Vfd recommendation for air compressor

[arangov3]

Just bought an air compressor which is 3 phase and I'm overwhelmed by the choices. It's a 5hp motor 3 phase, I'm mostly looking for the cheapest way to do this.

Its just me, in my home garage, who made a questionable purchase when complaining about the run time of my pancake compressor. I'm comfortable with electrical and mechanical work.

Would appreciate recommendations on what how large the wire should be for this run I'm considering 12/4 to a vfd.

Let me stop rambling, thanks.

 

[Sumboodie]

I have one I got for a 15hp compressor I don't need. Got it on sale for ~$500ish.

 

[gimpyrobb]

12g should be good up to 20amp, sounds like your on the right track. I've just started playing with VFDs and I think they are great.

 

[wyliesdiesels]

You need wire rated for 125% of NEC FLC table current

For 5HP 3p motor the table amps are 15.2. 19a rated wire needed

#12 NM-b will work

12/3 NM-b would be fine. Phase tape the white conductor with anything but gray.

 

[MichaelP]

...

 

[BillK]

The cheapest and easiest way might be to buy a 5HP single phase motor and sell the 3 phase one ?

 

[mike93lx]

The cheapest and easiest way might be to buy a 5HP single phase motor and sell the 3 phase one ?

Agreed. A decent 5hp, single phase input vfd is going to be $800+

Edit... Could roll the dice with **** like this ATO 5hp 3.7kW 19.2A VFD, 220V Single Phase to Three Phase VFD Variable Frequency Drive, Single Phase 220V Input to 3 Phase 220V/240V Output https://a.co/d/04bKxGpR

That said, I'm a big fan of getting pissed at an inadequate tool and swinging for the fences on its replacement!

 

[txvwnut]

A quick search and here's some pricing options. I went with a 10hp VFD as I size them like I would phase converter, more offered than needed.

Electric Motors - AC Single Phase Motors - Air Compressor Motors - Surplus Center

surpluscenter.com

https://www.amazon.com/s?k=10hp+vfd...aps,140&ref=nb_sb_noss_1&tag=atomicindus08-20

 

[Sumboodie]

This is what I have, don't need now.

Let me know.

 

[arangov3]

This is what I have, don't need now.

Let me know.

I think it's a little rich for my blood, I got the compressor for less than a steak at outback

 

[arangov3]

The cheapest and easiest way might be to buy a 5HP single phase motor and sell the 3 phase one ?

Wouldn't I need to replace the magnet switch if I did that?lmk if pictures would help

 

[arangov3]

Agreed. A decent 5hp, single phase input vfd is going to be $800+

Edit... Could roll the dice with **** like this ATO 5hp 3.7kW 19.2A VFD, 220V Single Phase to Three Phase VFD Variable Frequency Drive, Single Phase 220V Input to 3 Phase 220V/240V Output https://a.co/d/04bKxGpR

That said, I'm a big fan of getting pissed at an inadequate tool and swinging for the fences on its replacement!

I am seriously considering a bottom of the barrel vfd off amz, at 150 that's about as much that I spent getting the compressor between tolls, gas, and the compressor itself. It's the reason why I'm trying to cheap out.

 

[arangov3]

A quick search and here's some pricing options. I went with a 10hp VFD as I size them like I would phase converter, more offered than needed.

Electric Motors - AC Single Phase Motors - Air Compressor Motors - Surplus Center

surpluscenter.com

Amazon.com : 10hp vfd

Those motors are cheap I might actually replace it

 

[Sumboodie]

I think it's a little rich for my blood, I got the compressor for less than a steak at outback

Either swap the motor or run a VFD, neither will be the price of a steak supper ($25?... been many years sinceI've been in a sit down restaurant) unless you fall on some very great deal.... shoot just the scrap value of the motor is probably more.

Decent 240v 1 phase 5hp motor is around $3-400, plus shipping. Be mindful of rpms too, yours is likely 1700-1800. Lot of budget compressor motors run at around 3400.

Also may need a motor starter. (Not sure what your setup has) That's another $200 or so.

You'll likely need to wire it with 8 gauge, 10 gauge if it's a short run, so hopefully you've not already put in the 12 gauge run than was mentioned earlier.

Even the low end 60 gallon compressors are $1000+ these days, so don't hang up to much on that you got it super cheap.

 

[Sumboodie]

I am seriously considering a bottom of the barrel vfd off amz, at 150 that's about as much that I spent getting the compressor between tolls, gas, and the compressor itself. It's the reason why I'm trying to cheap out.

It's recommended to upsize vfd when using it to phase convert.

One that's rated for 7.5, even 10hp for a 5hp motor is recommended... compressors are fairly hungry in power... vs a lathe for example that you aren't firing it up in a cut.

I read that the cheap VFDs won't last long with an air compressor, but I'm by no means a subject matter expert.

