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Thread: 3 Phase compressor on a VFD?
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6th May 2014, 06:26 AM #1.
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3 Phase compressor on a VFD?
Does anyone have a 3 Phase compressor running on a VFD? I don't have 3 phase at my place but but I was thinking VFD and a 4HP 3phase motor compressor might deliver a bit more than the usual 3HP single phase hobbies. A ramped/soft start should ease the starting load and it looks like the triggering circuit on the compressor could easily be modified to switch the start/stop buttons on the VFD.
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6th May 2014 06:26 AM # ADSGoogle Adsense Advertisement
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6th May 2014, 09:09 AM #2GOLD MEMBER
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6th May 2014, 09:48 AM #3.
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6th May 2014, 10:09 AM #4GOLD MEMBER
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Hi Bob,
I assume you're worried about the load on the motor at start up? I think you should try it and see.
If its a fail you could always add a dump valve that closes when the VSD reaches set freq*. You had me thinking about being able to run at half speed to keep the noise down when full lower wasnt needed, but my compressor is splash lubricated so maybe thats not such a great idea.
Stuart
*assuming the vsd you have in mind has that option
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6th May 2014, 11:04 AM #5GOLD MEMBER
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6th May 2014, 11:10 AM #6Cba
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No problem. A VFD can cope well with hard to start constant torque loads such as an air compressor. You will get a smooth soft start too. You can use either a 4HP rated VFD with single phase input, or a properly derated VFD with 3-phase input but only one phase hoocked up (probably needs a 4-5KW unit, check with the installation manual before buying it). Be aware that a 4HP motor/VFD combo will have to be hooked uo to a 240V 20A single phase input.
EDIT: The pressure switch you will have to wire to the VFD control input, NOT just have it cut the motor! By the way, there are also nice programmable digital pressure switches with pressure display etc if you wanted something fancy...
If your intention is additionally to regulate compressor RPM, possibly even depending on air demand, things will get more complicated. For starters, you will have to make sure that the motor is getting proper cooling at lower speeds. Some hints here:
http://www.efficiencyvermont.com/doc...heet_FINAL.pdf
Me personally, I would think that two 2HP compressors in parallel would be cheaper than buying a VFD and having an electrician install a 20A powerpoint. It would also be more efficient, as you would only turn on the second compressor when the higher airflow is indeed needed (a VFD running constantly ay 50Hz has no efficiency advantage). Two smaller compressors is also more failsafe, unlikely both fail at the same time. And you could always "borrow" the second compressor to take to another location or remote worksite.
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6th May 2014, 11:49 AM #7SENIOR MEMBER
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That's more or less the approach I've adopted but not finally implemented - still got the plumbing to finish. I have a POS Bunnings compressor, a nice 8cfm Ingersoll-Rand oilless one, a Champion 80 cfm 4 cylinder unit and the 120 cfm Hydrovane. The 80 cfm unit is surplus to requirements but the price was right so I took it.
Anyway, one input manifold feeding through a big cooling unit then a water trap then the tank. Plumbing from there out is yet to be finalised. Aim was to have a good air reservoir and fire up the compressor(s) needed for the job. I want dry air both for the plasma cutter and for painting.
And yes, there is a lower speed limit for splash lubricated compressors. I was thinking of slowing the 80 cfm unit down to get say 20 to 30 cfm which is plenty for most of my needs, but no, too slow for proper lubrication.
PDW
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6th May 2014, 12:46 PM #8.
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Thanks for that.
Be aware that a 4HP motor/VFD combo will have to be hooked uo to a 240V 20A single phase input.
The pressure switch you will have to wire to the VFD control input, NOT just have it cut the motor!
If your intention is additionally to regulate compressor RPM, possibly even depending on air demand, things will get more complicated. For starters, you will have to make sure that the motor is getting proper cooling at lower speeds.
Me personally, I would think that two 2HP compressors in parallel would be cheaper than buying a VFD and having an electrician install a 20A powerpoint. It would also be more efficient, as you would only turn on the second compressor when the higher airflow is indeed needed (a VFD running constantly ay 50Hz has no efficiency advantage). Two smaller compressors is also more failsafe, unlikely both fail at the same time. And you could always "borrow" the second compressor to take to another location or remote worksite.
- currently have a 2.5HP Bunnings elcheapo compressor that does not have much life left in it.
- possibility of picking up a used 3 phase 3 kW compressor at a good price
- the compressor's acoustical enclosure is outside my shed but can only house one ~70 L compressor. Enclosure already has forced air cooling.
- I will do all the electrics myself - yes I know it's not kosher but then starting with the home made 22kW mains gas forge, very little in my shed is .
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7th June 2014, 11:01 PM #9.
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I bought a used Clisby 4 cylinder (V4) 3Ph, 20 CFM, 3kW/4HP Compressor and thought I would have a crack at seeing if I could get it to run via a single to 3 phase VFD.
I already had a 3kW VFD that I have been using to test out motors so I thought I was good to go.
However, despite a 30 second ramped start, the VFD would not run at 50Hz past about 80 PSI without drawing more than the 13A max rating of the VFD. At one point the current draw shot up to 15A and the VFD shut down, but it still runs fine.
This VFD could be kept running with this motor by backing off the frequency to ~45Hz (current was around 12.8A) but the best the motor could pull the compressor up to at this frequency/current was ~115 PSI.
