Hi again. Sorry if I asked stupid questions... Maybe the/a problem is just what red-alert says about max VDS. It's not always possible, but when I can I try to de-rate most components so they don't even break out into a sweat/don't have to bear a heavy load of any kind
. I imagine you can't start off low everything when testing then build up speed/frequency/voltage once it's working correctly?
A (non-polarised) capacitor across the motor terminals helps with the large current surge when a motor starts up, I imagine they are placed there as a small reservoir capacitor. I've even put MOVS as well as a capacitor across motors sometimes, just in case it defends the power supply against the motor tidal wave ripple at turn on and off of the motor, besides the "cage" diodes. Small motors in manufactured devices seem to usually have a ceramic 104 capacitor soldered directly to the terminals.
For what it's worth, in my small experience I'm used to transistor H-bridges that work with PNP/PMOS at the top and NPN/NMOS at the bottom to fulfil the push-pull necessary in order to do bi-directional driving, and I've only used the little L293D as a chip H-bridge with a tiny bipolar stepper motor, so 4 NMOS looks weird to me, even if it works.
I hope you've found some solution. If you have to using those specific transistors for a 48V motor, I have no idea if it's possible for this but it is for other stuff - maybe you could parallel two of them to split the voltage burden between the two.