# another rpc question.



## quickcut (Sep 22, 2017)

I have a 525volt 15kw motor that I would like to use for a rpc. I only have 380volt as an input. Will the difference in voltage make a difference ? or will the motor be suitable. 

thanks
charles


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## Linghunt (Sep 24, 2017)

Have to say, *I don't really know*.  Have to power the motor with and 380 to see what happens?  if it does run, measure the speed compared to the rated number.  Under voltage shouldn't damage the motor for a short test is my guess.

Waiting to see what others say, lots of smart folks on this forum. 

Look forward to hearing more information , this is interesting question.  Selling this motor and buying a different one was my 1st thought.


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## bjornsh67 (Sep 24, 2017)

I have a 630v 3 phase motor for my cva and the windings are 380v rated. Are you able to tell if the voltage rating is for delta or star configuration?


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## Ulma Doctor (Sep 24, 2017)

quickcut said:


> I have a 525volt 15kw motor that I would like to use for a rpc. I only have 380volt as an input. Will the difference in voltage make a difference ? or will the motor be suitable.
> thanks
> charles


Hi Charles,
i'm sorry but the 525v motor is not suitable to hook directly up to 380v single phase input.
you will need a 380v motor to make the RPC or a VFD to properly operate the motor.


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## Ulma Doctor (Sep 24, 2017)

bjornsh67 said:


> I have a 630v 3 phase motor for my cva and the windings are 380v rated. Are you able to tell if the voltage rating is for delta or star configuration?


some three phase motors, & most dual voltage motors, can be hooked up in the delta or the WYE(star) configurations


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## quickcut (Sep 27, 2017)

Ulma Docter, thanks a bunch , saved me a lot of head scratching. Would you mind explaining the theory behind this?


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## Ulma Doctor (Sep 27, 2017)

maybe this link may help explain things
https://www.allaboutcircuits.com/te...t/chpt-10/three-phase-y-delta-configurations/


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## Ulma Doctor (Sep 27, 2017)

Another bit of info,
Delta is used in the US for a lot of large hp motors in undustry.
Sometimes the motors are started in delta, to reduce current draw, and then run in the Wye for most efficient running current


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## Chipper5783 (Sep 27, 2017)

You should have no trouble at all running the 575V motor on 380V.  The issue that you need to watch out for is that you do not exceed the FLA (current) as shown on the motor name plate.  You certainly will not get 15kW - but to run this uncoupled and test it - not an issue.  Motor repair shops do this all the time on much more expensive motors (for example 13.8kV motors run tested at 4160V and the reason is that 13.8kV test gear and equipment is very expensive).  The motor will still run at close to the name plate speed (3 phase motor speed is determined by the # of poles, the line frequency and the "slip" of the transformer action - voltage and current are a lesser influence).

I have run 575V motors on 460V even with substantial load (talking 100HP motor loaded to 60HP) with no problem.  Whether this will work for your RPC application depends on how much load you will have on the RPC.  If you are only pulling 5HP, then you should be fine, and can easily confirm this with a current clamp.

Let us know how you make out.  David


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## Linghunt (Sep 27, 2017)

Chipper5783 said:


> You should have no trouble at all running the 575V motor on 380V.  The issue that you need to watch out for is that you do not exceed the FLA (current) as shown on the motor name plate.  You certainly will not get 15kW - but to run this uncoupled and test it - not an issue.  Motor repair shops do this all the time on much more expensive motors (for example 13.8kV motors run tested at 4160V and the reason is that 13.8kV test gear and equipment is very expensive).  The motor will still run at close to the name plate speed (3 phase motor speed is determined by the # of poles, the line frequency and the "slip" of the transformer action - voltage and current are a lesser influence).
> 
> I have run 575V motors on 460V even with substantial load (talking 100HP motor loaded to 60HP) with no problem.  Whether this will work for your RPC application depends on how much load you will have on the RPC.  If you are only pulling 5HP, then you should be fine, and can easily confirm this with a current clamp.
> 
> Let us know how you make out.  David



Sounds like a good plan, look forward to results and type of load currents of RPC in use.  Teachable moment for many.  Junkyard Wars RPC, kinda...


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## Ulma Doctor (Sep 27, 2017)

wow, we are talking about running an idler motor at 27.5% less voltage than nameplate.
i can't imagine a very long service life
we generally stay within 10% in my industry
the start up amps are sure to be huge to compensate for the 525v motor on single phase input.
but the delta hook up may help the current flow.
i'll be very interested to see how the experiment works out


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## Blackjackjacques (Sep 27, 2017)

Chipper5783 said:


> You should have no trouble at all running the 575V motor on 380V.  The issue that you need to watch out for is that you do not exceed the FLA (current) as shown on the motor name plate.  You certainly will not get 15kW - but to run this uncoupled and test it - not an issue.  Motor repair shops do this all the time on much more expensive motors (for example 13.8kV motors run tested at 4160V and the reason is that 13.8kV test gear and equipment is very expensive).  The motor will still run at close to the name plate speed (3 phase motor speed is determined by the # of poles, the line frequency and the "slip" of the transformer action - voltage and current are a lesser influence).
> 
> I have run 575V motors on 460V even with substantial load (talking 100HP motor loaded to 60HP) with no problem.  Whether this will work for your RPC application depends on how much load you will have on the RPC.  If you are only pulling 5HP, then you should be fine, and can easily confirm this with a current clamp.
> 
> Let us know how you make out.  David



Sounds like this is quickly swirling down the drain - given that a the RPC motor/generator is running on only two legs to derive three phase power, so at best, you can expect maybe 57% of RPC motor loading (at rated voltage), and then on top of that reduce the voltage another 30%.   If you were in the jungle somewhere and had nothing else and you absolutely needed a few turns of the lathe -- this could maybe work.


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