# 50 hp 480v VFD



## Jay Freeman (Aug 2, 2017)

I haven't done this with a VFD in particular but it is common to step single phase 480v down to 120v for control power which I do. I don't see any problem with doing this on your VFD as long as it's done on the line side of course.

If it's just a muffin fan it won't draw much current but you will need to make sure you pick a transformer with enough VA to handle it.


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## Cjd72090 (Jan 22, 2019)

yea the transformer for the fan came with the fan itself so its definitely rated for it. also there is a second transformer also tied to L1 and L2 to step 480 down to 240 to power a 240 volt pump also part off the homogenizer.its only 3.9 amps at 240 volts and the transformer is rated accordingly. so its ok to have 2 transformers to take power off L1 and L2?


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## glen1971 (Oct 10, 2012)

I've done this tons of times.. We've had to add extra fans to enclosures just to keep the air moving.. As Jay said, just make sure sure your transformer is sized properly, and properly fuse everything and you should be good to go..
To add more transformers, I would check your primary currents and you might want to use L2 and L3.. I'd be wondering why the homogenizer isn't fed separately, and is fed through a vfd cabinet..


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## micromind (Aug 11, 2007)

glen1971 said:


> I've done this tons of times.. We've had to add extra fans to enclosures just to keep the air moving.. As Jay said, just make sure sure your transformer is sized properly, and properly fuse everything and you should be good to go..
> To add more transformers, I would check your primary currents and you might want to use L2 and L3.. I'd be wondering why the homogenizer isn't fed separately, and is fed through a vfd cabinet..


Same here, it's very common to use 2 legs of the 480 to power a transformer. 

I agree with Glen, I very rarely use L1 and L2 mainly because just about everything else uses these 2 phases so I use either L1 and L3 or L2 and L3. 

You'll need to fuse the 480 side of the transformer but if the 120 side is 120 only and not 120/240, it doesn't need to be fused. The code allows a single-voltage secondary to be protected by the primary fuses. 

If you'd like the fan to run only when the VFD is in operation, simply program one of the relay outputs to close when running and use it as a switch to control the fan. There's a good chance that one of these outputs is factory programmed to close when running.


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## gpop (May 14, 2018)

To cool something you generally need air in and air out. As long as the air in has a filter and is placed in a way that its not directly pulling in water vapor it should be ok.

In real hostel environments they make cabinet coolers that exchange heat with out exchanging air.


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## just the cowboy (Sep 4, 2013)

*Best thing i did in our plant*



gpop said:


> To cool something you generally need air in and air out. As long as the air in has a filter and is placed in a way that its not directly pulling in water vapor it should be ok.
> 
> In real hostel environments they make cabinet coolers that exchange heat with out exchanging air.


Installed cabinet coolers was one of the best things I did in our plant. Besides keeping drives cool it keeps the dust out ( as long as some Idiot don't leave the doors open). We have a fine paper dust and before with just fans and filters it would get into everything in the cabinets. 


Cowboy


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## bill39 (Sep 4, 2009)

How else would you power the 480/120V control xfmr? The main thing is to provide O/C protection for it.

I gues you could run a separate 480 feed from somewhere to power it.


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## paulengr (Oct 8, 2017)

A lot of larger VFD's that have their own fans are actually wired exactly the same way. And a lot of the really big (medium voltage) drives work the same way except strangely enough they run the entire control and cooling package off a separate 480 V supply.


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## JRaef (Mar 23, 2009)

gpop said:


> To cool something you generally need air in and air out. As long as the air in has a filter and is placed in a way that its not directly pulling in water vapor it should be ok.
> 
> In real hostel environments they make cabinet coolers that exchange heat with out exchanging air.


I think this is the more relevant issue here. In order for a 50HP VFD to be in a *sealed enclosure with no ventilation*, the heat rejection of the VFD running a 50HP motor (1200W rejection) will require approximately 300 sq. ft. of surface area to dissipate the heat through the walls, _*assuming a 70 degree ambient air temperature*_. So using standard enclosure sizes, that's going to be no less than 90"H x 144"W x 36"D! If your ambient is 80 degrees F, that size almost doubles. 

Forget the stirring fan, you will need an air conditioner of some sort to deal with that heat and it's going to need a larger power supply source. My Hoffman enclosure A/C calculator puts is at about a 1600W A/C unit.

This by the way is one of the biggest mistakes people make in applying VFDs, they don't realize how much heat they put out and trapping it in a sealed box make the box an oven.


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## tates1882 (Sep 3, 2010)

JRaef said:


> I think this is the more relevant issue here. In order for a 50HP VFD to be in a *sealed enclosure with no ventilation*, the heat rejection of the VFD running a 50HP motor (1200W rejection) will require approximately 300 sq. ft. of surface area to dissipate the heat through the walls, _*assuming a 70 degree ambient air temperature*_. So using standard enclosure sizes, that's going to be no less than 90"H x 144"W x 36"D! If your ambient is 80 degrees F, that size almost doubles.
> 
> Forget the stirring fan, you will need an air conditioner of some sort to deal with that heat and it's going to need a larger power supply source. My Hoffman enclosure A/C calculator puts is at about a 1600W A/C unit.
> 
> This by the way is one of the biggest mistakes people make in applying VFDs, they don't realize how much heat they put out and trapping it in a sealed box make the box an oven.


That seems to a large effen cabinet. :surprise:

Is that mainly caused by having an oversized drive?


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## gpop (May 14, 2018)

JRaef said:


> I think this is the more relevant issue here. In order for a 50HP VFD to be in a *sealed enclosure with no ventilation*, the heat rejection of the VFD running a 50HP motor (1200W rejection) will require approximately 300 sq. ft. of surface area to dissipate the heat through the walls, _*assuming a 70 degree ambient air temperature*_. So using standard enclosure sizes, that's going to be no less than 90"H x 144"W x 36"D! If your ambient is 80 degrees F, that size almost doubles.
> 
> Forget the stirring fan, you will need an air conditioner of some sort to deal with that heat and it's going to need a larger power supply source. My Hoffman enclosure A/C calculator puts is at about a 1600W A/C unit.
> 
> This by the way is one of the biggest mistakes people make in applying VFDs, they don't realize how much heat they put out and trapping it in a sealed box make the box an oven.



Makes a good argument to forget the drive and just use a soft-start as every homogenizer i have installed runs at 60htz.


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## JRaef (Mar 23, 2009)

tates1882 said:


> That seems to a large effen cabinet. :surprise:
> 
> Is that mainly caused by having an oversized drive?


No. I based the heat rejection on the losses from running a 50HP motor.


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