I have a project where I have a 10-pound flywheel being spun up by a 48v 400w cnc spindle brushless motor at 5000 rpm, using a WS55-220S motor controller.

As such, when the power to the motor stops the motor/flywheel are still spinning due to the momentum of the flywheel. My concern is that this may be damaging the WS55-220S motor controller because of the regenerative energy being produced by the brushless motor/flywheel.

Or am I being overly cautious as the WS55-220S motor controller is capable of handling this regenerative energy? I should mention that the flywheel will be freewheeling, gradually spinning down and not come to a hard stop.

I tried looking online to find any answers regarding the WS55-220S motor controller's ability to deal with regenerative energy but cannot locate any mentioning of.

If I do need protection from the regenerative energy being produced, how should it be implemented?

Thank you

  • \$\begingroup\$ Dump the energy into a resistor. Probably use some zeners or something to protect your drive circuitry. The faster you can dissipate the energy, the faster it will turn off. You can also use regenerative braking to return the power to the source, but that's more involved. \$\endgroup\$
    – Hearth
    Sep 30 at 18:11
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    \$\begingroup\$ Could I just short the three wires from the motor which would effectively brake the motor? \$\endgroup\$
    – Tivity
    Sep 30 at 18:26

1 Answer 1


My concern is that this may be damaging the WS55-220S motor controller because of the regenerative energy being produced by the brushless motor/flywheel.

No, it won't damage the motor controller for two reasons:

  1. There is no regen power. If there were, the wheel would slow down.
  2. Yes, there is regen voltage (EMF), but it's lower than the motor terminal voltage before you stopped driving it. Therefore, it is not excessive and not damaging.

How to dissipate regenerative energy

It's not clear if you wish to dissipate it because you're worried about the controller or because you want the wheel to slow down.

  • You're worried: Don't worry; it's fine.
  • You want braking: place a high-power resistor across the motor terminals through a switch or relay that is turned on when you want to brake. If you want very fast braking, short across the motor terminals. Of course, you can always use a mechanical brake.

EDIT: You asked about regen. But others wondered about inductive kickback. The kinetic energy in the flywheel is some 3 orders of magnitude higher than the magnetic energy in the motor windings. The duration is some 4 order of magnitude longer. Regardless: a DC motor controller that can't deal with the kickback it itself causes by shutting down is not a well designed product.

  • 1
    \$\begingroup\$ Kickback or regen currents will be clamped to the dc bus by the mosfet body diodes in the controller. \$\endgroup\$
    – asdf30
    Oct 1 at 13:27
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    \$\begingroup\$ @asdf30 -- not really. The diodes route the kickback current but don't clamp it. They route the current to the power supply. The power supply capacitors absorb it (there isn't that much energy in the kickback) but don't clamp it. The voltage goes up a bit. Without actively using the motor controller for braking, there is no regen current, so that is not an issue. \$\endgroup\$ Oct 1 at 13:44

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