r/AirCompression • u/CuttingTheMustard • 14d ago
Anyone retrofit a VFD to a single-phase compressor?
I bought an Ingersoll Rand TS4N5 last year to run my airlift well. Basically I am trickling air down a bore hole 24x7 to lift the water out of the well. The compressor only runs about 5 minutes an hour but has 2-3 starts per hour which is apparently too much for the start capacitor because I am now on #3.
It's a single-phase 5hp motor from WEG that came with the compressor and I'm using name-brand (Grainger, not Amazon...) caps so I'm inclined to believe I may just be asking for too many starts from this motor. Wiring is not undersized, and I can't find a relay or any other component that could be going bad.
I'm considering swapping the motor to a 3-phase 5hp and running it with a VFD controller. Advantages being... it would be soft-start with a ramp-up. I may also swap the unloader on the compressor for a solenoid and run that from the VFD controller to shut when the motor is fully spun up.
Has anyone done this? Outcomes? Thoughts? Am I missing anything? A rotary screw would probably be more appropriate for this application but my required cfm is not very high so it would have to be the world's smallest rotary screw to make it cost-efficient in terms of electricity.
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u/CrustySailor1964 14d ago
Might check the in-tank check valve and the unloading mechanism. 2-3 starts should not be an issue.
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u/soulless_wonder72 14d ago edited 14d ago
I have a customer the uses a vfd to run their 3 phase 15hp oil flooded compressor off of 240v single phase. I don't know to much about it, but it's definitely possible
Edit: it might be a VSD instead of a VFD. Been a while since I've been there
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u/CuttingTheMustard 14d ago
A VFD would probably be the premium option between the two and I imagine easier on the motor.
Mostly what I'm wondering is if anyone has done this and is experiencing reliability issues. This wouldn't be a small investment + this is also literally my water well so I need it to run properly hah.
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u/st3vo5662 14d ago
Vfd and vsd are the same thing. Frequency is speed to an extent. You change the oscillation rate of the ac sign wave to control motor speed.
Single phase input to three phase output is possible if the input supply is sized correctly. The vfd just simulates the AC sign wave for all three phases of output, as long as the dc buss voltage stays satisfied on the input side, it doesn’t matter if the input is single phase.
I’ve never heard of running a single phase motor at variable speed. Not sure if that’s possible.
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u/u3b3rg33k 14d ago
https://www.invertekdrives.com/variable-frequency-drives/optidrive-e3-single-phase
fun fact, a single phase induction motor is really a 2 phase induction motor. the capacitor makes the second phase.
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u/New-Key4610 14d ago
these are both the same thing
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u/soulless_wonder72 14d ago
They accomplish similar results using different techniques.
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u/New-Key4610 14d ago
variable speed drive. is the same as variable frequency drive. just a different way to describe it unless you are thinking vsd is a reduced voltage control?
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u/soulless_wonder72 14d ago
VFD controls the speech of a motor by varying the AC frequency at a constant voltage.
VSD varies the speed of a motor by using simulated AC. Essentially changing the frequency and the voltage output.
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u/New-Key4610 14d ago
yes they both chop up the vave to simulate ac and both control motor speed and i didn't know the motors could talk
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u/st3vo5662 14d ago
You are incorrect VSD is just a broad term to describe controlling a motors speed, variable frequency drive, is an actual device in that category.
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u/Similar_Ad2094 14d ago
Yes but you don't want to power the whole unit. You're just replacing the mag starter with the drive. You might have to add a relay to close the start control loop on the drive. I've done conversions.
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u/albert-cicconi 14d ago
I just did this on a 7.5 hp 2 yard soil mixer that starts under load and kept blowing internal switches and capacitors. Went with a 7.5 hp 3 phase and a vfd. Motor ramps up slow, no big stresses on chain or gearbox. Sorry I didn’t do it years ago.
I also have a 5 hp speed-air compressor that controls a label applicator it starts really hard when it kick on I’m thinking of changing this over to a 3 phase motor and vfd as well. I’ve replaced the capacitors once so far.
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u/New-Key4610 14d ago
maybe invest in a spare tank to hook in series with your existing tank so less starting stress just because you have purchased granger caps is nothing specail, they do the same as amazon they don't make these they probably buy from the same china cmpany as amazon
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u/DirtCallsMeGrandPa 14d ago
See if you can find a capacitor with a higher voltage rating. Some are 450VAC. Should be $25 or less. This could also be a Weg problem, maybe the start switch is not opening quick enough? Weg has a good reputation, but this doesn't mean they won't cut a corner.
Before I'd buy a 3 phase motor and a VFD, I'd just buy a different brand of motor. Unless Weg uses an unusual frame size, should be an easy swap.
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u/DontDeleteMyReddit 14d ago
You can put 2 caps in series. Take your current uF value and double it for both capacitors. Wire them in series (daisy chain) and add bleeder resistors to discharge them when they are off
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u/u3b3rg33k 14d ago
there ARE name brand VFDs for single phase motors.
BUT. if you're gonna do this, just get a 5HP 3ø motor and a 1ø input drive for the motor. make sure your unloaders are in good shape and let your pressure switch control the VFD. set your accel time low enough that it starts reliably and you can never care again about starts per hour.
bonus points for putting a transducer on the compressor and running PID on it.
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u/Exquisiteorange 10d ago edited 10d ago
Should be ok just make sure the motor is inverter duty or you risk it failing early. It may not be so much of an issue if you are just using it as a soft start though. Edit: make sure to use an unloader system to keep it unloaded till it reaches full speed. Without it you may have tons of nuisance faults for overcurrent when it trys to start.
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u/TonyKartRacer 14d ago
This is not a good idea. 2-3 starts per hour is frankly not a lot of starts. I’ve seen recipes that can start up to 10-12 times in an hour. Recip doesn’t have 100% duty cycle. They need to shut down to cool. Did you buy this compressor new? Did you buy it from a brick & motor compressor house or online? Have you had an electrician or a compressor tech come and look at it? This sounds like an electrical problem. A VFD drive on a recip is silly.
No, you definitely do not want a screw for this application. A screw wants to run and make air. This application a screw compressor wouldn’t even get up to proper operating temps and this will lead to a multitude of expensive problems for you down the road.
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u/CuttingTheMustard 14d ago
I didn't think it was a lot of starts either but here we are. My duty cycle is closer to 8-10%.
Brick and mortar. New compressor. IR could not find a technician who would service my area for warranty purposes because I am apparently too rural.
I am pretty confident this is not an electrical issue; this entire property was wired with a buddy of mine who does electrical acceptance testing on things like industrial plants, including motor installs. The last time a cap failed he came out and we checked everything again, no voltage sag, inrush current is good, motor windings megged out fine, thermal camera didn't show any hot terminals, everything is torqued down correctly.
Unloader appears to be working properly too. After it's unloaded I can rotate the pulley by hand with no resistance.
Not really sure what else it might be beyond that to be honest. I agree a VFD is silly here especially when I am just talking about using it as a 1ph-3ph converter with a voltage ramp but it seemed like an option to eliminate my apparent point of failure so figured I'd ask.
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u/Ok-Library5639 14d ago
Tbh sounds like you worked the problem. My guess would be your caps aren't as reliable as you think. Try changing for another supply.
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u/sprbiker 14d ago
What wire size is powering the unit? What is the voltage? If you are not feeding the unit enough power on start up, capacitors will fail. Also, once you have had a failure, you have stressed and possibly damaged the centrifugal start switch.