VFD options - experiences with GE af60-lp

[Bob Wise]

The FM50 is a simple scalular VFD, great if all you want to do is convert from single phase to 3ph and speed control isn't a concern like for a TS, jointer planner etc. The down side is it's the bargain basement of VFDs which means it lacks many of the functions a little better quality drive has such as native 3-wire control and the ability to adjust output voltage.

In short, no you can't adjust the output voltage on the FM50, but to be honest it probably isn't going to matter to a bit. Unless you're running commercial shop were the motor is running for hours at a time every day it's probably not going to make a bit of difference. I've had a 208v motor on a sander running on a FM50 for years and it's still fine. Granted it only runs a couple times a week for a short periods (3min or less usually). But at the end of the day, unless the motor is a specialized motor specifically designed for the machine and is irreplaceable, I'd run it until it died and then replace it with a 220v if it ever does.

Mike

I'm not an electrical engineer so I'm willing to be corrected...

I believe that as VFDs reduce frequency in order to slow the motor down, they also drop the voltage. Voltage reduction/management is an inherent part of the design. The two kinds of VFDs I've used (the cheapo huanyangs and the nicer GEs, voltage configuration for the specific motor is required. I agree that I wouldn't stress about it the motor life even if this were not true, but I'm pretty sure it is.

If this discussion continues I'll have to step into the shop, pull the wire cover off the motor, run it at 1/4 speed and check the voltage. :-)

-bw

PS: Side comment, I'm only using the GEs now. The Huanyangs got me going on this cheap but not buying any more of those

[M Toupin]

Bob, I'm not really getting your point. All VFD's "reduce frequency in order to slow the motor down, they also drop the voltage". No argument there, that's how VFDs work. The voltage is adjusted to a percentage of the hertz output. So for example, at 230v the hz would be 60hz, at 115 volts the hertz would be 30hz etc.

But back to Marty's question - for the FM 50 the base is 230 volts and the drive scales the hertz to the base voltage ie 230volts/60hz, 115v/30hz etc. So if Marty wants to feed his 208v motor he'd have to scale the hertz back to somewhere in the neighborhood of 50ish hertz. No, I haven't done the math and I really don't want to get into a protracted discussion or math lesson, but for a general idea, 50ish hertz is close enough to get the point across. Point is, the base output voltage of the FM50 is set by the input voltage, there's no adjustment. On better quality drives the base voltage is adjustable so you can tune a drive to output a lower voltage say 200 or 208 volts depending on the motor.

But at the end of the day I think we can both agree that Marty will be just fine using his 208v motor.

[Bob Wise]

Bob, I'm not really getting your point. All VFD's "reduce frequency in order to slow the motor down, they also drop the voltage". No argument there, that's how VFDs work. The voltage is adjusted to a percentage of the hertz output. So for example, at 230v the hz would be 60hz, at 115 volts the hertz would be 30hz etc.

But back to Marty's question - for the FM 50 the base is 230 volts and the drive scales the hertz to the base voltage ie 230volts/60hz, 115v/30hz etc. So if Marty wants to feed his 208v motor he'd have to scale the hertz back to somewhere in the neighborhood of 50ish hertz. No, I haven't done the math and I really don't want to get into a protracted discussion or math lesson, but for a general idea, 50ish hertz is close enough to get the point across. Point is, the base output voltage of the FM50 is set by the input voltage, there's no adjustment. On better quality drives the base voltage is adjustable so you can tune a drive to output a lower voltage say 200 or 208 volts depending on the motor.

But at the end of the day I think we can both agree that Marty will be just fine using his 208v motor.

Agree that he should be just fine.

If that's a limitation on the FM50, totally understand your point. I'm a bit surprised by that I thought that even the really cheapo huangyan units had adjustable (downward from the input) output voltage.

[Marty Schlosser]

Thanks for your thoughts on this issue, guys.

Agree that he should be just fine.

If that's a limitation on the FM50, totally understand your point. I'm a bit surprised by that I thought that even the really cheapo huangyan units had adjustable (downward from the input) output voltage.

[Rollie Meyers]

It is a code violation to use a 208V (new rated voltage 200V) on 240 volts, a older 220V rated motor will do fine on either 208V or 240V, but a 230V rated motor cannot be used on 208V, or 200/208V motors on 240V, if a VFD that can have the output voltage adjusted lower then the input that is the easy way to do it, otherwise a buck/boost transformer to buck the voltage down to 208V is another option, in the case of a couple of Rockwell former school machines I bought that had 200V single voltage motors, the VFD's that were used on them allowed them to be adjusted to 208V output. Note: a VFD cannot output 240V from a 208V supply.