VFD Questions

[Harry Knutz]

Harry Here,

I bought an economy VFD to play with just to kind of learn how to wire and use them, I first found a 1.5 HP 3 phase motor at the scrap yard and took a chance for $18.00 and it works, I wired up the VFD on the bench and everything seems to work quite well, My question is this, The default HZ setting goes up to 65 HZ, Can you run the motor even faster if lets say you bump the HZ up to 80 or 90 HZ?

The instructions on programming are pretty vague and to be honest kind of intimidating. My plan may be to swap this motor onto the "Enco" 12x36 I got from Mr. Mike the motor makes noise and has been since I got the lathe back together. Just thinking out loud. I have been using the lathe and I'm actually pretty impressed with it.

 

[woodchucker]

You can but the motor may not handle it. Generally I think 10 percent above is max. A short burst above may not hurt the motor though. Extended runs above the bearings and insulation comes in to play.

 

[Harry Knutz]

You can but the motor may not handle it. Generally I think 10 percent above is max. A short burst above may not hurt the motor though. Extended runs above the bearings and insulation comes in to play.

Thanks, I guess that's why the default setting is 65 HZ, That's pretty close to 10% over.

 

[rabler]

Generally heat is what causes motor components to wear out or break down. Wire insulation and bearings both suffer at higher temperatures. Usually slowing the motor down is more problematic than speeding it up as with most motors the fan turns slower. At worse you're shortening the life of the motor by pushing the frequency range (either too high or too low), not introducing an instant failure. On a used motor, if it dies tomorrow, that may just be fate. My general rule is to run older motors that weren't specifically designed to handle VFDs between 40 and 90 Hz (ballpark). Other people may have different feelings.

There can be some other weird effects from VFDs on motors. This is associated with the carrier frequency (usually somewhere in the 5kHz to 15kHz range) than the drive frequency. That higher frequency sees a higher inductance in the motor windings and could cause high frequency voltages that exceed older motor insulation standards. But lots of older 3 phase motors work fine with VFDs. I wouldn't run the carrier frequency higher than you need to, but typically you increase that to something a bit above 10kHz to avoid an annoying whine from the motor (depends on your hearing). As always, make sure your motor frame is grounded.

 

[mksj]

A 1750 RPM (4P) motor are usually fine to run to 90Hz (2P is 125% of base Hz/speed), beyond that point the motor performance falls off. Most motors also will state their constant torque ratio, typical motors this is usually 2:1 or 4:1 which means it maintains constant torque down to 30Hz, or 15 Hz respectively. This usually applies to motors run in the VFD sensorless vector mode. Older motors a safe operating range is 30-75Hz, newer motors/inverter rated more like 15-90Hz, and vector motors pretty much from 0-180Hz. Put you loose the mechanical torque multiplication from gearing/belting so doesn't mean that the motor performance will be adequate at say below 20Hz. You also need to be careful of the top speed ratings of the gears and spindle if you are pushing a 50-100% speed increase.

 

[Harry Knutz]

Generally heat is what causes motor components to wear out or break down. Wire insulation and bearings both suffer at higher temperatures. Usually slowing the motor down is more problematic than speeding it up as with most motors the fan turns slower. At worse you're shortening the life of the motor by pushing the frequency range (either too high or too low), not introducing an instant failure. On a used motor, if it dies tomorrow, that may just be fate. My general rule is to run older motors that weren't specifically designed to handle VFDs between 40 and 90 Hz (ballpark). Other people may have different feelings.

There can be some other weird effects from VFDs on motors. This is associated with the carrier frequency (usually somewhere in the 5kHz to 15kHz range) than the drive frequency. That higher frequency sees a higher inductance in the motor windings and could cause high frequency voltages that exceed older motor insulation standards. But lots of older 3 phase motors work fine with VFDs. I wouldn't run the carrier frequency higher than you need to, but typically you increase that to something a bit above 10kHz to avoid an annoying whine from the motor (depends on your hearing). As always, make sure your motor frame is grounded.

A 1750 RPM (4P) motor are usually fine to run to 90Hz (2P is 125% of base Hz/speed), beyond that point the motor performance falls off. Most motors also will state their constant torque ratio, typical motors this is usually 2:1 or 4:1 which means it maintains constant torque down to 30Hz, or 15 Hz respectively. This usually applies to motors run in the VFD sensorless vector mode. Older motors a safe operating range is 30-75Hz, newer motors/inverter rated more like 15-90Hz, and vector motors pretty much from 0-180Hz. Put you loose the mechanical torque multiplication from gearing/belting so doesn't mean that the motor performance will be adequate at say below 20Hz. You also need to be careful of the top speed ratings of the gears and spindle if you are pushing a 50-100% speed increase.

Actually the motor I got at the scrap yard has an emblem that says "ISR" So it has windings that are made to run an inverter on. It had an inventory bar code from a local government facility, So there is no telling why it was scrapped. So I guess I got lucky there. The motor makes very little noise, But I can't hear schnitzel anyway

So as mksj has noted, I think I am going to try and set it to top at out 90hz. it's a 1740 rpm motor, I put a reflective tachometer on it and runs around 620 rpm at 20hz and at 65hz it was running a little over 1900 rpm.

I am still learning this stuff, But I must say, The wiring was very easy and straightforward, The programming part is what looks like its going to be tough.