The nice thing on a vfd is soft start.
At work, we just have a 10hp 240v compressor on 400 amp 3 phase service and it still momentarily flickers all the lights on startup from the draw.

 

[mm08822]

A single phase 5hp motor with integral overload protection and a 5hp rated pressure switch would be cheaper than adding a mag starter.

A pressure switch will outlast a vfd......or certainly much cheaper to replace.

 

[MichaelP]

And selling the $125 "mistake" and finding a single-phase replacement may be another way considering all costs and efforts of conversions. But I understand that this is not a GJ way.

 

[arangov3]

Either swap the motor or run a VFD, neither will be the price of a steak supper ($25?... been many years sinceI've been in a sit down restaurant) unless you fall on some very great deal.... shoot just the scrap value of the motor is probably more.

Decent 240v 1 phase 5hp motor is around $3-400, plus shipping. Be mindful of rpms too, yours is likely 1700-1800. Lot of budget compressor motors run at around 3400.

Also may need a motor starter. (Not sure what your setup has) That's another $200 or so.

You'll likely need to wire it with 8 gauge, 10 gauge if it's a short run, so hopefully you've not already put in the 12 gauge run than was mentioned earlier.

Even the low end 60 gallon compressors are $1000+ these days, so don't hang up to much on that you got it super cheap.

That steak reference was what I paid for the compressor. I need to confirm the stats on the motor but I'm concerned regarding compatibility with the other components in regards to the
switch and something else that I am not sure what it is just yet, I think it's a second switch only have a portion of the component in the attached picture.

I was surprised by the suggestion for 12 gauge when I Googled it I have a shorter run for my uni saw and that's with 6 gauge. I'd rather be conservative it go bigger.

 

[larry4406]

Check out @Bert_ ‘s thread where he is running a 3-phase compressor on single phase. All with home brew stuff.

 

[arangov3]

And selling the $125 "mistake" and finding a single-phase replacement may be another way considering all costs and efforts of conversions. But I understand that this is not a GJ way.

You're selling a vfd or motor? Stats? What you got?

 

[arangov3]

This is what I have, don't need now.

Let me know.

Afraid to ask how much

 

[MichaelP]

You're selling a vfd or motor? Stats? What you got?

I'm not selling anything. I'm talking about $125 OP mistakenly spent on a 3ph air compressor and now wants to adapt it to his 1-phase power. Although it's entirely possible, it may be easier and even less expensive to sell the compressor and find a single phase one. Just another option.

 

[MichaelP]

Afraid to ask how much

Don't be. The answer is in post #2.

 

[niget2002]

There's always a rotary phase converter. If you plan on getting other 3 phase devices in the future, it could be easier and cheaper in the long run.

But that's just me.

 

[Bert_]

If you can find the parts I can explain how to build a converter to run that 3 phase motor. I have one working right now that didn't cost me a dime.

 

[arangov3]

I'm not selling anything. I'm talking about $125 OP mistakenly spent on a 3ph air compressor and now wants to adapt it to his 1-phase power. Although it's entirely possible, it may be easier and even less expensive to sell the compressor and find a single phase one. Just another option.

It was 60 bucks, wasn't really a mistake more just I was gunning for other tools I lost out on. I have come to terms ordered 8/3 wiring conduit and reached out to a used dealer to see if they have either motor or vfd that meets my needs

 

[arangov3]

If you can find the parts I can explain how to build a converter to run that 3 phase motor. I have one working right now that didn't cost me a dime.

I'm listening, I tried to read through your thread but was gave up when the kids took over the day.

 

[arangov3]

Don't be. The answer is in post #2.

15hp would mean I would have to provide more electrical capacity? I'm gonna hold off on this to see if I can find something local.

 

[Sumboodie]

Don't be. The answer is in post #2.

No, that's what I paid for it.

 

[wyliesdiesels]

Wouldn't I need to replace the magnet switch if I did that?lmk if pictures would help

depends on the ratings. post a pic

 

[Sumboodie]

That steak reference was what I paid for the compressor. I need to confirm the stats on the motor but I'm concerned regarding compatibility with the other components in regards to the
switch and something else that I am not sure what it is just yet, I think it's a second switch only have a portion of the component in the attached picture.

I was surprised by the suggestion for 12 gauge when I Googled it I have a shorter run for my uni saw and that's with 6 gauge. I'd rather be conservative it go bigger.

Yes, I know.

You mentioned paying next to nothing "cost of a steak supper".

A decent commercial grade 5 hp compressor is around $2k new.... used... all depends. Maybe 700-1000?

You have $50? into a non working compressor.

It's going to take $300-400 at least to either put a single phase motor or vfd.

No idea what a "Unisaw" is, but unless it's pulling around 50 amps, or a very long wire run, it likely doesn't need 6 gauge wire.

