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Thread: Large motor advice

  1. #1
    Join Date
    Oct 2007
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    516

    Default Large motor advice

    I'm building a dust collector and need a somewhere in the neighborhood of 5hp or so to run the impeller. I've looked at a bunch of specs on a bunch of websites, and come to the conclusion that either I don't know two cents about motors, I don't know what I'm looking for, or I can't see through the marketing speak...

    Does anybody have any pointers if I state the following:
    I have up to 50A of 220V single phase.
    Sheave bore is 1-1/8".
    RPM is somewhere in the 3450-3600 range.
    Probably direct drive and vertical mounting (motor on top).

    I don't know what to think, because I've seen a price ranging from about $100 to about $1000, and I really can't tell much of a difference. Common sense tells me that what I'm looking for should be rated for at least 21A for continuous operation otherwise I'm looking at peak numbers.

    On the safety side of things, I keep reading about magnetic switches, though I'm having a hard time finding anything to handle a motor over 3hp. Does anybody have a good pointer for that as well?

    Lastly, is there any sort of balance or vibration switch/cutout device available for added safety? I'd hope I don't cause anything so drastic as to have a 5hp motor come out of a mounting and attempt to walk around the room, but I figure there can't be any harm in asking...

    Thanks in advance!

  2. #2
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    Jan 2008
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    southern delaware
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    1. are you sure you need 5 hp.? thats pretty powerful motor

    2. Magnetic starter can be found for well over 5 hp call you local electrical wholesaler and ask. square d is the one I prefer, expect to pay a lot of money for it.

    3. Consider using 3phase and making a converter from capacitors

    4. your service may not handle a 5 hp, if you are running 21 amps. the start up amps could be well over 50, look for locked rotor amps on the specs to see what it need to start up.

    5. if it is out of balance you will know right away,

    6. how big of a system are you trying to make? I have mine with two motors, one is an impeller, and then it feeds an old air handler squirrel cage that then feeds outside, its plenty powerful. If it cold I just use the one motor for the interior recirculation. the one impeller system is from a welding fumes evacuator, I think it is 1 hp at most but it is there phase.

  3. #3
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    Aug 2006
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    Taylorsville Ky
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    The sheave bore doesn't have to be 1 1/8", it only has to be the size of the motor shaft. You don't have to buy a motor based on the pulley size, buy the pulley to fit the motor shaft.

    I don't see the problem you do.

    Will it operate in a dirty dusty area? If so it needs to be a closed frame motor, if not it can be an open frame.

    Will it have a load while starting? If so it needs to be a capacitor start motor, if not a standard induction motor should work.

    I would recommend a motor starter relay or a fused disconnect.

    Are you building your own dust collector or are you buying a factory made unit? If your building one haven't you done research on what to use? Have you checked on factory made units to see what they use?
    It's only ink and paper

  4. #4
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    May 2003
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    Around here with the mines and the mills "large motor" generally means 50 hp and up.

    Go talk to an irrigation equipment supplier.
    Last edited by Evan; 02-19-2008 at 09:24 AM.
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  5. #5
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    Oct 2007
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    More specifically, I am working on building a dust cyclone, and the requirements are somewhere around 1000 CFM @ up to 10" water.

    If I was somewhere where I could exhaust outside, that would be the cheapest option. Some fraction of the power will be lost in sound management as well -- mostly the same reason why I can't exhaust outside...

    I've kicked around the idea of 3-phase, but don't know if I am quite ready to set up a phase converter for the shop yet...

  6. #6
    Join Date
    Jul 2007
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    1,474

    Default Large motor advice

    You dont need a very large motor. I have a 1100 cfm bag filter system with only a 2 hp motor. The fan unit is supposedly rated at 14" static. In any case, it will quickly eat a 3 1/4" nail, (which the fan REALLY doesnt like!) The losses across a cyclone will be similar to those across felt bags. If you are going to discharge into the room to conserve energy, it might be a good idea to use a couple of large engine filters for "polishing." they work a treat and last a long time. You might check out Onida Systems in upstate New York. They build "small" systems, which is what we are discussing, and advertise in Fine Woodworking since Termites make more dust than Blacksmiths.

