I am in need of controlling a 12vDC motor that pulls around 20A. I have been using a relay to turn it on and off, but I am destroying the drive belt on the motor because when the motor is turned on it is at full speed and the rest of the gears and pulleys take a second to wind up to full speed. This causes the teeth on my drive belt to be stripped off.
Can some point me in the right direction for a controller that can handle 20Amps and also use PWM? I have found plenty of smaller 1A controllers, but no luck on the larger ones.
Is that 20A continuous?
These motor drivers can do 20A continuous without heatsink:
Motor Controller and Driver 25A $48.05
Pololu High-Power Motor Driver 18v25 CS has current sense 25A $58.95
Pololu High-Power Motor Driver 24v20 20A $51.95
if you need cheaper option, this one can do 14A continuous and 30A peak and has current sense:
VNH2SP30 Motor Driver Carrier MD01B $34.45
you can look at all of them here:
http://www.robotsimple.com/Motor_Controller_and_Driver
They all ship free worldwide.
Yes it is 20A continuous.
You could use two IPS5451 and two VNP35NV04 in an H Bridge format. This will hold 40A.
Hi i just wanna know what your building 
I don't really have any advice...