Using weaker phase converter to slow down compressor?

[brewchief]

Big 3 phase compressors seem to sell pretty cheap, I think a lot of it is the places that really need that much air can afford new equipment and few smaller users have the infrastructure to run them.

Most utility companies will have a HP limit on motors, most the time I think it's around 7.5.

A 90 cfm diesel compressor rents for just over 100$ a day near me, if you had a full day of blasting on each of 7 cars that's still pretty cheap, if you can find a deal on one to buy it would be even better.

 

[BenKlesc]

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

Thank you, that is what I was very curious to find out.

That answers my question, I do not plan on making any purchases at this time.

 

[BenKlesc]

Big 3 phase compressors seem to sell pretty cheap, I think a lot of it is the places that really need that much air can afford new equipment and few smaller users have the infrastructure to run them.

Most utility companies will have a HP limit on motors, most the time I think it's around 7.5.

A 90 cfm diesel compressor rents for just over 100$ a day near me, if you had a full day of blasting on each of 7 cars that's still pretty cheap, if you can find a deal on one to buy it would be even better.

That's what I noticed too, they are very underpriced for what they are.

I was finding 40 and 50HP rotaries for under a grand, that surprised me a lot.

That's a grand cheaper than some of the 5HP single phase compressors at Home Depot.

 

[mcj115]

While the compressor may be cheap, upgrading your service and getting the right electrical install will cost you big.


For serious blasting (100 to 200lb blaster). I have always used a towable compressor, typically gas powered. When I have used blasting cabinets then a electric piston driven unit works well. Most gassers are ~ 100CFM and most diesels are ~175-200 cfm. I just looked on my local CL and a old towable IR gas compressors re ~$1000.
Even if you find an older Lindsey or other brand they are great. For an cheap older compressor you will probably find it to be piston driven. Typically a Wisconsin V4 with two cylinder to run and two cylinders to compress or a Ford V8 with four to run and 4 to compress.

Honestly when running a blaster like I envision you using it is better to use a portable one so you don't end up with a mess in your yard, if you can find a buddy with an industrial site to use it at that is ideal.

 

[alfredeneuman]

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

SCE won't hook up a motor over 10HP in a residential setting.

 

[BenKlesc]

SCE won't hook up a motor over 10HP in a residential setting.

Wonder if a gas 220V generator would power one, one that has enough wattage and amps.

Right now I am eyeballing a 13HP compressor.

That is the lowest amount I need to blast 50CFM. I really don't have any neighbors, I am building a garage next to my home where I will be performing bodywork. I live out in the country in Western Mass.

I have a sandblasting unit for dustless blasting, and one for crushed glass. Right now I have seven cars on the lot.

 

[bsaint]

Holy smokes this thread is ridiculous. Now we're talking about 50hp 480vfd in a residential setting haha.

Rotary screw compressors start unloaded. They do not pull nameplate amps running unloaded. Besides inrush current, unloaded current is roughly half the nameplate.

2nd its more involved to match a VFD to a screw. For one, if there's a control xformer, you will smoke your electronics. This is from experience.

3rd, 50cfm is about a 15hp compressor. They don't make a 13hp electric compressor.

 

[wyliesdiesels]

Holy smokes this thread is ridiculous. Now we're talking about 50hp 480vfd in a residential setting haha.

Rotary screw compressors start unloaded. They do not pull nameplate amps running unloaded. Besides inrush current, unloaded current is roughly half the nameplate.

2nd its more involved to match a VFD to a screw. For one, if there's a control xformer, you will smoke your electronics. This is from experience.

3rd, 50cfm is about a 15hp compressor. They don't make a 13hp electric compressor.

yes it is. thats why ive just sat back and watched with a bowl full of popcorn..

 

[dkmc]

I'm also finding this thread to be quite entertaining.

 

[Dagny]

Me three all his neighbors will kill him.

