Using weaker phase converter to slow down compressor?

[BenKlesc]

I am looking to install a 3 phase rotary compressor in my home garage, that is rated at 30HP. I don't have 3 phase power, and was told it is very expensive running a three phase motor on single phase.

I am looking to start a sandblasting side hobby on my projects and friends projects, and my sandblaster setup requires 45CFM to operate. I also found that it's extremely difficult to find piston compressors that output 40-50CFM that are not outrageously expensive.

I said to myself at that point, if I'm going to drop 3-4 grand I might as well get a rotary. Problem is I don't believe I need 30HP, more like 15HP is all I need. If I run a phase converter that is rated at 15-18HP hooked up to a 30HP compressor, would that slow the compressor down or not power it at all?

 

[mike93lx]

IMO, Not only do you probably not need 30hp, you won't be able to start it on residential service.

You are talking about a power level that i think requires checking with your POCO to see if your transformer can support it

 

[cgrutt]

By no means an expert with this but my general understanding is that you typically want to size the RPC ABOVE the load motor not the other way around. 30HP is huge. I'm assuming you have 220v single phase AC? Compressor motors will typically draw many times more current at start-up that what motor FLA is actually rated for. I would guess you are going to need at least a 50 HP RPC to run a 30 HP compressor efficiently. Good luck!

 

[Dmoen]

us a VFD, not a phase converter.

 

[BenKlesc]

I just looked up Variable Frequency Drive. That looks intriguing.

So if I got a 50HP VFD, I could technically slow down the speed of the motor to lower costs?

Also yes, I am using 220v single phase. May be too much I'm asking for.

 

[mike93lx]

Yeah, a VFD would let you slow a 3 phase motor.

Practically, you are better to either hire out the sandblasting to run a gas/diesel powered compressor

 

[930dreamer]

What's the size of the compressor your looking at? The general rule of thumb on a phase converter is the converter needs to be twice the hp of the motor your trying to operate, it will be running on 240v single phase. Here's my 30 hp 3 phase idler I was testing,I spun it up to speed first with another motor before starting.

 

[OccupantRJ]

You need a portable gas or diesel driven air compressor of more than sufficient cfm, in my opinion. Have you considered the wind drift of the abrasive? Neighbors do not like having their homes and vehicles dusted. I had a side business blasting about 30 years ago, and blasting makes a hell of a dust cloud. I blasted inside a ring of mature red tip bushes that acted as a dust suppressor. CFM requirements on a pressure blast unit are determined by the nozzle diameter. Society determines where you can blast.

 

[BenKlesc]

The sizes I was looking at were 70-80 amps that were available in my area, 30-40HP, 60 gallons. It gets to the point for some reason, where it's a grand cheaper to buy a 30HP rotary compressor that no one wants to put in their garage. Versus buying a 20HP 50CFM single phase piston compressor.

 

[930dreamer]

My .02, blasting in a cabinet in a home garage is fine, blasting outside would be out of the question in a normal neighborhood.

 

[BenKlesc]

As far as blasting I'll be using a 3/4" hose, and a 1/4" nozzle. 90PSI crushed glass.

Looking to blast seven project cars. I have a lot of room.

 

[930dreamer]

Single phase 10 hp screw compressor= about 35 cfm for $5700 do you have the blasting equipment?

https://www.compressorworld.com/sho...tgeFKpcA10Qs18Yq1p4Yovneip-P-DQBoCOpgQAvD_BwE

This looks like a good route to go;

15 hp, 62 cfm, $10500 single phase ALSO. VFD Soft Start Motor
Provides reduced energy demand & amp draw on start up.

https://www.aircompressorsdirect.com/EMAX-ERS0150001-Air-Compressor/p14518.html

 

[gorilla]

A lower rated rotary converter will not start a 30hp motor. Rule of thumb is twice the size for the idler motor. 30 hp run current at 240vac would be about 90 amps inrush (starting) current could be twice that. A rotary converter adds the load of running the motor to generate the third phase so the current draw is even higher. Installing a compressor this big requires a conversation with your power company about load on the pole pig that supplies your neighborhood. How big is the service to your shop/house?

 

[John in OH]

You need a portable gas or diesel driven air compressor of more than sufficient cfm, in my opinion. Have you considered the wind drift of the abrasive? Neighbors do not like having their homes and vehicles dusted. I had a side business blasting about 30 years ago, and blasting makes a hell of a dust cloud. I blasted inside a ring of mature red tip bushes that acted as a dust suppressor. CFM requirements on a pressure blast unit are determined by the nozzle diameter. Society determines where you can blast.

