VFD on single phase motor

[ching0n]

This is a bit of a thought experiment but I've seen a few videos of people controlling single phase motors w/VFDs with adequate results. I say adequate because the low rpm torque appears to be sufficient for some of the applications. The additional benefit of motor braking, reverse rotation, rpm readout, overdrive, and not having to retrofit a 3ph on certain devices that make it difficult goes without saying. What are the drawbacks in your opinion? Anyone doing it? Chinese VFDs make the barrier to entry worth it IMO.

The examples below use a speed controller that I'm not quite sure is a VFD but are popularly used w/single phase washing machine motors. I think it appears to be wired as above? I know there are washing machine motors that are 3 phase but that'd be wired just as a conventional VFD.

 

[wyliesdiesels]

Motors need to be rated for variable frequency/speed otherwise they can overheat. Even 3 phase motors get rated for VFD use (ive seen the labels myself)

Single phase motors arent typically built or rated for such use.

I havent watch the videos yet… did they have a load on the motors?

 

[walta]

I watched the first 2.5 minutes of the first video in which he makes it clear that his idea only works on PSC permanent split capacitor motors. This type of motor has so little starting torque they are really only useful for powering fans and other operations where the starting load is almost zero. Also, this type of motor tends to stall easily if the load changes quickly. Speed controller for this style motor have been around since the 1950 and sell for $30 or so they reduce the already limited ability of the motor.

https://www.zoro.com/dayton-speed-control-adjustable-rotary-120v-3a-22pp72/i/G5302385/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping feed&utm_content=free google shopping clicks&campaignid=19725515173&productid=G5302385&v=&gclid=Cj0KCQjwm66pBhDQARIsALIR2zBMnEr3ZRvRN0CIpD4K1l-irZ0E7ZOHU8J_vAuNm6-KaCc5JMsCaSgaApyQEALw_wcB&gclsrc=aw.ds#specifications



The second video at the 3:00 point the banner say do not operate below 80%. They do not say it but at slower speeds the start switch is likely to reclose and energize the start winding in the motor. The start winding is only designed to operate for a few seconds to get the motor quickly up to speed and then be deenergized before they over heat and are destroyed. -20 % to + 50% does not seem that useful to me.



The rest of the videos are showing universal motors that us brushes and commutator again nothing new about this type of speed control. This type of motor tends to be low horse power and inexpensive larger ones tend to be very expensive. This type of motor needs a power supply not a VFD.



I read the threads asking about speed control for single phase motors hoping there has been some kind breakthrough and end up disappointed Sorry to be the dream killer.



Walta

 

[Norcal]

Saw this, but let the buyer beware........

https://www.ato.com/vfd?affiliate=search

 

[ching0n]

Motors need to be rated for variable frequency/speed otherwise they can overheat. Even 3 phase motors get rated for VFD use (ive seen the labels myself)

Single phase motors arent typically built or rated for such use.

I havent watch the videos yet… did they have a load on the motors?

first one some light load (bench grinder), 2nd, no load, 3rd & 4th some load but not VFD

I watched the first 2.5 minutes of the first video in which he makes it clear that his idea only works on PSC permanent split capacitor motors. This type of motor has so little starting torque they are really only useful for powering fans and other operations where the starting load is almost zero. Also, this type of motor tends to stall easily if the load changes quickly. Speed controller for this style motor have been around since the 1950 and sell for $30 or so they reduce the already limited ability of the motor.

https://www.zoro.com/dayton-speed-control-adjustable-rotary-120v-3a-22pp72/i/G5302385/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping feed&utm_content=free google shopping clicks&campaignid=19725515173&productid=G5302385&v=&gclid=Cj0KCQjwm66pBhDQARIsALIR2zBMnEr3ZRvRN0CIpD4K1l-irZ0E7ZOHU8J_vAuNm6-KaCc5JMsCaSgaApyQEALw_wcB&gclsrc=aw.ds#specifications



The second video at the 3:00 point the banner say do not operate below 80%. They do not say it but at slower speeds the start switch is likely to reclose and energize the start winding in the motor. The start winding is only designed to operate for a few seconds to get the motor quickly up to speed and then be deenergized before they over heat and are destroyed. -20 % to + 50% does not seem that useful to me.



The rest of the videos are showing universal motors that us brushes and commutator again nothing new about this type of speed control. This type of motor tends to be low horse power and inexpensive larger ones tend to be very expensive. This type of motor needs a power supply not a VFD.



I read the threads asking about speed control for single phase motors hoping there has been some kind breakthrough and end up disappointed Sorry to be the dream killer.



Walta

First video, guy says not for motors w/centrifugal switch but 2nd as you say looks like it's permissible under the specified. What's curious to me is it appears some VFD manufacturers advertise the feature so it makes me wonder if changing the phasing as opposed to other form of control is preferable/more efficient.

As to the washing machine motor speed controllers, I think it got a bit confusing as some of the really cheap VFDs share cases w/these other types of speed controllers.....

I'm thinking of grabbing this unit in 120v->3ph 220v configuration (220v->3ph 220v also available but want to see how bad it is on 120).....I can't tell the versions apart so don't know if it's a simple firmware lock, bigger heat sinks, or what makes each flavor different from the other (besides the price):

https://www.aliexpress.us/item/3256805847776445.html?spm=a2g0o.cart.0.0.184338davJlGtf&mp=1&gatewayAdapt=glo2usa

Someone playing w/a different version of the above:

This speed controller which as far as I can tell is a fancier version of the washing machine ones, shares layout w/the above VFD which is what got me wondering.

https://www.aliexpress.us/item/3256802899030268.html?spm=a2g0o.cart.0.0.184338davJlGtf&mp=1&gatewayAdapt=glo2usa

 

[ching0n]

Another use case (need to turn subs. on). He brings it down to 120 rpm before this time stamp but I don't think the motor liked it here: