# Slow down 5HP motor



## Speedy Petey (Jan 10, 2007)

I have a take out restaurant with an old hood fan with a single speed 240v single phase 5HP motor. The motor is newer. 
What is the easiest way to get a slower speed? 
VFD?
2-speed motor?


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## Wirenuting (Sep 12, 2010)

2 speed motor. 
They won't remember how to work the vfd.

edit: since they have a new motor, do the vfd with 2 button input for speed ref. more $$ your pocket and might be quicker install.


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## MadDawg (Jun 12, 2012)

Why not just change the sheaves?


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## Wirenuting (Sep 12, 2010)

MadDawg said:


> Why not just change the sheaves?


Sounded like he wanted more then just 1 reduced speed.


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## Ultrafault (Dec 16, 2012)

I have never put a vfd on a non inverter duty motor. Have you guys had any luck on them. Id probably be concerned more since a commercial vent would be continous in my opinion. For sure put a line reactor on it since they probaly have computers off the same transformer.


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## Wirenuting (Sep 12, 2010)

Ultrafault said:


> I have never put a vfd on a non inverter duty motor. Have you guys had any luck on them. Id probably be concerned more since a commercial vent would be continous in my opinion. For sure put a line reactor on it since they probaly have computers off the same transformer.


We have done that here to a few hundred of them. Mostly pumps and air handlers. The failure rate wasn't to bad. The life span was shortened but not catastrophic. 
As motors burned out or drives were replaced, most systems received rewires from the main distribution panel to the motor. 
Motor replacement here seems to be every 10+ years. This is on units that are maintained by qualified people. The replacement is about every 5 years on motors that are maintained by,,, ahhh, lets say, "less then qualified" personal.


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## Jlarson (Jun 28, 2009)

If you want to use a VFD you will have to change the single phase motor out anyway. 


Is this project worth it, have you looked into any possible fire, health, mechanical code issues yet?


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## ampman (Apr 2, 2009)

Jlarson said:


> If you want to use a VFD you will have to change the single phase motor out anyway.
> 
> 
> Is this project worth it, have you looked into any possible fire, health, mechanical code issues yet?


i never thought about that, but then again all motors i have wired with a vfd have been three phase


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## frenchelectrican (Mar 15, 2007)

I know there are some VSD controller that can take 240 volt single phase input but be aware with the rating on monophase side you may need to bump up to larger size to handle the rating.

But to run VSD on monophase motour., genrally not the best idea at all and 5 HP is pretty good size unit so it cheaper to get triphase motour and get the VSD with single phase input.

If this is a non restuarnt useage the other option is use smaller fan with smaller motour so that is the other possiblity it can be done. ( I don't know how much noise it will crank with smaller prop units but I belive not much differnce ) 

Merci,
Marc


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## Toronto Sparky (Apr 12, 2009)

Just never change the filters and air flow will be reduced..


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## BBQ (Nov 16, 2010)

MadDawg said:


> Why not just change the sheaves?


If it is a typical commercial unit it will likely have adjustable sheaves any way.


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## Jlarson (Jun 28, 2009)

BBQ said:


> If it is a typical commercial unit it will likely have adjustable sheaves any way.


Just sent the bus boy up there when it's time to change speeds and have him roll the belt to a different step :thumbup:


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## micromind (Aug 11, 2007)

Jlarson said:


> Just sent the bus boy up there when it's time to change speeds and have him roll the belt to a different step :thumbup:


While it's running, of course.....


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## Big John (May 23, 2010)

micromind said:


> While it's running, of course.....


 "Why are all the dish washers missing fingers?"
"It's a long story...."


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## micromind (Aug 11, 2007)

Speedy Petey said:


> I have a take out restaurant with an old hood fan with a single speed 240v single phase 5HP motor. The motor is newer.
> What is the easiest way to get a slower speed?
> VFD?
> 2-speed motor?


Sorry, got off-topic there.....

As far as I know, a single phase motor cannot be controlled by a VFD. First, there's the start winding to run winding transition, plus every VFD I've ever worked with would see a single phase motor as a faulty 3 phase motor and would go into some sort of alarm. 

If the speeds needed to be changed regularly, a two-speed single phase motor would work. In this case, it'd likely be 5HP on high speed, 2HP on low. 

The other option would be to replace the single phase motor with a 3 phase one and get a VFD that would accept single phase input power. It'd be east to program it for two definite speeds and simply switch between two digital inputs, or install a speed pot (volume control type).


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## l0sts0ul (May 7, 2011)

Single phase vfds do exist. But the motor you have is probably not Vfd rated. 

Why do you want to slow down this motor?


