Hi all,
I'm working on an automotive alternator charge controller. The one I use for myself is built in to my DIY power system controller, but I have a couple of neighbors that want a stand alone version and I am working on a golf cart to ranch utility cart conversion that will have one as well. I am going to go all DIP parts and have a PCB layout that can be done easily by DIY'ers. The object is to keep it as simple and cheap as possible. Once it's done this will be an open source project.
Specs so far:
PIC16F88 for brains. There are cheaper and maybe I'll switch this later.
Allegro 100 amp current sensor. Might use an Amploc instead.
Programming in Pic Basic Pro. .hex and .bas files will be available.
Features:
Will be a two stage charger. Float charging with a gas motor is nuts!
User will be able to set max charge current, min charge current, charge voltage, and compensate for voltage drop between the alt and the battery bank.
Optional serial LCD output. Might do 4 bit interface instead if I have the I/O.
Optional automatic shut off relay.
Optional temp. compensation.
So, I am fiddling about with this project at the bread board stage and have a few questions.
1) Typical field coil currents. Looking around, what I can see is that most seem to draw less than 5 amps. Is that true? Both mine draw less than that, more like 3 amps at max current.
2) Right now I am using a couple of transistors to PWM the field coil. I am switching the high side for compatibility with more automotive alts. I could switch to FET's which would increase efficiency but also increase cost and make board layout more critical. I am kinda leaning towards sticking with transistors, you can get 'em from Rat Shack on a Sunday. I hate the big 10W base resisitor burning up juice but in the big scheme of things it's a pretty small thing.
3) Best PWM frequency?
4) Any other ideas/comments/observations?
Thanks for the input!
Jonathan