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wiring 240 volt magnetic starter for compressor

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  • Norcal
    replied
    You do not need 2 starters for your compressor (the manual Furnas starter does NOT qualify as a disconnect switch) a cheap 60 amp A/C pullout disco works well, and that exposed wiring is scary, conduit and proper grounding/bonding of all parts is required for the safety of you and others.

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  • Carl W.
    replied
    I would clamp a Amprobe on a lead and run the compressor up to the maximum perssure your pressure swith is set at and take a reading.
    Lower than the 26 amps your good to go, higher your overloading the motor
    and should down size the motor pulley until the amperage is at or lower than 26.
    Sorry i'm late finding this thread, got my attention when I saw that manual switch/overload protection you had, not a mag starter.
    Maximum locked rotor current is 6 times rated load current. Disconnecting means (your manual switch) shall be rated 115% of the full load current.
    For your 5 hp motor that requires a NEMA 1 starter.

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  • Knuk
    replied
    Good to hear a 3 hp might not do. This one dims the lights withs its 5hp as it starts but its good to go IMHO. Knuk

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  • Knuk
    replied
    Finally hooked it all up.

    Well I finally got it all together. I moved last month and had the garage to hook it all up in finally. I did find a magnetic starter at a yard sale of all places for $20 and upped the heater to 30 amp rating for the magnetic starter for another $20. The definite purpose switch I had a 33 amp heater in and put it before the mag as I had it anyway and gives me a shut off near the compressor. I ran about 35 feet of 8-2 wiring ($50) from the panel and used a 40 amp breaker there. So it works..no smoke to let out. I ran pressure switch wiring to points on the starter to activate the throws of the mag. The pressure switch is not doing activation of the motor as the mag switch does that task. Should save the duration life of the pressure switch that way.
    Pics attached of the final final.
    Attached Files

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  • Knuk
    replied
    Went to a real tool house today and was told that my mag starter isn't that, but just a manual starter...so still need a mag starter. They also said the head has the ability to run all the time, by some style pressure unloader built into those older heads. He also said that the easiest to do is get a check valve from the tank to the pressure switch, as there is none from the pics I posted, which I brought to the tool house. He figures the engine pulley is much to large for a 5hp...he figures 7.5 hp needed or bigger but it would run fine with 5hp and drop pump rpm to near 400. I told him about the 600-900 rating on pump but he said it is a splash type oil system head and would still be ok. He figured the head was working under pressure when starting as the pics didn't show any check valve.

    So I need a mag starter again. They had, but I'll try to find one used perhaps to keep my costs down.

    He offered to buy it a couple times also...lol
    Nah , Ill keep it.
    He said its an expensive head to rebuild.

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  • hankj
    replied
    Knuk,

    Sounds like it'll be a super set up. Your motor, being a "real" 5-horse and not a "special" like the ones you find on the cheaper machines (mine included) that draw 15-amps but are "rated" at 5-hp., will definitely make a difference. I'd think with the combo you have, no changes will be needed.

    Keep us in the loop, and don't forget pictures of the final-final!

    Hank

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  • storts
    replied
    To Hank

    Originally posted by hankj
    Knuk,

    How did you arrive at the 5-hp motor decision? From the pic's of the pump, I'd say it's a 10-horse, or at least 7.5.

    What is the displacement of the two cylinders? Is it stamped on the pump? Units I've seen with pumps that big are usually driven by motors larger than 5-horse.

    Hank
    Hank, When i sold my building,and alot of the older equipment, i had the twin to that ,wished i could find the pics(somewheres in the basement,in a box) and mine was 15 hp.went from 0 to 175 in under 3 mins.,,Dont know if that helps you or not,But had plenty of Juice at the old Joint,Jack

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  • Knuk
    replied
    The specs for this compressor head were available on line in the .pdf I had linked above. This is it http://www.devairusa.com/Devair_Pump...ns_pdf/432.pdf

    It's a 4 cylinder pump...2 cyl's are 3.25 and 2 cyl's are 1.75. The stroke is 3.5.

    Specs say the pump will run on a 3 hp up to a 10 hp.
    It was running on this 5 hp as shown now attached in this pic. It ran on that motor so thats what I happened to get. I traded off my 3hp motor I had to friend who has a 3 phase 3 hp... hence needed a single phase for his Ingersoll Rand 1963 era Model T30.

