120v single phase VFD connections

titan1021

Senior Member
I'm installing a 120v single phase SMVector VFD for a roof-top exhaust fan.

Line voltage is 120v and the fan (load) is also 120v


I am not sure where the neutral connection lands for the motor in the VFD. When I power up the VFD I get line voltage on all three load terminals. U-V-W. I've searched extensively online for the answer with no luck.

I've tried connecting the load neutral ahead of the VFD with the line neutral but get an error on the screen. F_01 1


Any input would be great.

Thank you
 
Last edited:

sii

Senior Member
Location
Nebraska
Post the specific model of the vfd.

That said, I believe you need a 3 phase motor based on the information you provided.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
As sii noted, the motor needs to be a 3 phase motor. For an OEM fan, 120 3 phase is certainly possible.

I downloaded the wiring diagram ... on page 17, the 3 motor windings go to U/V/W as normal. The PE (ground symbol) from the motor frame goes to PE next to W. I will assume single phase input ... that looks like what this model is designed to use. The instructions show (page 16) use of PE, L1, and N with L1 fused.

I see they note "If the kVA rating of the AC supply transformer is greater than 10 times the input kVA rating of the drive(s), an isolation transformer or 2-3% input line reactor must be added to the line side of the drive(s)." Your label suggests (at 120V input) an input kVA of 2.4 (20x120) so that transformer or reactor would be a good idea in most installations.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
You cannot use that VFD on that fan. That VFD takes in 120V single phase but the output is 230V 3 phase.

There are VFDs made for SOME single phase motors, but only two types; PSC (Permanent Split Capacitor) and Shaded Pole. You cannot use a VFD on any single phase motor that has capacitor starting or a centrifugal switch, which is most of them.

Chances are decent however that this is a PSC motor, many small fans are. But you will need a different VFD. There are only a few available and they are expensive compared to 3 phase VFDs because they are less common. In some cases I have found it is actually cheaper to replace the motor than to buy one of those.

If if you have to proceed with replacing the VFD, post that and I’ll get you the names of the few single phase OUTPUT VFDs I am aware of. If you want to keep that VFD, get a 230V 3 phase motors with the same frame size, mounting and shaft.
 

titan1021

Senior Member
You cannot use that VFD on that fan. That VFD takes in 120V single phase but the output is 230V 3 phase.

There are VFDs made for SOME single phase motors, but only two types; PSC (Permanent Split Capacitor) and Shaded Pole. You cannot use a VFD on any single phase motor that has capacitor starting or a centrifugal switch, which is most of them.

Chances are decent however that this is a PSC motor, many small fans are. But you will need a different VFD. There are only a few available and they are expensive compared to 3 phase VFDs because they are less common. In some cases I have found it is actually cheaper to replace the motor than to buy one of those.

If if you have to proceed with replacing the VFD, post that and I’ll get you the names of the few single phase OUTPUT VFDs I am aware of. If you want to keep that VFD, get a 230V 3 phase motors with the same frame size, mounting and shaft.
Thank you so much for the detailed answer!

This makes perfect sense, when I powered up the VFD without the motor connections I measured 118v from each of the output terminals. I didn't have any luck searching for a single phase 120v VFD when my client originally asked me to get one for the fan. I advised the client to contact the company that recently sold them the fan to have them track down a compatible VFD. The model above was what they sold my client for $350.

If you could recommend one that will work with this fan, it would be greatly appreciated.

Thank you
 

kwired

Electron manager
Location
NE Nebraska
1.5 HP is getting to be about largest PSC motor you will find in a general purpose motor. There are some definite purpose motors that are PSC that size or even larger, they are typically only intended for fans.

There are single phase SCR based controllers that are much less expensive than a VFD that work fine on PSC and shaded pole motors, especially for fans.
 

Russs57

Senior Member
You have the drive mounted, so I doubt you can return it. Ditto on the fan I assume. Don't compound this mess and give the customer something that will have him cussing your name in the future. A 1.5 HP, 56H frame, 3 Phase motor can be had for around $225. You can stay with the 120 VAC supply to the drive and replace the one neutral wire to the motor with a Red and a Blue. Fast, cheap, easy all with parts that are readily available in the future. Forget special drives and/or motors. No need to make matters worse just because you were sold a package that can't work together.

Just pick a motor sheave to go with existing one on the fan shaft so you don't exceed the max fan RPM of 1350 when drive is at 60 hertz. Keep in mind a higher RPM motor is cheaper.
 
Top