Too Much Air Compressor??

I need someone to either convince me to keep a giant air compressor and that there is no such thing as too much air or tell me I'm silly and to get rid of it!

Recently participated in a local machine shop auction and among a surface grinder and some tooling, absolutely stole a 25hp SpeedAire compressor.
Watched and heard it run, even has a signed service interval chart with it.


Why did I do this you may ask.
I occasionally (maybe 2-3 times a month) have to use my glass bead cabinet and my old DeVILBISS compressor barely keeps up.


As a matter of fact, the motor blew on it about 6 months ago and I upgraded it to a 7.5hp Baldor motor with a slightly larger pulley to max out the pump speed rpm to give me a boost in the CFM department. Still not enough.
So not a whole lot of blasting, but it does become tiresome waiting for it to kick off when I am going full tilt.

Here's the issue I'm faced with.
My shop has 240 volt, 400 amp single phase service running through two American Rotary 50hp ADX converters.
This nets me around 200 to 220 amps of 240 volt 3 phase.


My main machine is a Mazak SQT18MS which is currently run off of a 150 amp fused disconnect.
Nameplate rating is 125amps largest motor, 60kva total ~140amps.
I have changed accel and deccel parameters so it doesn't pull nearly as much when winding up.
I have put an ammeter on the lines to see how much current it really uses and during normal ops, its around 50 amps.
My ammeter does not have an inrush setting though, so I don't truly know what it's pulling.

Being that this compressor is 25hp with a nameplate rating of 75 amps, I am concerned about it kicking on while the CNC is running giving me a low voltage alarm or just doing funny things with the electronics.
With both in a constant on state, my converters should have no problem providing the correct power, it's the startup that I'm concerned about.

As a side note, I am currently looking at small VMCs as well, so there may be another medium load on the system.
I'm not worried about any of the manual machines as only 1 will be run at a time and their power requirements are pretty much nill.

Option 1: Hook both up and just test it out to see what happens.
Option 2: Purchase a Fluke 370 or equivalent with inrush settings to see what I'm actually working with.
Option 3: Sell both and purchase a 10 or 15hp compressor.
Option 4: ???

What say you??

don't know how it is where you are, but around here having a 25hp compressor will put you in the poor house from the demand charges when it kicks on. Other than that, I see no downside to a too big compressor.

bigpappy said:

Being that this compressor is 25hp with a nameplate rating of 75 amps, I am concerned about it kicking on while the CNC is running giving me a low voltage alarm or just doing funny things with the electronics.
With both in a constant on state, my converters should have no problem providing the correct power, it's the startup that I'm concerned about.

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Get yourself a large soft start unit from ebay like I did. The soft start units are designed specifically to reduce inrush current. The larger the unit, the more starts per hour it will handle. Google the part number for the unit to find a manual online and read the specs.

I scored a used 15 hp ABB soft start for $140 plus shipping several years ago for my big turret lathe and a 7.5 hp ABB unit for my air compressor. The inrush from the turret lathe used to knock out my big Mazak CNC lathe. Now I can run both machines at the same time with no issues and still have the air compressor run.

One thing to note, some sellers mistakenly list remote contactors as soft start units. Be sure you know what you are buying by Googling the part number.

You could downsize the motor (with a corresponding reduction in motor pulley size)
You can't slow it way down, it still needs to oil itself.
A little investigative work should find you the range of motors that pump can be run with.

Too big ?

Air compressors need to run long enough to get the oil hot, to drive off water
that condenses in the sump.

I think in your situation you want more tank not more compressor

sell it at a profit and find a big tank

i am running a 7 horse ingersoll into a 400 gallon tank

Or use it just for sandblasting

Or plumb both together and set the pressure switch 10 pounds lower so it only comes on when you are sandblasting

In my experience most of the inrush is accelerating the compressor flywheel. I had one that supplied a measured 14 hp from a 20 hp motor. Without the belts, the motor accelerated so fast that it was not visible. When the contactor closed, the motor was running at full speed. Belted to a big compressor, it took several seconds and would blow anything less than 200 amp slow blow fuses. Even running on a proper three phase line with its own transformer, it made the neighbor's light flicker, pulling the high voltage feeder down. A soft start unit or changing to a smaller motor pulley should do the trick, as long as you don't go below the minimum compressor speed.

