HP-41C printer

[Joe]

The battery pack for my 82143A printer will no longer hold a charge. I've tried using the printer with the AC adapter plugged in, but that does not help. So, for now my printer is dead in the water. Does anyone have an idea that can help me?

[Viktor Toth]

Joe,

If you have a soldering iron and a little bit of skill with tools, you can fix the battery pack easily yourself. In North America and elsewhere, Radio Shack/Tandy sells NiCd battery cells that are the right size ("Sub-C") and already have solder tabs spotwelded to them (Radio Shack part number is 23-190; you need two packages, each with two battery cells inside). You can pry apart the old battery pack with a sharp knife, remove the old cells, note their position and the order in which they're connected, and then cut off the old battery terminals. Don't throw the old cells in the garbage (they're poisonous; Radio Shack does, at least here in Canada, accept them free of charge for recycling.) Solder the new cells together at the tabs, and solder the old terminals onto them, and reassemble the pack. Just make sure that a) you never heat the cells themselves (they may explode), and b) you never short the cells (even a partially discharged "Sub-C" NiCd cell can deliver many amps of current, causing burns, overheating/damage to the cell itself, and worse.)

And if you don't like to do this yourself, there are stores that'll do it for you. I once had this type of a battery pack rebuilt by a Canadian "Battery Plus" store, which may or may not be related to the "Batteries Plus" stores in the US.

Viktor

[Jerry Doctor (US)]

I had the battery pack for my printer rebuilt at a Battery Patrol store in Nebraska. $15 and 2 days.

[Steve (Australia)]

Also check out the articles forum for a way to rejuvinate nicad packs.

It really does work, and if you're looking at having to replace the cells anyway, you've got not much to lose.

[Joe]

Thanks for all the help. If I can manage to get the printer working again, my 41's will also thank you. This is a terrific site! Thanks again.
Joe DeShon

[Dia C. Tran]

After rebuilding several battery packs I was tired of doing that again. I now run my printer with a 5V/5A regulated power supply

[Joe]

What does it take to do something like that? I'm not educated at all in electronics. I'm just a humble machinist. Any help is appreciated.

[Andrés C. Rodríguez (Argentina)]

In any case you use an AC power supply to replace NiCd batteries, please be sure that such power supply is REGULATED. That means it has an electronic circuit that will deliver always the same voltage, regardless of actual load. Simple AC adapters (transformer+diodes+capacitor) are not regulated and may damage your printer.

I don't know how to tell you how could you verify this, at least ask at the shop where you are buying the AC adapter, and be sure about:

- DC output (not AC, rather obvious but ...)

- Output voltage (Should match the battery pack you are replacing, each series-connected NiCd battery adds 1.25 V to the pack. For instance, 4 batteries = 4 x 1.25 V = 5 Volt)

- Regulator circuit (Has or has not? MUST have!)

- Polarity (Identify the positive and negative leads)

- Maximum output current (Must be enough for the load)

Other convenient features include:

- Short circuit protection

- Thermal protection (For overload conditions)

I hope this list may help you, at least to ask the right questions to the salesperson!

[Steve (Australia)]

Yoou can find some quite cheap switch-mode plug packs that have outputs rated at (say) 5V 2.5A.

These are a good option because they are well regulated, have high current output (NiCad can deliver several amps -- even the lowly card reader for the HP41 needs 250mA, with peaks up to 1A).

Also note that 4 well charged nicads can deliver in excess of 6V, so a 6V power supply is not too much.

Oh, and when I say "quite cheap" I mean quite cheap in comparison with transformer based regulated supplies of similar rated output.