Vfd questions

[500592]

Would this http://www.ebay.com/itm/VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-NEW-3HP-2-2KW-l7-/170636140761?pt=LH_DefaultDomain_0&hash=item27bab4e0d9 work on a 3hp baldor electric motor hooked to an Atlantic fluidics pump. If not what would work with out breaking the bank. Thanks a bunch.

[Tmeeeh]

I bought a 3 hp VFD recently. I looked at the one you show in your post. Decided against it even though all the specs look right. Instead I went for http://www.buyweaver.com/index.php?main_page=product_info&cPath=77_90_92&products_id=8938 because I already have one and like it. If you buy theone from ebay, let us know how it works out. I hope it has a good instruction manual in english or you have an electrician who knows how to set them up.

[Amber Gold]

When being used for phase conversion, the VFD should have a HP rating twice that of the motor it's running. i.e 6hp VFD to run a 3hp motor.

[Tmeeeh]

When being used for phase conversion, the VFD should have a HP rating twice that of the motor it's running. i.e 6hp VFD to run a 3hp motor.

Yes I heard that too I called Cerus when I was ready to buy the ones i'm using they said the 3hp VFD they sell was fine for a 3 hp three phase motor. You would think that if the input amperage rating of the VFD is the same as the full load amp rating of the three phase motor you would have 30% extra capacity in the VFD because the input of the VFD is single phase and the output is three phase. To confuse things further VFDs are often rated in HP not in amps.
Why would the rule of thumb be to use a VFD rated (in horsepower not in full load amps) twice that of the motor it drives?

By the way we used our cerus 3 hp VFD to drive a 3 hp vacuum pump nonstop all last season everything seemed fine both the VFD and the pump motor stayed nice and cool. I do have a clip on ammeter but didn't think to read the amps before and after the VFD.

[TheMapleMoose]

I had always heard the rule of doubling the hp rating on the VFD. But it sounds like that isn't true in your case. So does it depend on the mfg of the VFD?

[Tmeeeh]

I had always heard the rule of doubling the hp rating on the VFD. But it sounds like that isn't true in your case. So does it depend on the mfg of the VFD?

The nameplate on the my VFD says single phase input 220 volt and 21 Amp; 3 phase output 220volt 12 amp and it also says 3 hp. The three phase motor nameplate says 2.4 Kw and for 60Hz 220 volt operation 9.4 Full load amps. All these numbers work out just fine. I also don't understand why there is this rule about doubling the hp rating of the motor. Maybe the rule applies for larger motors?

[WMF]

You need to double the HP rating of the drive if it is three phase input and you are powering it up with single phase as you are essentially powering it up with 33% less energy and the drive will have more ripple to have to smooth out as it is missing a phase.
Most smaller drives (3hp) are available single phase input and three phase output at 100% rating. Larger drives typically are three phase input only and most manufacturers will allow you to leave one phase out as long as you double the HP.
Check with the drive manufacturer first before just doing it as some drives must be configured to run with a missing phase without detecting errors.

[TheMapleMoose]

That makes sense.

[Amber Gold]

I never heard the explanation why, but that makes sense. I have an electrical engineer friend who designs stuff for industrial facilities and by code, VFD's are double the hp of the motor.

TMEEH...maybe it's working find now, but maybe since it's not overrated it'll burn out sooner?? Not sure.

[500592]

Well I guess I do not need a vfd the pump I was going to buy was on eBay for 288 shipped! And when I went to buy it it had been sold darn it do they come up often on eBay.