Oversized Air Compressor

[Gaunt596]

I come seeking some guidance.

A few months ago i jumped on a deal for a 120 gallon, 10hp, 3 phase air compressor, along with a matching 120v air dryer. My shop does not have 3 phase electric, but does have single phase 200 amp service. i knew going in id have to replace the motor with a single phase unit, but i grossly underestimated the availability and cost of a 10hp single phase motor. The other idea i had was to simply derate the compressor using a 7.5hp single phase motor, however im having an extremely hard time locating any sort of documentation for the compressor pump, in order to figure out RPM and pressure limits based on the motor size. I took some time today to get pictures of all the data plates on it i could find. Im hoping this lets someone smarter than me figure out what all pump i have on this thing. I understand that the best bet with this kinda thing is to sell the compressor and buy a single phase unit, but a compressor this size isn't worth anything other than scrap in my area, and at the price i paid for these, even with i end up replacing both the pump and motor, im still coming out ahead.

 

[Sleeper]

Post some pictures of the whole pump body and then maybe someone will be able to recognize what you’ve got.

 

[MacMcMacmac]

By the numbers it looks like a Champion R30 10hp V4.

https://www.pacificaircompressors.c...bricated-compressor-pump-with-head-unloaders/

Rated 7.5 to 15hp. RPM range 575 to 1045.

Should last forever at 575rpm.

Serial number plate is a dead giveaway for a Champion.

 

[mille755]

You might see if you can find a used 15hp -20hp vfd on ebay. May be less expensive than a good motor.

 

[The Cobbler]

setting your upper pressure limit lower will enable a less HP motor too.
there's a handy calculator here to help with figuring out rpms etc https://www.blocklayer.com/pulley-belteng.aspx

 

[Lucid Moments]

I may be speaking out of ignorance here, and if I am please feel free to correct me. I learn a lot that way.

The way I see it the only numbers that are really vital here are the pump RPM of 740 and possibly the motor frame size.

Since you are going from 10hp down to 7.5 figure you need to slow the pump down to 75% of its rated speed which puts you at 555 rpm pump speed. Buy a motor the same frame size as the original and calculate the size pulley you need to drive the pump at around 555 rpm based on whatever motor RPM you select.

The pump's internal compression won't change so I don't see why you have to change the pressure setting at all. It will just take longer to get there. Of course if you do lower the pressure then the pump (and motor) won't have to work as long which should extend their life, plus cut down on your headaches from listening to the pump run forever. Not that it should be that loud going that slow.

 

[Gaunt596]

By the numbers it looks like a Champion R30 10hp V4.

Rated 7.5 to 15hp. RPM range 575 to 1045.

Should last forever at 575rpm.

Serial number plate is a dead giveaway for a Champion.

You sir a gentleman and a scholar, as that looks pretty darn close to what i have. and that seems like the path id like to go down, as 7.5 HP running at 575 would still move a ton more air than the little oil less 30 gallon that ive been using in the meantime. just to double check, and for prosperity, heres the pictures of the actual compressor. pardon the clutter, theres a lot of projects all running at once right now.

 

[Gaunt596]

You might see if you can find a used 15hp -20hp vfd on ebay. May be less expensive than a good motor.

I looked into that, a VFD of that size is right around $3500, and they all say they derate when used with a single phase feed. just buying a 10hp single phase would be less expensive, but thanks to the above, i dont need to go that route.

I may be speaking out of ignorance here, and if I am please feel free to correct me. I learn a lot that way.

The way I see it the only numbers that are really vital here are the pump RPM of 740 and possibly the motor frame size.

Since you are going from 10hp down to 7.5 figure you need to slow the pump down to 75% of its rated speed which puts you at 555 rpm pump speed. Buy a motor the same frame size as the original and calculate the size pulley you need to drive the pump at around 555 rpm based on whatever motor RPM you select.

The pump's internal compression won't change so I don't see why you have to change the pressure setting at all. It will just take longer to get there. Of course if you do lower the pressure then the pump (and motor) won't have to work as long which should extend their life, plus cut down on your headaches from listening to the pump run forever. Not that it should be that loud going that slow.

based on the pump charts, your pretty close to right. specs for a 7.5 motor give you an option of either 575 pump RPM with 175PSI limit, or a 670 pump RPM with a 125 PSI limit. since mines already setup for the 175, ill most likely be going with the 575 RPM option. Noise wouldnt be an issue either way, since i have an external enclosure for this to live in, but i suspect your correct in that it should be quite a bit quieter. we shall see once i get it fixed up and wired in.

