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  1. acmotorengineer

    stator slot pass frequency vibration

    Oh yeah - particularly with form wound, 2 pole stators where the coils are dropped in the slot to permit air to flow down the core. A 700HP 2P Horiz Chiller compressor motor was brought in with a vibration spectrum diagnosed as rotor problems - Rotor Bar Pass Frequency with 2X line frequency...
  2. acmotorengineer

    Stator/Rotor Resistance/Leakage Information

    BE CAREFUL - published speed torques may not be actual motor torque - rather NEMA minimums or statistically factored. AND: slip and torque at max breakdown is highly variable, difficult to measure due to rotor heating at this high rotor current. Consequently breakdown torque information is...
  3. acmotorengineer

    Shop practices for unloaded motor run

    I agree with aolalde - all incoming motors coming into our shop are checked before running whatever the reason for repair, even failed motors. Good insulation systems should be able to safely start even in a moisture rich, overnight, enviornment. However, I've had failed motors pass a "meggar"...
  4. acmotorengineer

    Typical difference between RTD and average winding temperature

    Electricpete 2. RTD vs Avg temperature difference is high with open motors since the principal heat transfer is thru the end turns and therefore have a significantly lower temperature than the slot where most RTD's are placed. The difference is closer with TEFC motor where the principal heat...
  5. acmotorengineer

    Motor Starting Characteristics

    Mark - We started this trend in the 1970's. Motors run more efficiently at less slip both in the 60 hertz AND 50 hertz world --- and subsequently higher starting current --- at NO INCREASE in cost. Designing motors for low starting current is a major reduction in running performance and the cost...
  6. acmotorengineer

    Motor Space Heaters

    rinezry the purpose of operating "space" type anti-condensation heaters at reduced voltage was a vain attempt to improve the abysmal life of cartridge type heaters. ( A wire encased in a refractory material ) Most of these heaters only lasted one year before they had to be replaced. A goodly...
  7. acmotorengineer

    Changing of 4 poles to 8 poles motor

    Actually it can be quite simple to convert a 4 pole motor to 8 poles. In some cases, All you have to do is to reconnect the groups to a consequent pole connection - all group ends are positive. This is the standard connection for one winding, two speed motors. Usually you would have to rewind...
  8. acmotorengineer

    Part Winding Start Motors

    to viperone: There is one case where the part winding start leads are larger. For 9-lead, delta connected, dual voltage, suitable for PWS on the low voltage, the 1-2-3 leads are normally larger than the remaining 6 leads. However this is for cost reasons rather than current sizing Also some...
  9. acmotorengineer

    Three phase to single phase motor

    axd38 - you're asking for major problems, I would recommend you replace the motor with a three phase motor. A much more reliable motor.
  10. acmotorengineer

    EExd Motor - Surface Corrosion

    ahr35181 don't worry about surface corrosion on cast iron motors UNTIL you can see electrical cores or rotating parts or violent vibration. I have a picture of a tin can type motor that was operating with half of the frame rusted away - running quite nicely. You could actually touch the rotor...
  11. acmotorengineer

    SINGLE PHASE ROTOR TEST

    electric pete is correct - use the lowest voltage that will give readable current and allow for small variation in current as you rotate the rotor - do the test quickly to prevent heating which will bias the test.
  12. acmotorengineer

    Is there a good electric motor design book?

    you might try: "Handbook of Electric Motors" Authors: Engelman and Middendorf Publisher: Marcel Dekker, Inc NY NY It is currently still in print - revison 2 out shortly.
  13. acmotorengineer

    Terminal markings for 3 phase motor

    the .5 and .9 ohm reading makes sense, however the 1.9 does not - you may have an odd one. I would expect 1.1 ohm for the high reading between leads. Have you checked the motor to see if it is OK - i.e. Hy Pot, Meg and Surge? For a normal two speed, one winding motor: If you draw a greek...
  14. acmotorengineer

    Terminal markings for 3 phase motor

    there are generally two common types of two speed, AC induction motors: one winding or two winding. IF you have a two winding, the windings are separate which you can easily determine by taking resistance readings between leads. You do not need markings, simply power one set and separately...
  15. acmotorengineer

    3-Phase Squrrel Cage Well Pump Motors

    I agree with electicpete, an IEEE 841 motor is pretty rugged. are you looking for vertical or horizontal motors? also what type of failures do you have?
  16. acmotorengineer

    Submersible motors

    depending on how accurate you want to know speed - for approximate speed, you can ask the manufacturer for a running speed vs current curve at operating voltage and frequency.
  17. acmotorengineer

    AC Motor Rotor Lam Design

    to Homemadesin In Fact the inner rotor core is quite essential to the operation of an AC Induction Motor - punching holes reduces the torque and increases the slip - until the motor cannot produce sufficient torque to carry any load. IN addition, a typical rotor OD for a 3/4HP 2Pole motor is...
  18. acmotorengineer

    Centrifugal Switch used in Single Phase Induction Motors

    The most cost effective switch is the cheap mechanical ones used by the motor manufacturers. My experience is the mechanical potential relay is not too reliable if used for heavy start stop duty - even with derating, unfortunately. There are some electronic relays which would seem to be more...
  19. acmotorengineer

    Minimum RPM for TEFC motor

    If the rolled steel frame is in direct contact with the stator core, the top dead center temperature measurement (out of air flow) should be approx 10C less than average coil temp. However the hot spot of TEFC motors is usually the end turns - add another 10C for hot spot. A round about way of...
  20. acmotorengineer

    slip in a cylindrical roller bearings

    for Alexsurf If you have a vertical motor with spherical thrust bearings, you must have axial load, typically 2000 to 4000 pounds for successful operation. no axial load, and the bearings skid - one skid and the bearing is damaged and will have short life.

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