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Single to 3 phase VFD

AKnate

Icehole
Joined
Mar 5, 2022
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4908
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Do the cheap VFDs work ok?

Have an air compressor with a 5hp 230/460v 3 phase motor. Has a Champion R15 pump, so like 20 cfm at 175psi?

Was thinking of a new motor, but found these for around 150$

VEVOR 3 Phase Converter - 7.5HP 23A 220V Single Phase to 3 Phase Converter, 220V-240V Input/Output, Digital Phase Shifter for Residential & Light Commercial Use (One Converter for One Motor Only)​

 
at least 30% over is what i was told. i have a 15 hp one in my shop i bought at auction. bought a whole pallet of them for cheap.
 
BUCKLAND said:
Might want to go up to a 10 HP VFD
Click to expand...
Why? It's already oversized to do what he wants since it's rated for 1ph input. You only have to oversize if you're using a 3 phase vfd so that the input rectifiers are big enough for the output.

OP needs to keep in mind that he isn't looking at a VFD, he's looking at a phase converter. It probably only creates 2 phases rather than creating 3 like a VFD does. This means it may not really do a soft starting or speed changes.
 
Last edited:
BUCKLAND said:
Might want to go up to a 10 HP VFD
Click to expand...
gunracer1 said:
at least 30% over is what i was told. i have a 15 hp one in my shop i bought at auction. bought a whole pallet of them for cheap.
Click to expand...

larboc said:
Why? It's already oversized to do what he wants since it's rated for 1ph input. You only have to oversize if you're using a 3 phase vfd so that the input rectifiers are big enough for the output.
Click to expand...

Exactly. The whole derating thing is old thinking from when you'd use 3phase input VFDs on single phase. In that case they were usually only good for 1/2 their labeled capacity. A true single phase VFD should be labeled for its true output and doesn't need to be derated.


larboc said:
OP needs to keep in mind that he isn't looking at a VFD, he's looking at a phase converter. It probably only creates 2 phases rather than creating 3 like a VFD does. This means it may not really do a soft starting or speed changes.
Click to expand...

Don't really need any of that with a compressor though. For $170, I'd probably give it a shot.
 
larboc said:
Why? It's already oversized to do what he wants since it's rated for 1ph input. You only have to oversize if you're using a 3 phase vfd so that the input rectifiers are big enough for the output.

OP needs to keep in mind that he isn't looking at a VFD, he's looking at a phase converter. It probably only creates 2 phases rather than creating 3 like a VFD does. This means it may not really do a soft starting or speed changes.
Click to expand...
The info says it's soft start. Have no need to adjust rpm
 
larboc said:
Why? It's already oversized to do what he wants since it's rated for 1ph input. You only have to oversize if you're using a 3 phase vfd so that the input rectifiers are big enough for the output.

OP needs to keep in mind that he isn't looking at a VFD, he's looking at a phase converter. It probably only creates 2 phases rather than creating 3 like a VFD does. This means it may not really do a soft starting or speed changes.
Click to expand...
Since the OP didn't link it we really have no idea what the chingrish listing is saying...
 
It will work until it doesn't. That's the way with chinesium. In this case, I'd give it a run. 50/50 the motor goes and now you have a 3 phase converter and you change the motor you were going to anyway.
 
I've never used one on a compressor, but have one running my mill and another running my lathe....the Teco Westinghouse (expensive sounding chinese unit) shit the bed so I replaced it with some garbage from Amazon for $100 or so 5 years ago and it's been flawless.
 
AKnate said:
The info says it's soft start. Have no need to adjust rpm
Click to expand...
You can adjust the ramp up and ramp down time and then lock it to 60 HZ.

Being that 3 phase has a single phase multiple of 1.73, I believe you can aerate the drive to 57% of the single phase load.

I will look at my setup that runs for 2 months a year 24/7 for the past 6+ years.
 
Oh... and boobies...

FB_IMG_1716109103061.jpg
 
300sniper said:
I always thought VFDs were specific to motor size and you don’t want to upsize them, like a RPC.
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They're just expensive to oversize. Going bigger doesn't hurt anything.

I hooked a 5hp one up to a 1/3 hp fan motor the other day, because it was provided and who am I to argue? :flipoff2:


Like anything they're still new to a lot of old hands. Stories have been told for the last 10-15 years that they've been somewhat common
Usually resulting from things that had nothing to do with the vfd were blamed on it because those old hands didn't know how the magic box worked and needed to explain to a customer why they were spending another $5k. :laughing:
 
1oddtech said:
You get what you pay for, Next month you will be posting about how to rig up the VFD you bought and why it wont operate your compressor.
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Nope. If it dies, it dies and ill put a 5hp single phase motor on it.
 
300sniper said:
I always thought VFDs were specific to motor size and you don’t want to upsize them, like a RPC.
Click to expand...
They are if you are using them 3 phase to 3 phase. It changes when you are supplying the VFD with single phase to power a 3 phase motor.
 
BUCKLAND said:
They are if you are using them 3 phase to 3 phase. It changes when you are supplying the VFD with single phase to power a 3 phase motor.
Click to expand...

I don't think it matters either way, as long as it's rated for the same size or bigger motor that you're running on it. What does matter is that you set all the motor specific parameters on the VFD so the overload protection works properly. At 15hp VFD would have no problem sending 15hp worth of juice to a 5hp motor, but it you tell it that it only has 5hp hooked up to it, it will limit the current to the proper amperage for that 5hp.
 
You are going to stess the hell out of a VFD starting an air compressor. Yes it will work, yes you can have a soft start (and stop), but you should be able to find a single phase 5hp motor used for the same or less monnaaaay.
 
bgaidan said:
I don't think it matters either way, as long as it's rated for the same size or bigger motor that you're running on it. What does matter is that you set all the motor specific parameters on the VFD so the overload protection works properly. At 15hp VFD would have no problem sending 15hp worth of juice to a 5hp motor, but it you tell it that it only has 5hp hooked up to it, it will limit the current to the proper amperage for that 5hp.
Click to expand...
I think its more of a volts/amps ratio issue when below base speed.
 
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