VFD Score

Yes, it's big enough. Most VFD need to be at least twice as big as the motor they intend to run if your going from single phase to three phase. Dick

Look at the output current ratings of the VFD's and compare them to your motor's full load current. I think you will find that the 2 hp GE is big enough.

Randy

Damn good deal.

He assumed what I did *not* say, and that is that it's a 4HP VFD, but it's rated at 3 phase input to 3 phase output. I would, of course, be running single phase input to three phase output.

I already have a rotary converter and it is in place, but I'm assuming it is worthwhile to replace it with the VFD. Correct? Ie. there's no advantage to using *both*, right?

--Donnie

Yeah. The best deal may have been the brand new Starrett dial gage. I forget the model number off the top of my head, but I looked it up one place and it was selling for $256. I got it for $5.

No, the stuff isn't hot...it's some sort of deal that is a large church group that gets donations of overstock stuff or whatever and sells it only to members. The companies get tax writeoffs for the stuff, and the church sells it to raise money. They would do a lot better putting stuff on eBay, but who am I to complain? :-)

--Donnie

I got some too, in a big military surplus pile. Look either new or not used much.

no reason to complain, as long as the deal was at arms length (ie you did not threaten them with weapons etc). Great finds, congratulations.

This was still in the box! Paperwork and all.

--Donnie

Very nice. I checked mine, it is also new old stock, in box, with not a single scratch. Military condition B.

it is called Kent Moore dial indicator.

Well, both converters are 3 phase input and 3 phase output, but my understanding was as long as you uprate it enough (ie. at least a 4HP converter for a 2HP motor, which was my original question) then you could safely run single phase into the converter anyway and still get three phase out. Which is why I was curious about leaving the rotary converter in the equation...it was sort of making me think you may not need to worry about the uprating, provided the rotary converter had enough output current capability. I didn't think about the cleanliness of the rotary converter, though...are they not-so-clean?

--Donnie

The output of the rotary converter is relatively clean in terms of spikes and tansients characteristic of semiconductor circuits and that can be death to downstream semiconductor devices (like VFDs). But the voltages, currents, and phase angles on the wild (developed) leg can be quite variable depending on the load. Since you are doing odd things to the VFD with either a single phase input OR a rotary converter, I have no clue which situation would work better. I suspect it is a function of the internal circuit design of your specific VFD.

I th> >

My 5HP VFD made by Sumitomo Heavy Industries seems to work fine running from my unbalanced 7.5HP 1750RPM phase converter. I use it to run my mill which is a 2HP machine and that way I get variable speeds. It may be since it is rated at much more than the load motor that it does not pose a problem.

Any ideas???

Thanks, Steve

The main problem in single phase driving a three phase input VFD is exceeding the ripple current rating of the DC link storage capacitor. This is because the single phase input refreshes the charge on this capacitor less often. In the absence of manufacturer guidance 2:1 derating is pretty safe.

If driven from a rotary converter this problem disappears and derating is unnecessary. The odd peculiarities of rotary converters will not bother the VFD because it rectifies and smooths this input before it allows it to reach any sensitive semiconductor.

Jim

OOOOOOOO!

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner