Quote:
Originally Posted by Kasmodean
Hello everyone,
First before I start I want to say awesome job to everyone involved with open revolt, especially you Paul.
I was trying to learn how to make a small dc motor controller for a robot I am building and came across the idea of PWM. I then figured after I made my robot to work, I could use the same principle to make a controller for my car. ( I have previously looked at doing a electric car conversion but controller cost has held me back.) The problem was it was one thing to make a robot controller with no safety features and making the same type for my car. It is then that I came across this forum. I have read up to page 150/370+, and I am still reading but I have a few questions on something that everyone seems to take for granted that are probably really simple, but I don't understand.
1) Every controller circuit I have looked at either has a capacitor connected to the motor's + & - terminals, or no capacitor, or capacitors around the + & - terminals and from + terminal to ground. In your schematic you have lots of capacitors from Batt + /Motor + to ground. How does that control the voltage spikes hitting the diodes from the motor - terminal while the mosfets are off? Or if that is not the purpose of them, what it?
2) Everything I have heard about diodes say they shouldn't be placed in parallel, especially if no equalizing resistor is attached. But your circuit has a bunch of diodes in parallel. How do they equalize and not have the best performer take more current then it can handle? This is also important because I was thinking of using IGBTs instead of mosfets and those aren't suppose to be in parallel either but everyone is saying you can do it.
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Kasmodean,
First, Where in MA are you located?
Second,
You can parallel diodes, you just have to watch for thermal sharing. You want them all to be the same temp all the time. Same thing with the IGBT's. It is very important for those that they do not get warmer then others or they will conduct more and you will end up with thermal runaway.
-Adam