Rotary Phase Converters, VFD, Compressor ????

[ColoradoDoug]

Okay, I'm trying to learn and have searched this forum as well as researched some elsewhere. Seems the more I think I'm learning the less I know . BUT, the more opinions there are out there about all of the options. To make this brief, I am constantly adding to my garage toys as time goes by. I have single phase power to my house/garage, but I have, and want more toys that seem to be offered more in 3 phase configuration. I'd like to plan this so it's done right, ONCE. I have a Quincy QR-25 5hp compressor that I recently purchased and it's 3 phase. I would assume I need to get a rotary phase converter, or digital/electronic converter (also called VFD?) strictly for the compressor. I figured as I get more things, I can get another converter for the other items. For now though, what is the best way to run this compressor? Who has the true knowledge that can help me? Because the compressor turns on and off as the demand is needed, what is the best way to go about doing this so as not to damage either the compressor, the converter, my wallet or my breaker box?

Thanks

 

[rsanter]

Re: Rotary Pase Converters, VFD, Compressor ????

If you search the net some people that have several pieces of 3ph equipment in their garage will have a single RPC and have it power all the equipment by running a separate circuit around the garage for the 3ph.
If you are alone and will only be using one machine at a time this could work good for you.
I have also seen where people will buy one VFD, mount it to the wall and have it connected to 2 or 3 machines. Again the plan is that they use one at a time so while this is not to code it will work great as long as the HP ratings of each motor is close or at least within the intended range of the VFD.
Before I had a VFD I used to have a static converter on my 3hp Lathe, and then I had the 1hp mill connected to the motor of the lathe so that when I wanted to use the mill I would disengage the gears and run the lathe in idle so it acted like it was a rotary phase converter so I would have full power on the 1hp mill

Now days ideal would benthat you have a VFD on each machine and each have a separate breaker in a sub panel you dedicate to your machines

Bob

 

[ColoradoDoug]

Other than the compressor, I plan to use one converter. My question is more about the best converter to run with a compressor that will cycle on and off. Will the motor
of the converter always be running or could it be setup to come on just before the compressor would kick on? Again, with regards to the compressor, is a VFD better than a rotory converter? I need schooled still.

 

[jayrush13]

Why not just get a single phase motor ?

 

[geardoc]

Why not just get a single phase motor ?

For many applications it is not practical. IE: different frame, different shaft size or length.

A good rotary phase converter can be built for well under $200. You then get a smoother running, longer lasting 3phase more.

A 3 to 5 hp single phase is quite expensive. And, as I said above you may play hell trying to get one that uses the same type frame, same mounting, same shaft size and length.

 

[firebox40dash5]

For many applications it is not practical. IE: different frame, different shaft size or length.

A good rotary phase converter can be built for well under $200. You then get a smoother running, longer lasting 3phase more.

A 3 to 5 hp single phase is quite expensive. And, as I said above you may play hell trying to get one that uses the same type frame, same mounting, same shaft size and length.

I wouldn't *think* it would be too hard to match frame and shaft on a large compressor. I swapped the motor on the old Speedaire at work, there were many choices in the right frame size (186 or something IIRC) and basically, the right shaft size was part of the frame size spec.

We ended up getting a steal on an old finned aluminum GE 5hp motor for $100, with greasable shaft bearings. Worst part of it was finding the right heater coils for the contactor we used, which came with the compressor and had coils for the lower-amp 3PH motor. I think just the coils cost almost $100, and were pretty hard to find for the old Cutler Hammer switch/contactor.

I personally wouldn't want to run a rotary for a compressor at home, or obviously even in a shop. Wouldn't it either be running anytime the compressor is powered (not necessarily running, but on) or require rigging some way to turn it on with the pressure switch, but ahead of the comp. motor?

 

[Griff93]

I have a 5 hp IR T30 that was three phase and is now single phase. The PO did this swap.

You could run a RPC triggered to come one with a relay from the pressure switch. You would then have to run a time delay relay for the compressor motor itself to give the rpc time to spin up. RPC are not that hard to build. We have made four of them. I recently got a VFD for my mill due to wanting to vary the speeds. A side benefit is it's very quite when the mill isn't running now. For things like mills where you will be spending quite a bit of time doing setup work, it's nice not to listen to the humming RPC motor.

 

[RCStocker]

It will be cheaper to change out the motor. With a converter you will loose a third of your HP. There are many ways to go and you can even build your own form larger motors.
In the end why bother on a compressor when a motor is so easy to swap out and much cheaper than a converter. Just my 3 cents worth

 

[jayrush13]

For many applications it is not practical. IE: different frame, different shaft size or length.

A good rotary phase converter can be built for well under $200. You then get a smoother running, longer lasting 3phase more.

A 3 to 5 hp single phase is quite expensive. And, as I said above you may play hell trying to get one that uses the same type frame, same mounting, same shaft size and length.

It's funny how some people expect someone to be able to build a phase converter. But think they couldn't possibly figure out how to adapt a different frame size or shaft length motor ? I am a maintenance electrician by trade and have switched out motors for non matching motors before. Sometimes it's a pain but most of the time maybe redrill some holes and maybe a different sheave.

