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Thread: VFD Application?

  1. #11
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    Quote Originally Posted by Besoeker View Post
    If it ain't broke, don't fix it?
    Yep!

    Same speed, same load, out in VFD and you REDUCE EFFICIENCY BY VFD EFFICIECY!!!

    2-5% more cost!

    Sent from my SM-G900V using Tapatalk

  2. #12
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    Pretty sure the VFD option will get approved based on lower mechanical maintenance cost running the conveyor at half speed almost all the time. Less friction loss as well according to the conveyor vendor. It is really a two speed application - about 1/2 speed most of the time there near 100% speed when they need to move twice as much. I had reached pretty much the same conclusion with respect to power consumption.

  3. #13
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    Quote Originally Posted by Fnewman View Post
    Pretty sure the VFD option will get approved based on lower mechanical maintenance cost running the conveyor at half speed almost all the time.
    Might be interesting to compare the expected reduction in maintenance costs with the additional operating cost of greater energy consumption.
    Si hoc legere scis nimium eruditionis habes.

  4. #14
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    Quote Originally Posted by Besoeker View Post
    Might be interesting to compare the expected reduction in maintenance costs with the additional operating cost of greater energy consumption.
    There is as good a chance that this scheme will INCREASE maintenance!

    Which is worse? 2x speed at 1/2 load or 1/2 speed at 2x load?

    In my book, things will wear out 4x FASTER at 2x the load!!

    Then you also add another 5% or so heat to the motor running on VFD instead across the line... Remember every 10C cuts life in half... Bet the VFD adds that 10C!

    Then you now have the VFD, contactor, maybe other added components that will eventual brake and need maintenance.

    KISS. Think this through a bit more would be my advice!

  5. #15
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    Quote Originally Posted by Fnewman View Post
    Pretty sure the VFD option will get approved based on lower mechanical maintenance cost running the conveyor at half speed almost all the time. Less friction loss as well according to the conveyor vendor. It is really a two speed application - about 1/2 speed most of the time there near 100% speed when they need to move twice as much. I had reached pretty much the same conclusion with respect to power consumption.
    Is that going to impact whatever the conveyor is feeding? Or are you going to put more material on the conveyor but run it slower?

    What about speed of the machine fed by the conveyor? If you are feeding it at half the rate is possible it can be slowed down as well.

  6. #16
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    Quote Originally Posted by petersonra View Post
    the VFD does not change how much energy is used to move the load other than by changing the PF to near unity on the line side. but that does not amount to much.

    as for starting, it may well prolong the life of the motor and the conveyor. but you can get most of the same benefits with a soft starter.
    Sounds like this machine only starts just a few times a year otherwise runs nearly all the time.

  7. #17
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    A conveyer VFD will have to be operated in "constant torque" mode. Energy consumption will be proportional to speed. That means running at 50% speed consumes 50% power. Other loads, like fans, go by the cube of the speed so energy savings are much more dramatic at reduced speeds.

    Right now you are operating the motor at full speed but consuming half the rated amps. That sounds like a roughly 50% reduction right there. Hard to see any ROI on going with a VFD (that will cost more than a "normal" VFD as it has to be rated for "constant torque").

  8. #18
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    Quote Originally Posted by Russs57 View Post
    A conveyer VFD will have to be operated in "constant torque" mode. ...
    rest of post ok, but I strongly disagree with this comment and suggest it be removed so the rest of the post is good?

  9. #19
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    Quote Originally Posted by Russs57 View Post
    A conveyer VFD will have to be operated in "constant torque" mode. Energy consumption will be proportional to speed. That means running at 50% speed consumes 50% power.
    Don't think so in this application. At 50% speed, the conveyor will have be loaded twice as heavily to deliver the same amount of material as it did at full speed.
    Si hoc legere scis nimium eruditionis habes.

  10. #20
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    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.

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