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Thread: phase converters?

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    gunco irregular moleman's Avatar
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    Default phase converters?

    I was looking to upgrade my 9x20 lathe and found a 11x30 clausing lathe at a reasonable price nearby. The only problem is that its power requirements are 3/60/220-230/460-480 for the 2 HP Main drive motor. I only have 110 and one 220volt 50 amp line in the garage. What are my options in order to get it working? Could I just replace the 3ph motor with a 220v motor?

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    Gunco Regular Rich's Avatar
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    I don't have any first hand experience with phase converters, but my neighbor used phase converters for his lathe and mill. He said his electric bills were lower than they would have been with single phase motors. Three phase equipment is cheaper to buy used in this area because three phase power is only available in commercial zoned areas.

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    TRX
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    [some simplification for clarity]

    Power comes from the plant in various ways; by the time it gets to town it's usually 3 phase, 240 volts. It takes four fires to move it - 3 110 volt legs and a "neutral" wire. Each leg is a full sine curve of alternating current, 120 degrees apart - that is, the three legs have equally spaced curves.

    "220" is two legs and a neutral. The two legs only cover 240 degrees of the full curve, so you only get 220v instead of 240v. Since each leg is 115v they push/pull to make 220.

    [EE heads explode about now]

    "115" is one leg and a neutral.

    The phase convertor takes any two legs and synthesizes the third. Solid state boxes do it by slicing and dicing the two inputs to make the output; this gives a "noisy" stairstep curve to the third leg. The better the convertor, the closer to a true curve. This is big marketing juju for the people who sell convertors, but it would only concern you if you were trying to run that old IBM mainframe you bought off eBay. 3 phase motors don't care.

    Rotary convertors use a three phase motor (sometimes specially wound, sometimes off-the-shelf) and use two legs to drive it. As it spins, the undriven part of the motor acts as a generator, making the third leg. It's a true sine curve, but due to losses the leg is usually a bit under voltage, plus it takes more power to drive a rotary convertor than a solid state convertor. Again, the power supplies in some big iron supposedly don't like the output of the convertor, but the motor in your mill still won't care.

    Rotary convertors are pretty much immune to the kind of load spikes that will pop the breaker on a solid state convertor.

    You can buy a solid state convertor big enough for most mills for $300-ish. Rotary convertors generally cost 2x that, but you can make one yourself if you can scrounge a three phase motor 1/3 to 1/2 again as large as the motor you want to drive. It's usually called an idler motor. For example, if your mill has a 5hp motor, the next largest standard motor is 7.5hp. Wire the neutral of your 220 line to the neutral on the idler. Then hook the two hot lines to the idler. Most 3 phase motors are marked A, B, and C. Say you hook your wires to A and B. Then hook the 3-phase motor on your mill to A, B, and C. Note A and B go from the wall socket, across the idler, and to the mill. C is the generated leg from the idler.

    When you plug the idler in, nothing will happen. You have to spin the shaft with your hand to get it turning. Once it comes up to speed, you can turn the mill on.

    If the mill motor spins the wrong direction, swap any two legs - ABC to ACB or BAC - and it will go the other direction.

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    Indian Admin Winn R's Avatar
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    Thanks TRX. I'd wondered how the motor ones worked.

    I run an old Bridgeport with one of these.

    Converter
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    Gunco Regular bsouthnow's Avatar
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    Before selecting a phase converter, you should consider a varible frequency drive (VFD). I use a Hitachi L200 to drive my 220 3 phase drive motor on my benchtop cnc and it works wonderfully. I also use a 5 hp rotary phase converter that I built out of spare parts and junk that for my bridgeport and it works OK but the electronic VFD would be my choice should the mechanical converter fail.
    Good luck.
    Bill
    Bill from Spartanburg

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    gunco irregular moleman's Avatar
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    Sounds like there's more than a few options. Thanks for the information. Still haven't made up my mind on it, but it sounds like the 3 phase ones can be the better buy than the 220v ones.

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    Gunco Member 2ndamndmnt's Avatar
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    moleman, i have bridgeport and leblond that are both 3 ph, both run off of one static phase convertor, just not at the same time. nver had any problems. i have a rotary converter that might work for you, brand new and cheap. pm me

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    TRX
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    Quote Originally Posted by Winn R View Post
    I run an old Bridgeport with one of these.

    Converter
    That's the same one I have. It works fine on everything except my Coates wheel balancer. Apparently it *way* exceeds the nameplate rating on the motor when spinning up a tire, but it's on for maybe five seconds per minute, so the motor doesn't overheat. The Phase-A-Matic was not impressed, though.

    I have an old 7.5hp motor I spin up by hand as an idler to run the wheel balancer.

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    Gunco Member alpine44's Avatar
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    moleman,

    The phase converter is the cheap way (I have seen them for ~$60). It works similar to the starting circuit in your single phase capacitor start motor. The capacitors in the phase converter shift the phase for the other 2 windings of the 3-phase motor. After the start of the motor the phase converter does nothing as the 3 phase motor will keep running on one phase once rotating. Just keep in mind that you have to suck all amps necessary out of one phase rather than 3 so size your breakers and feed wires accordingly.

    The VFD is the much slicker but unfortunately also more expensive solution ($200+). This will allow you to change the motor speed. I have a VFD on my conventional mill and would not want to be without it. It even does jogging for threading, etc. and ramps up the motor gradually to prevent the breaker from tripping.

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    Gunco Veteran Markp's Avatar
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    Quote Originally Posted by moleman View Post
    I was looking to upgrade my 9x20 lathe and found a 11x30 clausing lathe at a reasonable price nearby. The only problem is that its power requirements are 3/60/220-230/460-480 for the 2 HP Main drive motor. I only have 110 and one 220volt 50 amp line in the garage. What are my options in order to get it working? Could I just replace the 3ph motor with a 220v motor?
    I have a 5 HP rotary phase converter I would like to get rid of (in other words it has the phase converter and a 5 HP 3 phase motor) which would supply plenty of 3 phase power to run that thing.

    Make me a fair offer plus shipping and it's yours. I used to run my CNC bridgeport with it.

    Mark

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