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What is the size?

JOHN1

Aluminum
Joined
May 27, 2006
Location
SHREVEPORT, LA.
I have a rotary phase convertor which was constructed by a retired electrician about 6 yrs ago. It works fine but I don't recall what size it is and there are no marking or labels on it.

Is there any way to determine what "size/hp" it is?

John
 
Hi John,

Motors come in a number of standard sizes, identified by an alpha-numeric "frame" number.

Measure your motor, including the mounting dimensions, the shaft diameter and length, and the distance of the shaft centerline above the mounting surface. From this you should be able to determine the frame ID (perhaps more than one). You can look up possibilities at Grainger www.grainger.com and other online sources.

Once you know the frame number, you'll find a few different size motors which match. Compare the current drain specs with the fusing on your RPC input. This should get you pretty close.

- Leigh
 
Thanks Leigh:

Will the "size" of the motor determine what size RPC it is , in other words will it tell me what I can "drive" with tha RPC.

As you can tell I am not up on RPC'S?

John
 
Simpler way as some motors could be specials that won't be found on charts
Get a volt\amp meter
multiply amps x volts divide by 746, that gives you approximate horse power at no load
multiply that by 2.5 gives you approximate HP at a service factor of 1.0
If anything this method will end up a little under so you can safely run anything as large
or smaller than the number this method comes up with,..........Bob
 
Dualkit:
#1 Am I measuring amps of draw of the RPC or the output to the lathe etc; ?

#2 How do I calculate how many machines it will handle, lathe 7.5 hp etc, or do I take the amps they require?

I think I am confusing myself and need a class on RPC's.

Thanks for your patience!

John
 
You are just going measure the draw of the RPC only as it is idling not connected to anything
else.
Depending on what type of machines you want to run, the RPC will start any motor up to
it's size in horsepower as long as the motor is not severely loaded.

Let's say your RPC calculates out to 7.5HP it will start any motor up to 7.5HP as long as that
motor is not started against a strong load, by strong load start an example would be an air compressor or hydraulic pump, for that it might only start 5HP. Usually you can safely run
up to double the RPC output off of one RPC in horsepower, just always start the largest motor
in the line first and never start motors simultaneously.

Your standard RPC will run manual equipment as stated above, for CNC
equipment the rules change.
 
John,

One word of caution all phase converters have a wild leg that can have voltage to ground
of up to 195 volts, keep that one out of all control circuits where magnetic contactors are
involved they can blow the coils,...........Bob
 
The high leg is usually 165-195 on an average, where the other 2 will be 110-125 depending
on your line voltage, should be easy to spot even with a cheap meter. That is the "manufactured leg" that the phase converter creates.
 
Question??? What are you trying to run off this phase converter? If it is a mill there is probably
no concern where the high voltage leg goes, as the average mill ( Bridgeports and their clones)
use drum type switches and contact blocks, and have no magnetic contactors that will be adversely affected by high voltage. On the other hand most lathes are full of magnetic contactors, and most 3-phase band saws and compressors contain at least one. Hope I am
being of some help. I have built my own phase converters, that are still in use, and wired my
own shop and a few others without incident, if you want more assistance it would probably
be best if we talked on the phone, weekend cell minutes are free! Send me a private message if you would like my phone number,...........Bob
 
Bob:

Thanks a lot.
Have Andrychow 1660 lathe, 7.5 hp
Supermax Mill (BP Clone) 2 hp
Chevalier Surface Grinder, can't remember HP

All are 3 phase

Have run them all on this RPC but everything has been in storage since my move from Phoenix 4 years ago, just now setting shop up and can not remember how this RPC is connected.
I will try to photo and include tonight and the phone thing would be much appreciated.
Let me get some more info and run the voltage etc;, will post and go from there.

John
 
I can understand the fog associated with 4 years between wiring jobs especially if over 40,
( like me!). Out of your equipment list only the
Supermax ( I have 2 of them) is safe from too much voltage in the control circuit, as it has no
magnetic contactors, only problem, the spindle may rotate in the wrong direction, but that would be solved by switching any 2 lines. The other equipment would need the high leg attached to line 3, and if they rotated in the wrong direction just switch line 1 with line 2.
Enough babble, if you have problems when your hooking everything up just PM me,........Bob
 








 
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