I made another battery holder just a block of wood with a screw to tighten against the AA cell. This screw tightens up against the negative end. The positive end just rests against the wood. I plan on putting the wire between the wood and the positive and tightening the screw to hold it there . I’ll clip an alligator clip of the negative lead on the screw threads.
The question “why not just use a battery holder from the store?” comes up, and there are 2 answers. The battery holders from the store are so cheap that between the springs, the rivets and the thin wires, the I2R (I squared R) losses add up to an excessive amount. I took a brand new single AA cell holder out of the package and tested it with my ohmmeter. I put a short alligator clip between the spring and the other contact and measured the resistance at the ends of positive and negative leads. My very accurate ohmmeter measured between .195 and .21 ohms. At 1/2 amp current, that’s one tenth of a Volt, or about 7 percent of the one and a half volts of the battery lost and wasted in the holder.
I thought I had solved this problem by using 2 button magnets. These neodymium magnets are very strong and make good contact with the AA cell. Well, they make good contact as long as the cell is made out of iron or steel. But I’ve been buying packages of cheap batteries that have contacts made of a nonferrous metal such as brass, so the magnet won’t stick to the contact.
So there are the two answers for why I am building my own battery holder. Here’s another.
I’ve been making my own battery holders because the ones from Radio Shack are so lousy quality that the first time the battery leaks, which inevitably happens when the JT drains them completely dry, then the spring and contacts rust and the battery holder makes poor contact. Of course that might be a good idea if you want your JT to look like a candle flickering.
Building it myself also gives me the opportunity to use up some old terminal strips and contacts. One that I use occasionally is the Fahnestock clip. This spring clip holds one or two wires. It’s available from Mouser.com.
For the body of the battery holder I used a piece of soft pine wood. I drilled a few holes in a rough pattern of the AA cell. I used a small chisel to cut out most of the wood. Then I used a Dremel mototool to cut out the remaining wood so that it looked somewhat like the battery. I used the chisel and mototool to cut out the wood until the battery fit. After this I drilled a hole in the end for the screw.
I used a number 8 by 2 inch sheet metal screw. I filed down the sharp end so that it would hit the battery with a flat area, not a point. I screwed the screw into the wood to put threads in the hole, and then removed it. I dipped the wood in clear polyurethane and let it dry. While it was drying I found a large nut and soldered it to the head of the screw so that acts like a knob. After it dried I screwed the screw into the wood and put a battery in the hole, and tightened the screw. It held the battery securely. The polyurethane made the wood hard enough so that I could put a wire between the wood and the battery and tighten the screw and the wire wouldn’t sink into the wood too much. It works good enough to skip putting a contact on that end (I had planned to).