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HP Forum Archive 19

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OT: Canon Pocketronic rebuild advice
Message #1 Posted by Michael Meyer on 9 Jan 2011, 8:48 p.m.

I'm finally getting around to rebuilding a Pocketronic in beautiful condition. Fortunately, the batteries did not leak much. Unfortunately, I do not have a charger, and I don't like rebuilding with rechargeables anyway. I'd like to rebuild it with non-rechargeable lithium cells. There is an assortment of cells inside, including a double and triple cell (2.4v, 3.6v) I have some Duracell photo AA's that are 3v. Does anyone see a problem with me mixing 1.5v lithium cells with 3v cells? I only plan to keep it on long enough to show it off (if I can even get it to fire up), so I don't think I'll overheat the cells. Any advice?

Re: OT: Canon Pocketronic rebuild advice
Message #2 Posted by Palmer O. Hanson, Jr. on 9 Jan 2011, 9:14 p.m.,
in response to message #1 by Michael Meyer

Somewhere in my collection I have an inoperattive Pocketronic so I will be interested in any advice.

I have found the mint condition 20 ampere high speed battery charger which came with it including the carton. Not suprisingly it is a big beast for a battery charger -- about 2" x 2" x 5".

Re: OT: Canon Pocketronic rebuild advice
Message #3 Posted by Katie Wasserman on 9 Jan 2011, 11:21 p.m.,
in response to message #1 by Michael Meyer


I have a couple of Pocketronics and a Monroe 10 (the same thing in a slightly different case). Like you, I've retrofitted virtually all my calculators to use Energizer lithium cells.

The Pocketronic uses two voltages : 7 x 2/3AA nicads (8.4 volts nominally) and 6 x AA nicads (7.2 volts nominally). The trick is to come up with battery holders for AAA size cells that can both fit in the provided spaces and can be wired in series to provide adequate voltages. I was able to do this using the following (I'm doing this from memory, so don't hold me to it):

1 2xAAA holder where the cells are front to back (not side by side)
2 1xAAA holders (side by side)
1 4xAAA holder (side by side)
1 3xAAA holder (side by side)

(Mouser sells these, the 2xAAA holder front to back is hard to find elsewhere.)

That's a total of 11 cells: 6 for the 8.4 volt nominal supply and 5 for the 7.2 volt nominal supply. There's only one way you can position these 5 battery holders in the Pocketronic cavities but there are several ways you could wire them up in series -- have fun with that!

Also, in case you loose track of the current wiring in the process of replacing the cells, it's this:

violet color wire is the common for both voltages
green color wire gets +7.2 volts
orange color wire get -8.4 volts

The craziest color scheme I've come across in a calculator but they are very consistent from unit to unit (I've rebuilt several of these over the years) even in the Monroe 10.


Edited: 9 Jan 2011, 11:58 p.m.

Re: OT: Canon Pocketronic rebuild advice
Message #4 Posted by robert rozee on 10 Jan 2011, 4:57 a.m.,
in response to message #3 by Katie Wasserman

hi, any chance of a photo of the machine? if going for non-rechargeables for just demo purposes i'd consider using a pair of 9v batteries, with a few diodes in series with each to drop down the excess voltage. provided, of course, they would fit in the available space - or you can leave the two battery snaps hanging out a convenient hole.

but do also consider that ni-cads will peak at 1.5 volts each when fully charged, so you will likely be ok just using the 9 volts direct. non-rechargeables don't have nearly so high a peak when brand new.

i remember once re-wiring an electric excavating arm that was used for demo purposes at a place where i worked (a JV with caterpillar). it had a reach of about 1.5 metres, with some hefty motors running it. i amazed everyone by running it off two little tiny 9v batteries in series while carrying out testing... worked fine, though obviously drained the batteries extremely quickly.

cheers, rob :-)

Edited: 10 Jan 2011, 5:01 a.m.

Re: OT: Canon Pocketronic rebuild advice
Message #5 Posted by Katie Wasserman on 10 Jan 2011, 3:43 p.m.,
in response to message #4 by robert rozee

I'm away form my collection for some time, but I'll try to post a pic in a week or two. Two 9V batteries might not work, the print head and drive motor both draw a ton of current in very short pulses. AAA lithium cells are more than up to the task but I don't think that a 9V alkaline battery is.

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