My concern was whether my 7.5HP RPC would supply the proper 3 phase to allow the 2HP VFD to provide the proper output without derating and having to buy a bigger VFD.
The reason I do not want to buy a 1 phase in/ 3 phase out is cost.
If the RPC will put out the proper 3 phase then I can use a 3 phase in/
3 phase out for $179. The other VFD that is single in/ three out is 2x the cost.My RPC is not balanced and the lathe is all it controls.
So cost is the driving concern here.
Thanks, Steve
Steve, unless its a very old VFD, derating the vfd about 25% at most is what I suggest when running it off single phase.
And to be blunt..Ive run 7.5 hp lathes, starting in back gear, off a
5hp vfd ON SINGLE PHASE. Set your acell time for a bit longer.Gunner
Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats. H. L. Mencken
Steve,
To answer your question, based on my understanding of VFD's, I think what you are attempting should work fine. Disclaimer: I haven't actually tried it myself.
However I agree with others that having a single phase in is preferable. It would cost more in electricity to run the RPC/VFD combo. RPC's are not efficient, where VFD's are.
Look at the price for a Leeson sgl ph drive. I had bought one for a 3 hp drive for around $250. The 2 hp should cost less. The only reason I didn't keep it was because I wanted to use all the lathe controls and remote keypad at the same time. That particular drive didn't support it. I finally found 1 manufacturer that would support what I want.
leeson.com, part# 174933 I tried to call these guys, but they had just closed. Them and one place on the web had them them at a cheap price. Everyone elses was very expensive. McHenry Electric & Supply Co Inc - 0.1 miles SW - 4012 Main St, McHenry,
60050 - (815) 344-5121 McHenry Electric & Supply Company - 0.1 miles SW - 4012 Main St, McHenry, 60050 - (815) 385-5530Let us know how it works out.
Wayne D.
Buy a used VFD. With some patience, you can get an industrial quality 3 HP drive for less than that. I've had good luck with AB drives.
Three phase power can be rectified and will have much less ripple than single phase power. Your unbalanced RPC won't be quite as good in this respect, but will be almost as good. I think you will have no problems using it to supply the VFD, however you might check the voltages and see that the generated leg is not much higher than the single phase line.
Balancing a RPC is not a big deal. Pretty easy to do.
Dan
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