Hi
I will use a PWM for driving a DC-motor.
Microcontroller: SAMD21
Full H-Bridge: L6203 (4-quadrant controller for polarity switching and speed-control of a DC-motor)
PWM: 30kHz.
Vss: 18V
To taming the DC-motor-"Beast", Freewheeling-diodes are needed.
The L6203 data sheet recommends one BYW98 in blocking-direction to GND on each side of the H-Bridge (Load). In addition, a BYW98 on each side of the H-Bridge (Load) in forward-direction to Vss.
But: Could also do the same job (on principle) a bidirectional suppressor diode (eg. 30V/5kW) parallel to the Load (Motor)? Thank you for a brief note.
The data sheet actually implies that no flywheel diodes may be needed as the intrinsic diode may do the job (see page 10) but it can't do any harm to include them. Conventionally connected flywheel diodes limit the voltage excursions of the output pins to within the supply voltage range whereas your suggestion could allow them to exceed this (though given the intrinsic diodes this may not matter). Personally I'd take the conventional approach.
It shouldn't be the diodes that absorb the energy but the resistance of the motor. The diodes are just to allow current to keep flowing while this happens.
Diodes always absorb energy when conducting. The power absorbed (which heats the diode) is the diode forward voltage drop times the current.
Need to know the motor specs to guess at the actual values, but the "flyback" current won't be higher than the motor current at the instant the H-bridge cuts off the motor supply.
That's quite correct, but nevertheless much or most of the energy should be dissipated in the winding resistance. Not with a motor, but if driving an inductance which needs to switch off quickly a resistor in series with the diode is useful.
Whether that is true depends on the winding resistance, which the OP has not shared. In the hypothetical case of zero winding resistance, all the energy is dissipated by the diode.
So use a resistance meter and measure the resistance of the winding.
You can measure the winding resistance with a multimeter. The motor must be disconnected and the shaft very slowly rotated by hand, while you make the measurement. The brush contact resistance will be noisy, so take the lowest value you see.
It is hard for me to believe that a manufacturer would be reluctant to release basic performance parameters for a product, unless this is a proprietary design.
In any case, all interesting parameters can rather easily be measured with the proper equipment.
If that 6 mOhm figure can be believed, (depending on the supply voltage) the start/stall current of that motor may be much higher than the rated 10A nonrepetitive maximum for the L6203 chip.
Hi,
If you can find which model engines the motor came out of, sometimes the model railway manufacturers will publish engine specs, which may help.
Can you measure the no load current of your motor at full applied voltage?
Thanks.. Tom.. 
No, you can't always see optical or thermal damage except in the case of gross overloading, most of the time components just stop working with no sign of damage at all.
It seems that the belief in no physical damage = no damage, is a beginners internet myth.
Agreed. I don't know where these ideas (so confidently stated!) come from.
It usually takes a rather catastrophic failure to induce observable physical damage in a chip, like connecting a beefy power supply backwards.
Back in day of quartz-window UV eraseable chips, I recall a couple of reports of "backwards power supplies" leading to visible GLOWING of the chip (and/or bond wires), with the chips still working after the problem was corrected.
But the whole "visible damage" thing is mostly found on power components like TO220 transistors and voltage regulators and such. Microcontrollers tend to fail less visibly.
Thank you for your passive aggressive reply. I hope that we have corrected some misinformation that you have picked up over the years.
Oh by the way this forum has the ability to block selected members on an ignore list. Welcome to mine.
I suggest you remain focused on the problem, answer the question in reply #16. If everyone wasn't put off by your advice and so following it...