 

[larry_g]

based on the pump charts, your pretty close to right. specs for a 7.5 motor give you an option of either 575 pump RPM with 175PSI limit, or a 670 pump RPM with a 125 PSI limit. since mines already setup for the 175, ill most likely be going with the 575 RPM option.

I agree with the above. Once you get things going then monitor the motor current. If it is close to overcurrenting at cutout pressure then you can back off the cutout pressure. Me personally I back off the cutout to 155-160 psi as a matter of course. It takes near exponentially more power to raise the pressure each increment.

lg
no neat sig line

 

[u3b3rg33k]

a 10hp phase converter drive can be had for $1200. no need to spend 3x that.

 

[matt_i]

a 10hp phase converter drive can be had for $1200. no need to spend 3x that.

I agree on cost but its still flushing $1200 to then start fresh on a new solution as its going to be derated because of single phase input and thus unsuitable for use.

The easiest calculation to make given the switch from 10hp to 7.5hp is to measure the OD of the motor's sheave and multiply by 0.75 and select a new one closest but not over to the reduced OD.

The fan-sheave could also be reduced but those are typically larger, have the fan blades cast into them and are generally rarer and more expensive. Wheres taperlock sheaves for motors are relatively plentiful.

Some good reading is a Martin Sprocket catalog, it has a load of information on sprockets and gears not needed for this project and eventually one gets to ho-hum sheaves. But its all in there. A person can buy those NOS or buy new from places like Motion Industries.

 

[u3b3rg33k]

the phase converter drives do not need de-rating. they are already designed for single phase operation.

they also allow you to set an acceleration rate, so you can keep it close to nameplate running amp draw on startup. certainly lower than an equivalent 5hp compressor motor, with a 120+ amp locked rotor nameplate.

reducing the size of the pump sheave will increase pump speed, that seems counter productive.

 

[MacMcMacmac]

Ok, so it's not quite an R30, since it has reed valve heads by the look of it, but I'd be surprised if the bore and stroke are different. It's definitely something Champion built, probably an earlier cheaper line for Grainger to sell as a Speedaire or Dayton. I'd do some measuring of the pulleys and calculate the current running rpm with the motor it has to see if it works out to be the same as the rpm specs for the R30. I'm confident there is little difference, but I wouldn't want to send you off with incorrect info. It should be a very good unit for you if it is in good shape.

 

[strutaeng]

I have a homemade air compressor with a Curtis ES-100 (I think.) I found a 10HP electric motor, but reduced the pump rpm because only needed about 7.5 HP worth of air. It spins around 550RPM if I recall. It's still way too much for what I need. I only fire it up when the HVLP/RP spray guns come out.

I checked amp draw and I think it's just a bit more than 30A at shutoff, maybe 32A? Can't remember. It's a single stage pump and have it set to like 115-125 psi. Change your heaters on the magnetic starter accordingly.

I actually bought a pair of these pumps for like $450. I sold the other one for about that much. It has the disc valves.

 

[mike93lx]

Is this residential? I would check with your Poco on how big of a motor you are allowed to run. Some limit it to 5hp, some 7.5hp. Either way, a 10hp motor is probably not going to fly

 

[ekimneirbo]

Probably your best bet is to just bite the bullet and buy a 10hp 1725 rpm motor off ebay.
I say that for several reasons since I have converted some compressors already. You get into lots of other things when you run a phase converter. I made my own phase converter for a milling machine Its worked fine for 30 years. It took a little work and was cheap.....but the thing is that I don't leave my mill on for hours like I would with a compressor. The converter would need to be shut off to keep from consuming electricity when the compressor is pumped up, or if you turn it off, then the compressor doesn't automatically kick on. Not a good choice for a compressor.
Withe the electric motor change, you need 1725 (appx) rpm, not 3450. The 1725 is more expensive but thats the way to go. They have Weg 10 HP on Ebay for about $750. Try to get one that has the same size shaft as your 3 phase so you can use the same pulley. Pulleys can be expensive and hard to find the right one. I believe you can use the same "starter" if you disconnect the extra 3 phase wire but I am not sure about that. They also can get expensive but you have to have one. Look at it this way, if you bite the bullet and do it right you will always have a really good setup. If you try to save too much money it usually bites you later.