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## l0sts0ul (May 7, 2011)

If you are tryin to reduce air velocity or volume it's cheaper to change the shiv and of the squirrel cage or fan blade. Less pitch means less noise and air volume


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## Toronto Sparky (Apr 12, 2009)

Slowing down the hood fan may also affect fire suppression system..


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## frenchelectrican (Mar 15, 2007)

Toronto Sparky said:


> Slowing down the hood fan may also affect fire suppression system..


 
Thanks for bring that subject up but if you have two speed motour once the fire suppression system do kick in there is a override switch which it will force the exhaust fan motour to high speed mode reguard of what it is on the wall switch left on.

That something else it should be brought up to the attetion when you change the motour set up.

Merci,
Marc


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## Vintage Sounds (Oct 23, 2009)

The chances are that place has 3 phase available, so if he's going to replace the motor and use a VFD, wouldn't it make the most sense to use actual 3 phase power rather than a manufactured phase?


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## frenchelectrican (Mar 15, 2007)

Vintage Sounds said:


> The chances are that place has 3 phase available, so if he's going to replace the motor and use a VFD, wouldn't it make the most sense to use actual 3 phase power rather than a manufactured phase?


That is a very good question and I will let SpeedyPete answer that queston due he is working on that place so he will know the answer to confirm your question on that one.

And some of the smaller restuants that I have ran into some of them do still use single phase supply instead of triphase supply for various reasons.

Merci,
Marc


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## BBQ (Nov 16, 2010)

Vintage Sounds said:


> The chances are that place has 3 phase available, so if he's going to replace the motor and use a VFD, wouldn't it make the most sense to *use actual 3 phase power rather than a manufactured phase?*


All phases on the load side of a VFD are manafactured.

The only advantage of supplying the VFD three phase is that it might reduce the size and cost of the VFD.


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## Vintage Sounds (Oct 23, 2009)

BBQ said:


> All phases on the load side of a VFD are manafactured.
> 
> The only advantage of supplying the VFD three phase is that it might reduce the size and cost of the VFD.


I was under the (possibly mistaken) impression that the output power quality was better when true 3-phase was supplied to the drive. Not true?


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## frenchelectrican (Mar 15, 2007)

Vintage Sounds said:


> I was under the (possibly mistaken) impression that the output power quality was better when true 3-phase was supplied to the drive. Not true?


Genrally the power quality is better on true three phase supply supply to the drive contoller which it will converted from AC to DC then back to AC and the ripple effect and other stuff is much lower on true three phase supply than single phase supply.

I know one of our motour guys will chime in here and fill you the details.

Merci,
Marc


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## Wirenuting (Sep 12, 2010)

Jlarson said:


> If you want to use a VFD you will have to change the single phase motor out anyway.


I forgot about that. We have so few single phase motors it slipped my feeble mind.


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## BBQ (Nov 16, 2010)

frenchelectrican said:


> Genrally the power quality is better on true three phase supply supply to the drive contoller which it will converted from AC to DC then back to AC and the ripple effect and other stuff is much lower on true three phase supply than single phase supply.
> 
> I know one of our motour guys will chime in here and fill you the details.


I hope one of the motor guys does pop in because I don't see how it would make any difference.

The AC is converted to DC and then the DC is used to manufacturer all three phases. I don't see how single or three phase supply would change anything other than the loading of the VFD.


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## JRaef (Mar 23, 2009)

So many issues...

As mentioned, ALL 3 phases of a VFD output are "manufactured", that's why you can use a VFD to run 3 phase motors from a single phase supply. Yes there is more ripple, but all you need is more bus capacitance. Small VFDs, 3HP and under, are for the most part now designed with enough capacity to do this without derating, above 3HP 230V you need to double the size of the VFD to get that (plus get more thermal capacity of the diode front-end, because the input current goes up by the sq. rt. of 3).

Yes, there are VFDs for single phase MOTORS, but not ALL single phase motors. You *must not* vary the speed of a single phase motor that has a centrifugal switch, so that eliminates about 75% or more of them right there. Single phase output VFDs can only be applied to Shaded Pole and PSC motors. Many Shaded Pole motors can be speed controlled with a simpler rheostat, so a VFD for those is a waste.

VFDs that work for single phase motors are rare, which means they are expensive. If all that is needed is a 2nd speed, replacing the existing motor with a single phase 2 speed motor will be cheaper than adding a VFD (if even possible).

If you cannot change the motor, *and *it is a PSC motor, *and* your customer is not concerned with the cost, the best one out there is the OptiDrive made by Invertek in the UK, sold in the US by Anacon and Bardac. Google is your friend. The drive will cost you around $500, plus whatever else you will have to change in the circuit to use it.

Don't worry about "inverter duty" issues with 230V motors, it's important for 480V but 230V is relatively OK in most cases.


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