# VFD for a 120VAC motor??



## Electrorecycler (Apr 3, 2013)

So here's my situation. I've got a little cottage up north that has a rather damp crawl space. I'd like to put a 120 volt inline fan in to exhaust the air and control the speed using 0-10 volts DC form a LOGO!. The LOGO! will have a 0-10VDC signal from a humidity sensor. I've been looking but haven't been able to find anything that will give me speed control over a 120 volt motor AND allow for a 0-10VDC input.

Anyone have have any ideas here?


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## MikeFL (Apr 16, 2016)

We just use a humidistat for on/ off.


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## Electrorecycler (Apr 3, 2013)

I could do that, but it's more fun to vary the speed. 


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## JRaef (Mar 23, 2009)

Only specific TYPES of single phase motors can have their speed controlled, and a VFD to do that will likely set you back a LOT more money than you may be willing to spend. There are only 2-3 companies that even make them.

Cheaper and easier, if you have not yet bought the fan, is to buy one with a 230V 3 phase motor, and buy a cheap little VFD that will accept 120V input to give you 230V 3 phase output.

Cheaper yet, IF your little fan motor is of the "Shaded Pole" variety, is to just use a voltage controller that accepts a 0-10VDC input, i.e. a remote controllable dimmer.

The key is to start with what motor you have. A lot of single phase motors CANNOT be speed controlled.


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## Electrorecycler (Apr 3, 2013)

JRaef said:


> Only specific TYPES of single phase motors can have their speed controlled, and a VFD to do that will likely set you back a LOT more money than you may be willing to spend. There are only 2-3 companies that even make them.
> 
> Cheaper and easier, if you have not yet bought the fan, is to buy one with a 230V 3 phase motor, and buy a cheap little VFD that will accept 120V input to give you 230V 3 phase output.
> 
> ...




I was thinking along the lines of a 230 volt motor. Automation Direct makes a little $99, 120 to 230 single phase VFD. But I never even considered a remote controllable dimmer. I might just look into that along with a shaded pole motor. 


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## sparkiez (Aug 1, 2015)

If you really want to do it with the control loop, use a small 3 phase motor and a 240 to three phase 208 vfd. Regardless, you are going to have to use a different motor for anything more than on/off control.


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## dronai (Apr 11, 2011)

Electrorecycler said:


> So here's my situation. I've got a little cottage up north that has a rather damp crawl space. I'd like to put a 120 volt inline fan in to exhaust the air and control the speed using 0-10 volts DC form a LOGO!. The LOGO! will have a 0-10VDC signal from a humidity sensor. I've been looking but haven't been able to find anything that will give me speed control over a 120 volt motor AND allow for a 0-10VDC input.
> 
> Anyone have have any ideas here?





MikeFL said:


> We just use a humidistat for on/ off.


This ^

Or you do what others are suggesting and spend a few thousand dollars to keep your crawl space dry in your cottage up north :thumbup:


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## splatz (May 23, 2015)

How about a DC motor? There are lots of DC drives with 0-10v speed controls...


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## frenchelectrican (Mar 15, 2007)

splatz said:


> How about a DC motor? There are lots of DC drives with 0-10v speed controls...


that may be a best answer if the motor is under 1/2 hp size so it may work better that way on costwise .,, 

I agree with other posting that most common single phase motor do not work very well with VSD unless it is PSP ( perament split phase ) or shaded pole motor then it may work but for fan it maybe ok but for other type of loads forget it.


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## nrp3 (Jan 24, 2009)

What my customers have been doing is remove the fan/humidistat setup and go to a dedicated dehumidifier for their crawl spaces. Condensate goes into a condensate pump and then into a drain. The fan thing hasn't been doing much.


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## splatz (May 23, 2015)

nrp3 said:


> What my customers have been doing is remove the fan/humidistat setup and go to a dedicated dehumidifier for their crawl spaces. Condensate goes into a condensate pump and then into a drain. The fan thing hasn't been doing much.


Are people using some special dehumidifiers made for crawl spaces or just regular appliance store dehumidifiers? 

I'd guess a good dehumidifier can do a lot more than an exhaust fan. There are so many days with high humidity in the summer. I could see the exhaust fan just guaranteeing the dehumidifier could never catch up. 

The OP could have some fun putting both an outside and inside humidistat on a comparitor and only blowing when it's worth it.


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## Electrorecycler (Apr 3, 2013)

Man, this is getting expensive! On/off humidistat it is! The machine builder in me wants to keep it complicated, but I don't have the same budget at home that I do at work. I've killed a few dehumidifiers over the years and the ones designed for crawl spaces are thousands.


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## oliquir (Jan 13, 2011)

here are some speed controller that accept analog signals but it depends on the type of motor you use
http://controlresources.com/ac-fan-control-ac-motor-control-smartfan/


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## nrp3 (Jan 24, 2009)

They have been using Mega Dry dehumidifiers. Inline thing that either sits on feet on the ground or sometimes suspended from the ceiling. No, they aren't cheap.


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