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I have a single phase cutting SAW , 3 years old , yesterday i was cutting thick material it stalled as usually happens , but when i turn it off and then On again now it doesn't rotate , it just makes a humming noise .

motor type :

1-AC single phase 220v 2KW motor .

2-it has 6 wires coming out of the motor 2 red 2 black and 2 green wires .

3-Capacitors 200uF 250v and 35v 400v .

Full Circuit diagram

steps that i have done :

1- tested capacitors using FLuke , 200uF measures 220uF , and 35uF measures 22uF.

2- tried rotating motor by hand , i runs smoothly and freely ( no bearing problems and such)

3- i disassembled the motor , it is surprisingly very clean from inside , the centrifugal clutch seems OK , the contacts are clean , i wiped them and re-oiled them and continuity test seem OK ( the 2 green wires ) .

Question : and what could be the problem ? is it a shorted winding and how to know exactly

thanks in advance ...

EDIT :

As advised by the commenter , i made some tests using an LCR meter ( with 100hz lowest frequency) it appears that the stator coil from black wire 1 to black wire 2 has 30mH inductance . BUT from Red to red which is supposed to be the main Coil there is very high inductance (3000 Henry) and resistance is in the Mega Ohm range. I donot know if this is an indicator of short coil or open coil maybe the connecting wire is broken ?? does anyone has know how to fix this ?

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    \$\begingroup\$ After you check the clutch switch which sees heavy spike currents then check the inductance of the windings .I hope it is not burnt out \$\endgroup\$
    – Autistic
    Mar 25, 2017 at 11:59
  • \$\begingroup\$ @Autistic , how much the inductance should be ? and shall it be measured by an LCR meter at 60hz ?? \$\endgroup\$
    – ElectronS
    Mar 25, 2017 at 12:01
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    \$\begingroup\$ Low values are bad .Inductive reactance determines stall or starting current which may be sat 4 times the run current .The run current will be on the nameplate .If your measured inductance implies some big mains current then there will be a big current while the motor is sitting and humming loudly. \$\endgroup\$
    – Autistic
    Mar 25, 2017 at 12:07
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    \$\begingroup\$ If it "usually happens" (your words) that you're stalling your saw, then it isn't the right tool for the job, and you are seriously abusing it. It isn't at all surprising that one of the motor windings burned out or developed an internal shorted turn from the heating caused by the excessive current. In other words, the next step is to get a bigger saw. \$\endgroup\$
    – Dave Tweed
    Mar 25, 2017 at 12:25
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    \$\begingroup\$ This motor for high torque, you got 2 secondary coil, first with a static capacitor (permanently secondary winding), second is initial starter with switch. Which winding is damaged (or switch)? Secondary permanent winding provide a speed limiting, but all related to load effect, when motor speed is down your per. sec. wind lose phase angle, so go to nearest main winding phase. \$\endgroup\$
    – dsgdfg
    Mar 31, 2017 at 6:38

2 Answers 2

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If the centrifugal switch is OPEN when at rest, that's your problem. It should be CLOSED at rest and OPEN when at 80% speed.

When you stall and try to keep using a single phase capacitor-start motor, it slows down, then the centrifugal switch re-closes, putting the start winding and cap back into the circuit. But that winding is not designed to be used under load, neither is the centrifugal switch. You burned out the switch, maybe the winding insulation too.

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  • \$\begingroup\$ the switch is normally closed , so its probably OK , the winding is probably burnt \$\endgroup\$
    – ElectronS
    Mar 29, 2017 at 15:39
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After taking the motor to a repair shop they dissembled it and it was the MAIN COIL damaged , The wire was broken due to temperature they suggested. They Rewind the Coil and the motor is working again . Saved me from buying a new one :) YAY ..

I posted the answer to help anyone find the problem quickly if he/she had same symptoms.

thanks for your comments and answers

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