 

[Falcon67]

Then the EPA will grind his bones. Before OP starts hosing down cars with paint for a "hobby" or part time business, better read up

https://itstillruns.com/laws-painting-car-home-6919383.html

https://www.sema.org/sema-enews/2011/03/epa-spray-paint-requirements-take-effect-for-auto-body-shops

"The regulation does not apply to paint stripping and surface coating performed by individuals as part of a hobby, or for maintenance of their personal vehicles so long as those activities do not exceed two motor vehicles (or the equivalent in pieces) per year. Additionally, the rule does not apply to painting done with an airbrush or hand-held non-refillable aerosol cans. "

 

[alfredeneuman]

OP said nothing about paint.
He wants to do sandblasting.

 

[ez-duzit]

You must paint immediately after sandblasting.

 

[WhoWhatNow]

Oh, just build one and be done with it....

https://www.doityourself.com/stry/how-to-convert-a-v8-engine-into-an-air-compressor

 

[alfredeneuman]

You must paint immediately after sandblasting.

One company could do the sandblasting, and moved to another company and location to paint. It happens all the time.

 

[sberry]

First comp and finds the hardest way to do it, likely bigger than he needs.
But, easy cheap way would be 3 cheap air comps. Even cheaper used.

 

[MrSurly]

but, easy cheap way would be 3 cheap air comps. Even cheaper used.

^^this^^
Also simple enough to 'stage' their pressure switches such that they never start together.

 

[Worsedog]

Oh, just build one and be done with it....

https://www.doityourself.com/stry/how-to-convert-a-v8-engine-into-an-air-compressor

Awesome. Six simple steps. Shouldn't be more than a three beer afternoon project.

 

[OccupantRJ]

I have a Gordon Smith 302 Ford monoblock compressor. There were once popular units for the tool rental places. 110 cfm output.

 

[BenKlesc]

Well the **** just hit the fan.

Just bought a 15HP 440V Quincy QT-15 piston compressor I got a deal on for a grand.

They retail for six grand. This one is a 2005 model. It's 35 amps.

I will be buying a step up transformer from 220 to 440. This project will be done by the summer. A bodyshop paints them, I just sandblast and weld in my driveway.

 

[dkmc]

QT15 and yer gonna run that on 120 single phase, boosted to 220, then to 440?
Gonna convert that to 3 phase, or not so much?
Seems like a long belated April fools joke.



At this point it feels like a waste of time, but I'll mention it anyway....
When a motor name plate specifies 35 amps, that's Full Load run amps.
Starting amps, can be much higher.

 

[BenKlesc]

QT15 and yer gonna run that on 120 single phase, boosted to 220, then to 440?
Gonna convert that to 3 phase, or not so much?
Seems like a long belated April fools joke.


At this point it feels like a waste of time, but I'll mention it anyway....
When a motor name plate specifies 35 amps, that's Full Load run amps.
Starting amps, can be much higher.

Nope that was my mistake.

It's a 220V outlet. I am up converting 220 to 440V single phase.

Then I'm buying a 440V phase converter to three phase.

So I will be running a three phase 440V motor on single phase power.

 

[BenKlesc]

The motor says it runs on 230/440v.

It has a 440V plug though, it would have to be rewired.

 

[ez-duzit]

...it would have to be rewired.

Not exactly, just reconnected. Easy and quick.

 

[dkmc]

It's going to take a lot of amps at 220 1Ph to start and run that motor up to full tank pressure, less starting if a VFD were in the mix. 15HP VFD's don't come cheap.
Might think about installing one of the Harbor Freight V Twin 22HP gas engines on it instead of electric.

 

[7635tools]

I have a 40hp rotary convertor in my shop. I’m in a residential setting and I have no problems starting it up. Been running it for about 3 years now. Just gotta have the power to do it. Proper wire size to the convertor is very important.


