1000 to 1 VFD Motor
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  1. #1
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    Question 1000 to 1 VFD Motor

    Was chatting with the WEG rep today he told me thy have a constant torque 1000 to 1 VFD rated motor with the optional blower so that an 1800 motor could be run as low as 1.8 RPM.

    Somehow this sounds a bit over ambitious with out the blower attachment the motor is VFD rated 20 to 1 and the motor is totally enclosed.

    The motor # is A 3HP 1800RPM 3 phase foot-mount part number 00318ETE182T and the blower part number is BLB-ID180 could not find a picture of the blower.

    Would like your opinions before I spend the big bucks on this.

    Marci

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    Aside from my personal bias against Weg motors, it's probably legit. The only real limitation on motor speed is cooling, so if they are saying they will guarantee the motor as being capable of running full torque indefinitely at 1.8Hz with their blower, then they have most likely tested it to that performance level.

    Baldor has a similar motor and it has been out for a long time now. Given the "lead vs follow" nature of the motor business, I would say this motor offering from Weg is their answer to Baldor's success with their version in that low-speed inverter operated world. Did you check them to compare?

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    Depending on what you are trying to accomplish - the 1000:1 motor is probably overkill.

    I have used standard off the shelf TENV motors and run them at 100% torque on a continuous basis in marine winch applications . . . throughout the day the motor makes mabey upwards of 20 revolutions as the tide goes in and out.

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    standard off the shelf TENV motors and run them at 100% torque on a continuous basis
    +1

    I'm amazed that the WEG tech rep didn't recommend a TENV over a TEFC plus external fan. More compact, fewer things to go wrong, built exactly for low speed/high torque apps.

    --------------
    Barry Milton

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    Thanks guys.

    Marci

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    Quote Originally Posted by motion guru View Post
    Depending on what you are trying to accomplish - the 1000:1 motor is probably overkill.

    I have used standard off the shelf TENV motors and run them at 100% torque on a continuous basis in marine winch applications . . . throughout the day the motor makes mabey upwards of 20 revolutions as the tide goes in and out.
    Fairly low duty cycle though eh? I would imagine any decent quality motor would be fine in that application.

    I have tried using standard TENV and even TEFC motors on a low speed conveyor application where there were periods of prolonged use at very low speeds, the 1000:1 Baldor was the only one that survived.

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    You will never go provably wrong huffing and puffing about the need for a fan or supplemental cooling air on motors run at lower than nameplate RPM. Much depends on duty cycle. If the motor is run continuously at full load Amps below say 40 Hz and heating or the smell of hot insulation can be detected then certainly a fan is called for. If the motor is operated intermittantly or at near idle current at low RPM then a fan may not be required even over a 1000 to 1 range.

    BTW, 1.8 RPM is well below the slip/torque limit. Closed loop feedback is required for reliable low RPM operation of inducton motor from VFD's.

    Manual machine tool duty for a motor is like embassy duty for a Marine. Most of the time all that' required is a presence and authority. Once in a while real work is called for and a heavy cut is taken (or a mob quelled) and that's were a motor or a marine earns its keep. This is low duty cycle. Many factors contribute to the need for external cooling and lower than name plate RPM is only one. Other factors motivating a decision to add a fan are high duty cycle, high ambient temperature, nearby sources of radiant heat, lack of local air circulation, low line voltage, frequent momeentary overload, dust infiltration and accumulation, and probably more that I can't flog from my morning brain.

    A fan is not an automatic requirement for a machine tool motor powered from a VFD. Try it on your machine and see but have a back up plan in mind. No point in adding cost and complexity if there is no need.

    A good supplemental cooling solution is a 250 CFM (or more for larger motors) biscuit fan ty-wrapped to the fan shrould grill. A better one would be the same fan fed through a nap action thermostatic switch bonded to the stator iron.

    Similarly, it's often stated you should select a three phase rated VFD 1 1/2 times the power of the driven motor HP when running it from single phase. This is true of saws, machine tools etc that may be run ad full load Amps but at relatatively low duty cycle.

    For pumps and compressers that run full load from start you have to select a three phase rated VFD double the driven motor HP for single phase feed. Premature failure is quite possible for the rectifier to fail. One limtation is the overload capacity of the input diodes. Another is the ripple current capacity of the filter capacitors. Another that's seldom mentioned is the effect of the 120 hz ripple superimposed ripple on the VFD's output circuitry.

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    jraef - the application was holding a barge in position while unloading. Highest loads were during tide changes where we were at rated motor current for several hours. Most of the time the motors were at 20 - 50 percent current depending on whether they were on the upstream side or downstream side of the port.

    Because the application was basically holding the barge in position while trains were pulled on / off - the motors often never moved more than a few revolutions for several hours - always holding the load.

    4 coordinated winches on a 100 ft x 400 ft railcar barge. One in Galveston, the other in Coatzacoalcos Mexico. The motors are Baldor TENV 10HP and the drives were Getty's line regenerative spindle drives.

    I did that project in 1993 in the midst of a cholera epidemic in Coatzacoalcos - we stayed hydrated drinking Modelo after the bottled water ran out! Can't say the quality of the wiring was that great after about the 4th beer every day.

    One other comment - these drives were closed loop AC Vector - and as a result, the torque / amp was as efficient as it gets. Tests done for Burlington Northern at the time showed 100% torque at stall for 24 hours did not raise the temperature of the winding anywhere near insulation rating (Class H) - in fact, you could put your hand on the motor case and it was hot, but not so hot you could keep your hand on it for 10's of seconds.

    Using an open loop drive (without encoder feedback) would not be nearly as efficient at stall and motor heating would be significantly more.


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