VFD Braking Qustion

kvom01 · Dec 6, 2008

I am running an AutomationDirect 2HP GS2 VFD on my 1HP BP mill. I just got the power running today and programmed the VFD. I do not have braking resistors.

How fast can I reasonably set the braking time without unduply straining either the VFD or the motor?

JunkyardJ · Dec 6, 2008

There's not a definite answer.

What will happen is it will push the DC bus voltage up more and more with the faster you set it. Eventually it will give a DC bus overvoltage trip. I've heard of times as low as 3 seconds. Start at 5 and work your way down. The top speed for the spindle will keep it spinning the longest. I dunno how fast you'd be able to set it. :cheers:

JST · Dec 6, 2008

Your VFD may also have DC braking.

That will slow it rapidly without the "boosting" that increases the bus voltage in normal braking. it may be locked out at high speeds, since it is a fairly violent stop, can be a half second.

Normal braking is a speed decrease, and the phasing of the pulses effectively turns the system into a "boost converter" with no direct upper limit on voltage other than the settings...... otherwise it could go to 1000 volts.

DC braking is a DC injection, without the phasing issues, and wastes the rotational energy as heat in the rotor.

kvom01 · Dec 8, 2008

Setting the time seems to have no effect on the actual stop time. From 60Hz to 0 takes about 4 seconds. When I set the VFD stop time to 2 seconds I also got a fault.

I can live with it as-is, since it's a home shop hobby mill.

The super low speed will make tapping a breeze.

JST · Dec 8, 2008

Th fault is probably an overvoltage..... that is what the brake resistor fixes.

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