 

[wyliesdiesels]

That steak reference was what I paid for the compressor. I need to confirm the stats on the motor but I'm concerned regarding compatibility with the other components in regards to the
switch and something else that I am not sure what it is just yet, I think it's a second switch only have a portion of the component in the attached picture.

I was surprised by the suggestion for 12 gauge when I Googled it I have a shorter run for my uni saw and that's with 6 gauge. I'd rather be conservative it go bigger.

The dial you pictured is the solid state overload relay FLA setting

but i can see the coil in the contactor is rated for 208v so that isnt gonna work for you. you would need to swap the coil to a 240v rated one or use a step down transformer. post a pic of the contactor so we can see what it is.

 

[MichaelP]

Using RPC (rotary phase converter) for a compressor may not be a very good idea unless you need the compressor for a short time and only occasionally. Otherwise, you'll have to keep RPC on for the entire time when you expect your compressor to switch on automatically as needed to keep its tank pressurized.

And since RPC is better to be rated, roughly, twice higher in HP to reliably serve a 5HP air compressor (which motor is always loaded), we're talking about 10HP RPC motor wasting power while the compressor is in a standby mode (=ready to add air to its tank as needed). Sure the idling RPC motor will not consume tremendous power, but it'll definitely consume more than you want to waste.

Although my home shop is on 15HP RPC, I wouldn't like to use it for my compressor which is free to start any time of the day to add pressure as needed. I turn my RPC on only when I need to use my other 3-ph machinery such as lathes, Bridgeport, surface grinder, buffers, sanders, etc. It may be 1-3 hours a day, but not 12-24 hours a day or a few days in a row when my compressor needs to be on standby.

So, a reasonable approach should be either to replace the 3-phase compressor motor with a single phase one, use a VFD or just sell the one you bought and get a 1-ph air compressor if you can find one in a decent condition and reasonably priced. Single phase compressor will be more expensive than a comparable 3-phase one simply because of higher demand (not many people have 3-phase power in their garages, and that's why you got yours for a pocket change).

 

[tarbellb]

Grab a 5.5kw or 7.5kw cheap VFD, more then enough to run your 5hp motor

Hooking up VFD is just asking Ai these days. 10g wire should work, 6g on your table saw is total overkill.

 

[Norcal]

When buying a VFD, do NOT get a off breed unit from China due to limited support or none, this is a sticky from one site, https://www.practicalmachinist.com/forum/threads/huanyang-vfds-banned-from-discussion.338416/ Huanyang VFD's are found on Amazon.

 

[tarbellb]

When buying a VFD, do NOT get a off breed unit from China due to limited support or none, this is a sticky from one site, https://www.practicalmachinist.com/forum/threads/huanyang-vfds-banned-from-discussion.338416/ Huanyang VFD's are found on Amazon.

Wow. Banned from even discussing them, feels like a engineers over reaction

Are no-name VFDS as good as Hitachi, Siemens, Fuji.... NO. But these arent running industrials plant operations that cost millions of dollars for downtime or put lives at risk.

But these no-name VFDs are running millions of motors at this point, and there has been huge improvements in all things tech since that was posted (2017)

 

[Cruzan80]

In fairness, lots of stuff is banned at Practical Machinist, because of the target audience. The idea is that it is for working machinists, not hobbyists or others whom it is not a primary job.

You could also add Atlas to that list, and they aren't made in China.

 

[mm08822]

Or look at it this way...how many times do you want to cry/curse?

Buy once, cry once. Move on to the next project w/o needing to look back.

 

[MKSJ]

Last person I know bought HY VFDs for his compressor, the first two failed and one actually caught fire. Piston compressors are a very hard start, so you need some headroom in the VFD running capacity (output amps in constant torque in HD mode as well as short term overload). When also asking them to run off of single phase, the typical derating for a VFD is a factor of 2 when they specify 3 phase input, and that also includes the use of a DC reactor/choke.

But if you want to give it a whirl, buy a higher capacity cheap VFD from eBay/Amazon and give it a try, if it blows up, then you can return it. Vevor VFDs grossly overstate their capacities, as well as others like Lepond, HY, etc. so I usually recommend doubling their capacity, as well as using them for very simplistic applications. Having done 100's of VFD installs, I wouldn't use them, but cheap is cheap. Otherwise just replace the motor with a single phase motor and be done with it. I would also check the motor RPM, my 5Hp Champion compressor uses a Marathon 1750 RPM compressor motor.

https://www.amazon.com/VEVOR-220V-240V-Variable-Frequency-0-400Hz/dp/B0CNK125HF/?tag=atomicindus08-20

 

[472scout]

I was surprised by the suggestion for 12 gauge when I Googled it I have a shorter run for my uni saw and that's with 6 gauge. I'd rather be conservative it go bigger.

6 gauge might be required for a large welder, but not a table saw. Even a 240v 5hp motor is only about 22 amps.