[jderou]

I am looking at replacing my vfd with a hitachi unit for the vector capabilities. My setup is rotary converter into a 45kva transformer stepping it up to 480. Question is do I stick with 480 or go with the 240 unit and rewire. If I rewire I could eliminate the large transformer. Amperage would be higher I know. Are there any other drawbacks to 240?
This is a 7.5hp motor, and I plan to go with a 15hp vfd (overkill?)

[DareBee]

Other than the amperage, Your next machine might be 480 volt

[Al_The_Man]

Also keep in mind if converting a machine to the lower voltage, power fuses and wire gauge may have to be changed.
Al.

[jderou]

Good points. Chances are if I need 480 in the future I wont find a transformer for what I paid for this one.
Is 15hp overkill for a 7.5hp motor? Can I get away with a 10hp?

[Feeler_Gauge]

I am looking at replacing my vfd with a hitachi unit for the vector capabilities. My setup is rotary converter into a 45kva transformer stepping it up to 480. Question is do I stick with 480 or go with the 240 unit and rewire. If I rewire I could eliminate the large transformer. Amperage would be higher I know. Are there any other drawbacks to 240?
This is a 7.5hp motor, and I plan to go with a 15hp vfd (overkill?)

The reason you'd want higher voltage is to deliver more power over the same gauge of wire, assuming that you keep amperage constant and only increase voltage. It's cheaper to step up voltage than to rewire a building.

Going down to 240V from 480V, amperage would not just be higher, it would double to maintain the same level of power...so for 7.5HP at 240V you'd need 25 amps. I would say that it's best to minimize voltage step-ups or step-downs in the chain between your power source and the motor itself. If the VFD accepts 240V in and can output 480V or whatever voltage your motor requires, then the VFD is going to draw right around 25 amps of power from whatever you are feeding it with when your motor is running under load. The overall efficiency should be a little better by removing the transformer and letting the VFD step up the voltage to 480V...again, I am assuming that your motor is 480V since you didn't mention that.

Good points. Chances are if I need 480 in the future I wont find a transformer for what I paid for this one.
Is 15hp overkill for a 7.5hp motor? Can I get away with a 10hp?

A 10 HP VFD should be fine for a 7.5 HP motor...it falls under my guideline of using a power source that is rated at 125% of the power you'll actually need.