Vfd recommendation for air compressor

[mike93lx]

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

At least he improvised on something he didn't understand to the safe side, albeit wasting money and effort in the process.

 

[472scout]

At least he improvised on something he didn't understand to the safe side, albeit wasting money and effort in the process.

He's all set to plug in a 250 class MIG welder.

 

[Norcal]

The NEC requires that you size the conductors at 125% of the rated input of the drive, when oversizing a drive for single phase use , that can costly with copper prices today.

 

[fitter30]

Unless the vfd is set up by the drives manufacturer strictly for single to three phaze motor and labled that way. A normal vfd can be programmed to work 1 to 3ph but it has to be rated twice the hp or more to for the amperage.
Does the compressor have unloading? Might have a 1/4" copper tubing from the head to a funny looking valve opposite side of pulley crankshaft.

 

[MKSJ]

If you have a 3 phase input VFD, it is not well defined what the input current rating is when running on single phase in derated mode. You still need to comply with the NEC input wiring requirements if there isn't a plug to attached to the VFD but what input current are you using. An example in this case if the budget allowed would be to use GS23-2010, a 10 Hp rated VFD, which is rated at an output of 33A and 16.5A with single phase input. The rated input current is still listed as 39.6A and does not state the single phase, only 3 phase input, so basically 50A wiring ampacity using the 125% rule.

 

[arangov3]

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.

I bought it for 60 including loading fees, taxes, buyers premium and the cost of the compressor. It was working when I removed it, of course I currently have it disassemble as I couldn't remove it from the pickup truck alone with it being top heavy.

Unisaw is an old delta table saw.

 

[arangov3]

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.

I think this is what you're asking for also posted the badge on the motor

 

[arangov3]

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).

I feel like the vfd is the best way to go, rpc sounds fun and I'm sure I could trigger it to turn on in anticipation of needing power with a microcontroller but I'm not interested.

I posted pictures to add context as I think the motor replacement isn't a direct drop in.

 

[arangov3]

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)

My opinion, I think the off brands are fine if you're not dependent on them working. I need my compressor every two weeks if the vfd shits the bed I can use hand or battery tools or just wait.

Safety is another conversation I intend to cut power when I'm not in the shop as my kids have access to the area which should limit fire to when I can maintain line of sight.

 

[arangov3]

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

Doubling their capacity has brought them to a different price tier that puts me in reach of some Japanese brands like hitachi, which is the direction I intend to go

 

[arangov3]

At least he improvised on something he didn't understand to the safe side, albeit wasting money and effort in the process.

Its what I had on hand from swapping our range from gas to electric, it was a 70 foot run. The table saw plug is 18 inches of wire from outlet to breaker. But I've been conservative on all my electrical upping the gauge so long as the fixtures could accommodate it.

 

[arangov3]

Unless the vfd is set up by the drives manufacturer strictly for single to three phaze motor and labled that way. A normal vfd can be programmed to work 1 to 3ph but it has to be rated twice the hp or more to for the amperage.
Does the compressor have unloading? Might have a 1/4" copper tubing from the head to a funny looking valve opposite side of pulley crankshaft.

It does have a small line from the pump to the tank but it's not from the head of the pump

 

[arangov3]

I think this is what you're asking for also posted the badge on the motor

Just learned I shouldn't put a magnetic start betya vfd and motor, which means the starter isn't mandatory simplifying te replacement of the motor

 

[Sumboodie]

I have that new 20hp Lapond if you're looking, though not sure if shipping would be economical. It won't fit in a flat rate.

 

[arangov3]

I have that new 20hp Lapond if you're looking, though not sure if shipping would be economical. It won't fit in a flat rate.

What are you looking to get

 

[mike93lx]

A 20hp motor is the solution to basically nothing in a residential setting. You won't be able to run it

 

[Sumboodie]

What are you looking to get

$275. About 1/2 of what I paid for it.

 

[Lassen Forge]

Either go big with your VFD so you can power that cheap shaper or lathe you score later, or change to a 1ø motor. Me? I'd get big VFD and buy that lathe I've been puttng off, and then upgrade my compresor later to a rotary unit...

BTW - 20 HP is a LOT of power, but if your electric service (and wallet) can handle it, go for it.

 

[arangov3]

$275. About 1/2 of what I paid for it.

Wait is this a motor or vfd I should have asked first sorry

 

[mike93lx]

Wait is this a motor or vfd I should have asked first sorry

My bad, it's a vfd

 

[arangov3]

Either go big with your VFD so you can power that cheap shaper or lathe you score later, or change to a 1ø motor. Me? I'd get big VFD and buy that lathe I've been puttng off, and then upgrade my compresor later to a rotary unit...

BTW - 20 HP is a LOT of power, but if your electric service (and wallet) can handle it, go for it.