    My devilbiss has 19 inch flywheel and the motor pulley is 8 inch ( outside edge diameters). So with a 1740 rpm motor according to this site http://www.aircompeq.com/formulas.html
    the pump should be running at 733 RPM. I've seen 10hp motors that were less in size than this one...its a fair size 5hp.

    I dont have it hooked up yet so its up against the wall... I heard it should be back 12 inches off the wall to give the flywheel some air to move the cool the head.


    The pump has a tag saying low speed 600 high speed 900. So it's good as is I figure for pump rpm.... and I could slow it down some yet probably to 618 RPM with a 6.75 inch pulley on motor.

    I believe it's a 1970 now..found stamp on tank that year so figure pump probably near the same.

    It may not have an unloader, but looks like one can be added as per the pdf devair site link.

    I'll plug away at it or it will sit till I get a good power source somehow..might have to move to get that...
    Attached Files

    Leave a comment:


  • hankj
    replied
    Knuk,

    How did you arrive at the 5-hp motor decision? From the pic's of the pump, I'd say it's a 10-horse, or at least 7.5.

    What is the displacement of the two cylinders? Is it stamped on the pump? Units I've seen with pumps that big are usually driven by motors larger than 5-horse.

    Hank

    Leave a comment:


  • Rvannatta
    replied
    Originally posted by Knuk
    Just thought I'd throw it back up top to see if anyone had any tips.

    The mag switch good enough to go?

    Pic of the compressor head in above post...dosen't look to be an unloader as shown on the devair site link, but that's newer style in link compared to pic of actual.

    Knuk
    You have a better chance of starting a 3 HP motor. If you put a pully on it half the size of the one you have so, you would slow the compressor by half so 3 hp should work with half the output---unless of course it is a compressor that expects the higher speed to make the lubrication system work or something and then soon you have no compressor.

    IF you happen to have a Miller Bobcat around--- even the older 16 HP
    models---they put out 8KW and will start a 5 hp motor---barely.

    Leave a comment:


  • Knuk
    replied
    Just thought I'd throw it back up top to see if anyone had any tips.

    The mag switch good enough to go?

    Pic of the compressor head in above post...dosen't look to be an unloader as shown on the devair site link, but that's newer style in link compared to pic of actual.

    Knuk

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  • Knuk
    replied
    The pressure switch has 4 poles. Only 2 seem ever used.

    The bottom of the mag switch has markings of T1-T2...while the top has L1-L2

    I would need a counter clockwise rotation according to the arrow on the compressor head, so I think I was right in the T1-T5, & T4-T8

    I thought that the power was just activated by the pressure switch, not connected to it in it's path to the motor.

    The motor has 3 capacitors on the top of it. Not sure how there wired, but it did work.

    Looks like this model could of had an unloader according to the devair site, although its probably the older style which dosent seem to be shown.
    http://www.devairusa.com/Devair_Pump...ns_pdf/432.pdf


    Thanks.

    Leave a comment:


  • Knuk
    replied
    I was reading the numbers on the mag switch cover which to me looked like this mag can handle 35 Amps max load. Pic attached.

    The mag has another sticker on the side saying single phase 230 volt 5hp rated, pic attached.

    The compressor is a 1976 Devilbiss with a 432 model head and 60 gallon tank, pic attached. Unloader.....not sure? I heard it run and seemed to exhaust at end of cycle to clear things out and avoid starting motor on compression.

    I thought I was there with what I needed...am I way off?

    I can see the amps of a generator not covering it...but I was hoping I could drop the amp draw somehow.

    I could maybe get a 3hp motor with a swap type deal.

    Remote location, so no power but generator.
    Attached Files

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  • hankj
    replied
    Knuk,

    Bruce gave you the correct wiring info. I couldn't see the contact rating on the mag starter's nameplate, but that motor will draw 26 amps at full load, and, as stated, depending on it's winding and capacitor arrangement, might pull anywhere from 35 to 50 amps to start, especially if your compressor has no unloader.

    There's no hope of running that motor from a 5KW genset, even by changing the pulley arrangement.

    Hank

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  • dyn88
    replied
    I appologize, I was looking at 26 amps, and thinking 26 horsepower. Sometimes I am an idiot.

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