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

  1. #16
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    The VFD's we use are Powtran and they have excellent documentation and factory support. There would be hundreds in service driving CV's in Oz and I know of one failure and it was running continuously 8 hours a day in a commercial workshop.
    Last edited by Chris Parks; 05-18-2018 at 8:35 AM.
    Chris

    Everything I like is either illegal, immoral or fattening

  2. #17
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    Quote Originally Posted by Chris Parks View Post
    The VFD's we use are Powtran and they have excellent and factory support. There would be hundreds in service driving CV's in Oz and I know of one failure and it was running continuously 8 hours a day in a commercial workshop.
    Several past threads discussed this. Here's one from 2011: https://sawmillcreek.org/showthread....art-on-Cyclone

    JKJ

  3. #18
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    2011! Time flies when you are having fun. My comments in that thread were written before I had become the CV distributor for Australia and my cyclone was using a Huanyang VFD. Shortly after I began selling CV's in Australia Huanyang kindly discontinued the model we were using and fortunately I was forced to find & use the Powtran which was a very good move as it had so many advantages, was a far better specced unit and way better made. I can't speak too highly of the company to tell the truth.
    Chris

    Everything I like is either illegal, immoral or fattening

  4. #19
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    Quote Originally Posted by John K Jordan;.[/I

    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 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.


    JKJ
    Hi John, a lot of the heat is also in the rotor where the aluminum bars are located. This is the winding in the rotor and it can be damaged by excessive slip (overload or frequent starting).

    Regards, Rod.

  5. #20
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    Quote Originally Posted by Rod Sheridan View Post
    Hi John, a lot of the heat is also in the rotor where the aluminum bars are located. This is the winding in the rotor and it can be damaged by excessive slip (overload or frequent starting).

    Regards, Rod.
    I'm sure there is a lot of heat in the rotor, but is it higher than in the stator. When studying this once I remember that for induction motors the hottest place in the motor was the stator coils, perhaps because they are directly powered to produce the fields that induce current in the rotor coils. Baldor indicates the hottest place in a motor is the stator slots. And everyone agrees that heat in the motor is a primary killer since it causes the insulation to break down and short the coils.

    Regardless, the temperature inside will be hotter than the outside. I read one source that said a large TEFC motor might be 25 deg C cooler on the outside of the case than in the windings! (They didn't say how large the motor was.)

    JKJ

  6. #21
    I suppose heat on the rotor is of less concern, but it's possible to have a wound-rotor induction motor (instead of a squirrel cage), and the failure of insulation, there, could kill the motor. Even in a squirrel cage, insulation between the laminations could fail.

    What's interesting, though, is to consider how heat gets out of the rotor. Take a TEFC for an extreme example: while the stator coils are in contact with the outside case (which is cooled by a fan), the only ways to get heat out of the rotor are via radiation TO the stator coils, or conduction out the shaft or to the stator coils via the air gap. Obviously, the rotor could be very hot without the case being hot, at all.

  7. #22
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    Quote Originally Posted by John K Jordan View Post
    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
    I guess I might fall into the person with anecdotal experience of the user mentioned above but only with Leeson three phase motors...do they behave differently to single phase? I have no idea.

    I sold many three phase Leesons on Clearvues and to this day I know of no failure with any of them using a VFD and with no restrictions specified on the number of starts per hour. Certainly my personal CV is started whenever I want it to be running with no evident problems. I can't comment further than that and I would be interested if the start per hour figure is different single phase to three phase.
    Chris

    Everything I like is either illegal, immoral or fattening

  8. #23
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    Quote Originally Posted by Chris Parks View Post
    I sold many three phase Leesons on Clearvues and to this day I know of no failure with any of them using a VFD and with no restrictions specified on the number of starts per hour. Certainly my personal CV is started whenever I want it to be running with no evident problems. I can't comment further than that and I would be interested if the start per hour figure is different single phase to three phase.
    I think the VFD would be a great addition - I suspect the gentle start would be a big help to motor life. I don't know anyone here using a VFD on a cyclone. Leeson or one of the other respected motor companies (Baldor?) might have starting guidlines for both 3 and single phase power you could compare. Or ask them.

    I also have a 5hp single phase motor on my air compressor. When I'm using air tools that cause it to cycle a lot I worry about the number of starts per hour. I didn't find any recommendations in the manual.

    I also wonder about the usually unmentioned factor in motor life - the wiring size and length of run. If not careful it would be easy to size wiring too small or right on the edge such that the voltage drop would cause increased current draw and higher temperatures leading to higher resistance in the wiring and higher current draw in the motor, etc, etc. I ran #6 wire about 40' to the air compressor/cyclone closet in my shop to make sure of this. I know a lot of motors have failed from trying to pull too many amps through wire too small. I suspect three-phase would help with that problem as well.

  9. #24
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    I think the VFD is a great addition to a cyclone and there is nothing stopping anyone from ordering with a three phase motor. It must be far kinder to the motor to ramp it up to speed over a few seconds than hit it hard with an on/off switch. When the US govt legislation caused Leeson to change the original motor supplied to Clearvue we sourced a motor from Australia which has been equally as reliable.
    Chris

    Everything I like is either illegal, immoral or fattening

  10. #25
    For what it's worth industrial and utility fans used in thermal power plants ie boiler forced draft (think combustion air supply) and induced draft (think combustion products exhaust ) fans with motor HPs in the hundreds or even thousands are always started with the dampers fully closed to protect the motor from burning out. This is from my experience as a boiler engineer (retired).

  11. #26
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    Quote Originally Posted by Doug Garson View Post
    For what it's worth industrial and utility fans used in thermal power plants ie boiler forced draft (think combustion air supply) and induced draft (think combustion products exhaust ) fans with motor HPs in the hundreds or even thousands are always started with the dampers fully closed to protect the motor from burning out. This is from my experience as a boiler engineer (retired).
    The obvious sometimes escapes us!
    Chris

    Everything I like is either illegal, immoral or fattening

  12. #27
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    Quote Originally Posted by Doug Garson View Post
    For what it's worth industrial and utility fans used in thermal power plants ie boiler forced draft (think combustion air supply) and induced draft (think combustion products exhaust ) fans with motor HPs in the hundreds or even thousands are always started with the dampers fully closed to protect the motor from burning out. This is from my experience as a boiler engineer (retired).
    Good idea, it won't take much effort to turn it on before opening the gate.

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