I hate inadequate compressors.

Bill

I think your concerns about voltage stability are valid, and I'd go with the soft-start controller. A big tank is of no use unless you go really big and your blasting jobs are short. Even then, a large reservoir with a small pump means l o n g waits for fill when it does kick on.

bigpappy said:

I need someone to either convince me to keep a giant air compressor and that there is no such thing as too much air or tell me I'm silly and to get rid of it!

View attachment 261198

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You have too much motor there for a 60 or 80 gallon tank. I'm using 1/5 the motor Hp on a larger air compressor tank. Originally had a 5Hp single phase motor.
I switched to a 5Hp three phase motor and VFD which is programmed for a 5 second start ramp time.

I have that compressor. Resale on those big units seems to be very low, so a soft start would be the best usage. For a big piston its noisier than some, but not to bad. It is a splash lube compressor. It will allow you to sandblast much better.

Woah, thanks for all of the quick replies!

Looks like a soft start would be the best choice for my application.

Larry, I am quite fortunate with how my service is setup up over here. The 400 amp service is still considered residential so my rates are normal. My shop bill is actually less than my house bill every month.

Philabuster, thanks for the advice! From my initial search it looks like ABB has top quality soft starters with prices that aren't too crazy. If I can find one on eBay, even better.
I've read many of your posts over in the Mazak forum from when I first purchased my SQT18 to now, and have learned so much from what you and the others have shared, so thank you.
But I do have one more question for ya. What amp service are you feeding your Mazak lathe with? It was either you or CNCToolCat that said the nameplate ratings are ridiculously overstated.
I do not have a 3 phase circuit panel yet and in doing some research and calling the local electric supply houses, if I follow the 60 KVA or 150 amp rating on the nameplate, it looks like I may be into bolt-in breaker panelboards rather than a standard plug-in, for a 200 amp main breaker panel.
It looks like the "norm" is 100 amp breakers which will work for every other piece of equipment I have.

Regarding downsizing the motor, changing pulleys, or even getting a larger tank, although all viable options, I'm thinking a soft starter will be the easiest route while still keeping the compressor in "stock" form. Another tank would be nice, but I have very limited space.

Gbent, I'd have to agree on the resale. I actually posted both of these compressors for sale locally and have only received hits on the DeVILBISS. Actually right after dinner tonight, someone offered $1000 for it, there's my soft start!
I did hear it run and even though it's no screw compressor, I do think it's quieter than my current compressor, most likely because of the pump speeds.
How do you like yours? Any issues?
I was able to find the operating, maintenance, and parts manuals online and it looks like they actually still make that same pump! So parts are very much readily available.

Again, thank you all for your responses and pointing me in the right direction.

Air is F'N expensive!!!!!!

A few years ago, my big compressor motor shit the bed... Temporary fix was to fire up the backup compressor, which is a little 20 gallon Craftsman. It would run the mills, but not the lathe.. OK.. Orange cheap tool store... Here we come... $149, 21 gallons 120psi. The crapsman did the millss, and the cheap chinese compressor would run the lathe.

Then the motor on the crapsman died(set at 140psi).. And what do you know.. The cheap POS from that store that smells like rotten cosmoline could run all the machines..

Weird.. And the electric bill.. It went down by $150 a month.. And as time went by, I've had to buy a few more $149 compressors, but I've fixed a lot of air leaks, both in the lines and in the machines. I've also learned to dial back the pressure, I now cycle from about 94 to 114, not like 120 to 145 in the big one..

A lot of air leaks fixed, with the machine all hooked up, it cycles about every 3 hours when nothing is happening.. And I shouldn't say "About". Its on the F'n nose. 3 hours to the minute. If I pull the air lines off of my 2 worst offending air leakers, it will hold pressure for 3 days now.

Sand blasting. Yeah, that sucks.. And the worst part is, that years ago, I bought a new motor for my big compressor, and its still sitting up there, not hooked up. Its on my list.

