What makes a cheap motor fail soon.
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  1. #1
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    Default What makes a cheap motor fail soon.

    I understand that many cheap foreign made ac motor do not last long. What is wrong with them? I assume cheap bearings fail soon, bad start switches on single phase ones. Are the coils too small of wire for the load, bad insulation, or something else. Forrest would say the coils need to be removed and given a dip and bake.
    Is there anything that can be done if I buy a machine with a cheap motor to increase the time before failure in a home shop situation.
    Bil lD

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    The number one single phase failures I've seen are the start and run capacitors, they are made so poorly it seems they burn out a little with every use and rely on the "self healing" factor until they fail.

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    Quote Originally Posted by Bill D View Post
    Is there anything that can be done if I buy a machine with a cheap motor to increase the time before failure in a home shop situation.
    Bil lD
    if the motor is only lightly used, you can wire the motor for 240 and run it on 120. you'll get 25% of the torque out of the motor but it will never warm up and as such, there will be very little thermal expansion friction between the windings and the core, and as such it might last 100 times as long if the bearing don't fail.

    typical 1 hp motor (and even some 1/2 hp motors) consume 200-250 watts no load and are 50-65% efficient under full load. only way to guess as to how to prevent early motor failure is to take a close look at all the components. some cheap motors with aluminum windings are actually very well made. others, not so much. don't wait for the bearings to fail and the rotor smash into the rotor and short out the windings.. they will make a lot of noise long before that (unless its a journal bearing and lubrication was neglected)

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    Couple items. Low temperature wire insulation and poor quality wire coating. Running the temperature rise up by reducing turns and driving the iron harder, cheap grade of lamination steel, increasing the lamination thickness, eliminating hydrogen anneal. These are items that will cause the temperature to rise with time and hence, damage the wire insulation.

    Tom

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    I disagree. #1 Running motors under voltage usually caused from bad connections and/or undersized wire for the load. Next would be overloading the motor and/or exceeding the duty cycle.

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    Many Chinese motors, especially DC motors are under wound to save copper. They then draw too much current and over heat. Add poor heat resistant wire insulation and you have imminent failure guaranteed........just beyond the guarantee of course.

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    Iif you pull the end bells and see that the wire is not tied and varnished on the "end turns" of the winding where it reaches over to the next "slot", soaking some glyptal varnish into the windings can help prevent the wires from vibrating and either breaking or fretting off the insulation against one another.

    I have not had glyptal damage the varnish coating, but I suppose there is always a first time, depending on what garbage the wires in a chinese motor are already coated with. Even the chinese admit that they make bad motors.

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    I have a customer that has lathes that can't be mentioned on PM. 5 are high use, and 4 others are lower use.
    They were intended to run on 240 Volt single phase.
    The newer chinese built contactors used very poor material for the contacts and wore out rather quickly. Replaced with Telemecanique.
    The newer motors were much worse. The capacitors did not have any discharge resistors at all. Would hold a 300+ volt charge for hours.
    The contacts in the starting switch were made of Copper. They would work for a few starts then the motor would hum and not start.
    Wait overnight and things would work again for a few more starts then just a hum. The plastic of the junction box that held the caps was broken up from shipping.
    We switched the newest motors to 3 phase to get away from the starting switch issues. Nearly 2 years later, one maybe 2 contactors that were well used to start with wore out. just replaced them with new ones.
    The older motors had starting switch issues and some capacitor (starting mostly) issues, lead burning off and opening internally.
    When the across the pond motors failed, they were replaced with Baldor, and still had starting switch failures. But we could order replacements and change out a bad switch in a few minutes.

    Bill

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    Sand doesn't help either.

    20190409_083236.jpg


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