I need to find a safe and reliable way to power a DC hobby motor off mains supply. The motor is large (i.e. 500W) 14.4V. Therefore, the current requirements are large i.e. 35A for a 14.4V supply.
I can't find such a power supply to purchase and my budget is small. Therefore, I thought I could use an ATX power supply from a computer. They typically have a high current 12V line that can deliver the required current, 42A in this case.
I will be using a power MOSFET to regulate the power going to the motor by switching it on and off using pulse width modulation PWM. There should be some huge inductive spikes created. I need a way to protect the power supply from these.
I was thinking of using several layers of protection just to be safe as long as they are compatible with each other. There location in the order that I mention them is arranged starting closest to the motor and moving towards the supply. The first line of defense is a freewheeling diode put in parallel with the motor forward biased from 0 to the positive supply direction. In addition, perhaps an RC snubber also in parallel. Then a 12V standoff TVS also in parallel in case the other two fail. However, this will short the power supply if it is triggered. If the supply doesn't have over current protection it will kill the supply. I need some sort of fast acting fuse or polyswtich to at as a current limiter in series with the supply. I've noticed that a the polyswitches are very slow. like 9 seconds to "disconnect" the line and I don't want to use a fuse that I have to replace when this happens. Is there a good solution to this problem, or is this all too much? That is, should I just leave the TVS and polyswitch out of the design?