I have 200 amp outside the shop with the range, ac and house electronics going we draw around 60, if it's a vfd I think it's a great opportunity. There is a sb lathe and have been chasing a pm planer for a while with no success. 20 ho vfd would be a solution for flexibly but I want to isolate the compressor as I would use it in conjunction with other tools and fear 20hp vfd brings me close to capacity.

 

[mike93lx]

I have 200 amp outside the shop with the range, ac and house electronics going we draw around 60, if it's a vfd I think it's a great opportunity. There is a sb lathe and have been chasing a pm planer for a while with no success. 20 ho vfd would be a solution for flexibly but I want to isolate the compressor as I would use it in conjunction with other tools and fear 20hp vfd brings me close to capacity.

If you want to power multiple machines, a rotary phase converter is generally the best way to go. Vfd's are almost always installed specifically to a single machine

 

[MichaelP]

^^this.

And for VFDs many machines, including compressor, require rewiring. VFD is not an analog of a wall receptacle or RPC output.
For example, you shouldn't use machinery ON/OFF switches as they are wired originally, but should use VFD to turn them ON and OFF.

VFDs are not designed to replace a utility power line: they don't like any sudden large changes in loads and prefer to control the process.

So by now you you should learn the following:

1. You cannot plan to use a powerful VFD to feed multiple machines. You need a dedicated VFD for each machine,

2. Using VFD requires machine rewiring,

3. RPC, as an analog of utility power, will be able to serve all machinery without any rewiring. But it'll need to be ON for an extended period when your want your air compressor to switch ON/OFF automatically,

4. Replacing 3-ph motor with a single phase one will require finding a suitable replacements which is not always easy. And then it will require installation labor,

5. Ditching or selling your $60 bargain compressor and investing into a single phase one is a headache free solution, but as everything above, will require money

Choose your poison.

 

[txvwnut]

I have 200 amp outside the shop with the range, ac and house electronics going we draw around 60, if it's a vfd I think it's a great opportunity. There is a sb lathe and have been chasing a pm planer for a while with no success. 20 ho vfd would be a solution for flexibly but I want to isolate the compressor as I would use it in conjunction with other tools and fear 20hp vfd brings me close to capacity.

A single VFD is not what you want for multiple machines, a rotary phase converter is what you want for power to multiple machines.

For example, you shouldn't use machinery ON/OFF switches as they are wired originally, but should use VFD to turn them ON and OFF.

I seem to be the anomaly in this statement as my VFD is wired just like my static phase convertor was. I use the switch on the mill to turn on and off the machine and have a soft start programmed into the VFD so it ramps the motor up instead of hitting all at once. The only thing about doing it this was is you cannot rapidly reverse the machine like I could if I had the switch wired through the VFD. Been this way for a little over ten years and haven't had any issues.

 

[wyliesdiesels]

Most PoCos have a limit on motor HP. you should check with your PoCo first before attempting to run such a large motor

 

[Bert_]

I've been wiring a vfd this morning, 40hp motor, single phase input.

From a user perspective they are awesome. Seamless operation.

The downsides are cost, and lifespan. I figure a 10 year life. I've replaced some sooner and they aren't Chinese ones

 

[arangov3]

^^this.

And for VFDs many machines, including compressor, require rewiring. VFD is not an analog of a wall receptacle or RPC output.
For example, you shouldn't use machinery ON/OFF switches as they are wired originally, but should use VFD to turn them ON and OFF.

VFDs are not designed to replace a utility power line: they don't like any sudden large changes in loads and prefer to control the process.

So by now you you should learn the following:

1. You cannot plan to use a powerful VFD to feed multiple machines. You need a dedicated VFD for each machine,

2. Using VFD requires machine rewiring,

3. RPC, as an analog of utility power, will be able to serve all machinery without any rewiring. But it'll need to be ON for an extended period when your want your air compressor to switch ON/OFF automatically,

4. Replacing 3-ph motor with a single phase one will require finding a suitable replacements which is not always easy. And then it will require installation labor,

5. Ditching or selling your $60 bargain compressor and investing into a single phase one is a headache free solution, but as everything above, will require money

Choose your poison.

I'm committed to option 2, the rewiring I assume is removing the magnetic switch? I'm going to roll the dice on a Chinese vfd from home Depot and use my store card so I can return it if it pops within the year.

Option 4 honestly doesn't seem worth the effort of finding, the few close options didn't match the shaft size so I would have to find another pull

I'm too lazy to move this again option 5 is a no

 

[arangov3]

Most PoCos have a limit on motor HP. you should check with your PoCo first before attempting to run such a large motor

Looks like 6.5 is the limit for single phase

 

[micromind]

Option 4 honestly doesn't seem worth the effort of finding, the few close options didn't match the shaft size so I would have to find another pull

The existing motor is 184T frame. Any 184T frame will fit.

The existing RPM is 1745. Any RPM from 1700 to 1800 will work.