  7. #7
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    For efficiencies sake I don't think you should use a Rotary converter to run a blower motor.

    You have the current draw of the rotary converter plus the current draw of the blower motor.

    If you use just a 220v blower motor it will be more efficient.
    It's only ink and paper

  8. #8
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    Oct 2003
    Location
    Richmond, VA
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    I've used & maintained a few 5 hp dust collectors over the years in jewelry shops. Serious filters are a necessity there because otherwise you would be throwing away considerable quantities of precious metal dust. I would expect that a system without adequate pre-impeller filtration would load up the impeller quickly and cause vibration problems. I have used (& now own) smaller systems with less efficient filters, and it is a pain in the you-know-what to clean the crap off of the vanes.

    We used 5 hp (or more) systems in large polishing shops because of the need for multiple stations. A single inlet of any reasonable size would take less. Proper ductwork design makes a big difference, too.

    I currently use a 5 hp 240V single phase (WEG brand bought new from Surplus Center) on my air compressor and have had no problems with startup. You definitely want a TEFC (totally enclosed fan cooled) motor with a magnetic starter. I prefer the traditional kind with heaters (gizmos to match the protection/relays to the load) rather than the solid state kind.

    What Carld said on converters. Also, in my exp. the average electrician doesn't know his a** from a hole in the ground when it comes to 3 phase or motor starters. Burnt up a motor with a wiring error myself one time, but I made no claims about actually knowing what I was doing, and I worked a lot cheaper.

    If you exhaust inside, understand that it will be LOUD. As long as you keep the impeller from loading up with dust, vibration should not be a problem. You'd probably have to ignore a *lot* of rattling before a motor started walking around. I've never seen that happen, but that could just be good luck. Locktite the bolts if you're worried.

    Be sure you never suck sparks into dust collector filters. There's plenty of draft to get things going. Don't ask me how I know this.

    BillB

  9. #9
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    Jan 2008
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    southern delaware
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    Quote Originally Posted by Carld
    For efficiencies sake I don't think you should use a Rotary converter to run a blower motor.

    You have the current draw of the rotary converter plus the current draw of the blower motor.

    If you use just a 220v blower motor it will be more efficient.
    Do you think he could use a static converter on that setup and there is not that much weight to overcome on startup?

  10. #10
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    Jun 2007
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    Anderson SC
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    Quote Originally Posted by 2ManyHobbies
    More specifically, I am working on building a dust cyclone, and the requirements are somewhere around 1000 CFM @ up to 10" water.

    If I was somewhere where I could exhaust outside, that would be the cheapest option. Some fraction of the power will be lost in sound management as well -- mostly the same reason why I can't exhaust outside...

    I've kicked around the idea of 3-phase, but don't know if I am quite ready to set up a phase converter for the shop yet...
    I helped a friend design the electrical for a nearly identical system. 5HP single phase, 3450rpm, cyclone type for his woodworking area.

    A 5hp single phase will need a 30amp circuit and breaker. Standard breakers will handle the short durations starting current just fine.

    As for a magnetic starter... Mag starters are used because its pretty hard to find a standard switch that will handle the large inrush current without burning off the contacts. Also, mag starters typically have heater elements which serve as circuit breakers to protect the motor. If you want the cheap way out.... contactors for central air conditioning system condensors come in 40amp size and will handle the 5hp motor nicely. The have a 24 volt AC coil which works out nicely for a low voltage remote on/off switch. Air Conditioner contactors do not have heaters or other overload protection however. They sell wholesale for about $12. Thats what my friend used on his dust collection systems and it works nicely.
    A 5hp single phase motor comes in many sizes and duty cycles as you have seen. A very common one is the nema 184 frame size, quite heavy duty, weighs in at 100lbs or so and has a 1-1/8 shaft I believe. A little shopping around can find a new one for about $150

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