7.5 HP compressor on single phase?

[DanielVetpath]

I looked at a used IR T30 compressor today with bad 10 HP motor, 120 gallon tank. The seller will replace the bad motor with a new 7.5 hp motor. My question is whether I can run a 7.5 hp electric motor with my single phase service in my shop? It would be a single phase motor. Just don't know if it is practical. He said it would take a 70 amp breaker to run it based on start up load. Any advice? thanks

 

[Charles (in GA)]

A 7.5 hp motor will draw about 32-33 amps running. I have a Husky/Campbell-Hausfeld 7.5hp two stage/80 gal, and am running it on a 50 amp breaker. It really could be run on a 40 but on dedicated motor circuits, you are allowed to upsize the breaker if necessary to keep the breaker from tripping on startup. I have mine wired with #6 copper, which is also overkill, #8 would have worked but I ran it to a subpanel at the compressor thinking I might want to run other circuits off of it, which I never did. The subpanel is supplied with a 60 amp breaker, the short run from the sub to the compressor is supplied with the 50 amp.

Charles

 

[larry_g]

http://www.engineeringtoolbox.com/electrical-motor-hp-amps-d_1455.html

With a 70 amp breaker are you planning to run this on 120 volts?

Other things to look at are pressure cutout and pump speed. Going to a lower hp motor will require a change to the pulley ratio and/or the max pressure you set the cutout at. Assuming that the setup on there is correct and set up for 10hp motor then with the 7.5 hp motor you will have to change the pulley to 75% of what it is now or lower the cutout pressure to 75% of what max is now. To check all this you need to monitor that the motor current does not exceed the FLA rating while at cutoff. You can excees the FLA for a short time at cutoff but not to much or your starting to reduce the life of the motor.


lg
no neat sig line

 

[DanielVetpath]

Thanks for the replies so far. It is being sold by a local electric motor shop that also sells and repairs compressors. He said he would be putting on a smaller pulley and reducing the maximum pressure (down from 175 psi, I believe). I intend to run it on a 220 circuit using 6 ga wire, located within about 10 feet of my load panel. Will it dim the lights every time it kicks on? I have never owned a piece of machinery with an electric motor anything this big before! I don't know what to expect. The compressor currently has an air cooler (looks like a radiator) and low oil shut off. Any ideas what I might expect to pay for something like this in good used condition with a new motor? Thanks.

 

[79firebird]

Yup will work. at work we have a 200 amp panle that runs our 10hp compressor 50 amp braker and our 5hp with a 30 amp and never had a prob.

 

[Mmfh]

Thanks for the replies so far. It is being sold by a local electric motor shop that also sells and repairs compressors. He said he would be putting on a smaller pulley and reducing the maximum pressure (down from 175 psi, I believe). I intend to run it on a 220 circuit using 6 ga wire, located within about 10 feet of my load panel. Will it dim the lights every time it kicks on? I have never owned a piece of machinery with an electric motor anything this big before! I don't know what to expect. The compressor currently has an air cooler (looks like a radiator) and low oil shut off. Any ideas what I might expect to pay for something like this in good used condition with a new motor? Thanks.

I have that exact compressor, its about a year old. I bought mine with a pump that had a rattle noise for $400. Now a days I watch Craigslist and compressor of that size don't sell very fast, if at all. I've seen the even bigger ones sit there for sale and never sell as far as I can tell.

Just sold a 7.5hp, 80 gallon, vertical for $800. This thing was like brand new although it was several years old. It was the gray color, now they are that cream color, and have the black pump and motor. If you have the one I think you have the number on the pump will be a 2545, that's the one I have.

The one I just sold was the 2475. Like I said I got $800 for that and it took a while to get it.

You can buy that 2545 new now for about $1800 if you look around. Not long ago they were 3k plus.

I would think if they were going to set it up for you with the correct pulleys and a single phase 7.5 you would want to pay around the $800 to $1000.

Is it the gray one or the cream colored one?

