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Thread: VFD Application?

  1. #21
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    Quote Originally Posted by Fnewman View Post
    Since some things have wandered off the facts a bit, here is an expanded restatement.
    There are actually two identical, parallel conveyors presently equipped with constant speed motors each operating at about 45% FLA. The process runs 24/7, so start frequency may be 1-2 times a month at the most. The design is such that if one conveyor is out of service the other can carry the total load. Typically that would occur only 1-2 weeks per year at most. So, the proposed VFDs would operate at approx 50% speed nearly all the time. The conveyor vendor says that slower speed = longer conveyor belt and mechanical component life as well as reduced friction.
    But.........
    At 50% speed the conveyor would have to be loaded twice as heavily to deliver the same quantity of material. Did the conveyor vendor take account of that for friction and belt life? Is conveyor belt life a problem currently anyway? Is it an expensive replacement cost and, if so, how frequently?

    And why would the conveyor vendor recommend something that could, if he is right, reduce his potential sales revenue?
    Something doesn't add up here.
    Si hoc legere scis nimium eruditionis habes.

  2. #22
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    There are many solutions. To pick the best one depends on the goals.

    In general, the biggest advantages to adding a drive are speed control (which you seem to have no need of) and control of inrush current (which again you seem to have no need of). There are other advantages but one must be willing to pay for a drive with the right control logic and someone to set it all up. You would want to read up on 4 quadrant operation and open/closed loop vector controls.

    But really a lot more information is needed....things like does the conveyer move product up or down an incline.....would it ever need to start up fully loaded....would it ever need to hold a load in place....and tons more. Now if everything is level, rate of delivery doesn't matter, and you don't start/stop/reverse/hold the load or vary the speed of it, then I would find it hard to justify the cost of the drive.

    Heck, ever thought of getting a 50 HP motor and another gear box?

  3. #23
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    Quote Originally Posted by Besoeker View Post
    But.........
    At 50% speed the conveyor would have to be loaded twice as heavily to deliver the same quantity of material. Did the conveyor vendor take account of that for friction and belt life? Is conveyor belt life a problem currently anyway? Is it an expensive replacement cost and, if so, how frequently?

    And why would the conveyor vendor recommend something that could, if he is right, reduce his potential sales revenue?
    Something doesn't add up here.
    Kind of what I was trying to say from the beginning. Just because the thing is only about half loaded now, doesn't mean you can just run the motor at half the speed it currently runs at. If it were a fan or pump you could slow it down if not using all the potential capacity, but say conveyor were currently dumping 100 pounds per minute of material into whatever the next stage of the process is. If only thing you change were to cut the speed of conveyor in half, you now are only dumping 50 pounds per minute. To get back to 100 pounds per minute you need twice as much material on the conveyor. Next question is can the conveyor handle twice the weight even though it is running at half the speed? Since they currently do run more material at times the answer is probably yes, but still all you did was spend $$$ on a VFD but still are using close enough to same amount of energy that it makes the investment questionable, unless you have gained some other benefit by slowing it down.

  4. #24
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    Quote Originally Posted by kwired View Post
    Kind of what I was trying to say from the beginning. Just because the thing is only about half loaded now, doesn't mean you can just run the motor at half the speed it currently runs at. If it were a fan or pump you could slow it down if not using all the potential capacity, but say conveyor were currently dumping 100 pounds per minute of material into whatever the next stage of the process is. If only thing you change were to cut the speed of conveyor in half, you now are only dumping 50 pounds per minute. To get back to 100 pounds per minute you need twice as much material on the conveyor. Next question is can the conveyor handle twice the weight even though it is running at half the speed? Since they currently do run more material at times the answer is probably yes, but still all you did was spend $$$ on a VFD but still are using close enough to same amount of energy that it makes the investment questionable, unless you have gained some other benefit by slowing it down.
    Like I said, on the basis of the information we have, there is no case for spending money to install a VSD. And some points against doing so.
    Si hoc legere scis nimium eruditionis habes.

  5. #25
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    Also begs the question of why not run one conveyer close to 100% loaded and let the other one sit idle? Alternate on whatever schedule you like. Seems like running half as many hours would extend life and save energy and maintenance costs.

    Still trying to wrap my head around a process where delivery speed doesn't matter, just share volume.

  6. #26
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    Quote Originally Posted by Russs57 View Post
    Also begs the question of why not run one conveyer close to 100% loaded and let the other one sit idle? Alternate on whatever schedule you like. Seems like running half as many hours would extend life and save energy and maintenance costs.

    Still trying to wrap my head around a process where delivery speed doesn't matter, just share volume.
    I like that idea, probably does save some energy costs.

  7. #27
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    Notwithstanding all insights regarding the need or lack of it, there are benefits from deploying VFDs.

    The mfg entity must have been mulling about this, not just because the idea came out of thin air.

    I'm sure they have consulted several experts (or are still) getting inputs from several engineering consultants whether deploying VFDs would be beneficial.

    This is something that a scope of the NEC forum cannot very will serve the need. This would involve sizable investment and cannot be easily carried out with a “shooting from the hip” decision making process.

    I suggest consulting an Industrial Engineer with a cadre of mechanical and electrical engineers getting their heads together and not arm-wrestling of individuals which is really nothing but offer confusing and unsupported “do this-do that” that don't really offer a discernible solution.

    One member even suggested that one poster be “shut out” to arrive a consensus.

    Is this really how to foster exchange of ideas?

  8. #28
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    Quote Originally Posted by myspark View Post
    Notwithstanding all insights regarding the need or lack of it, there are benefits from deploying VFDs.

    The mfg entity must have been mulling about this, not just because the idea came out of thin air.

    I'm sure they have consulted several experts (or are still) getting inputs from several engineering consultants whether deploying VFDs would be beneficial.

    This is something that a scope of the NEC forum cannot very will serve the need. This would involve sizable investment and cannot be easily carried out with a “shooting from the hip” decision making process.

    I suggest consulting an Industrial Engineer with a cadre of mechanical and electrical engineers getting their heads together and not arm-wrestling of individuals which is really nothing but offer confusing and unsupported “do this-do that” that don't really offer a discernible solution.

    One member even suggested that one poster be “shut out” to arrive a consensus.

    Is this really how to foster exchange of ideas?
    Some of the people responding have quite a bit of experience in the type of thing being discussed here.

    Who suggested shutting out someone else? There may have been replies that disprove or at least oppose an idea here or there, but that is a little of what a forum is about isn't it?

    OP can take the good and the bad and make a better informed decision then he had before posting here, things come up he maybe never thought about.

  9. #29
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    Too little info
    need info on the process
    what feeds the belt, what the belt feeds, it must be coordinated
    is the material like coal/gravel or discrete like boxes
    what kind of power are we talking about

    P = work/time = Weight x dist / time, in this case
    so if time gets bigger, ie, slowed down, and weight gets larger, ie, more loaded, They offset and P ~ the same



  10. #30
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    Myspark, good post and I agree 100%.

    I jumped to a conclusion that this was to be an "in-house" solution carried out by maintenance techs and that was why he was asking questions here.

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