On a machine that would run constantly like a lathe or mill I wouldn't bother but a compressor that will cycle on and off I would not use a converter or VFD just my professional opinion

 

[2mJps]

Phase converters are very easy to build. I got a book for less than 10.00 and have built 3. But i would never run a compresser of one unless it was temporery.

 

[ColoradoDoug]

Phase converters are very easy to build. I got a book for less than 10.00 and have built 3. But i would never run a compresser of one unless it was temporery.

Why? Please explain.


I would rather keep the 3 phase motor and have a dedicated converter (which ever type) for the compressor. I'm just trying to figure out exactly which type would work best for a compressor, and how to wire everything up. When I acquire some of the other 3 phase toys, I plan to run them off of one converter separate from the compressor. Additionally, IF I wanted to go the single phase route, this is a 5 hp 3 phase motor now, what would be able to compare in a single phase motor and be fine with my breaker box?

 

[ColoradoDoug]

Is there anyone that is currently running a compressor on a converter of some sort? What is you experience with the setup and what would you recommend after using it.

Thanks

 

[jayrush13]

Why? Please explain.


I would rather keep the 3 phase motor and have a dedicated converter (which ever type) for the compressor. I'm just trying to figure out exactly which type would work best for a compressor, and how to wire everything up. When I acquire some of the other 3 phase toys, I plan to run them off of one converter separate from the compressor. Additionally, IF I wanted to go the single phase route, this is a 5 hp 3 phase motor now, what would be able to compare in a single phase motor and be fine with my breaker box?

Hp is Hp wheather it is 3ph or single phase so a regular 5 hp motor preferably the same frame size and shaft length and dia would work. But differences in motor frame and shaft size can be overcome with modifying the mount or different sheaves

 

[jayrush13]

Why? Please explain.

As far as why not to run a compressor on a converter

Just to be clear i have never used a rotary phase converter but have used VFD drives that will convert 1ph to 3ph Most of what i deal with has 3ph so its not an issue

When you talk about a Electric motor the hardest part on them is the starting. Especially under load like an air compressor would be. So the constant cycling on and off you would either need the converter turning on and off with the compressor or on constantly when ever you wanted the compressor running

And as far as my understanding of phase converters very few run at full hp maybe rotary ones but i have no experience with them so you wouldn't be getting your full potential out of your compressor. It would be like trying to start a V6 car on 4cyl in gear and get it going

 

[SVE Performance]

Moved my shop from a building with 3ph to one without .Talked to the people who make VFD's and was told a compressor was a poor application for a VFD. Ended up changing the 5 hp 3ph for a 5hp single ph compressor duty Baldor motor for $250 .That was 3 years ago compressor runs all day every day with no problems .Bill

 

[RPH]

A compressor is a huge start up load. Both converter types will have to be oversized to carry the start up load. I vote for motor change. In the end it will be the simplest.

 

[2mJps]

The best reason is because it will come on by its self and every other motor is going to come on when you turn it on and it will be starting under a very big load. THINK about it do you want to trust a motor to come on and of under a load with maybe less than 100% power. I am sure you have better things to do than baby set a compresser. Get a motor for it and build a rotary converter to run other stuff from. This is what i did and i dont worry about what my compresser is upto.

 

[930dreamer]

Is there anyone that is currently running a compressor on a converter of some sort? What is you experience with the setup and what would you recommend after using it.

Thanks

I run my Champion 5 hp three phase compressor from a 10 hp rotary phase converter (RPC). Zero issues! If you need any help post or PM.

I'll travel for Fargo's Pizza!

 

[garboui]

A compressor is a huge start up load. Both converter types will have to be oversized to carry the start up load. I vote for motor change. In the end it will be the simplest.

This is one good argument for a VFD. Most of not all will have programmable ramp up/down (speed) rates and current limits. This will allow the compressor top come up to speed a little slower but with hardly the start up current draw. This will both make the load on your panel better (esp if already heavily loaded) and lessen the amount of heat and stress generated in the motor.

Most VFD's will have digital I/O That can be driven from a signal sourced from the pressure switch relay. In your case only one input would be needed, the 'Go(enable)' one. the rest of the inputs, speed, direction, etc., can be permanently set. Inexpensive VFD's can be had from places like automationdirect.com .

 

[cnc-me]

Your best bet is to swap the motor for a single phase.
A rotary converter is going to have to run, when the compressor is in standby mode and
will probably consume at least 500 watts idling.
As much as I like VFD's I don't think this would be a good application for one.
Just swap motors you won't be sorry, besides you could use the old compressor
motor to make a convertor for your other equipment.

 

[ColoradoDoug]

I will admit, my electrical abilities are very limited. IF I swap my 5 hp 3 ph. for a 5 hp single ph. motor, do I use the same electrical box next to the motor? I also know there are a couple different type single ph. motors? I know to match frame size, shaft size, etc, but what do I need to look for (mag starter, or not)? Can I get the info off of the 3 ph. ID plate? I starting to lean toward swapping motors, I just need to figure out how exactly to do it. I won't be running this compressor non stop as it's only in my garage, not a fulltime shop and I don't want to leave a converter on all of the time. I also want to be able to allow my kids to use it for bike tires when I'm not around.