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Solution Needed: Air Compressor

Aaron Venable

Plastic
Joined
Jan 31, 2012
Location
Texas
To not completely hijack the other recent compressor thread, I've started this one.


I have an IR T30 2545E10V with a Baldor 215T frame 10 HP motor 200/3/60 33A.

I've moved it from work and now need to power it with 1 PH service from my home shop.
GOPR0236.jpg


from similar thread...
I put a 4hp three-phase motor and a VFD on it... and reduced the drive ratio so that the motor would run the compressor slower at standard motor speed, then I increased the VFD's max frequency to about 100hz, and set the start ramp to bring it up to speed at a rate which doesn't put an incredible spike on the load.

By belting down a smaller motor, it took less motor torque to bring it up, and came up faster, with lower starting current. The pump runs at it's normal speed, just the motor's spinning faster... unloader works fine, and the lights don't dim when it ramps up... and it's QUIET.

I really like this idea for a dedicated setup, but I've got a few uncertainties about making it work for this compressor:

>For the drive, I've calculated a current ratio of 1.64:1. So at 1725rpm my compressor should be around 1054rpm. I've found a 5hp Baldor 184T 1725rpm motor locally that I'm interested in using. Assuming @ 90Hz this motor will produce roughly 2600rpm, and if I reduce the pulley size by a little over 30% I could maintain my 1000rpm at the compressor. During ramp up @30Hz the compressor would only produce 350rpm, and @60Hz 700rpm, etc.

Would this be a sufficient underdrive for the motor's hp?

> In the scenario above, I would need a 7.5" pulley for the 184T motor. Any thoughts or links on sourcing a pulley?

>I know there are many different technologies in VFD's now, and I'm not certain what would be adequate for this application. The ones I've found in this hp range are almost as much as a RPC, maybe I'm not looking in the right place?

I would like to use this setup so I could keep the 10hp motor to build a RPC at a later date, for multiple, light load motors.

Alternatively, I would keep the current motor and build a 20 hp RPC to run it from. Ugh...

Any help will be appreciated. Thanks

edit: I just ran across Maska's website for the "sheave" that I need, but if anyone knows an alternate source.....
 
I have a 10HP compressor at home running off of single phase power.

First off, forget the 5HP motor, I tried this, geared to where the 5HP motor was running at it's full load amps rating, it was not turning the compressor fast enough for the centrifigul unloader to close and start building pressure. Lubrication may also be a problem at that low of speed if you chose to modify the unloader.

Keep in mind even if you figure on running the 5HP motor at 90Hz, you will be running in constant horsepower above 60Hz and your torque will drop off........meaning you won't have enough HP to run it.

What I ended up doing: 10HP Baldor single phase motor, about 150 Amps inrush, about 46 full load amps, works great.

Your options,
1. 10HP single phase motor.
2. 7HP single phase motor, change pulleys for slower RPM, most 10HP compressors are rated with an RPM range to run with a 7-10 HP motor
3. Keep the 10HP 3 phase motor and run it with a heavy duty VFD, if you have trouble starting it , add a solenoid unloader valve and control it with one of the digital outputs that some drives have and set it up to remain open until the drive gets ramped up to speed. I am considering converting my compressor to this setup and setting it up to run at a slower 7HP speed except when I need the increased CFM.

A cheaper setup for a drive, is if you could find a 15KVA 480/240V transformer, and reverse it to step up your 240 to 480, then you could run a 480v 20HP rated 3 phase input VFD, which can be picked up relatively cheap on ebay, you would need the 20HP VFD rating to run a 10HP motor because you would be using a VFD that is rated for 3 phase input power and running it on single phase input power.

If you are wanting to use a homemade RPC for this you may want to consider a 30HP instead of a 20HP due to the high starting torque of the compressor, then you would also need a control to turn on the RPC, and then when it's up to speed, start the compressor

PJ Ritz


Your choices
 
Hi if this was mine id find a 7.5 hp 1ph motor to run it. My thought is that if this is your main compressor you have it on while your in your shop air at the ready and I dont like run rpc all the time only when i need it. For instance I have a 10 hp compressor that I plumed in to my shop 5hp compressor I run the 10 on the rpc when i need extra air for the blast cabinet. the other reason is a 7.5 1ph is alot easer to find $ surplus $ you will have to slow your pump down just abit but it will increase the life and lower the sound. if you look at good industial compressors/ older ones they used whats now days a pump one size bigger and slowed down like my 10hp IR with a 7100 pump now days thats ther 15 hp pump. Its cheaper for companys to put a smaller pump run it faster/hotter - less life and you having to buy another one from them
 
First, thanks for the advice

A few of my thoughts, I'm not very electrically inclined so please bear with me.

