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Thread: Does it hurt the dust collector to have all gates closed?

  1. #1
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    Does it hurt the dust collector to have all gates closed?

    Does it hurt to shut all gates then turn it off a few seconds later? Or to shut it off and immediately close the gate while it's still spinning? Start it then open a gate? The way I work and the shop is laid out, I often want to hit the on switch then open a gate, and maybe close the get before turning it off. Or at least shut the gate while it's still spinning down.

  2. #2
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    No it does not hurt it. It's counter intuitive but the more air the collector moves the higher the current/power consumption. The less air moving the lower the power consumption. So all gates closed is the lowest power consumption for the dust collector. Shop vacs often have the cooling air for the motor in the air you are moving so if your collector is like that then it could still overheat even though no airflow is the lowest power consumption.

  3. #3
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    Years ago here at SMC, a member actually measured the current with all the gates open and all the gates closed. He confirmed, with the gates closed, the motor draws the least amount of current as it is working less hard.
    Ken

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    Thanks, I was aware of the power thing, but not sure if there would be an issue with the bearings. I know DCs don't really suck like vacuum cleaners, but not sure how much pressure would be put on the mechanical parts. Good point on cooling, it's a normal TEFC motor with a blower, so it's still being cooled. It's in a small space (outdoor shed) which could get hot if I ran it a long time that way, but that wouldn't happen. I guess the most would be ten seconds if I leave it running, close a gate, and move to another tool.

  5. #5
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    Quote Originally Posted by Ken Fitzgerald View Post
    Years ago here at SMC, a member actually measured the current with all the gates open and all the gates closed. He confirmed, with the gates closed, the motor draws the least amount of current as it is working less hard.
    Me maybe? ; https://sawmillcreek.org/showthread....dux)&highlight=


    Less load = less work being done = less heat generated.

    Induction motors never exceed synchronous speed, so there is no impact on the bearings regardless.
    Last edited by John Lanciani; 05-16-2018 at 4:16 PM.

  6. #6
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    John, I was thinking of the US Navy Corpsman who did it. He was stationed aboard the USS Constitution at the time. We called him Doc. He later became a Command Chief Petty Officer IIRC and was doing some independent duty with some special forces.
    Ken

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    So the bottom line is that if I undersize my tubing I will save on electricity?? WIN!!

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    Quote Originally Posted by Ken Fitzgerald View Post
    John, I was thinking of the US Navy Corpsman who did it. He was stationed aboard the USS Constitution at the time. We called him Doc. He later became a Command Chief Petty Officer IIRC and was doing some independent duty with some special forces.
    I measured mine too, some time back using a clamp-on amp meter. The current was significantly lower with all the gates closed, due, I understand, of the ease of spinning the impeller in lower pressure (partial vacuum).

    Carlos, some people place a vent/duct in the shed down low to pull air in from the bottom by convection and another up high near the motor to release warmer air.

  9. #9
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    There is a gap at the sides of the roof and a gap at the bottom back. When air is moving into the system, of it's blowing out the heat. If there were no air flow then convection would still help, but I can't imagine running it more than a few seconds without at least one gate open.

  10. #10
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    Quote Originally Posted by Carlos Alvarez View Post
    There is a gap at the sides of the roof and a gap at the bottom back. When air is moving into the system, of it's blowing out the heat. If there were no air flow then convection would still help, but I can't imagine running it more than a few seconds without at least one gate open.
    I often leave mine (5hp) running for minutes at a time with the gates closed to minimize the noise from the air. It's in a closet; no sign of overheating by touch. If concerned you can measure the temperature with a thermocouple or a non-contact IR thermometer.

    JKJ

  11. #11
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    Oh, no concern really. My only thought on potential damage was about the bearings "pulling" against non-moving air. Well, and any other unknowns.

    Why do you leave it running for so long? To move between machines I assume? But that's a long time. I turn it off if I won't be cutting for a while.

