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Back EMF or motor voltage back to the supply

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bdesvaux
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Back EMF or motor voltage back to the supply

Hi,

I'm having some trouble using a Vesc-based ESC (Flipsky mini FSESC 4.20) on a system that works at variable loads. In short, the motor expands and retracts a piston which faces a pressurized environment. I power the ESC with a PSU, and control the motor speed using the duty cycle of a PWM signal. There is no issue in the expanding phase, but when retracting the piston, the pressure pushes it back and the ESC does not achieve speed control properly. After a short time, the PSU raises a security alarm, which I see either as back-EMF flowing back to the PSU or overvoltage. I've been tuning a few parameters in order to avoid that from happening but I didn't quite succeed (max battery voltage, current regen parameter, acceleration and deceleration ramps...).

Has anybody ever had the same kind of issue ? How did you deal with it ?

I'm aware that using a rechargeable battery to power the ESC would probably solve the issue (not sure though ?) but I'd like to be able to test it first with a PSU if there's a way.

Thank you !

 

frank
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The PSU can't swallow the regeneration currents and from there things go south. A battery would work both ways. If you don't want to use a battery, you would need a more complicated waste gate, controlled by a microcontroller and burning off the regenerated energy. This could be a resistive load, big enough to swallow the currents without overheating.

Also this ESC is not a very precise unit, having only two low side shunts and no phase filtering. You probably want to a proper original VESC6 instead.

What is the voltage range the ESC needs to operate in?

 

bdesvaux
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Hi Frank, thank you very much for the reply ! Ok, I was hoping that in some way the ESC itself would be able to dissipate the regenerated current. I've been retracting the piston successfully under pressure previously, but then changed the gearbox and the ESC settings and can't make it work again. I'll power it from a battery then, it sounds like the only proper solution.

The ESC operates at 24 VDC when powered by the PSU. Once embedded, the battery voltage will be used (20-30 V depending on the SOC).

frank
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We can't store energy into the universe yet, so it has to go somewhere and that is the battery....

At 25V the VESC6 EDU might be a good match. But 30V is too much.

bdesvaux
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Ok, thanks, I'll take a look at the VESC6 EDU. I was thinking of dissipation as heat, which basically is a way of storing energy into the universe.