 

[ekimneirbo]

Is this residential? I would check with your Poco on how big of a motor you are allowed to run. Some limit it to 5hp, some 7.5hp. Either way, a 10hp motor is probably not going to fly



As long as the service coming to the building has a sufficient rating there shouldn't be any issue with the power company. I don't think they care what you run, they just hope you use a lot of their electricity. The question in my mind would be if your home/shop has a full 200 amp service coming to it. Many shops tap off the homes panel and may not have the full 200 going to the shop. There are ways to get the full 200 from the home panel if needed. Even so, the 10hp isn't going to need all of that, its just nice to have the extra power for other tools besides the compressor.

 

[mike93lx]

Is this residential? I would check with your Poco on how big of a motor you are allowed to run. Some limit it to 5hp, some 7.5hp. Either way, a 10hp motor is probably not going to fly



As long as the service coming to the building has a sufficient rating there shouldn't be any issue with the power company. I don't think they care what you run, they just hope you use a lot of their electricity. The question in my mind would be if your home/shop has a full 200 amp service coming to it. Many shops tap off the homes panel and may not have the full 200 going to the shop. There are ways to get the full 200 from the home panel if needed. Even so, the 10hp isn't going to need all of that, its just nice to have the extra power for other tools besides the compressor.

That isn't true at all in residential. 10hp is beyond the capacity of most services and transformers as the startup loads are massive. Way beyond 200a

 

[The Tool Tyrant]

MacMcMacmac is hot on the trail...


The 'RV' in the model number gave it away. Looks to be the RV-30 pump.

Specs for 7.5 HP show 628 RPM for125 PSI and 570 RPM for 175 PSI

Driven Sheave: 18.875Ø 570 RPM ÷ 1725 RPM = .330 X 18.875 = 6.24Ø drive sheave.

 

[redmondjp]

Ok, so it's not quite an R30, since it has reed valve heads by the look of it, but I'd be surprised if the bore and stroke are different. It's definitely something Champion built, probably an earlier cheaper line for Grainger to sell as a Speedaire or Dayton. I'd do some measuring of the pulleys and calculate the current running rpm with the motor it has to see if it works out to be the same as the rpm specs for the R30. I'm confident there is little difference, but I wouldn't want to send you off with incorrect info. It should be a very good unit for you if it is in good shape.

It is the "value" line of the R15/R30 pumps called their "RV" series - it has less fins on the cylinder, and an integrated (one-piece) cylinder head with reed valves. The other cost-savings is that there is no centrifugal unloader - the housing is still there, but it is only used for the crankcase vent line connected to the air inlet on the head. I just bought the RV-15A version of this pump (also a Speedaire) for my brother two weeks ago so I had to figure all of this out to see what I had.

The compressor in this case uses the Champion RV-30A pump. I have the brochure for it - for 7.5HP it is spinning at 628rpm for 29.8CFM @ 125psi, or 570rpm for 24CFM @ 175psi.

Minimum RPM is 400, so I see no reason at all why a 5HP motor couldn't be used with this pump (napkin calculation, around 450rpm? - check my math here).

 

[Gaunt596]

so, to follow up on the posts, MacMcMacmac was damn close, tool tyrant figured it out the same time i did, it is indeed an RV-30A, the compressor is a speedaire brand. I was told when i bought it that it was a backup air supply for some form of die casting machine, and based on the condition and some of the markings on the compressor, im inclined to believe that was the case. Really, the only damage i can find anywhere on it is the electrical wiring was mangled by whoever removed it from the facility it was in, and they just sawzalled the piping connecting the dryer and compressor, so theres a good possibility of the tank and dryer have metal shavings in them, so ill need to clean both units out well once i get them running.

As far as VFD's go, i have next to no interest in one, between cost and added complexity, its just not worth it since i can downsize the pump and run it on a smaller motor. I do not truly need 10hp worth of air, but the deal i got on this was too good to pass up. theres also a possibility of me moving into a shop with 3 phase later on, and id like to just store the current motor until then.

onto the electrical, this is a residential shop. when i built it, i had my electrician size the wire running to the shop (its detached from the house) to accommodate a full 200amp load, and the power company came out and redid the hookup so that the shop is running completely separate from the house, with a shutoff for the garage located near the meter. they also upgraded both the line running to my house and the meter to handle the combined load. while they were out, i asked them about running larger motors/phase converter drives etc, and they said that with the new service, im good to run up to a 10hp motor, as long as i use an appropriate mag starter or VFD to manage the startup current. with the mag starter that is on it now, id love to re use it, i did some digging ant it appears that i can indeed reuse the current mag starter, im just not entirely sure if it has enough capacity for the 7.5hp motor on single phase. ill dig more into it once i have the motor in my hands and can see exactly what it needs.