Neighbors won't like the noise either.

 

[John in OH]

A lower rated rotary converter will not start a 30hp motor. Rule of thumb is twice the size for the idler motor. 30 hp run current at 240vac would be about 90 amps inrush (starting) current could be twice that. A rotary converter adds the load of running the motor to generate the third phase so the current draw is even higher. Installing a compressor this big requires a conversation with your power company about load on the pole pig that supplies your neighborhood. How big is the service to your shop/house?

Totally agree. Your local power company is definitely going to want to be involved in this project. Get them involved before you spend any money or it may be money thrown away.

 

[OccupantRJ]

Here is some more info for you. Note the cfm requirements for a 1/4” nozzle.

http://www.hironsmemorials.com/Blast_Nozzles_Selection_Guide.pdf

 

[ez-duzit]

I am looking to install a 3 phase rotary compressor in my home garage, that is rated at 30HP....my sandblaster setup requires 45CFM...If I run a phase converter that is rated at 15-18HP hooked up to a 30HP compressor, would that slow the compressor down or not power it at all?

Makes no sense at all.

As has been pointed out, a rotary phase converter of ~ 2X the compressor's HP will be required. Better rethink this and do proper due diligence.

 

[Slowgsr]

Operating an electric compressor will be very very expensive.

Go with a diesel mobile compressor

 

[Norcal]

I would not be surprised if the PoCo nixes a 30HP motor in a residential situation.

 

[930dreamer]

You could just rent a diesel compressor when needed.

 

[BenKlesc]

Here are my two nozzles, 1/4" and 3/16". Maybe I would be better off using a 3/16.

I'm building a small hobby shop next to my home, and am looking for a permanent fixture.

I will be looking into painting these projects as well. I am still intrigued at how a VFD would work on a rotary. The question really comes down to, do I really want to spend five or six grand on a piston?

I almost feel like I would be getting more of a bang for your buck, if I had the power to run one the many rotaries that are for sale around my area. 3 phase is not an option out here.

 

[cgrutt]

I will be looking into painting these projects as well. I am still intrigued at how a VFD would work on a rotary. The question really comes down to, do I really want to spend five or six grand on a piston?
.

Not even sure if a VFD with single phase 220v input is even available to run a 30HP three phase motor, but it wouldn't surprise me if that alone cost several thousand dollars if it was...

 

[930dreamer]

A 25 hp compressor would need a 50 hp rotary converter, the soft start vfd function on the new rotary compressors would reduce to starting amperage issues.

 

[OccupantRJ]

I am usually the last person to be a naysayer, but I don’t think this is going to turn out how you want it to.

 

[BenKlesc]

"50 HP, VFD, Variable Frequency Drive, Inverter, Phase Converter, 3 Phase Input or 1 Phase Input, 400-480 Volt. FRN050F1S-4U Fuji. The amp rating is 72.0 amps for three phase input/three phase output and 30.0 amps single phase input/three phase output. Can be used to control the speed of an electric motor in variable torque applications such as pumps or fans up to 50HP."

https://www.electricmotorsforless.com/-50-HP-VFD-Variable-Frequency-Drive-Inverter-Phase-Converter-460-Volt-FRN050F1S-4U-_p_1100.html?_vsrefdom=googleads&gclid=EAIaIQobChMIp4OPvreA4QIVx42zCh3cewnnEAQYASABEgLU3vD_BwE

"Your Price: $2,623.50" Yowza!

 

[cgrutt]

"50 HP, VFD, Variable Frequency Drive, Inverter, Phase Converter, 3 Phase Input or 1 Phase Input, 400-480 Volt. FRN050F1S-4U Fuji. The amp rating is 72.0 amps for three phase input/three phase output and 30.0 amps single phase input/three phase output. Can be used to control the speed of an electric motor in variable torque applications such as pumps or fans up to 50HP."

https://www.electricmotorsforless.com/-50-HP-VFD-Variable-Frequency-Drive-Inverter-Phase-Converter-460-Volt-FRN050F1S-4U-_p_1100.html?_vsrefdom=googleads&gclid=EAIaIQobChMIp4OPvreA4QIVx42zCh3cewnnEAQYASABEgLU3vD_BwE

"Your Price: $2,623.50" Yowza!

