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  1. #21
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    Lemme chime in.

    My maybe 1940 BP M head 3-phase motor runs silent, excellent, at around 80 years of age with a VFD.
    The AC induction motors for lathe and saw at 1.5 kW and 2.2 kW mass less than the BP motor.

    BP is 18 kg.
    1/2 Hp.

    New 2.2 kW AC 3-phase motor (output), EU 240 V, 3000 rpm, is about 14-16 kg.
    10x the power of the Bp motor (5 hp of 0.5 Hp), and most likely less than half the lifetime if used at rated output in extended use.

    The lathe 2.5 kW cont. output AC servo motor is about 20x better than the Bp, and maybe 3-5x better than any of the 3-phase motors.
    It accelerates to 3000 rpm in 20 ms or less, no-load.
    Yes, 0.02 secs to 3000 rpm.
    And stays fairly cool under no load, medium load, and max load.
    And is about 16 kg.
    And reacts in about 12 kHz, aka 0.001 secs to any error in speed/position, making for much better smoothness and surface finish.

    At 30 Nm peak, 1:3 belt drive, I get 90 Nm torque at spindle (3 secs) and 0.01 secs stop on any error like a crash.
    I have effective 11 kW AC 3-phase motor torque, for 1/3 the mass and size.
    Q:
    The Haas ST10 11 kW has 102 Nm peak at 1200 rom, and less at other speeds.

    The servo might last 10.000 hours.

  2. #22
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    Quote Originally Posted by hermetic View Post
    A motor that is rated at 1hp produces 1hp of mechanical energy. A motor rated at 746 Watts, the theoretical equivalent of 1hp does not produce 1hp of mechanical energy, it produces 1hp minus the efficiency rating of the motor, which is somewhere in the region of 80% to 85%. If the motor you buy is rated in Watts, as most are today, you need to know the efficiency rating, and calculate the losses to get a motor of equivalent hp to the one you are replacing. Sorry, but I dont buy tne "all modern motors are more efficient" story. Very high end expensive motors can be made more efficient, but the standard 3 phase motors have been at around 80% efficient for many years.Single phase are much less efficient. I dont go for the tale about "modern varnishes can run hotter" either. Firstly, a motor is designed to produce mechanical energy, not heat, if it is producing heat, it is dissipating energy as heat rather than torque and is therefore inneficient. I think the new high temperature varnishes allow manufacturers to produce over rated cheaper motors that will run hotter without actually burning out!
    I disagree with your statement about varnishes. Higher temperature varnishes allow the wire to carry more current which in turn produces more flux that can produce higher torque. Thinner insulation allows more copper per sq unit of winding area.

    The copper doesn't care about temperature nor does the steel. So the higher the temperature, the more powerful the motor. Just won't last as long. As far as efficiency, heat goes up as the square of the current, but so does the torque. What could happen is that as the iron is driven closer to saturation, the iron losses will increase non-linearly.

    Tom

  3. #23
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    Quote Originally Posted by TDegenhart View Post
    One test is worth a thousand opionions.

    Tom
    When you're right, you're seldom wrong.

  4. #24
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    Read my post again! I did say that single phase motors are much less efficient than three phase, it is only three phase motors that get to 80% and beyond. I live in the UK, virtually all motors sold in Europe are no longer marked with the HP, all marked with Watts and kiloWatts now!

  5. #25
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    I fully understand that the copper doesn't care about the temperature, but the fact still remains that the heat comes from Watts dissipated as heat rather than torque, and it is rapid heating and cooling cycles that loosens laminations, and generally kills motors.