I do appreciate all the info flowing about pulley sizes and motor selection. I have the ability to run a 7.5hp motor and that is looking like the best solution, although from a budget standpoint the 5HP is much easier on my wallet, im just not sure if i like losing that much flow capacity, as i do run tools that can use quite a lot of air, and id like to make sure this compressor can flow enough around 90-100PSI to keep up with them.

Overall yall have been a huge help, you figured out in less than a day what i had put several months worth of googling into, and ive seen that im not the first or last to ask the questions i did after they bought a wayy too big air compressor.

 

[redmondjp]

im just not sure if i like losing that much flow capacity, as i do run tools that can use quite a lot of air, and id like to make sure this compressor can flow enough around 90-100PSI to keep up with them.

If you only care about the flow at that low of a pressure, you will have no problem at all using a 5HP motor.

My calculations show, at 175psi, that spinning the pump at minimum rpm (400, or a bit higher) with a 5hp motor will give you around 17scfm. If you set your pressure limit lower, you can increase the pump RPM and not overload the motor. Final QC check is with an AC ammeter monitoring motor current at the point that the compressor turns off. At 100psi you could likely get 20+ SCFM and not overload the motor.

 

[Gaunt596]

If you only care about the flow at that low of a pressure, you will have no problem at all using a 5HP motor.

My calculations show, at 175psi, that spinning the pump at minimum rpm (400, or a bit higher) with a 5hp motor will give you around 17scfm. If you set your pressure limit lower, you can increase the pump RPM and not overload the motor. Final QC check is with an AC ammeter monitoring motor current at the point that the compressor turns off. At 100psi you could likely get 20+ SCFM and not overload the motor.

well, i used that as a specific example, but im just looking at the overall picture. just need to take the time to do all the math and figure out if a 5 or 7.5 is the better motor for my use. current compressor flows a measly 4SCFM at 90PSI, so even at min RPM this thing will blow that out of the water by a fair margin. and i do plan to QC all my math with an amp clamp, as thats the final word in if i did all the math right or not.

 

[u3b3rg33k]

while they were out, i asked them about running larger motors/phase converter drives etc, and they said that with the new service, im good to run up to a 10hp motor, as long as i use an appropriate mag starter or VFD to manage the startup current. with the mag starter that is on it now, id love to re use it, i did some digging ant it appears that i can indeed reuse the current mag starter, im just not entirely sure if it has enough capacity for the 7.5hp motor on single phase. ill dig more into it once i have the motor in my hands and can see exactly what it needs.

FWIW a mag starter doesn't do anything to manage current (it can have an overload in it, but that's for motor protection), unless it's 3 phase and you're doing a Y-∆ start. all it does is not fail like a switch/improper contactor.

There's a world of difference in startup draw between a DOL mag starter and a VFD/soft starter.

 

[redmondjp]

well, i used that as a specific example, but im just looking at the overall picture. just need to take the time to do all the math and figure out if a 5 or 7.5 is the better motor for my use. current compressor flows a measly 4SCFM at 90PSI, so even at min RPM this thing will blow that out of the water by a fair margin. and i do plan to QC all my math with an amp clamp, as thats the final word in if i did all the math right or not.

Figure out the cost difference between a 5HP motor and a NEMA Size 1 starter, and a 7.5HP motor and a NEMA Size 2 starter. You decision will be made for you.

 

[Bert_]

A new 10hp 1 phase baldor runs about $1200. Somebody mentioned a weg for $750. Weg is a good motor.

If you want to drop to 7.5hp I'm guessing you could just reduce pump speed by 25% and check the motor with an amp meter.

10hp is no big deal on a 200A service unless the Poco has rules against it. 10hp will run on a 60A unless it's a high inertia load. Then I do a 100 for start up. Can run several 10 hp motor on a 200A main.

 

[Gaunt596]

FWIW a mag starter doesn't do anything to manage current (it can have an overload in it, but that's for motor protection), unless it's 3 phase and you're doing a Y-∆ start. all it does is not fail like a switch/improper contactor.

There's a world of difference in startup draw between a DOL mag starter and a VFD/soft starter.

very true, thats just what i was told by the power company crew. im guessing they only mentioned the mag starter to try and prevent me from burning up a larger motor.

Figure out the cost difference between a 5HP motor and a NEMA Size 1 starter, and a 7.5HP motor and a NEMA Size 2 starter. You decision will be made for you.

yeah, its not cheap. a 5HP WEG motor is $360, the eaton mag starter for it is another $165, for a $525 total cost, the 7.5HP motor is $545, with the mag starter being $195, for a $740 total cost. just to put all the numbers here, the 10HP motor is $829, with the mag starter another 920, total cost 1749. Thats with eaton mag starters. i see that WEG makes mag starts as well, ranging between $115 and $160, for the 5-7.5-10hp models. Given those prices, im mostly likely gonna **** up the price and go with the 7.5, as a buy once cry once move. i can always run the thing slower if that turns out to be too much air.