Sand blasting.. That's what we were talking about. But before that.. More air leaks fixed, in both the machines and the lines, and a $40 a month electric use lighting change.. My bill has gone from $500+ a month to $260 to $280. If I'm running machines A LOT, it might crack $300.

Sand Blasting.. SUCKS!!! If I have more than one little tiny thing to do, I just run it a half mile down the street to one of my customers who is sandblasting all the time. Gas driven compressor type sandblasting, way out back, takes his helper about 2 minutes to do what it would take me 2 hours.. And I buy him a 12 pack..

One of these days, when I get the big compressor going again.... And its SOOOOOO close. I'm going to turn her way down to 90-110 psi, and then wire/plumb in a second pressure switch for 125-145ish for when I need to sandblast or run air tools. And if my electric bill goes up, I'm just going to go back to the cheap compressors, the big one was set WAY too high, I'm hoping its more efficient than the little ones running pressures I actually need.

And just for fun, since somebody is going to crawl up my ass for using a HF air compressor. They make great accumulator tanks. Should I buy a 20 gallon accumulator from McM for $360, or buy a 20(21) gallon accumulator tank from some cheap chinese store that has a fully functional 3+ cfm air compressor attached to it for $149????

Long story short, keep it and use it only when you *need* it, or sell it.

I fixed one air leak at a place I worked when I became the manager. Electric bill went from $600 plus for years, to $300!

bigpappy said:

Philabuster, thanks for the advice! From my initial search it looks like ABB has top quality soft starters with prices that aren't too crazy. If I can find one on eBay, even better.
I've read many of your posts over in the Mazak forum from when I first purchased my SQT18 to now, and have learned so much from what you and the others have shared, so thank you.
But I do have one more question for ya. What amp service are you feeding your Mazak lathe with? It was either you or CNCToolCat that said the nameplate ratings are ridiculously overstated.
I do not have a 3 phase circuit panel yet and in doing some research and calling the local electric supply houses, if I follow the 60 KVA or 150 amp rating on the nameplate, it looks like I may be into bolt-in breaker panelboards rather than a standard plug-in, for a 200 amp main breaker panel.
It looks like the "norm" is 100 amp breakers which will work for every other piece of equipment I have.

Click to expand...

First off, you're welcome.

I have a Phase Perfect PT380 feeding my entire shop through a 3 phase panel with bolt in breakers. I got the panel and breakers at a local electrical surplus shop for cheap. Each of the Mazak CNC lathes are being fed with 100 amp breakers and 2ga wire. I reduced the accel and decel on the lathes so "Big Zak" is pulling about 75 amps when it accelerates and "Junior" is only pulling around 40 amps.

I did notice you didn't mention that you know your ADX type American Rotary RPC's have CTR (current transient reactor).

They are good for 250% over current for starting compressors and machines with big inrush currents without the voltage moving around.

I have a Doosan DNM5700 mill and Hyundai/Kia SKT 250 lathe and I run both and the 5hp Atlas/Copco rotary compressor at the same time with no issues at all.

I use a ADX 75 with is rated to max at 208 amps. This is with a 400amp single phase service. The only thing I could see that you didn't mention was that I had originally had a small transformer on the pole outside my place and #2 wires. It would error out when the TSC kicked on in the mill.

I had PG&E upgrade to a 50kw transformer (for me only) and 4/0 wires. All problems ceased after that. Both machines on, coolant going on and off, deep cuts, spindles spinning up at the same time, everything works great.

The house is on the same line as the shop so I also can have stoves, dryers, TV's, A/C also all running. Still no issues. Just some information for reference.

Bob, air leaks are the worst! Thankfully my shop is small and there are minimal pipe joints so leaks aren't too much of a concern. If I keep my current compressor powered on, it may kick in once a day with no use.
Good call on turning the pressure down though. The large one is currently set between 140 and 175 if I'm not mistaken.
As for selling it....I may already have my other one sold for 3 times what I paid for the big boy.