If you do buy it, I would like to know what size pulleys they put on as I want to change mine to a 7.5 single phase as well.

Mm

 

[Mmfh]

A 7.5 hp motor will draw about 32-33 amps running. I have a Husky/Campbell-Hausfeld 7.5hp two stage/80 gal, and am running it on a 50 amp breaker. It really could be run on a 40 but on dedicated motor circuits, you are allowed to upsize the breaker if necessary to keep the breaker from tripping on startup. I have mine wired with #6 copper, which is also overkill, #8 would have worked but I ran it to a subpanel at the compressor thinking I might want to run other circuits off of it, which I never did. The subpanel is supplied with a 60 amp breaker, the short run from the sub to the compressor is supplied with the 50 amp.

Charles

That's a interesting stand you have your compressor sitting on, did you make that? Does it help with keeping it a little quieter? Better for the welds on the tank?

Mm

 

[DanielVetpath]

The compressor is gray. He is thinking 1700 including new 7.5 hp single phase motor, appropriately sized pulley and new belts. Estimated 23.2 cfm output.

 

[rlitman]

My 7.5HP compressor is running on single phase, and runs fine on a 30A breaker.
Never had it trip, BUT I have 6 gauge wire feeding it.

 

[Charles (in GA)]

He said he would be putting on a smaller pulley and reducing the maximum pressure (down from 175 psi, I believe). I intend to run it on a 220 circuit using 6 ga wire, located within about 10 feet of my load panel. Will it dim the lights every time it kicks on?

He will need to reduce the pulley size due to the smaller motor, but there is no need to reduce the pressure. A two stage has a high (shut off) pressure of 175 and a low (kick in) pressure of 145 in most cases. You really don't want to change this, there is no reason to. This is the purpose of a two stage is to cram more molecules of air (ie. more standard cubic feet) into that tank, so it provides you with air for a longer period of time between cycles (assuming you regulate it to 100-110 psi. Turning down the pressure defeats the purpose of having a two stage in the first place. If the motor pulley is sized properly, the motor will be quite capable of pumping up to the full 175, its just that it will take longer than it would have with the 10 hp motor.

I think $1700 or so for this compressor is way too much. Indeed, it is more than the usual compressor, having a 120 gal tank, and the larger pump, but if you really don't need it, its not worth paying for.

That's a interesting stand you have your compressor sitting on, did you make that? Does it help with keeping it a little quieter? Better for the welds on the tank?

Mm

I made this stand when I got the compressor. On three legs, they are not the most stable thing, and I wasn't about to be redneck enough to leave it on the pallet, and did not want to anchor it to the floor, so this gives it stability, I have the ability to move it if needed, and I can level it. It probably helps with the noise, in a very minor way, but the intake system of the pump is where the noise is at.

Charles

 

[Mmfh]

The compressor is gray. He is thinking 1700 including new 7.5 hp single phase motor, appropriately sized pulley and new belts. Estimated 23.2 cfm output.

I would keep looking if I was you. Remember its a buyers market right now and a lot of times you can name your own price.

If you have a price you are comfortable with, offer it. If he says no, leave your number and go home. When he is having trouble making payroll, he can always get some quick cash by calling you about the compressor.

I don't think I would give anymore than $1k. If the original motor smoked, I would wonder how much longer the pump is going to last. Its been my experience that the pump always goes first. Just keep that in mind.

You say it will put out 23 cfm, with the 10 hp as it was originally setup it does 35cfm. I need 35 cfm for my blast cabinet but if you don't need that much for sure go smaller.

Mm

 

[DZL JIM]

I had to get a new Baldor 10 hp single phase motor for my compressor and I found the place on eBay, they are up in the northeast. WECO company or something. Anyway, I think it was around $750 shipped to my door. It's a lot of $$$ but it's a lot of motor. I wouldn't downsize the motor, if it had 10 hp, stay with a 10 hp. The 10 hp motor should have the same shaft size (mine did) just swap the pulleys, no need to change pulley size unless you really want less hp motor.

