The project is getting more complex then I hoped.
MUR1620 is not suitable. Too high loss. For 24V operation, get 40 or 60V schottky. For 48V supply, get 100V schottky.
Can you define too high of what loss?
And also 20 to 30 amps is a work for one TO247 mosfet or two pieces TO220.
I am running 5 TO220. The existing CanaKit circuit did well with 1 TO220 and a heatsink and small fan.
The diode must be rated the same current as the mosfet is rated for - both are rated for nominal motor current - 30 Amps.
I have 3 MUR1620 for a total of 48 amps.
Not mentioning tha 30A switching stuff requires proper layout and circuit construction. The diodes should be directly near the mosfet, absolutely not on the motor itself.
They are at the FETs. I also have the 8A8 at the motor itself as it really helped the CanaKit. So I left them.
Where can I find your schematic diagram of the whole power stage? I only saw some schematic on the first page, which was badly wrong.
They are all wrong. This is the last idea, but it's changing.
https://dl.dropboxusercontent.com/u/24907255/CapOptions.pngAnd I noted here a word "arduino"? I have suspiction, that arduino trash can't generate fast enough PWM signal to be used for such motor control. You need something like at least a few kilohertz, better 15k to 20k. That's work for hardware PWM timer, not that arduino software PWM libraries.
I was thinking something along the same lines as for the frequency of the Arduino.
Can we solve most of this with out reinventing the wheel? How about I use an off the shelf motor controller and just boost the current capability with the MOSFET.
I have used this Polou controller before on smaller motors.
https://www.pololu.com/product/1378It will handle the volts I need, provide the fast switching of 22k, and give the control I need from the Arduino.
The gate of each FET will have about a 100 ohm resistor and connect to one output of the motor controller. Source to ground. Sure reverse won't work, but I don't need that.
Will this do the trick in providing a gate driver and the higher frequency needed?
Yansi and peter.mitchell have also been providing great help. But I am a bit worried about my skills in making a gate driver from scratch.