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schematic

simulate this circuit – Schematic created using CircuitLab


The schematic is what I observed and imagined from measurement of the six terminal connections. This is a 120V 2HP electric motor with two external capacitors. The only way I can get it to come to speed it disconnect the 400uf cap and wait for it to slowly get to speed and hear the centrifugal switch open. It then works as expected under load conditions. 1) U1,U2 goes open at speed 2) Reconnect 400uf cap when at speed no effect 3) Disconnect 47uf when at speed draws 2 more amps going from 5 to 7 amps 4) Try to start with 400uf draws 50 amps will not go to speed for centrifugal sw to open 5) starting without 400uf draws 40 amps, takes 5 to 10 seconds to come to speed. 6) Lines V2,Z1 and U2,V1 control direction of motor, if connected V2,U2 and Z1 V1 would reverse direction. Something appears to prevent normal startup of an inductive motor. It was made in China and expects 50hz but was told this should not be the problem running on 60hz.

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    \$\begingroup\$ Sounds like you need to test the 400uF capacitor for excessive leakage (or a dead short circuit). \$\endgroup\$ Apr 1 '18 at 11:06
  • \$\begingroup\$ My Fluke 289 Meter reports the cap as ok as well a new one I tried just in case. \$\endgroup\$
    – L.McAndrew
    Apr 3 '18 at 1:14
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    \$\begingroup\$ Thanks for the input. I had ordered a 100uf thinking the 400uf was ok and different value was needed, the motor starts up just as one would expect, only 32 amps on start and 5 for run, 10 amps lower on startup. Must have been a bad 400uf cap, I will continue to use the 100uf until I get another 400uf to try. \$\endgroup\$
    – L.McAndrew
    Apr 3 '18 at 1:33
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I think the drawing is correct except that the terminal numbers may not be correct. There is nothing else related to the centrifugal switch. There is likely some kind of over-current or over-temperature protective device that would disconnect the motor from power if it opens.

Operation at 60 Hz might have some effect on motor performance, but not likely the problem described. It seems likely that the 400 uF capacitor is shorted.

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  • \$\begingroup\$ Hard to know, the motor's label is in Chinese. I went on-line to try to get a reference for what the letters stand for and got conflicting results. In addition the wired terminals are a mirror of the label so the only thing I know is the measured two coils and the switch goes open when I hear it get to speed. \$\endgroup\$
    – L.McAndrew
    Apr 3 '18 at 1:18
  • \$\begingroup\$ There are a number of ways in which the motor could be defective from the factory or as a result of something done by a previous owner. If it draws no more than rated current without getting too hot under load you will know you have a useable motor, but it still may not be as 100% as it should be. \$\endgroup\$ Apr 3 '18 at 2:57

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