What I ended up doing: 10HP Baldor single phase motor, about 150 Amps inrush, about 46 full load amps, works great.

I initially looked into this option and despite the astronomical cost of the motor (for what it is), it is also my understanding that it will cause a large surge across my 200A service. I need this compressor to operate (on the shop panel) without disrupting any of the home utilities. Would this be a issue???

Your options,
2. 7HP single phase motor, change pulleys for slower RPM, most 10HP
Hi if this was mine id find a 7.5 hp 1ph motor to run it.

I wouldn't mind switching to this motor and re-gearing, as it seems like a happy medium. However this will be my main source of compressed air for a blast cabinet/sanders/painting and I will need large amounts of cfm at random times throughout my work day(weekends mainly). My only other compressor is very small portable 13gal job, so I won't have another to throw in for additional aid. It does seem less expensive than the 10hp 1ph motor, even with the new pulley and belt, but for the money spent, I'm not sure if I would be happy running at this level.

3. Keep the 10HP 3 phase motor and run it with a heavy duty VFD, if you have trouble starting it , add a solenoid unloader valve and control it with one of the digital outputs that some drives have and set it up to remain open until the drive gets ramped up to speed. I am considering converting my compressor to this setup and setting it up to run at a slower 7HP speed except when I need the increased CFM.

What would be considered "heavy duty"? I am definitely for being able to reduce output for normal use and increase when needed.

A cheaper setup for a drive, is if you could find a 15KVA 480/240V transformer, and reverse it to step up your 240 to 480, then you could run a 480v 20HP rated 3 phase input VFD, which can be picked up relatively cheap on ebay, you would need the 20HP VFD rating to run a 10HP motor because you would be using a VFD that is rated for 3 phase input power and running it on single phase input power.

photo6.jpg


I have access to this step-up transformer. Could it be used as is, with the 480v 20HP VFD? And is this the size/type VFD needed?
Electric Gear Motors | AC Parallel Motors | Leeson AC Controls Vector Series Drive VFD,NEMA 1,3PH,10HP,200/240V | B587889 - GlobalIndustrial.com

If you are wanting to use a homemade RPC for this you may want to consider a 30HP instead of a 20HP due to the high starting torque of the compressor, then you would also need a control to turn on the RPC, and then when it's up to speed, start the compressor

At this point, an RPC is almost out of my mind for the reason that I would have to build and run such a large RPC and wire in the needed switches for automatic operation of the compressor.

I know it's a long winded post, but thanks for the help.
 
What is all that chain doing on the compressor? A couple of years ago I rebuilt a 40 hp organ blower and had to get inside with a torch and hammer to beat out the chain dents. My Sheldon horizontal mill has similar dents on the belt guards. People who treat machinery that way don't deserve to have it.
Bill
 
I am not confident enough to comment on the transformer whose label you show, but I use single phase transformers to step up the input to the drives. Works great, you can find 20hp 480v drives very cheap used or quite reasonable NOS. You should have a 50 or 60 amp dedicated circuit to power a 10hp compressor with a vfd.
Rob
 
I looked this pump up its actualy rated for three motors. 5hp 500rpm 16cfm you need a 5.75 sheaveif motor is 17--rpm. 7.5hp 825 rpm 27cfm motor sheave 8.95 with 17-- motor again and 10hp 1050rpm 35cfm motor sheave 11.35 with 17-- motor. My personal thought is a good compressor should run in the 800rpm or less range witch make life alot better there not as noise dont get as hot wicth = last longer and make cooler air les moisture problems. I know there alot of ways of powering this but if it take a degree in elictrical enginering its probaly not worth it. A basic RPC can be easy to build or difilcult depends on the bells and wistles you want in it rop start it or fully automatic. Again though you have to have it runing while using air. So its back to single phase a 10 hp 1ph motor would be great not so easy to find and require lots of power and to buy new probaly more then you compressor is worth. That takes you back to a 7.5hp the best thing hear is you should be able to find a used/surplus one pretty easy and at a good price. I just bought a 7.5hp baldor at a local hardware store that brings in surplus stuff on the side they had 100 on it i oferd 75$ and got it brand new not a scatch in the paint. and with a 7.5 @ 27 cfm @175 psi you should make plenty air for blasting turn your regulator down to 100-125psi that will inturn give you a few more cfm as your air will last longer. I dont think ther much else you will do that eats air like blasting.
 
I forgot to say thi is based on you having 18" flywheel. The sheave sizes are what they show id just round then off 5.75 -6 ,9",11-11.5"and you should be fine hope this helps and im not just adding to the bla bla bla chains. Every ones got diferent ideas.
 
