I came across this Hackaday article highlighting this post by folks who need to provide long-lasting power to some calculators being demoed at World Maker Faire. Coincidentally, I have a battery-powered clock that I want to do something similar with. Seemed like a great Saturday afternoon project.
Here’s the (back of the) clock in question. It’s a simple, inexpensive battery-operated clock I picked up at a local store. (Amusingly, inside the box for the clock was the 5-year warranty information. The instructions said to send it via paid-up shipping along with $5.00 handling fee. $5.00 is more than I paid for the clock!) The clock takes a single AA battery.
As with lots of inexpensive electronics, the battery contacts are flimsy little pieces of metal held in place with the molded plastic. Before I saw the Hackaday post, my plan was to solder a couple wires to the contacts, but that can be a pain. Sometimes solder doesn’t adhere very well, and it’s far too easy to start melting plastic.
The Cemetech guys needed AAA batteries, which gave them more restrictive size constraints than I had. For the larger AA battery, I was able to use a 6-32 machine screw for the positive terminal and a 8-32 machine screw with a washer for the negative terminal. I decided to forego the idea of a “pocket” for the negative terminal as it seemed much easier to just put the screw and washer through the bottom of the cylinder.
Click to enlarge.
Here’s the model I created using OnShape and one of the resulting prints. The angled shape at the top is there to avoid the need for any supports. Without them, the arc at the top would have printed very badly since it’s not even a straight line bridging operation. As it is, this part of my prints came out pretty messy but it doesn’t affect the functionality at all.
It works like a champ! Here you can see the battery form in a couple different battery holders:
Here are some size comparisons. The overall length for my printed form is 0.5mm longer than the real battery because I originally thought I was going to use a screw with a shallower head and integrated washer. The model and STL file have been adjusted for future prints.
Thanks to the Cemetech folks for the original idea. I can take no credit for coming up with this. But it’s gotta be one of the most useful things you can whip up in a single afternoon.