Unicorn? 1ph 110v in 1ph 110v out VFD for $140

i4Marc said:
Could be useful for my disc sanders.
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That was my thought also, but I don't know enough about it to know if it might work.
 
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Well, I'm going to put it on a 1hp 110v grinder, so I'll let you know.

I have a feeling this will come with a 33% power loss.
 
Yep, I've got a dandy 1hp 1780 rpm capacitor start motor I'd like to use that on. Looking forward to how it works out for you. I'd seen those listed, but wasn't at all sure if they would actually work or not. The video you linked to is the first I've seen. I wish he'd went a bit more in depth on the input and output wiring. This thread is tagged for future reference.

kuraki, you posted while I was writing - even if it does have a 33% power loss, that's still 2/3 hp available from a 1hp motor. Plenty for a disk grinder.
 
Yep just pointing it out based on only using 2 output legs. I'm going to put it on my horizontal belt. Now I'm thinking it's a 1.5 hp I have on it. Can't remember. First 2x72 I built.
 
I personally do not see how this will work. Especially with capacitor start motors. From what I know a capacitor start motor has a switch that disengages the caps once the motor is up to speed. If this switch does not switch off the caps then the motor burns out. The switch is RPM driven.
 
That is broadly the case JT. However, I have come across some single-phase motors that do not have a centrifugal switch but have a capacitor that incorporates a switch that disconnects the capacitor shortly after the motor starts. I am guessing it reduces cost, mainly because it was on cheap equipment that did not work at all well. I have not had a capacitor apart to see how the switch thing works. I am guessing it is a simple time-delay. Whilst I am pretty certain a centrifugal switch will not work, I am much less sure the capacitor/switch will not work.

The Travers manual is online and shows a capacitor but no centrifugal switch.

In the video, he seems to say the output voltage is a constant 110V. With almost every VFD I have used, the Voltage and Frequency ramp up together when the frequency/Voltage are below the motor rated Voltage, then maintain constant (rated) Voltage above the motor rated speed. The HuanYang drive might allow the rated Voltage to be set to 10 or 20 Hz to get the Voltage constant over the speed range required.

I got the impression it could work, but would probably take quite a lot of time playing with VFD parameters to make it work well.
 
I have severe doubts. Something like this may work, but it may not work well …. or be good for the motor.
 
Unless I'm mistaken, you shouldn't even need the capacitor any longer, as the VFD should be able to start the motor on its own. You'd probably be better off to just disconnect it anyway.
 
A single-phase motor will not usually start without a start winding because there is only one field providing push/pull in only one direction.

I think of it like a disabled cyclist with no knees. Initially, pushing down a pedal will only get him as far as the straight up/down pedal position. Give him a push and he’ll have enough inertia to carry him through that position and be able to do work pushing the pedal down again. A cyclist with working knees can use them to apply a (relatively small) force fore-and-aft at the up/down position and can get away without a push.

The motor start system uses a capacitor to cause the waveform to the start winding to lag behind the main waveform and give a push, analogous to the working knees, at an an angle to the main winding. Effectively the motor starts on 2 phases, dropping out the second phase once it is running fast enough to ride out the zero-torque orientation.
 
Well, we'll see. The video I posted is a year old. I commented to see if he had any updates on how it's working.

Worst case I kill the motor I have no use for anyway and get a 3ph motor. Then maybe use this drive as a router speed control rather than a variac.
 
timgunn1962 said:
A single-phase motor will not usually start without a start winding because there is only one field providing push/pull in only one direction.

I think of it like a disabled cyclist with no knees. Initially, pushing down a pedal will only get him as far as the straight up/down pedal position. Give him a push and he’ll have enough inertia to carry him through that position and be able to do work pushing the pedal down again. A cyclist with working knees can use them to apply a (relatively small) force fore-and-aft at the up/down position and can get away without a push.

The motor start system uses a capacitor to cause the waveform to the start winding to lag behind the main waveform and give a push, analogous to the working knees, at an an angle to the main winding. Effectively the motor starts on 2 phases, dropping out the second phase once it is running fast enough to ride out the zero-torque orientation.
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I understand that, but won't the VFD essentially be simulating the capacitor "phase"? If you're running 2 of the 3 phase output I mean.
 
knife to a gunfight said:
I understand that, but won't the VFD essentially be simulating the capacitor "phase"? If you're running 2 of the 3 phase output I mean.
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”Twophase” is antiquated system yet still in service in very limited region or generated locally to operate ancient machinery. Just like threephase, it requires 3 (or 4, depend on configuration) conductors. One of major reasons twophase went quickly obsolete.

Using only 2 of the threephase 3 conductors is considered singlephase as the load still ’sees’ singlephase sinewave.
Does not matter if supply (or this case VFD output) is delta or star configuration.

This grinder example interesting thing. Something I never played around with.
Quite sure its only successfull on ’cap-start/’cap-run motors as all other singlephase induction motors aside from shaded pole use a centrifugal switch what cuts out their starting circuit at approx 70% of normal RPM.
I suppose a centrifugal switched motor could be modified so it will start & run normally at standard frequency but manually bypass (switch off) its starting circuit before slowing the running frequency. Just remember to restore its starting circuit before next start-up. Or one could easily automate that bypass function...

BTW, Notice that video starts the motor at 60Hz, then speeds it down & up.
Remember. if fan cooled, running slower than design speed reduces cooling too.
 
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Any way to externally differentiate from cap start cap run and switch motors?

I also had a thought about modifying a centrifugal switch to disengage at the lowest desired rpm... instead of 75% of full speed.
 
Cap start, cap run usually have 2 capacitors. The run cap is permanently fed while the motor is running and is the more expensive one.

On some IEC frame (metric) motors, the capacitors are mounted in the terminal box. I have seen cap start motors with the same terminal box as cap start,cap run but without a run capacitor in. I have no experience of NEMA-frame motors.

Externally, only having one capacitor location should mean it is not cap start, cap run. Having 2 capacitor locations should mean it’s likely to be cap start, cap run, but it’s worth pulling the cover to check.
 
Tim's stated it nicely. If it's a two capacitor motor, one is start, other is run. The start cap will have a centrifugal switch to drop out the start cap after it gets spinning. Normally you can hear the switch drop out during stop, and perhaps switch in on start also. As Tim says, the capacitors can be mounted direct to motor, or even in a separate terminal box.
 
Some motor capacitors are two capacitors in the same package. They typically have three terminals on capacitor body, So only only lump is external on the motorcase.
 
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