Rotary Phase Convertors

[bleeth]

Looks like the old dog needs to learn some new tricks for a change.
I'm moving shortly and have had big time issues finding the right space with 3PH in it. I run a 10HP 3PH compressor and 7.5 HP regen. The rest of the stuff is 1PH

My neighbor just offered me a 3PH rotary convertor for pretty much nothing but the motor is 40HP! I'm in the dark with how much Amps I will need to run the convertor. The charts (pretty much like some equipment manufacturers I know!) seem to indicate a lot of Amps to run the Convertor, but I've read some stuff about not really needing near that much. All informed replies welcome. Feel free to PM or e-mail me (just click my sign-in name)

Dave

[Ajcoholic]

Hi Dave
In our previous two shops, which were fed by 600V three phase off the pole - it was simple, as you know. When I built my new shop in 2010/11, I am about 2 miles from the main line and my shop is only serviced by the standard (here) 240V " two live, one neutral" and generally 200 Amp service is standard. Any more and you pay a large premium.

That being said, I trusted the advice of my machinery dealer/sales, and purchased a RPC from them. I believe it is a Dyna-phase brand, made in Canada. I am not sure of the HP of the idler, but the RPC is rated to run up to 75 HP combined, with the largest single motor being a maximum of 25 HP. Reasoning is, my largest motor is the 20HP in my wide belt sander, with the majority of the others falling between 5HP and 10HP. With three of us working now, I have only tripped the main breaker once, when we tried running the SHopbot & 10 HP regen, the wide belt sander and someone turned on the 7.5HP planer.. while the 7.5 HP duct collector was also running. Of course if you have something that draws a lot of current (like my 10HP compressor) it might be under the max limit yet cause too large a surge current.

Anyhow, I believe my feed is somewhere around 120 Amps to the RPC. I can check tomorrow exactly.

After 5 years, I have to say it is not as worrisome as I expected. I just grease it once a year. I start it up first thing in the morning and let it run all day until I close down the shop.

Just to give you an idea of what I run (remember there are three of us and we are usually all working on different machines at the same time)..

WBS - 20HP + 2 HP feed
regen blower, compressor - 10 HP
planer, jointer, DC, shaper, large panel saw, spray booth exhaust, stroke sander - all 7.5HP
table saw, RAS, band saw(s), edge bander, - 5 HP
numerous other sanders, lathe, etc from 2 to 3 HP.

I did install a timer with a solenoid valve, on my compressor. I found at time, the compressor would labour trying to start if I was running several other pcs of equipment. Now, the solenoid opens effectively unloading the cylinders, for 3 seconds, allowing the motor to come up to speed before going under load. No issues since.. going on three years.

I havent blown any capacitors either, although I did add two or three large ones when we set up the RPC initially with the electrician. Trying to balance the legs equally as possible and also avoiding drop out current when starting the heavy loads.

Do you know what the RPC youre looking at is rated for? Is the idler a 40 HP motor or is the capacity 40 HP?

[Ajcoholic]

I dont think the unloaded RPC draws a lot of power... I tried turning it on and off for a while (a PITA) when I was just starting up and was working without employees. I didnt notice much if any different in my hydro costs.

I prefer to leave it running all the time were there.

[Brian Harnett]

I have a much smaller converter 7.5 hp for my metal lathe when I hooked it all up years ago I ran an amp meter on the wires it was very little current with no load, I don't remember the numbers though.

[mark_stief]

Dave My 40hp is on a 125a breaker and it will pull 110-115a when running my moulder Did the same thing Andrew did with caps to try and balance the legs the best we could

[donclifton]

spend the bucks and get a VFD, They are cheap (relatively) quiet and will reduce your power bill. I have 4 in my little shop and when I was the engineer for the airport we ran every pump and air handler off of them. we put two 75hp pumps on two VFD and our electric bill dropped $20,000 a month.
Don

[bleeth]

Well, with what you guys said and the results of some research it looks like I'm in a tough spot.
To run both compressor (Checked closely and it's a 7.5 Motor pulling 28 A and blower is same power and draw) it takes a 20-25HP Convertor and 125Amps of power. The locations I'm looking at typically have a 100 Amp panel or so.
If they had a 200Amp service they would have 3PH already typically around here.
For the VFD's I would need 2 15HP VFD's, also needing a bunch of amps. Path of least resistance to blower is change to universal vacuum with LH motors and black box rig.

My neighbors 40HP idler Regen would need a ton of power to run. He says he "didn't have that big a breaker on it" but doesn't recall, and it was hell on startup. I suspect that is because it wasn't getting enough juice for a clean start.

Changing out my like new 120 Gal IR Compressor's motor (The whole rig is only about 7 years old) for a single phase seems as absurd as selling it to buy a lightweight.

This is getting tougher by the day. Need a magic bullet!

[donclifton]

If you have a spindle and a VFD read the amp rating and then take a true RMS clampon amprobe and read what it pulls. My 18amp spindle only pulls 1.5 amps per leg. also most rotory converters are inbalanced because the third leg is generated from the other two.
Don

[Ajcoholic]

Mine is rated for 116 amp max draw. I'm assuming that is fully loaded.

If you just want to run those two motors you can get one rated for 25 hp max, 10 hp largest single motor which would be fine on you 100 amp service.

But it's not the one your friend has... I see these up for sale often enough. I had one rated for 7.5 hp I almost gave away.