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Thread: rewiring 360-400 volt motor to 220 volt

  1. #1

    rewiring 360-400 volt motor to 220 volt

    Okay, so I have a chance to purchase some new old stock slightly weathered electric motors on ebay for very cheap and close by my work. They are 5 hp 3 phase but wired for 360-400 volts.

    I have a 10 hp rotary phase converter but only have 220v.

    My question is... Can the 380v motor be rewired to run on 220v? It is a 60hz and my converter is 60hz. I have been reading for 3 hours and some indicate yes; others no. I would be inclined to buy just to learn more about it, but with electricity... I try not to "play" with anything more than 110volt.

    The auction ends tomorrow.

    http://www.ebay.com/itm/BRAND-NEW-Ma...item4aba4f13f6

  2. #2
    Senior Member TRYPHON974's Avatar
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    Don't know if it can be rewired, not sure it is an economical option. I'm pretty sure that under 1,5hp, it can be run on 220V with a capacitor which simulates the third phase. For a 5hp motor it doesn't work as far as I know. Sorry not to be helpful.

  3. #3
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    Umm, Yes a 360v 3 phase motor will run on 220V 3 phase. You are already generating the third leg with your RPC so everything is fine. Just plug it in (at your own risk of course). It will however not develop 5hp. Here is how I understand it and a real electrical guy can correct me or confirm me.

    The speed your motor runs at is defined by the winding configuration in the motor and the frequency of your AC. Usually it is 3450 or 1750 or something close. That is just because of the way the windings are distributed in the motor. For instance VFD changes the frequency which changes the speed. Somewhat like a govenor on a diesel, if the load increases, the injection system will meter out more fuel to compensate and hold the RPM constant. The electric motor will try and run at 3450RPM no matter what voltage you feed it if it is 60hz supply. If you apply a load and draw down the RPM, the motor will draw more current to compensate. Like the nameplate says, it is rated for a 5hp load. Any more and the motor will draw more current either overheating or tripping a breaker. Now if you run it on 240V, it will still run at 3450rpm, but adding the same load the motor will draw more current proportionally than it would have on the higher voltage. So in order load it with 5hp some much greater amount of current will be drawn and trip breakers or melt stuff. So, getting to the point, if the nameplate says 360V-400V and draws 15A, put a 15A breaker on it and run it or use it at a lower power rating that draws less than 15A.

    Did I explain it and get it right?

  4. #4
    Quote Originally Posted by vmipacman View Post
    Umm, Yes a 360v 3 phase motor will run on 220V 3 phase. You are already generating the third leg with your RPC so everything is fine. Just plug it in (at your own risk of course). It will however not develop 5hp. Here is how I understand it and a real electrical guy can correct me or confirm me.

    The speed your motor runs at is defined by the winding configuration in the motor and the frequency of your AC. Usually it is 3450 or 1750 or something close. That is just because of the way the windings are distributed in the motor. For instance VFD changes the frequency which changes the speed. Somewhat like a govenor on a diesel, if the load increases, the injection system will meter out more fuel to compensate and hold the RPM constant. The electric motor will try and run at 3450RPM no matter what voltage you feed it if it is 60hz supply. If you apply a load and draw down the RPM, the motor will draw more current to compensate. Like the nameplate says, it is rated for a 5hp load. Any more and the motor will draw more current either overheating or tripping a breaker. Now if you run it on 240V, it will still run at 3450rpm, but adding the same load the motor will draw more current proportionally than it would have on the higher voltage. So in order load it with 5hp some much greater amount of current will be drawn and trip breakers or melt stuff. So, getting to the point, if the nameplate says 360V-400V and draws 15A, put a 15A breaker on it and run it or use it at a lower power rating that draws less than 15A.

    Did I explain it and get it right?
    Very good, greatly simplified, correct enough to not get anyone into trouble. Unless you are engineering a motor, counter emf and so on are concepts not needed by laymen. That is my greatest fault, a guy asks for the time and I build him a watch.
    Last edited by poetwarrior; 08-02-2012 at 04:22 PM.
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  5. #5
    Senior Member machinemaker's Avatar
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    most of the off the shelf 3 ph motors I see have 9 leads coming into the j box and depending of which 3 you use to connect to the line and how you connect the other 6 in pairs determines whether you run it off of 220 or 480. not sure if that is any help.
    kent
    Kent
    There is beauty, power and excitement in simple old technology!

  6. #6
    Thanks for that vmipacman, explains why my surface grinder is low on power. Might change the motor for a 220 3 phase as there dosnt seem to be an easy way to rewire it.
    The mill had a junction box and wiring diagram and was plated 220 or 440, the grinder motor only says 440 and has no junction box.

    Poetwarrior, dont suppose you know what time it is by any chance do you!

    Donk
    Needs must while the devil rides.

  7. #7
    It is a 9 wire system and it can be wired for 360v OR 400v. I thought this was a range but it is for two seperate voltages.

    I have been researching this subject and it seems it WILL work. However... to put it into terms I can understand. Running the motor on lower voltage will increase the amp draw. As long as I do not exceed X amount of amperage, it will run fine. If I overload it, the smoke will be let out and I have some copper to harvest for my furnace. As vicpacman described, I just can't expect this motor to put out its full HP rating on my voltage.

    Interesting enough, using the formulas on the net, this motor is more like an actual 6.75 hp. I am betting it is underrated intentionally.

    If I win the auction, the motor will be installed onto my air T-30 Ingersoll-Rand compressor. I will measure the amp draw and if it exceeds the 8.1 amps max I will use it on my upcoming muller project.


    Thanks all,

    Justin

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