Classic Battery Terminals

[DanLewis]

Does anyone know what the terminals for the classics were made from? Some of the gold plating on my 35's negative terminal is flaking off and I can see that the metal beneath is silver in color, but it does not seem to have any rust on it. Could it be stainless steel? Or maybe copper plated in something before the gold plating?

When I received my HP-65 about 2 years ago, the gold plating was completely gone and it looked like the terminal was made of copper. I tried hammering some 14 gauge copper wire flat, but it did not have the same elasticity as the original terminal, so the battery connection was always intermittent. Now it has gotten to the point that the terminal is about to break because of excessive bending, so I'd like to make a new one, but I don't know what to make it out of.

Is there some type of heat treatment I could give the hammered flat wire to strengthen it? I'm not too knowledgeable in the materials part of engineering, but I think I would have better luck with some copper or brass sheet stock, like the stuff used to make the 65's card reader leaf springs. It seems to be a lot more flexible and elastic than the wire I hammered flat.

[aj04062]

My guess these are either phosphorous bronze or beryllium copper. The BeCu can be formed in a half hard state then heat treated to give a very high spring rate. If fact, I would lean towards these being BeCu.

I've spent a portion of my career in RF broadcast product manufacturing and most electrical contacts like this were BeCu.

[Marcus von Cube]

I can't comment on BeCu but I have a possible alternative that is easy to find. The battery terminals of a 4.5V flat battery:

[DanLewis]

Thanks guys, I'll look into these!

[jjohnson873]

Just a cautionary note: Beryllium Copper (BeCu) is acceptable to work with if you're not grinding or machining the material. However it is recommended to use gloves and a mask when working with this material. The problem is that Beryllium is a known cancer agent when microscopic particles or fumes are ingested into the lungs. Beryllium can cause irritation to the eyes, lungs and skin. BeCu is used in many electronic and industrial applications due to it's superior properties. Several applications have moved from BeCu to Cu-Ni-Sn to reduce any cancer risks.

[aj04062]

(11-22-2014 03:25 PM)jjohnson873 Wrote:  Just a cautionary note: Beryllium Copper (BeCu) is acceptable to work with if you're not grinding or machining the material. However it is recommended to use gloves and a mask when working with this material. The problem is that Beryllium is a known cancer agent when microscopic particles or fumes are ingested into the lungs. Beryllium can cause irritation to the eyes, lungs and skin. BeCu is used in many electronic and industrial applications due to it's superior properties. Several applications have moved from BeCu to Cu-Ni-Sn to reduce any cancer risks.

I completely concur, I came into RF engineering when this was being realized and worked to redesign several BeCu connectors/contacts to use different materials.

Phospor Bronze is also an alternative to BeCu, however it cannot be spring tempered like BeCu.

[DanLewis]

How about this stuff?

http://www.ejbmetals.com/p/25/C17200

Someone has quite a lot of it in .125" by .002" for sale, I could make enough terminals for a "few" machines.

[jebem]

I would use Marcus suggestion above:
The 3LR12 / MN1203 4.5V batteries are a good supply for battery terminals, and easy to solder to the calculator PCB.

In my case, as I had a bunch of spare micro switches, I just have cut the lever to the correct length and have soldered it to the PCB.
It works nice and you can find these parts in any electronics store for a few cents each.

[DanLewis]

That didn't even cross my mind! We probably have a bunch of these at work, so that should be no problem. Thanks!

[DanLewis]

I tried salvaging a lever from a micro switch, but this particular one was made of steel, so I couldn't solder the wire to it

At this point, I think the best idea may be to salvage a terminal from a junk calculator. The bends in the terminal are critical to the elasticity, and snatching an already made terminal will assure the bends are made correctly.

I have never seen one of those 4.5 V flat batteries before, and I would hate to buy one just to use it for the terminal.

[DanLewis]

I don't know why I didn't think of it before, but the solution was so simple!

A few years ago, I built a VHF antenna out of some PVC pipe and a tape measure. The tape measure elements work well because they are easily foldable and lightweight (and REAL easy to measure!).

I had some extra steel tape from this tape measure laying around, so I just cut a piece of it to size and voila, it works! The tape used in a garden variety tape measure is about the springiest stuff out there, and although it is very thin, it's still enough to handle the current drawn when pulling a card through the reader (about 300 mA).

I was able to solder the wire to the terminal even though it was made of steel. I think this particular type of steel takes to the rosin-core solder better than whatever that micro switch lever was made of.

Another interesting happening:

When I took the machine apart, the two wires that power the display had broken off from excessive bending.

When I soldered them back on, there must have been a poor solder joint on the black wire (the one closer to the bottom of the machine) because when I powered the calculator up before completely reassembling it, everything worked fine. BUT, when I tightened the screw in the upper right hand corner (underneath the corner of the card reader bridge board) the top row of LEDs would not light up, and the corner of the little tan box (I think it's a group of resistors?) that's soldered to the board behind the LEDs became very HOT!

I checked to make sure this only happened when I tightened that screw, and sure enough, that was the case. I reheated the black wire's solder joint, making sure to flow the solder more evenly onto the board, and everything is now ship-shape.

[DanLewis]

The display problem in the 65 had returned, so this time I replaced the wires that run from the power connector to the display, and everything is in working order again. I think the wires were just too short and they were smashed between the circuit board and the display driver. The longer wires I added now travel up and over the circuit board, so this problem has been eliminated.