 

[MichaelP]

...the rewiring I assume is removing the magnetic switch?

Controls like pressure switch. It should tell the VFD to turn the power ON or OFF.

 

[MichaelP]

I seem to be the anomaly in this statement as my VFD is wired just like my static phase convertor was. I use the switch on the mill to turn on and off the machine and have a soft start programmed into the VFD so it ramps the motor up instead of hitting all at once. The only thing about doing it this was is you cannot rapidly reverse the machine like I could if I had the switch wired through the VFD. Been this way for a little over ten years and haven't had any issues.

VFDs may tolerate certain abnormal connections to some degree (I need to look into your soft start closely: it might be a reason it still works). Some people even connect a few machines to a single VFD, and sometimes it works. Until it fails.

I wouldn't cut corners trying to use VFD incorrectly.

 

[arangov3]

Controls like pressure switch. It should tell the VFD to turn the power ON or OFF.

Would you spoon feed me when the vfd gets here

 

[Sumboodie]

Wait is this a motor or vfd I should have asked first sorry

20hp vfd

 

[MichaelP]

Would you spoon feed me when the vfd gets here

Sorry, I will not. I installed the last VFD long ago, and it required detailed research on how each model works. Paperwork is often incomplete and misleading, esp., Chinese manuals.

But I'm sure we have a few people here or on other forums who do it often enough and are hands on. You may try Practical Machinist, Home Shop Machinist or industrial electricians' forums. Google and AI should be helpful too, but don't trust everything AI says: recheck the validity of its reply (it gives BS info way too often).

I'd start with research: deciding which compressor parts need to be connected and controlled by VFD, choosing a model that provides the connections/switching/control and only then buying it.

 

[mm08822]

Sorry, I will not. I installed the last VFD long ago, and it required detailed research on how each model works. Paperwork is often incomplete and misleading, esp., Chinese manuals.

But I'm sure we have a few people here or on other forums who does it often enough and is hands on. You may try Practical Machinist, Home Shop Machinist or industrial electricians' forums. Google and AI should be helpful too, but don't trust everything AI says: recheck the validity of its reply (it gives BS info way too often).

I'd start with research before choosing a model and buying a VFD.

Download the manual before purchasing.

Aside from the wiring details, programming parameters are needed. Many can stay at default values, some are motor nameplate specific, and the rest are application specific.
It's not really that bad at all with a good manual written in English (not Chinglish).

 

[txvwnut]

VFDs may tolerate certain abnormal connections to some degree (I need to look into your soft start closely: it might be a reason it still works). Some people even connect a few machines to a single VFD, and sometimes it works. Until it fails.

I wouldn't cut corners trying to use VFD incorrectly.

I saw somewhere where someone used one VFD to run several machines. It was not setup to run all at once but they had a system of disconnects so one machine couldn't be used while another one was in use. I need to look at my VFD's instruction manual again as I think it stated in it you could do the power switching either way if you programmed it a certain way.

 

[MichaelP]

Of course you can find a way to switch multiple machine controls so that only one is connected at a time. It may be very cumbersome, but doable nevertheless. It's just that this arrangement shouldn't be misunderstood as VFD providing power and control to all shop machinery.

 

[MKSJ]

I saw somewhere where someone used one VFD to run several machines. It was not setup to run all at once but they had a system of disconnects so one machine couldn't be used while another one was in use. I need to look at my VFD's instruction manual again as I think it stated in it you could do the power switching either way if you programmed it a certain way.

Yes and no, a VFD parameters and motor tuning are specific to an individual motor, most lower cost (cheap) VFDs only can be setup for one motor/machine. Some more expensive VFDs allow two sets of motor parameters to be used, and a programmed input is used to switch the motor parameters (but not the other parameters), this is more applicable to using a VFD with a 2 speed motor or say two motors in a mill such as a horizontal and vertical mill. To use one VFD between different machines is a bit foolish given the price of smaller VFDs these days, as well as significantly compromising the safety and overload differences. There are cases where a single VFD may be used for multiple motors of the same specifications, and there are limitations to this arrangement and each motor requires its own overload device.

In some cases individuals have used a much larger VFD at least 4-5X the maximum load as a fixed power source for multiple machines and requires the VFD to be run in V/Hz configuration at a fixed frequency/voltage for all motors. There is no motor tuning, braking, acceleration, etc., just a fixed power source. You also have the issue in that the VFD output is still PWM w/o filtering and does not play nicely with machine control systems. If you want 3 phase power similar to that from the power company from a single phase source, then I would recommend the Phase Perfect digital phase converters that generate the third phase that is sinusoidal and tightly regulated.

 

[arangov3]

waiting on a reply on this any reason this wouldn't work

 

[mm08822]

waiting on a reply on this any reason this wouldn't work

Post 16 had this option.

Possibly 3600rpm is better....depends on pump sheave, pump max speed and guarding size.