I looked this pump up its actualy rated for three motors. 5hp 500rpm 16cfm you need a 5.75 sheaveif motor is 17--rpm. 7.5hp 825 rpm 27cfm motor sheave 8.95 with 17-- motor again and 10hp 1050rpm 35cfm motor sheave 11.35 with 17-- motor. My personal thought is a good compressor should run in the 800rpm or less range witch make life alot better there not as noise dont get as hot wicth = last longer and make cooler air les moisture problems. I know there alot of ways of powering this but if it take a degree in elictrical enginering its probaly not worth it. A basic RPC can be easy to build or difilcult depends on the bells and wistles you want in it rop start it or fully automatic. Again though you have to have it runing while using air. So its back to single phase a 10 hp 1ph motor would be great not so easy to find and require lots of power and to buy new probaly more then you compressor is worth. That takes you back to a 7.5hp the best thing hear is you should be able to find a used/surplus one pretty easy and at a good price. I just bought a 7.5hp baldor at a local hardware store that brings in surplus stuff on the side they had 100 on it i oferd 75$ and got it brand new not a scatch in the paint. and with a 7.5 @ 27 cfm @175 psi you should make plenty air for blasting turn your regulator down to 100-125psi that will inturn give you a few more cfm as your air will last longer. I dont think ther much else you will do that eats air like blasting.

I forgot to say thi is based on you having 18" flywheel. The sheave sizes are what they show id just round then off 5.75 -6 ,9",11-11.5"and you should be fine hope this helps and im not just adding to the bla bla bla chains. Every ones got diferent ideas.

Thanks for the hp/sheave sizing, I haven't ran across anything like that for this pump. I called Ingersoll a month back and the conversation with the technician ended soon after the mention of swapping motors, as if he no longer knew anything about the pump. Yes, it is an 18" flywheel and thanks for the heads up on the OD's and ID's on the sheaves. You're right about the EE degree, the time involved figuring out these alternate methods of powering this pump isn't worth the compressed air it will produce. I'm just trying to utilize what I already have and/or obtain the fewest amount additional components.

I'll be on the lookout for a 7.5hp motor. I'd gladly purchase one for that deal you got!


definitely a good laugh at the chain comment, I won't elaborate as to their purpose, but I will post a picture of a couple of other items I have that I probably don't deserve. The real expensive stuff I keep inside the building!
photo1.jpg
 
Thats to funny looks like we shop at the same spots I have an atlas copco ga7 seting in my shop. My brother works at a coal mine and it was in ther emergecy vehical shop to mantian air for the air starter and brakes on the trucks. they got rid of it cause it dont auto restart after a power outage so it went to bid and buy. 17.00 later he bought me a awsome compressor for pennys. Down side its 10 hp plus with the ac cooler and it 480v. I have a 60a 1ph panel in my shop so im here working on my EE. he also gought me my 10hp IR came out of a drag line was used for operating the oil/grease pump and it was timed out off to bid and buy lol and yes Ir is a dead end. the plus side of Ir is type 30 pumps are supper easy to rebiuld if you need parts i found compressor parts store is the cheapest for the most part. But ill warn you if you open one of these pumps up you will be diapoint it at how simple and cheapy biult they are camparing to a qiuncy champion etc.
 
The concept in the original post is interesting. You need X horsepower to run a pump at the speed to get max air output. You are cheap, so you put on a smaller motor and a VFD. You start it slowly, then you overdrive the motor's frequency to get it to run fast enough to get the same air output.

Couple of big ass problems here! First, at e.g. 120Hz you aren't getting your rated horsepower out of your smaller motor, you're getting *maybe* half of it. You think half of a smaller motor's horsepower is sufficient to generate all the air you can pump with the full horsepower from a larger motor? Second, it sounds like you are planning to run this smaller motor nearly 100% of its life at 120 Hz (or whatever) - do you really think it's going to last that long run like that?

You don't get energy for nothing. I realize that cheap compressors without unloaders face large starting loads and thus have to oversize the motors somewhat. But I still don't like your concept and really doubt it will work out in the real world.

metalmagpie
 
Your location of "Texas" doesn't help the PracMach gang to look around on ebay and craigslist (using SearchTempest) to see what is out there as to good deals on VFDs or single phase motors.

I tend toward VFDs, but it's your money, and a good deal on a single phase might sway the decision.

HOWEVER, you will need to put that motor starter on the shelf and get a really large one for that single phase motor. So budget for a contactor capable of single phase operation in 5hp or 7.5hp or 10hp.... Start looking.

I would spend $800 -$1000 on a constant torque VFD, at least a 10hp vfd, and run it at 30hz, to generate 5 hp at 500 pump rpm, without changing the starter, without changing the pulley (watch out for groove centerlines), without buying new belts, etc.

You may find that a 25% derate of a 10hp VFD will allow you 45hz, and 750 pump rpm, and 7.5 hp.