Philabuster, I definitely think a bolt-in breaker panel board is the way to go, especially for future expansion, but darn if those things aren't a pretty penny. Keeping an eye out for used ones now.
But it would also be kinda nice to get a standard 200 amp 3 pole from literally anywhere and fill it with plug-in breakers on the cheap. It's that 100 amp breaker size limit that I'm questioning.
Which big zak do you have again? One of the first things I did, after learning how to turn the thing on and make my way around the screens... was to turn the accel and deccel way down.
How are you measuring the amps during accel and deccel? Is a normal clamp on meter "fast" enough or are you using a higher end Fluke?

Jaxian, I did see that 250% value when I went back into the specs to check everything out. I guess I didn't put two and two together about the voltage drop, or not dropping, though.
Where did you find that 208 max amps for your ADX 75?
Looking at a spec sheet it shows 210 for yours.
It also shows 140 for one of my ADX 50s. Since I have two running in parallel, does that mean I have 280 max amps available?
As for the transformer, I do not know what size it is, but Atlantic City Electric installed a pole for me with an absolutely massive one on it. It is for my shop only. I ran 750 MCM from the pole to my 400 amp meter socket. Think I should be ok on that end!
Either way, I still think a soft start is the way to go.

Thanks again for the continued advice!

industrial air compressors and i am talking 1000hp or higher have yearly maintenance done. there are check valves sometimes called reed valves that i have taken apart and replaced broken springs.
.
just saying talk about a air leak in the compressor when parts are broken inside. basically efficiency drops rather than say 500 cfm air compressed you only getting 200 cfm cause internally it has parts needing repair and or replacement.
.
old compressor might appear to be working ok but who actually measures the compressed air volume per minute is dropping off ?? like less than 50% air compressed compared to when new
.
closest analogy is new car getting 25 mpg gas mileage and when older only getting 20 mpg mileage

bigpappy said:

Which big zak do you have again?

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Big Zak is a ST30 ATC/MC. The machine has a 15" chuck on it and a 22kw spindle motor.
Junior is a QT10N ATC/MC. It looks like a smaller version of the big lathe, but with an 8" chuck.

I have a Fluke 177 meter (I think so--going off memory here) with an accessory 200 amp clamp on probe.

For sandblasting I installed a 200 gallon receiver and sized the sandblast gun to use the entire 56 CFM that the compressor supplied. I modified a foot valve with a second valve that was normally open and connected it to the tank through a check valve and an electric one just before it controlled by the pressure switch on the tank. The contactor for the compressor was connected to the pressure switch and in another position kept the compressor running with the air blowing off at low pressure. If I set the switch for intermittent running, the compressor cycles normally. If I am blasting, the compressor runs continuously, feeding the tank or venting as required when not blasting at the moment. General purpose shop air comes off the tank and even when blasting all day, there are enough pauses to change parts or rearrange them that the shop air stays up.

As I was working all this up as well as modifying a Gardner Denver ACR compressor for two stage operation, I learned that I couldn't say anything about it to experts because they would be horrified and predict all sorts of dire consequences. The problem is that many people cannot deal with a setup that is not normal, even though it stays within the envelope.

Bill

Honestly, if I had to pay for the operating costs, I think I'd be all over putting a air tank in line with the original compressor, and setting the pressure switches up to best take advantage of whatever pressures I needed to bead blast with.
And put a coffee pot near enough, so as to make waiting not so bad.

The 'more power' in me, wants to put about a 50-100 hp of gas or diesel engine on the big compressor, and only run it when needed, and leave the rest of the shop air alone.

Gordon Heaton said:

I think your concerns about voltage stability are valid, and I'd go with the soft-start controller. A big tank is of no use unless you go really big and your blasting jobs are short. Even then, a large reservoir with a small pump means l o n g waits for fill when it does kick on.

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A 1000 gallon tank give 666 scf starting at 175 psi, and dropping to 100 psi. If your blast cabinet needs 50 scfm, it will run it for 13 min, plus whatever you compressor makes in 13 min.

Around here, you can get a propane tank that fails inspection pretty cheaply. I paid $400 for mine to get the best of a 20 tank batch. If needed, I could probally have it retested at 200 psi.


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