That's 400-480v input and only rated for 30A with single phase input.

Here's one 220v single phase input 40 HP three phase output...

$8000+ lol

https://www.wolfautomation.com/products/ac-drives/200_240v_single_ph_only-40_hp

 

[mike93lx]

You're just intentionally ignoring everyone, right?

 

[BenKlesc]

You're just intentionally ignoring everyone, right?

I honestly did not know, will be a first compressor purchase.

 

[BenKlesc]

That's 400-480v input and only rated for 30A with single phase input.

Here's one 220v single phase input 40 HP three phase output...

$8000+ lol

https://www.wolfautomation.com/products/ac-drives/200_240v_single_ph_only-40_hp

At that price you might as well route three phase to your home, lol!

 

[Bert_]

Not even sure if a VFD with single phase 220v input is even available to run a 30HP three phase motor, but it wouldn't surprise me if that alone cost several thousand dollars if it was...

I've wired about a dozen 30hp motors powered with a vfd on single phase input...

Of course it's going to cost several thousand dollars. Nobody should be surprised when your dealing with this size equipment.

 

[Alber ring]

Using a phase converter does not slow down the compressor, and a single to three-phase power converter does not have any drawbacks other than being a bit expensive

 

[sberry]

Get a couple 7.5 comps

 

[mike93lx]

I honestly did not know, will be a first compressor purchase.

You have a lot of people telling you it is either a bad idea, waste of money or not possible, but yoy aren't ackowledging any of it. Do what you want, but why ask for help?

 

[Smittybert]

How about a tractors pto driving the compressor. Seems like you live in a rural area might have a tractor already?

 

[Dragfluid]

OP, do you happen to know a member here by the name of 1930?
Just curious.

 

[gorilla]

Electric motors are not like gas engines they will not use less power if you run them slower. If you use a VFD to slow a motor down in a constant load application like a air compressor the motor will over heat. What you want to do repeals the laws of physics it won't work no such thing as a free lunch.A gas/diesel compressor is the best solution to your problem.

 

[86turbodsl]

If you look at my shop thread, "86's 50HP shop" you will see i spent a lot of time trying to run a 10HP compressor on single phase cheaply. In the end, i have a couple of 5HP quincies. I had a 50hp phase converter. It pulls something like 200A on startup WITH a pony start motor to get it going. And it would be undersized for a 30hp compressor. Rule of thumb is 2.5-3 times for your RPC.

If you were to run a VFD for your compressor, you would need one that was ok without the phase loss protection and rated for about 4X your starting current. you will have a heart attack when you price it out.

If it was me and i needed that kind of volume, i would look straight at an engine driven compressor. If you are handy, it's possible to turn a V8 into a half compressor/half engine. They are just air pumps after all.

Listen to these folks. You've received a lot of good advice so far.

 

[slow]

with soft start, you might not need 4x the starting current, but you definitely need to upsize the VFD. I have some 10hp drives running single phase input on 7.5 hp 3 phase motors. You should also run line reactors to prevent the noise on the line. I remember paying a lot for those as well.

What duty cycle do you need that air requirement? how many hours a day/project. Might be cheaper to do a engine powered compressor.

 

[TRWham]

Electric motors are not like gas engines they will not use less power if you run them slower. If you use a VFD to slow a motor down in a constant load application like a air compressor the motor will over heat. What you want to do repeals the laws of physics it won't work no such thing as a free lunch.A gas/diesel compressor is the best solution to your problem.

While the OP's proposal is a bad idea, VFDs actually do work quite well when applied to compressors, especially recips, for capacity control and do reduce energy consumption. A compressor does less work with decreased speed because it moves less air. The pressure differential may be the same, but the mass flow is reduced, therefore the work done per time is reduced.

 

[rsanter]

First off you are bouncing all over the place...

They make screw compressors in both fixed drive and variable drive.
Do not put a VFD of a fixed drive compressor and slow it down. The screw compressor geometry is different and when slowed down you will lose output efficiency like crazy.

Next, get eye compressor you need, don’t try to slow down or speed things up. That is what you do for a bargain used buy when you have to. If you are dropping that much money on something then buy what is right for your usage.

If you use a VFD as a phase converter, buy what is right for then application, you can’t buy a smaller one thinking it will save you money or I prove things.

VFDs can help you get big energy efficiency gains. The gains are the biggest in low load applications like fans and such but there is gain in compressors and the such if things are selected/designed properly