VFD Questions

[Brian Holcombe]

Thanks Malcolm! Much appreciated and now it makes sense. Woof,,,40 amps for 10hp! Looks like a 15hp covers that and the 3hp will require a 5hp unit. Any issue in oversizing these?

Replied at the same time, I found 40 amp, but you may be right could be 50 Amps. I may rethink this machine, seems like overkill.

[Malcolm McLeod]

Thanks Malcolm! Much appreciated and now it makes sense. Woof,,,40 amps for 10hp! Looks like a 15hp covers that and the 3hp will require a 5hp unit. Any issue in oversizing these?

Replied at the same time, I found 40 amp, but you may be right could be 50 Amps. I may rethink this machine, seems like overkill.

No issues with over-sizing, excepting cost. You can set the VFD parameters to limit the power applied - - so a 20Hp VFD could safely operate a 3Hp motor, if you program it to do so. (I'd probably go "belt & suspenders" with this big a discrepancy, by putting a 3Hp overload/CB inline between the VFD and motor.) You just have to re-program every time you plug the 10Hp motor into it. (We all have different pain thresholds.)

Before you splurge on the 5HP VFD, Huanyang lists 3Hp VFDs on the Bay, seemingly rated for 1-ph OR 3-ph. Several SMCers have gone this route...? Just not me. Yet.

[Brian Holcombe]

Cool, thanks Malcolm! Much appreciated. I think I'll use separate units for each machine.

[Brian Holcombe]

Well, I thought I had this all figured out but apparently not so much. The phase converter must be derated from what I've read for anything above 3hp, which actually seems like for anything 3hp and above and they start getting (as you noted) pretty expensive.

I'm in the territory where it is actually starting to look less expensive to simply buy a rotary converter for the 3hp motor and dump my plans of a 10hp planer and instead get something smaller and single phase.