Motor Controller Flyback

Ricketty C · 2020-06-04T06:40:14+00:00

I've been asked to include a motor controller on a board I am designing. T he motor is from Pololu The controller is a VNH5019 from ST ons/ It seems they recommend a capacitor to absorb the flyback current on switch ing to prevent power from flowing back into the PSU. I have no idea how t o size this cap. They recommend 500 uF for each "10 amps of current". It seems to me the capacitance would also depend on the inductance of the moto r since that would determine the energy stored in the magnetic field and so the energy stored in the cap. Is there something about motors that make the inductance not a factor, like it approximately scales with the current??? Also, wouldn't the capacitor size be related to the square of the current??? The motor is 5.5 amps stalled, so I suppose I could put a 470uF part on the board and be happy. I just don't like winging it when I build things. I' d like to show the reasoning for selecting this part. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code -

Jun 04, 2020 20 Replies

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John S 6 years ago

Well, practically speaking, bearing friction probably doesn't amount to much. So windage would be the winner. I don't disagree with your statement. I think the more important factors are load friction and load inertia. What do you think?

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