  6. #26
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    Quote Originally Posted by hermetic View Post
    I fully understand that the copper doesn't care about the temperature, but the fact still remains that the heat comes from Watts dissipated as heat rather than torque, and it is rapid heating and cooling cycles that loosens laminations, and generally kills motors.
    Quite honestly, I have never seen a motor fail from loose laminations, or for that matter loose windings. For a motor to be U/L listed for class H or other high temperature insulation systems, not just the varnish, but ALL insulating materials must be listed for that class of temperature. In a general statement, the materials have to withstand the temperature, say 200C, for 200,000 hours then pass a series of mechanical and electrical tests. The varnish that the motor is soaked in is one of the components. This effective encapsulates the entire lamination and wiring system into a solid block.

    So what factors do cause failure? Obviously bearing and lubricants. Lack of adequate cooling. A lot of the old open drip proof frame motors fail from a accumulation of dirt and oil blocking cooling passages.

    One area that few people are aware of is the quality of varnish. Magnet wire used to be available in single, heavy and triple build insulations. Partly for the added thickness but also to cover pinholes. When solvent based varnishes cure, the solvents leave behind pinholes. Too many pinholes can allow for dielectric failure winding to winding. NEMA standards allow for the number per unit length of wire. Normal hipot tests on a completed motor will not detect these voids. What will find them is a surge test. The test consists of a high voltage pulse, upwards of 10,000 volts or more with a rise time .2 microsec or so. There are different specifications for this. This puts a tremendous voltage stress on the initial and final turns and layers of the coil due to the incremental inductance. Not only pinholes but poor winding construction can be outed by this. In actual service, this is what the motor sees when switched off. Once the arc goes out, the remaining energy in the magnetic field produces a high voltage pulse and oscillation to dissipate the energy. Most good motor shops will have the equipment to perform this test.

    Oh, and in addition to my bit of wisdom above, it is well known that a single awshit wipes out a thousand attaboys.

    Tom

  7. Likes Bob-J-H, hermetic liked this post
  8. #27
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    Quote Originally Posted by hermetic View Post
    Read my post again! I did say that single phase motors are much less efficient than three phase, it is only three phase motors that get to 80% and beyond. I live in the UK, virtually all motors sold in Europe are no longer marked with the HP, all marked with Watts and kiloWatts now!
    Yes and that is the watts output of the shaft.

    Multiply volts x amps x pf x efficiency it should equal the kilowatt rating of the motor.

  9. #28
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    Quote Originally Posted by johansen View Post
    Yes and that is the watts output of the shaft.

    Multiply volts x amps x pf x efficiency it should equal the kilowatt rating of the motor.
    Yes it SHOULD, but it is rated by the amount of Watts it dissipates, not the amount of energy it produces, so as I said in the first place, a motor which dissipates 746 watts, will not produce 1hp of mechanical energy, or if you want it the other way round, a 1hp motor will dissipate more than 746 Watts. The above calculation (transposed correctly) would produce a Wattage figure which would be less than the motor actually dissipated. Given the reports in this thread of supposedly wattage equivalent motors not being up to the jobs they should be able to perform, we can take a rough guess that manufacturers are using wattage ratings to thier financial advantage.

  10. #29
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    Quote Originally Posted by marka12161 View Post
    I got a quote back from the motor shop to repair the old motor. Basically they will steam clean, bake, megger re-lead, change bearings, re lube and fix any insulation problems. It won't be cheap but it saves me a bunch of work adapting a new motor with a different frame size.

    Regarding the discussion on the topic of flux density inside the motor, i would be careful not to over-simplify this. It's a complex physics problem that requires a detailed understanding of the inductances in the motor windings, the physical dimensions of the components involved and, as i recall, the mutual inductance between the stator windings and the rotor under various transient and steady state conditions. The phasor diagram is complex and it's been too long since i've looked at it carefully. Having said that, it is fun to kick around these ideas.
    Which shop?

  11. #30
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    Quote Originally Posted by markz528 View Post
    Which shop?
    KJ Electric in Syracuse NY.

  12. #31
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    Quote Originally Posted by marka12161 View Post
    KJ Electric in Syracuse NY.
    I would use AAI over KJ. But for what you are doing you are probably ok with KJ. AAI is not far from KJ.


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