Whats a good compressor for my situation?


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    Default Whats a good compressor for my situation?

    Hello, I have an old Haas machine, soon to be two in my garage shop.
    Desperately needing to upgrade my compressor but not sure power-wise if Ill have enough to go around. ???

    Have 100 amp service running a 25hp rotory phase converter that is running a 98 20haaspower VF-0E. Soon to be another as well.
    Sounds marginal, but works fine so far.
    But my compressor will soon die because it can barely keep up with the haas as it is.

    All I need running at once is the Haas, (hopefully 2), the compressor and the lights. No other equipment running along with those.
    Need some advise on what is a good compressor for the money that will make my power and air concerns go away.
    Dare I add a compressor to my 3ph circuit, go 220v single phase or is there perhaps a decent 110v solution?
    Any help would be greatly appreciated!!!


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    Community Moderator Jim Dawson's Avatar
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    Default Re: Whats a good compressor for my situation?

    On a 100 amp service I would say you are right near the limit. Your Haas/RPC system is around 60 amps. A 5 HP compressor is around 25 amps @ 240V single phase. That gives you enough left over to run a couple of light bulbs.

    There ain't no free lunch, your power problem is not going to go away. Let's look at the numbers:

    (I'm not going to figure in power factor and efficiency here, we're just going to treat this as resistive loads, close enough for this calculation)
    You have 24000 watts total power available. 1 HP = 746 watts, so we'll round that to 750 W/HP

    Spindle
    20 HP * 750 = 15000, 24000 - 15000 = 9000 W left

    Compressor
    5 HP * 750 = 3750, 9000 - 3750 = 5250 W left

    That means you have enough power left to run a 3 HP (2250W) knee mill and still have enough reserve for a couple of light bulbs.

    Now throw in the power that the RPC is using itself and your breaker trips.

    Now your Haas is not running at full load all the time, so we can add back a little reserve, but not much.

    I also have 100 amps of 240V single phase. I'm faced with the same problem but I approached it a bit differently, I looked at the power first and bought machines to match.
    Haas TM-2p 7.5HP, running on single phase, 5625 W
    CNC lathe, 10 HP spindle running on a 15HP RPC, 9000 W
    3 HP knee mill, 2250 W
    5 HP compressor, 3 phase, but running on a VFD fed by single phase, 3750W
    So my total is about 22,000 watts max load. The only way I get away with this is that none of the machines run at full power all of the time. With all of the machines running my total power draw averages about 12,000 watts with peaks to around 20,000 watts. You have to have enough power available to handle the peaks or you are going to be tripping the main.

    Bottom line is you can add a 5 hp compressor, but not another Haas.

    EDIT: corrected the compressor power usage.

    Last edited by Jim Dawson; 02-08-2020 at 03:23 PM.
    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Whats a good compressor for my situation?

    Quote Originally Posted by Jim Dawson View Post
    On a 100 amp service I would say you are right near the limit. Your Haas/RPC system is around 60 amps. A 5 HP compressor is around 25 amps @ 240V single phase. That gives you enough left over to run a couple of light bulbs.

    There ain't no free lunch, your power problem is not going to go away. Let's look at the numbers:

    (I'm not going to figure in power factor and efficiency here, we're just going to treat this as resistive loads, close enough for this calculation)
    You have 24000 watts total power available. 1 HP = 746 watts, so we'll round that to 750 W/HP

    Spindle
    20 HP * 750 = 15000, 24000 - 15000 = 9000 W left

    Compressor
    5 HP * 750 = 3750, 9000 - 3750 = 5250 W left

    That means you have enough power left to run a 3 HP (2250W) knee mill and still have enough reserve for a couple of light bulbs.

    Now throw in the power that the RPC is using itself and your breaker trips.

    Now your Haas is not running at full load all the time, so we can add back a little reserve, but not much.

