VFD Motor amps

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Vince Justus

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I have a new blower fan with a 480v 3phase motor
9.7 RLA 1.1 SF 1765 RPM The vfd was set up with this data and started. The motor draws 11.0 amp at 60hz.
I will adjust the fan wheel pulley to lower the amps. But for now I have limited the max feq to 54hz which reduced the motor amps to 9.7. My question is will this damage the motor if left this way.
Vince
 
No, it will not unlkess the 6 htz difference in airflow due to different fan speed causes a problem. A 60 htz motor can operate fine 40-90htz. But if you're gonna run it much below 40 htz, you need and AUX cooling fan to run full speed, even when the motor is not. I've got 4 50 hp motors 60 htz, that have been running at 85 htz for about 10 years now.
 
Did someone just guess as to the amount of airflow that was needed?

If you get the cfm you need @ 54 hz I wouldn't bother with the pulleys, but then what is the low end of the CFM you need? That may put your motor at risk of overheating.

The other option is to adjust the air flow somewhat, a damper, until the current is reduced to what you want @ 60hz.

Is this fan just moving air or will it be used to move product of some sort? Material handling will require that you have a minimum of product flowing before you take amp readings of the motor. It acts much like a damper in that it restricts the flow of air thus causing the current to go down on the motor. Do you have leaks in the duct? Has the duct been completed, if new construction?
 
Vince Justus said:
I have a new blower fan with a 480v 3phase motor
9.7 RLA 1.1 SF 1765 RPM The vfd was set up with this data and started. The motor draws 11.0 amp at 60hz.
I will adjust the fan wheel pulley to lower the amps. But for now I have limited the max feq to 54hz which reduced the motor amps to 9.7. My question is will this damage the motor if left this way.
Vince
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Probably not. But I would monitor motor temperature for a while. It's a small motor so it shouldn't take all that long for the temperature to stabilise.
As others here have pointed out, if you reduce speed you significantly lose cooling.
 
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