A new 10hp 1 phase baldor runs about $1200. Somebody mentioned a weg for $750. Weg is a good motor.

If you want to drop to 7.5hp I'm guessing you could just reduce pump speed by 25% and check the motor with an amp meter.

10hp is no big deal on a 200A service unless the Poco has rules against it. 10hp will run on a 60A unless it's a high inertia load. Then I do a 100 for start up. Can run several 10 hp motor on a 200A main.

good to know weg motors are decent units, that helps out in the budget department vs a baldor. i did check again with the power company on rules about motors, since im a "Heavy Up" customer, my meter is fused for 400A, per the phone conversation i had, and if i can start a 10 on 100A, i should be golden with a 7.5 motor. im still undecided on the pump speed, the spec sheet shows 575 for a 7.5HP, but im not sure if thats the raw edge limit, or if theres some overhead on that number. I may just go on the safe side of things and spin it around 525 or so. also, seeing the earlier comments about the lack of centrifugal unloader, ill have to look at adding that, as letting it start fully unloaded will definitely help with not burning out motors and wiring on startup.

 

[bsaint]

Since you dont need 175# I would go for 628 RPM and 30 CFM.

 

[sberry]

If I was doing it would be 7.5 at 175.

 

[The Tool Tyrant]

If I was doing it would be 7.5 at 175.

X2! Lower cut-out pressure = less usable air volume = more motor starts = less motor life. The pump and motor are designed for it, so why not use it!

 

[TonyJ]

X2! Lower cut-out pressure = less usable air volume = more motor starts = less motor life. The pump and motor are designed for it, so why not use it!

I’m with you on this one. Usually when a pump is rated at something then that’s the spot it’s the happiest. Also the bigger compressors that are run way slower than they should be doesn’t have the chance of getting the oil hot enough to keep water from forming inside the pump


Tony

 

[Gaunt596]

Since you dont need 175# I would go for 628 RPM and 30 CFM.

i actually do need 175, some of the rally tires i have can take upwards of 160-170 to seat the beads.

If I was doing it would be 7.5 at 175.

X2! Lower cut-out pressure = less usable air volume = more motor starts = less motor life. The pump and motor are designed for it, so why not use it!

I’m with you on this one. Usually when a pump is rated at something then that’s the spot it’s the happiest. Also the bigger compressors that are run way slower than they should be doesn’t have the chance of getting the oil hot enough to keep water from forming inside the pump


Tony

7.5 at 175 cutout/575 rpm is the plan. no need to screw around with pressure switches and other things that way. ill keep an eye on the water/oil issue, may look into a heater if its a problem.

 

[bsaint]

How often are you seating rally car tires??

 

[mike93lx]

How often are you seating rally car tires??

Once or everyday, does it matter?

 

[bsaint]

Once or everyday, does it matter?

Yes. Cost of ownership is huge with an air compressor. If you use 50hp once a month and every other time you use 7.5hp, why would you buy a 50hp?

 

[mike93lx]

Yes. Cost of ownership is huge with an air compressor. If you use 50hp once a month and every other time you use 7.5hp, why would you buy a 50hp?

Who is talking about 50hp?

If the guy needs and wants 175psi,let him go for it.

I think it is silly to spin a 7.5hp motor to run small tools like an impact and a sander, but to each his own

 

[bsaint]

Who is talking about 50hp?

If the guy needs and wants 175psi,let him go for it.

I think it is silly to spin a 7.5hp motor to run small tools like an impact and a sander, but to each his own

Itll last way longer at 125.


Sent from my iPhone using Tapatalk

 

[mike93lx]

Itll last way longer at 125.


Sent from my iPhone using Tapatalk

So 2 lifetimes instead of 1?

 

[MacMcMacmac]

If I was doing it would be 7.5 at 175.

Me too. Seems like a waste to have a two stage compressor cut out at 125.

 

[TonyJ]

Me too. Seems like a waste to have a two stage compressor cut out at 125.

I have mine set up with two pressure switches so I can choose between cutting off at 135 or cutting off at 175. Mine is 10hp running at full rpm so one way I can run lower psi and the other I can higher but at the end of the day it still runs at the rpm and hp it was designed for


Tony