I probably will never actually finish this project to my satisfaction. If you have been following this for the last many months, you might remember that I started off trying to get a float charger for lead acid batteries that actually worked and didn't dry the cells out in a couple of weeks ruining the batteries...without paying U$50 or more for each of them. Rural living requires a lot of batteries for various machines that we use a few times a year and it is really annoying to have the battery fail between uses because of inattention. Anyway, the latest charger variation (see part 3) works really well to keep the batteries charged with minimal loss of water, but checking on it is a pain in the butt.
I have to hunt down a multimeter and traipse out to the barn and check the voltage on each device. It would be nice to have a voltage indicator on them to tell me if it is working correctly. So, off to ebay I went and ordered a few of these:
These little guys just hook to the wires and get power from the source being measured. Not the perfect situation since you have to power the LEDs from the supply that you are using, but it's a battery charger, not a lab instrument, so this will be fine. To test them, I just hooked it to the charger output and stuck it on the wires leading to the battery on one of the cars. This thing is cool.
The actual measured voltage is 13.4 on my multimeter, so it is relatively accurate and it gives me a highly visible indication of the state of charge from across the room. Now, I have to figure out how I want it hooked into the circuitry and what form factor I'll use for mounting and using it. The little black box I have in-line won't do the job, so I'll have to look around for something to house the display.
This brought up another idea: suppose I use one of my XBees and transmit the battery voltage over my network? I could then check the state of charge from anywhere (yes, anywhere in the world) any time I wanted to. I could even set up an alarm to send me email or a text message when something went wrong like a rat eating through the wiring.
I know what you're going to say, "What happened to the U$50 price goal?" I don't have a good answer to that question; the parts and pieces so far are around 15 bucks, the little voltage display cost me a little under 3 bucks, and now I'm looking at an enclosure and an XBee. This will push the total cost up into the 40+ range.
I guess I'll just have to compromise my principles.....