3 phase converter question
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  1. #1
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    Default 3 phase converter question

    I just received a prototrak lathe, and am trying to figure out what kind of VFD or converter to use with it.

    The confusing part to me is that although it has a 7 1/2 HP spindle motor, the nameplate on the lathe calls for 3 phase input of 25 amps. The spec also calls for a source of 9.5KVA That's enough for 12.5 HP, far more than 7.5 HP. Checking other motor manufacturers, I'm finding that a 7.5 HP 3 phase motor typically calls for around 10KVA. ??? The efficiency for that comes out to around 0.6 Doesn't make sense to me.

    I'm finding that digital phase converters for this power level are extremely expensive. Beginning to investigate VFDs, but not sure I'm going to find a single to three phase VFD at that power level.

    This is my first time around this block, so any helpful comments would be appreciated.

    thanks, rex

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    Call the factory,They are just around the corner from you. People are helpful and friendly. Look them up on the net under Southwestern Industries.

    Tom

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    A motor rated for 7.5 HP continuous can chooch more than that momentarily. It'll probably have high load on startup for example.

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    I called the factory. I wasn't able to get hold of anyone who knows more than to repeat the spec. However, the lathe has a 3 phase to 3 phase VFD in it that's rated 10 HP. I assume the input power to the lathe is spec'd according to the internal VFD with some margin, rather than to the motor.

    I've also found that I can't put a single to 3 phase VFD in front of the VFD that's already there. A VFD needs an inductive load to operate correctly.

    I talked to Yaskawa and they suggested swapping out the VFD in the lathe. I'm reticent to do that because it's a new lathe and that would probably break the warranty. Besides, any time I want support, they'll tell me it's an "unsupported configuration"... been there. Also, a VFD has a lot of settings that I would have to somehow reproduce if I put a new one in. I'm pretty sure the factory won't be helping me with that.

    That said, this is all uncharted territory for me and I probably don't know what I'm talking about. I just want to start making chips.

    So, I need a bonafide phase converter. The one recommended by the factory is a static (non-rotary) model costing $3500. Seems a bit rich. The rotary ones are cheaper, but the good ones seem to be around $2500.

    Any suggestions for the right phase converter?

    thanks, rex

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    Call Jim Gorman at Phase Craft. He set me up with my 20hp RPC

    PM member: phase-craft

    (714) 710-9094

    [email protected]

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    I just got an American Rotary Converter for a Star CNC in my garage. 3 phase, 10 HP. so far it works great, but it's only been less than a week. cost me $850. look into it.

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    I would go with the rotary. I run phase converters in my shop. Larry with southern converters worked with me on two of the three converters I have. If you are a growing shop I would go ahead and invest in larger than you need. I do know you will need twice the horse power of what you want to run. When I was researching it was my understanding that a static converter actually just fools the machine making it think it has three phase. So you lose about 1/3 to 1/2 of your actual power. The lathe might be like my cnc mill it has a 7 1/2 spindle but a 23kva transformer. Your axis drives and such all operate from that. So go with the recommended kva for wiring and phase converter selection. I'm just an old country boy but I went through all this earlier this year. Hope this helps.

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    If you're gonna use it regularly(everyday?), Phase Perfect is the best thing. If you're gonna get a 10hp, might as well spend a little more for a 20hp and be able to run more things later on, so long as you got enough 1ph power to feed it.

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    Quote Originally Posted by SND View Post
    If you're gonna use it regularly(everyday?), Phase Perfect is the best thing. If you're gonna get a 10hp, might as well spend a little more for a 20hp and be able to run more things later on, so long as you got enough 1ph power to feed it.
    2nd this.

    May be expensive, but losing 1-2 drives for bad input power is more than the cost of a 20HP PP.

    I took this advice and do not regret it!

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    There is a separate sub forum here that covers the subject...

    http://www.practicalmachinist.com/vb...rters-and-vfd/

  12. #11
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    Rotaries are cheap, and they work.. BUT.. They suck..
    They are loud, and they are POWER hogs.

    I'd rather be a vegetarian than use rotaries for a permanent solution.

    Temporary until you can get a phase perfect or get REAL 3 phase..

    And you can always sell the rotaries, somebody is always looking for one.

    3 phase day.. I actually got to run the big lathe in High Gear, it was awesome.



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