  12. #12
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    Starting too often

    Quote Originally Posted by Carlos Alvarez View Post
    Why do you leave it running for so long? To move between machines I assume? But that's a long time. I turn it off if I won't be cutting for a while.
    These cyclones are designed to run all day. Sometimes I close the blast gates and leave it running while I figure out how best to set up another cut on the bandsaw when I'm processing green wood into turning blanks - 30 seconds turns into 2 minutes. Maybe I'm just lazy, but I understand that since startup current is high, it's supposed to be hard on the motor to start it too many times without a rest for cool-down. ClearVue said the startup current for the 5HP motor with the impeller attached is 105 amps! (until it gets up to speed).

    How often restarting in what time period is too much? I don't know since there are a lot of unknowns, but Bill Pentz wrote this:
    "Barry (Electric Motor Warehouse) explained that dust collection motors tend to be the heaviest we use in our shops so he recommends buying the best quality possible. Unlike a fan, dust collection equipment uses very large heavy impellers with lots of air resistance that cause very high starting loads. Any except heavy duty motors built to handle these high startup loads will burn up. Even these heavy duty motors come with a caution to not start them more than about 6 times an hour. The startup load is so high that it takes at least ten minutes of running to get rid of the extra heat. If started too often that heat builds too fast and the motor will burn up. Most compressor, pump, and farm duty motors will handle these high startup loads and up to the six starts an hour.

    Note that this extra heat is in the motor windings and will not be immediately noticeable on the outside of the motor. Excess heat can break down the insulation on the windings and cause an internal short.

    Note also that there is always someone who will give the anecdotal "evidence" that this is bunk because they have started theirs more often than recommended for years and the motor is still working. I prefer to listen to the manufacturer. Before I bought the ClearVue I did a lot of research. I found where Leeson recommended a maximum of (I think) 5-8 starts per hour for the 5hp motor on the CV1800.

    I'm not at all concerned about the electrical cost of running it. I know that with the blast gates closed the current draw and stress on the motor is less and monitoring the motor shows no increase in temperature when it runs "idle".

    I would not worry about stress from pulling on non-moving air - you may actually have it backwards. As ClearVue put it, "the blower does more work when moving air and therefore will put more of a load on the motor when a blast gate is open." Once it pulls the air out of the ducts the air pressure in the ducts and around the impeller is lower so it is spinning in a slight vacuum which is far easier on the motor than when moving air. I think this is also the reason ClearVue warns to never start the cyclone without the ducts attached because the startup load will be very high for a much longer time and may blow the circuit breaker or overheat and damage the motor. In fact, some people recommend always starting the cyclone with the ducts closed since the motor can pull the air out of the ducts and get up to speed quicker with less load and less heat. One motor expert recommended not shutting off the cyclone if you would be using it again within 15 minutes. However, if mine was not in a sound-insulated closet I'm not sure I could stand the noise!

    At the lab where I used to work we had experiments with extremely high-speed motors - these motors were run in a vacuum chamber since they ran so much faster and used less power when not working against the heavy air. The lower the air pressure, the better they ran so the guy used very a good vacuum pump.

    JKJ

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    I have an amp meter permanently mounted on my DC and I can confirm what others are saying.
    NOW you tell me...

  14. #14
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    The start up current draw is one very good reason to use a three phase motor and a VFD as it soft starts the motor and that soft start time can be custom changed to suit the operator. I would say that 99% of CV's in Australia use three phase motors on 240V and the start up current peaks at around 16 amps momentarily then falls back depending on how many gates are open. Using a VFD also removes the start limitation per hour and is way kinder to the motor.
    Chris

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  15. #15
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    Quote Originally Posted by Chris Parks View Post
    The start up current draw is one very good reason to use a three phase motor and a VFD as it soft starts the motor and that soft start time can be custom changed to suit the operator. I would say that 99% of CV's in Australia use three phase motors on 240V and the start up current peaks at around 16 amps momentarily then falls back depending on how many gates are open. Using a VFD also removes the start limitation per hour and is way kinder to the motor.
    That's an interesting take on 5 h.p. cyclones with their startup load. I imagine 5 h.p. 3 phase motors are pretty reasonable $ wise. New 5 h.p. VFDs ain't cheap though.

    Edit: I guess the VFDs on Ebay are pretty reasonable as long as you knew what you were doing, I suspect the documentation wouldn't be great.
    Last edited by Curt Harms; 05-18-2018 at 8:01 AM.

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