I bought a few bricks of 40 AAA cells at Fry’s, mainly because they were only $4.20 each, or about ten cents apiece – that’s cheap! But I really needed AAA cells because of all the Fenix LD01 and similar flashlights I now have. But I have so many AAA cells that I’ll never be able to use them up by their 2017 expiration date. Unless… I start substituting AAA cells for AA cells in low current devices like my Blue Blinky flashers. So I had to come up with an adapter.
I bought a handful of AAA to AA adapters from Dealextreme; each one is a plastic snap apart case with a metal button on one end to extend the length. They’re not bad, but they’re not available at the local store like the ones I made below.
The AAA cell sill fits into an AA cell holder, but it’s too loose and may fall out. So I needed a metal spacer to go between the AAA cell and holder to take up most of the room and make the spring pressure high enough to hold the AAA cell securely. What have I got plenty of that’s about that size? A NUT! Yeah, a nut from a quarter inch screw is thick enough to make the spring tight. But I have only a few 1/4″ nuts. But Burt used to tell me, “There’s no shortage of nuts around here!” and he was right. So I looked into another screw drawer and found that I had plenty of 8-32 nuts.
I grabbed a few and tried them between the AAA cell and the AA holder. They worked good enough, so I took ’em out and put them on a burn proof surface and soldered them together. After cooling off, I put the pair of nuts back into the AA holder along with the AAA cell, and that left me only one thing to do: make the on/off switch – see the photo.
I took a scissors and cut out a section of the side of a plastic pudding cup. This L shaped section included the rim and part of the wall. The wall is the part that goes between the battery contact and the holder, and the rim acts as a finger pull tab. It can also be seen in the picture. It fits nicely between the side of the battery and the holder during use.
I wrapped enough black electrical tape around the middle of the AAA cell to help center it in the holder so it makes good contact. But with the nuts in place, the battery is secure enough without the tape.
One thing I noticed about AA and AAA cells in general: different manufacturers make them different lengths. One may be several millimeters shorter than another. I noticed that with the two #8 nuts, the spring was compressed down to its minimum, and the AAA cell just barely fit. With the two #6 nuts, the spring isn’t so compressed and the cell fits snugly but not tight. So I may choose the #6 solution for most of the holders. But the #6 nuts are smaller in diameter and tend to fall down and make contact off center with the spring. But the holder still works okay.
Many of my projects have low enough battery current that will allow the AAA cells to be used and still have a reasonably long battery life. The only problem is that some battery holders may have four cells, which means I’m going to be soldering a lot of nuts together!
Back to nut soldering…