This one is $780, for 10hp http://www.driveswarehouse.com/Drives/AC+Drives/Sensorless+Vector+VFD/WJ200-075LF.html

This one is $900, for 15hp
http://www.driveswarehouse.com/Drives/AC+Drives/Sensorless+Vector+VFD/WJ200-110LF.html

When you consider derating a VFD, you are entering "Contact the factory" territory, so do your homework.
 
Thats to funny looks like we shop at the same spots I have an atlas copco ga7 seting in my shop. My brother works at a coal mine and it was in ther emergecy vehical shop to mantian air for the air starter and brakes on the trucks. they got rid of it cause it dont auto restart after a power outage so it went to bid and buy. 17.00 later he bought me a awsome compressor for pennys. Down side its 10 hp plus with the ac cooler and it 480v. I have a 60a 1ph panel in my shop so im here working on my EE. he also gought me my 10hp IR came out of a drag line was used for operating the oil/grease pump and it was timed out off to bid and buy lol and yes Ir is a dead end. the plus side of Ir is type 30 pumps are supper easy to rebiuld if you need parts i found compressor parts store is the cheapest for the most part. But ill warn you if you open one of these pumps up you will be diapoint it at how simple and cheapy biult they are camparing to a qiuncy champion etc.

I haven't had time to go to many auctions. Bought those two brand new about four years ago, at only a small discount. Yes, quincy makes a nice compressor. We still have a recip. quincy, 35hp model that has ran almost constantly since 2006 with only one rebuild.

The concept in the original post is interesting. You need X horsepower to run a pump at the speed to get max air output. You are cheap, so you put on a smaller motor and a VFD. You start it slowly, then you overdrive the motor's frequency to get it to run fast enough to get the same air output.

Couple of big ass problems here! First, at e.g. 120Hz you aren't getting your rated horsepower out of your smaller motor, you're getting *maybe* half of it. You think half of a smaller motor's horsepower is sufficient to generate all the air you can pump with the full horsepower from a larger motor? Second, it sounds like you are planning to run this smaller motor nearly 100% of its life at 120 Hz (or whatever) - do you really think it's going to last that long run like that?

You don't get energy for nothing. I realize that cheap compressors without unloaders face large starting loads and thus have to oversize the motors somewhat. But I still don't like your concept and really doubt it will work out in the real world.

metalmagpie

meatgalpie,

I wouldn't call it my concept. I quoted board member Dave Kamp, from this thread http://www.practicalmachinist.com/v...erters-vfd/air-comp-rpc-advice-wanted-240592/

I could have taken that out of context, but I'm fairly certain that he had my application in mind also. You should contact him and tell him your feelings on the matter.

Your location of "Texas" doesn't help the PracMach gang to look around on ebay and craigslist (using SearchTempest) to see what is out there as to good deals on VFDs or single phase motors.

I tend toward VFDs, but it's your money, and a good deal on a single phase might sway the decision.

HOWEVER, you will need to put that motor starter on the shelf and get a really large one for that single phase motor. So budget for a contactor capable of single phase operation in 5hp or 7.5hp or 10hp.... Start looking.

I would spend $800 -$1000 on a constant torque VFD, at least a 10hp vfd, and run it at 30hz, to generate 5 hp at 500 pump rpm, without changing the starter, without changing the pulley (watch out for groove centerlines), without buying new belts, etc.

You may find that a 25% derate of a 10hp VFD will allow you 45hz, and 750 pump rpm, and 7.5 hp.

This one is $780, for 10hp http://www.driveswarehouse.com/Drives/AC+Drives/Sensorless+Vector+VFD/WJ200-075LF.html

This one is $900, for 15hp
http://www.driveswarehouse.com/Drives/AC+Drives/Sensorless+Vector+VFD/WJ200-110LF.html

When you consider derating a VFD, you are entering "Contact the factory" territory, so do your homework.

Plenty of useful information, thank you.

Knowing that my current starter would not work, I've been waiting to hear back from my compressor rebuilder to see if he could round me up a used motor and starter. His price for me would likely consist of lunch.This could be that "good single phase deal." And make the belt/pulley issue a little more bearable.

Thanks for the links on the VFD's. In derating them, I stumbled across the general rule that "The VFD input current must be equal to or greater than the Motor Current Rating * 1.73" My baldor is rated at 33A and using this yields input current of 57A. Which is exactly the input current of the 15hp VFD in the link.

I haven't done my homework on types of VFD's yet and as a consequence I do not know the required type for my application, be it Volts per Hertz (V/Hz), closed-loop vector, or open-loop vector (Sensor-less Vector). Both links you posted lead to sensor-less vector VFD's, I'll assume for now these are fine for my application.

I'm located in the Dallas/Fort Worth area.

I would appreciate any insight you have to offer,

Thanks
 








 
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