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American Rotary Phase Converter voltage issue

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Janderso

Jeff Anderson
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Hi,
My son and I Installed a sub-panel in the shop today. We also installed my new RPC to run my 3 phase machines.
Question, the voltage at the disconnect to the lathe and mill with no load is 121-121-191. The 191 is the value from the idler motor or third leg.
Please explain why I may have this issue.
I purchased a 10 hp ADX.
The machines perform just fine but I am concerned about the difference in values.
Oh and this RPC is very quiet.4C4D1AB7-65A6-453D-99AE-054BD2AF40C5.jpeg
Thank you,
Jeff
 

Janderso

Jeff Anderson
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I should add, the voltage in my post was measured from ground.
If I measure balance between each phase, I get 227-231-239
Normal?
 

JimDawson

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227-231-239 seems about normal, could be balanced a bit better, but OK. Check it with the machine running, I would expect it to be better. The measurements you got to ground seem about right also, but you really can't measure to ground, measuring phase to phase is the correct way.
 

Eddyde

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Those voltages look to be within about 5%, which is good for a RPC. When I built mine, I spent a couple of hours swapping out various capacitors and couldn't get much better than that ( I got maybe 3%). As long as the motors are running smooth there should be no problem.
 

Janderso

Jeff Anderson
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After reading your post Eddie, I went back out to the shop this morning, flipped on the RPC.
I was using numbers my son checked when first turned on, going by memory.
My memory scrambled a bit.
I got 244-250-250. The manufactured leg is 244.
Better. Right?
When I get home from work I’ll check it with the lathe under load. Too early right now.
 

Martin W

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Should not be a problem. You will open up a new world. Used three phase equipment is usually cheaper to buy and heavier built.
Cheers
Martin
 

dennys502

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One leg is going to be high. 120/120/208 If you're not accustomed to 3 phase with the high leg be careful you don't have 120v circuits hooked to the high leg.
 

Janderso

Jeff Anderson
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Checked it before I left the house this morning. Under load (turning an 8" chuck-not facing etc.)
241-241-238.
Dang, I think that's really good.
The other thing I didn't notice, it starts as if it was in the warehouse on 3 phase. The RPC is performing exactly as it should.
I'll check the voltage when there is a good load on the 7.5HP motor on the lathe. It's a Clausing 15" with a clutch.
Thanks for all the advise.
 

Eddyde

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After reading your post Eddie, I went back out to the shop this morning, flipped on the RPC.
I was using numbers my son checked when first turned on, going by memory.
My memory scrambled a bit.
I got 244-250-250. The manufactured leg is 244.
Better. Right?
When I get home from work I’ll check it with the lathe under load. Too early right now.
Those are great for no load and the numbers under load are fantastic! Your RPC should purr like a kitten!
 

Janderso

Jeff Anderson
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It's very quiet Eddyde. Surprisingly so.
 

Bi11Hudson

Artificer00
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Store-boughten 3 phase converters are generally connected "delta", most shop motors are wired "star". One will run on the other, either way. Just don't try to use the "neutral/ground" to get 120 volts.

What you are seeing is called the "wild leg", at least what we called it in my day. Two of your phase leads are connected directly to the incoming line. The third leg is synthesized by the rotary converter, basically a three phase motor and a handful of capacitors. The 1.73 factor is the square root of 3, a function of the third phase, showing up as a "wild leg" to the reference, usually neutral/ground. As long as phase to phase is correct within 5 or 10 percent, you're good to go.

By the way, that factor is also used for current...
 
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