# MCC for Grain leg operation



## nolabama (Oct 3, 2007)

The VFD will do the phase conversion for you. I believe you would need a drive for each motor.

If all you want to upgrade is the auger then a VFD will be fine. You have to upsize the drive when doing a phase conversion. How much I'm not sure.


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## Jlarson (Jun 28, 2009)

nolabama said:


> The VFD will do the phase conversion for you. I believe you would need a drive for each motor.
> 
> If all you want to upgrade is the auger then a VFD will be fine. You have to upsize the drive when doing a phase conversion. How much I'm not sure.


Like double when you get up to that size, big drive, big conductors too feed it too. Doing single to three phase means higher current draw, heat and stress on the bridge rectifiers hence the upsize. 

An RPC won't be cheap either. Adds another maintenance point too. 

First question I'd be asking is how hard would it be to get a 3 phase service? It's the wiser option over the long run.


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## nolabama (Oct 3, 2007)

If he is a farmer and already bought a RPC then odds are he can't get three phase.


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## Jlarson (Jun 28, 2009)

nolabama said:


> already bought a RPC


Glad you can read :laughing:, I read it like they wanted to get an RPC


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## xlink (Mar 12, 2012)

Double the vfd hp for phase conversion is my understanding, too. The largest motor I've run that way is 10 hp, but it has been going for a few years.

I don't think any VFDs are hazardous location rated. It's an issue handling grain. If it's outside, the nema 4 enclosures are pricey.


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## nolabama (Oct 3, 2007)

xlink said:


> Double the vfd hp for phase conversion is my understanding, too. The largest motor I've run that way is 10 hp, but it has been going for a few years.
> 
> I don't think any VFDs are hazardous location rated. It's an issue handling grain. If it's outside, the nema 4 enclosures are pricey.


Move the drive to a non hazardous location. If that is an issue.


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## John Valdes (May 17, 2007)

With single phase being the only option and having 15 HP and 7.5 HP motors, the RPC might just be the best bet.
All this mess can be cleaned up and there is no reason to use drives unless you need speed control.
The motors are sufficient in size and the VFD's would require significant derating.
Might be to expensive to go the VFD route.


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## JRaef (Mar 23, 2009)

brmemmer said:


> I want to upgrade our current setup at the farm and I am looking for advice and suggestions.
> 
> Currently I have 2 - 15 hp and 3 - 7.5 hp motors. Only 3 motors are used at one time. We only have single phase available so we have a 3 phase rotary convertor. Magnetic starters, 3 are Square "D" and 2 are Siemens.
> 
> ...


If using a VFD as a phase conversion, you need a VFD for each motor. In your case, all of those motors are too big to fit behind non-derated VFDs, so you would need to buy drives that are 2X the motor HP size for each one, so 30HP VFDs for the 15HP motors, 15HP VFDs for the 7.5HP motors. As mentioned, this will be expensive and the motor starters will become unnecessary.

I'm a big proponent of VFDs, but in this case, an RPC is a better plan. Clean up the mess, put the controllers in one area with a 3 phase panelboard feeding them, don't waste a lot more time agonizing over it.


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## Ultrafault (Dec 16, 2012)

I just did an install exactly like this a couple months ago. How big is your phase converter. I used a plc and a push button station as you can get in a big bind if you have one of your augers turn off in the wrong order.


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