I made this thing to power my digital photo camera. I don't use batteries in it because it doesn't like rechargeable batteries.

I already had something like this, which just had the coax jack, the voltage regulator (which is hidden behind the capacitors in this photo), and the plug that goes into the camera, but it was failing to power my cameras. So I tried adding some capacitors, but that didn't fix it, and so I plugged it into a wall wart rather than the 8-cell battery packs I usually use, and that worked.

I'd been thinking about making a new one so that I could plug in the rechargeable lipo batteries I have for RC stuff, so this seemed like the time to finally do it. So I designed a PCB for it since I can do that now. (The old one was made on perforated prototype board.)

There's kind of nothing to the circuit itself.

The XT60 connector has round terminals, so I cut slots for it, but then decided I didn't want it to stand upright, so I attached it differently. Anyway, the slot-cutting ability is something I added to my PCB software just for this project. I did actually use it though, as also the 2.1 mm DC power jack isn't the correct kind for PCB mounting as it has these big tabs with holes in them, so I had to cut slots for those tabs to fit through too.

The lipo battery works so much better. This made me figure that it's probably because it can supply much more current, like it's supposed to be capable of 20 amps. However, surely the camera doesn't need that much, which made me start wondering how the failure is occurring with the old 8-cell NiMH battery packs I was using.

So I connected the oscilloscope to see what exactly happens when I try to power on the camera with the old battery.

Looks like it dips from 12 volts to about 4.5 volts. So I connected a 1 ohm resistor in series and another probe, so that I could calculate current.

The resolution of this scope sucks, so I had change the vertical scale and offset to try to get the most out of it, but it looks like it peaks at about 400 mA. The batteries should be capable of at least ten times that.

So I guess my batteries just have a really high internal resistance. They are pretty old. Also though this makes me wonder how much of this might be the problem when trying to run the camera on NiMH cells directly. I've never really thought about the battery's internal resistance before.