I tried a different 3kW motor, same problem.
I was beginning to think that a 4HP motor was perhaps on the light side for this compressor.
I had several communications with JHovel and he suggested trying a bigger VFD so I bought a 5HP (18A) version.
I received it a couple of days ago and when I tried it out it was even worse than the 3kW unit as the motor would not get past about 30Hz during the ramp up whereby the motor was drawing about 16A (i.e. starting to get hot!) so I did not force it.
A few hours ago I realised I had a 4kW/5HP ∆ connected WEA motor and pulled it out of the pile of wood under my table saw.
I bought this motor a few years ago for $30 from a guy who bought a big table saw but did not have 3 phase in his workshop and had converted the saw to a single phase motor.
Fortunately the motor had the same shaft diameter, keyway size and mounting point separation as the motor already on the compressor.
I bunged it onto the compressor and connected up the 4kW VFD and it runs like a charm.
It comfortably does 50Hz all the way up to 125 PSI (and higher) but I have set it to cut out at 125PSI , and I was able to drop the ramp up time to 10s - it probably could do better than this but that's fine for me.
At 125 PSI just before it switches off it draws 15.4A (it has a limit of 18A) so it's well within the comfort zone.
This motor has a BIG fan on it so cooling is not a problem.
The pressure switch also works well in turning the VFD ON/OFF as required.
A few pics
Here is the 4kW VFD (LHS) next to the 3kW (Middle) and a 2.2 kW unit (RHS).
Most of the extra volume of the 4kW is taken up by a very large heat sink
Most of the internal components look identical but the power connectors are significantly bigger which makes it much easier to connect terminals
Here is what the new motor looks like on the compressor.
There is one problem I need to attend to and that is the belt alignment between the motor and the compressor is not as close as I would like it to be so I will have to make up an adapter plate to fix that.
I must have spent a dozen hours on this swapping out motors and VFDs without zapping myself. I'm not sure what I have learned but hopefully it will gel over the next few weeks. It's weird how one seems to run around in circles for a while and then it all seemed to just sort itself out in 3 minutes!
This compressor will (just) fit into my acoustic compressor enclosure outside my shed provided I cut away 10 mm of the 40 mm foam insulation on one wall where the tank end plug is located.
I'm not worried by the by the noise as this compressor is considerably quieter than my current 2.5HP cheapie.
The VFD is going to be located inside the shed alongside an ammeter and some other controls like a timed off switch and an auto vent, enclosure cooling etc that I describe in the Electronics section of the Forums.
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8th June 2014, 11:57 AM #10
It is good to see that you have got this problem sorted Bob. That VFD looks like it is the same as the one on my lathe. I was surprised by the difference when I got the 1.5kw version for my drill.
When I finally get around to getting a compressor enclosure built outside the shed, one of the things I will have is a red light in the shed to tell me when the power is turned on so that I do not have the situation where I am in bed, just getting comfortable and warm, starting to head for zees, and I hear the compressor start up. Hopefully won't hear it with an insulated enclosure, but ........
Dean
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8th June 2014, 12:55 PM #11SENIOR MEMBER
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8th June 2014, 02:24 PM #12.
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That's how mine is set up, At 9pm each night it automatically shuts off the compressor and vents the tank.
See https://www.woodworkforums.com/f271/compressor-control-circuit-184962
I had it on an old timer that could only turn the vent valve (a garden retic solenoid) on-off in increments of one hour but the elcheapo solenoid I was using got very hot over the that hour.
I have since replace the old 10A timer with this 16A one from Altronics http://www.altronics.com.au/p/s0045-...-timer-switch/
This allows for 15 minute increments and seeing as the first 3-4 minute the tank is venting it actually cools the valve so another 10 minute of getting warm again is not so bad.
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8th June 2014, 02:47 PM #13GOLD MEMBER
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Well with a little maths you could make a restriction so it takes longer
Why let it all out, why not just 10 seconds worth?
I solve the compressor problem in my shed(and everything else for that matter, like cheap VSD's, wifi etc) by flicking the main switch on the shed sub panel. Lucky I can reach it from the door lol
Stuart
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18th June 2014, 11:37 PM #14.
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I spent some of today chasing leaks on my retic comp air system with a bucket of soapy water and a paint brush and found a number of them, some on the Nitto connectors themselves and a couple on hoses. Some of these leaks have probably been there since I first put the retic comp air system together some 3 years ago as I did not perform a really thorough test at the time and some may have developed over time. Anyway, it looks like I have lost no pressure for the last 6 hours so I am pretty happy with that.
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7th July 2014, 01:46 PM #15.
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Just wanted to report that the compressor is running very nicely.
The Compressor enclosure is outside the shed immediately behind the wall shown in the photos and all the power and controls pass through a PVC lined hole in the wall shown towards the bottom of the first photo.
Inside the shed I tidied up the control wiring for the compressor by covering as much of as it that I could inside a 100 mm PVC 1/2 pipe.
LHS box provides timed 15A power for the VFD and 24VAC for the compressor auto vent system.
RHS box under power point provides power and timing control for the enclosure exhaust fan
I also added a pressure gauge inside the shed so I can see what is going on
The other small box on top of the 15A GPO is a temperature gauge to monitor how hot it gets inside the enclosure.
And now with cover on
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