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  #11  
Old 05-04-2012, 09:35 PM
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shortbus shortbus is offline
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I thought your lathe motor was 440 - 220 3PH? Why not skip the transformer and connect for 220 3PH ?
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  #12  
Old 05-05-2012, 12:48 AM
catman81056 catman81056 is offline
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If I supply the 440 3ph I don't have to change anything, nothing else to convert on the machine. I picked up a 20 hp 3ph idler for a RPC. I'll just rig a pony motor to start the 20hp so the inital current draw will be lower.
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Old 05-05-2012, 02:40 AM
gerty gerty is offline
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I'd really like to see a schematic of what you have in mind.
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  #14  
Old 05-05-2012, 03:09 PM
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Quote:
Originally Posted by catman81056 View Post
If I supply the 440 3ph I don't have to change anything, nothing else to convert on the machine. I picked up a 20 hp 3ph idler for a RPC. I'll just rig a pony motor to start the 20hp so the inital current draw will be lower.

The change is just a few wires in the "pecker head", versus the cost of the transformer and the power loses in it.
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  #15  
Old 05-05-2012, 04:17 PM
gerty gerty is offline
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[QUOTE]I thought your lathe motor was 440 - 220 3PH?[/QUOTE

Which post was that in?
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  #16  
Old 05-05-2012, 10:15 PM
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[QUOTE=gerty;483894]
Quote:
I thought your lathe motor was 440 - 220 3PH?[/QUOTE

Which post was that in?
http://forum.allaboutcircuits.com/sh...ad.php?t=68528
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  #17  
Old 05-05-2012, 11:08 PM
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OP - The lathe is powered by a 440v 3ph, 5hp motor that pulls 8.8amps

So he wants to power this motor from 200 volts (using 15kW transformer, 200 --> 440 volts)? Is this correct?

(440/200) * 8.8 = 20 Amps input (w/o losses).

Also it's not clear how much the transformer will draw w/o load (since it is used in reverse).
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  #18  
Old 05-05-2012, 11:20 PM
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Quote:
Originally Posted by takao21203 View Post
................
Also it's not clear how much the transformer will draw w/o load (since it is used in reverse).
A normal power transformer draws only a small magnetizing current, either forward or reverse, as long as its voltage ratings are not exceeded.
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  #19  
Old 05-06-2012, 12:43 AM
catman81056 catman81056 is offline
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I think it's alittle more than switching a few wires, I have all the stuff needed, 3ph 20hp idler, 3 hp 220 1ph pony motor(I'll use this to bring the idler up to speed before applying power), the 6ga wire, and the 60 amp breaker box. All thats left to do is run the wire and fab up the frame work to mount the idler and pony motors. Thats some thing I enjoy doing. Here's what the electric panel looks like. It's alittle over my head.
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Old 05-06-2012, 07:50 AM
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Well here we can see the control box.

More information is required or advice can only be guesswork:

-Type of motor, 3-phase, or eventually additional starter coil?
-Any capacitors used?
-How many phases on the grid? Single phase 200 volts? 3 phases?

-Any switches or buttons on the control box?
-Are the relays used to change between star/delta configuration?
-Or are they used to switch an external motor/generator? Is this done manually eventually for startup?

-Have you connected the transformer already?

Here a page I found containing information about "idler motor" circuits (to convert single phase to tri-phase).
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

Last edited by takao21203; 05-06-2012 at 07:58 AM.
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