VFD Carrier Frequency?

[Dabbler]

@Dabbler, the Teco derating for the carrier frequency applies to the VFD, not the motor.

@rabler I'm sorry that I didn't notice we were talking about two different things.

The thing you need to know is that the duty cycle of the mill is lowered.

When using the motor off 60 cycles you reduce the efficiency of the whole system. The efficiency loss will have 2 consequences: reduced torque and increased heating. When using it near 60 cycles, the effect is not noticeable. If you use it at the extreme ends of the spectrum, at 10 Hz and 110 Hz for instance the losses are pretty large and you have to be careful. By reducing the duty cycle, or your torque expectation, you can still use a non-inverter motor quite nicely at those resultant speeds.

This is the 'derating' I was referring to.

 

[Ken226]

Yep. It's up to you whether you want it to start whining, or you want it to trip offline completely (quit working until it is power cycled or reset). Of course it really is unlikely you'll ever overheat it, unless you're just pushing it for fun to see how big of a chip you can cut. I actually set mine up so the Analog output pins were showing motor rated current (parameter 04-11), and then hooked those pins to a simple digital voltage display (on amazon) so I can tell what load I'm drawing. Did that to help tweak some of the overcurrent protection parameters as I was initially tripping my VFD with an overcurrent condition when engaging the clutch in higher gears.

My panel doesn't compete with yours! But you can see the LEDs in the center.

You can see my enclosure with a fan on the right.

View attachment 364924View attachment 364925

edited to add:
The analog output can drive 0 to 10volts. I adjusted the scaling parameters so that it reads 7.5 volts at 100% motor current. 10volts would correspond to 133% rated current for the motor. I just remember those numbers.

Ok, thanks. I'll set it up so to reduce the carrier freq. The whine will serve as a warning to find a stopping point soon, or slow down.

I'd hate for it to just cut off in the middle of something precise and expensive.

 

[Ken226]

@rabler I'm sorry that I didn't notice we were talking about two different things.



When using the motor off 60 cycles you reduce the efficiency of the whole system. The efficiency loss will have 2 consequences: reduced torque and increased heating. When using it near 60 cycles, the effect is not noticeable. If you use it at the extreme ends of the spectrum, at 10 Hz and 110 Hz for instance the losses are pretty large and you have to be careful. By reducing the duty cycle, or your torque expectation, you can still use a non-inverter motor quite nicely at those resultant speeds.

This is the 'derating' I was referring to.

You guys are a wealth of good info. I appreciate it. I've used BLDC motors alot, but this is my first AC VFD setup.

So, I have my VFDs lower frequency limit set to 20hz and the upper limit set to 70hz. Combined with my lathe's gearing, this gives me a spindle speed range from about 8 rpm, up to 2500 rpm. It covers most all of my potential needs on a 13x40 lathe. I don't mind shifting gears to get the speed I want. And I would rarely ever need the lowest end of that. Likely I could set the lower limit to 40hz and be happy with a lowest speed of about 20rpm.

Am I being too conservative?

 

[Dabbler]

Not really. You lose a lot of torque at both extremes - the upper torque loss will be less apparent. To get the lower speeds you will want to gear down and run the motor at, say, 30Hz. At 30 Hz you might experience, approx 10-20 percent torque loss. At 20 Hz, it might be 50%.