Yes, lights will dim on start-up. It's a lot of juice to get going, you just get used to it. I don't worry so much about the lights dimming as I do the locomotive sound that jumps out of nowhere when it fires up.

 

[Mmfh]

That Locomotive sound that jumps out of no where when it starts! I know exactly what your talking about with that one! What kind of compressor do you have? What type of air filter do you have?

What I did on mine that seemed to really help. I took a old marine flame arrestor. Its a marine air filter made of metal that you see on open engine boats, jet boats and the like. Its small in diameter, about 6" or so and about 3" tall. I put that on the intake, over that I put a air cleaner assembly off a early chev PU with a 350 4 barrel. When you look at it you see the old air cleaner with the snorkel sticking out from it.

I bet it at least cut the noise in half! Before I did that, if you were standing near it when it started it would almost make you poop your pants. That's a exaggeration but you know what I mean.

Also, that 10 hp single phase motor you have, that thing must be a monster! I bet shipping for that was almost as much as the motor itself. What size breaker can you get away with running that big motor?

Mm

 

[Charles (in GA)]

According to NEC 430.248, the Full Load Current for a 10 hp single phase motor is 50 amps. for a 7-1/2 hp motor it is 40 amps. I find these numbers to be high, for example, the FLC for my 7-1/2 hp Emerson on my compressor is 33 amps If I recall correctly. A 10 hp would probably need to be breakered at 70 amps to keep the breaker from tripping on startup.

Charles

 

[DanielVetpath]

Thanks for the continued input Charles, et al. I am waiting to see what he exactly comes up with. More than I could pay, I know. But for me, it is a local small business that would help me keep it running, etc. Shipping would not be a factor and, to tell the truth, it just felt good to be in his shop and to have such personalized service. He dug out a key for the back storage shed and led me through a darkened room full of sleeping giants (enormous lathe, Bridgeport mill, etc) to look at this compressor. I admit, I am a sucker for anything that feels authentic these days. Been through the large online auction site routine and paid my dues there! Box stores? Got bunches of them. But the real McCoy, chain smoking, hobby race car driving man that has served businesses in an old railroad town in west-central Pennsylvania? Worth the price of admission and satisfaction that every time that beast kicked on I would have some kind of connection to a real person in a real place and not just another machine shipped to a North American port in a big metal box. Call me crazy, but that's my take on life in a part of this fine union that is having to face some troubling news this week.

 

[DZL JIM]

That Locomotive sound that jumps out of no where when it starts! I know exactly what your talking about with that one! What kind of compressor do you have? What type of air filter do you have?

What I did on mine that seemed to really help. I took a old marine flame arrestor. Its a marine air filter made of metal that you see on open engine boats, jet boats and the like. Its small in diameter, about 6" or so and about 3" tall. I put that on the intake, over that I put a air cleaner assembly off a early chev PU with a 350 4 barrel. When you look at it you see the old air cleaner with the snorkel sticking out from it.

I bet it at least cut the noise in half! Before I did that, if you were standing near it when it started it would almost make you poop your pants. That's a exaggeration but you know what I mean.

Also, that 10 hp single phase motor you have, that thing must be a monster! I bet shipping for that was almost as much as the motor itself. What size breaker can you get away with running that big motor?

Mm

Not sure on the make, it's 3 head from an old car dealership, about 40 cfm. I was told it's probably more so I think it's a concervative #.

Air filters are 2 - 6" round, about 2" thick. They look like small 350 Chevy air filters.
I will be moving it to a new part of the shop, set on thick rubber pads up on pallet racking and plan to pipe the intake into the attic, if it's possible.

I use a 60 amp breaker, just to make sure it won't pop on start-up. Plus, I think I had an extra 60 when I hooked it up...

No idea on shipping the motor, pretty sure they covered it. I have purchased 3 or 4 motors from them, always a great price shipped to my door. Local motor supplier is double the cost even when you figure shipping.