    I also have 100 amps of 240V single phase. I'm faced with the same problem but I approached it a bit differently, I looked at the power first and bought machines to match.
    Haas TM-2p 7.5HP, running on single phase, 5625 W
    CNC lathe, 10 HP spindle running on a 15HP RPC, 9000 W
    3 HP knee mill, 2250 W
    5 HP compressor, 3 phase, but running on a VFD fed by single phase, 5250 W
    So my total is about 22,000 watts max load. The only way I get away with this is that none of the machines run at full power all of the time. With all of the machines running my total power draw averages about 12,000 watts with peaks to around 20,000 watts. You have to have enough power available to handle the peaks or you are going to be tripping the main.

    Bottom line is you can add a 5 hp compressor, but not another Haas.


    That is all good information and I appreciate every bit of it. I am told that the horsepower on a Haas was just a sales tool and doesn't even come within 50% of that claim.
    With that said, also motivated by others that are doing this very thing. Running multiple machines simultaneously. However in the back of my mind, what you are telling me has been nagging at me. Currently have a 10hp ac/servo industrial cnc router in the shop also. Although I have tested running them at the same time and with the compressor on, I have not done it much.

    I dont know. Will be an experiment I guess.




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    Default Re: Whats a good compressor for my situation?

    You could try and add a 60-100 gallon tank to your current compressor. This will give you some breathing room without a single amp more of electrical capacity needed. Should give your current compressor a chance to take the occasional breather that any compressor needs for longevity.



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    Community Moderator Jim Dawson's Avatar
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    Default Re: Whats a good compressor for my situation?

    What I would do is to get a clamp on ammeter and look at the actual current draw as things are running. There is really no other way to tell what is going on. https://www.amazon.com/s?k=clamp+met...b_sb_ss_i_4_11

    Fluke or Klein meters are good, don't buy the $25 ones.

    These wired in panel meters work also, https://www.ebay.com/itm/100A-AC-Dig...oAAOSw68NdTUG8 I have tested these against my Fluke meters and found them suprizingly accurate. I use them on my RPC, one on the incoming line and one on each leg of the output. I installed them so I could easily balance the RPC.

    I also have continuous data logging set up on my power system, so I can watch the graph data in real time. That's how I was able to give you real world numbers above under running conditions. https://www.theenergydetective.com/

    the_gentlegiant raises a great point. More air storage capacity will make a big difference in your compressor cycle time. I have 260 gallons, two 80 gal tanks at the compressor, and one 100 gallon tank after the air dryer. Also running the compressor from a VFD, I'm able to ramp it up to speed over 10 seconds thus keeping the start load to not more than the running load. When kicking the compressor on with a switch, the start load can be as high as 3x the running load. I have burned up a few good (Baldor and Leeson) compressor duty single phase motors with high cycle rates. Ended that problem when I went to extra air capacity and a 3 phase motor.

    Jim Dawson
    Sandy, Oregon, USA


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    Community Moderator Jim Dawson's Avatar
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    Default Re: Whats a good compressor for my situation?

    I didn't answer your question about what compressor, this one is not bad https://www.harborfreight.com/5-hp-6...sor-93274.html. They actually have good pumps on them. Run it until the motor fails, then replace it with a 3 phase motor.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Whats a good compressor for my situation?

    Quote Originally Posted by Jim Dawson View Post
    I didn't answer your question about what compressor, this one is not bad https://www.harborfreight.com/5-hp-6...sor-93274.html. They actually have good pumps on them. Run it until the motor fails, then replace it with a 3 phase motor.

    Seems Harbor freight is getting a good rep these days with some of their tools and certainly their new line of tool boxes and carts.

    Hearing really good things about the Eastwood Elite QST-30/60 Scroll Air Compressor. May end up going with it. But not for another week or so. Will update the thread if any changes.


    Thanks Jim & TheGentleGiant!



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Whats a good compressor for my situation?

Whats a good compressor for my situation?