38C Battery Question



#8

Hi there,

I recently aquired a 38C HP calculator and found some batteries in there that i've never seen before, they seemed to have two negatives, so either side of the top and bottom of the battery was female rather then male. The size is AA, nd the batteres are no name brand, just black.

Currently the calculator doesnt swutch on but im sure that becasue the batteries are about 25 years old and dont work anymore.

I'd like to replace the batteries but where would i find these exotic AA's?! Or are those the wrong batteries and i can just use regular AA's?

Thanks for your help,

Marc


#9

Hi, Marc;

many original NiCad´s that came with portable devices have a 'flat' positive pole. Consumer rechargeable batteries usually have a visible, thicker 'tip'. If you take a closer look at the ones you have in your 38C, you´ll see that one of the poles is actually isolated, while the other is actually the bottom of the battery 'can'.

Because consumer rechargeables have this 'extended' tip in their positive poles, they are not the best choice for the Spices (HP3xE/C series: HP31E, 32E, 33E/C, 34C, 37E and 38E/C) because they bend the contacts too much, causing them to break after some time. I have some Spices with broken contact... 8^(

As a reference: the contact closer to the edge of the calculator case (topmost) is actually the negative pole.

Best regards.

Luiz (Brazil)

Edited: 5 Sept 2006, 2:25 p.m.


#10

Thanks for explaining Luiz, thats very helpful!
I will try it out tonight when i go back home.


#11

Luiz is correct. Also; most of the stainless battery clips have a + & - faintly embossed on them.


#12

This is wonderful information. I had no idea that AA batteries were made this way. I was going to try to install new batteries in my HP-67 module with Radio Shack replacements. When I took the module apart and looked inside I said "no way"! I noticed the old batteries did not have a tip on the positive terminals. I then had them replaced (no tips) by a professional shop in my area and everything works well. I thought I could do this because I successfully replaced the batts in my HP-25C and 31E.

tm


#13

Thanks for the responses,

I have another question. What I dont understand is that there are no points for the flat AAs to touch on the opposite side, I have uploaded some pretty shoddy camera phone pics, if they dont help let me know and I'll rephotograph them!

http://tex-server.org/temp/hp38c/IMAGE_00045.jpg

http://tex-server.org/temp/hp38c/IMAGE_00046.jpg

As you can see the one side has connectors (one of the flat bits unfortunately broke off, but I still have the little piece) and the other side has an old bit of white foamy tape.
Surely current can't flow if the negative side of the battery is not touching any circuitry?

I suspect i need to take it in for repairs, could anyone recommend how to go about repairing the hp38c in London?

Later and thanks!

Marc


#14

Hi Marc,

The batteries on your spice machine are in series (not in paralell), so there should only be a set of contacts on one end of the battery compartment. Your machine is as it should be. The original battery holder completes the circuit by bridging the other ends of the batteries together. The top contact on the calculator is the negative, and the bottom is the positive, so put the top battery in with it's negative end on the left (as you look at the back of the calculator), and the bottom battery just the opposite (positive end on the left). If you don't use the original battery pack housing, you'll need to find another way to jumper the other ends of the batteries together.

Hope this helps.
Best regards, Hal


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