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[dkmc]

I have no doubt you can start your 40hp converter up.
Can you start a 40hp motor (under partial load) with your converter?
How about a 15HP motor?
If you can't answer yes to the second question, what you're saying is pointless as to the OP's situation.

I have a 40hp rotary convertor in my shop. I’m in a residential setting and I have no problems starting it up. Been running it for about 3 years now. Just gotta have the power to do it. Proper wire size to the convertor is very important.


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[Strouty]

My 40 HP rotary phase converter will run two 15 HP motors.

I run a 10 HP single phase compressor with no problems. They also make 15 HP single phase motors, so the OP could buy one and make things work.

As for stepping the voltage up, you will still need some serious amps, you can use VFDs on single phase motors to soft start them, that would help with any issues with the POCO.

 

[CGT80]

Is the Quincy rated at 35 amps at 230v or 440v?

If it is at 440v, then double that for your 240v service, and then increase that because the load will only be spread over two phases/legs on your service vs. three listed on the nameplate. 35 x 2 = 70 amps on 3 legs.

When move the load to two legs, would it come out to 110 amps per leg? That part I do not have the answer to, without some research.

The 5hp baldor (1 3/8" shaft, 105 lbs weight) motor on my compressor jas a nameplate of 28.5 amps 1.15 service factor and I load it to 30 amps at 170 psi......less amps at lower pressure. It pulls 169 amps on 240v single phase, on one of the legs, when starting up according to my clamp on meter.

How much will 15hp draw to start?

Piston compressors have a minimum rpm for lubrication as well, so that rules out turning one extremely slow. Often times a pump will have specs for 3 different size motors. Smaller motor, lower rpm, less cfm, less noise.

My family has a blasting business and used a 25hp 97cfm at 125 psi Westinghouse air brake company 3 piston compressor for big blast cabinets and 175 to 250 cfm diesel trailer units for blasting power plant steam turbines and similar equipment with 1/2 nozzles.

Engine driven or a series of smaller compressors with a staggered start is the way to go.

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[BenKlesc]

It's 35amps @ 230V.

18amps @ 460V to be exact.

1760RPM.

 

[wyliesdiesels]

What size service do you have and what loads do you have?

Your poco may have limits on HP too

 

[alfredeneuman]

You got the compressor for $1K.
If you can change the motor from 460 to 230 you'll save in the long run. The diagram is given on the nameplate, or sometimes a label is on the inside cover of the wiring enclosure. It's a really easy diagram to follow.
There are no single phase to 3 phase 480v VFDs that I know of.

You'll might not think it is such bargain when you see the price of the VFD alone.
https://www.amazon.com/dp/B07H5BRC9R/?tag=atomicindus08-20

 

[BenKlesc]

Here is the diagram.

 

[alfredeneuman]

Did you get a motor starter with that compressor?

 

[BenKlesc]

Did you get a motor starter with that compressor?

Doesn't look like it. No box.

 

[alfredeneuman]

https://www.amazon.com/dp/B07KS7WWYR/?tag=atomicindus08-20

EDIT: You'll also need a disconnect before the VFD if the breaker panel is not in sight and 50' or less.

 

[BenKlesc]

I'm probably not doing a VFD anymore, just a magnetic starter from Weg. I can find starters anywhere from $100-2000. Not sure why the prices are so drastically different.

 

[American Locomotive]

Prices vary based on amp, voltage and motor horsepower ratings. You will need a 15HP 230v rated motor starter.

35A @ 230v 3-phase is 60A 230v single phase. Add in the phase converter's power consumption, and you're probably looking at an 80-100A circuit just to run this compressor. Start-up current is going to be extremely high - close to 200A if not more.

 

[alfredeneuman]

I'm probably not doing a VFD anymore, just a magnetic starter from Weg.

A 3 phase motor won't even start on single phase supply

 

[Norcal]

A 3 phase motor won't even start on single phase supply

But it will hum on a single phase supply because it does not know the words.