearing what folks think about the advisability of modding the battery pack and installing two AA Alkaline batteries. If anyone can point me to a site that shows a how-to for this, I would appreciate that, as well.

Thanks,
smp
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11-15-2015, 10:22 PM (This post was last modified: 11-15-2015 10:28 PM by Harald.)
Post: #3
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.

smp

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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11-15-2015, 10:25 PM
Post: #4
RE: AC Charger for HP-21
(11-15-2015 10:22 PM)Harald Wrote:  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.

Excellent! Thanks very much for your advice. Now, I will have the confidence to proceed with doing this mod.

smp
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