| Electronics > Repair |
| Motor start capacitors rated 110V being used in 240V motors and failing |
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| calzap:
Not the first time, I’ve found failed start capacitors rated 110V being used in 240V motors. See pic of most recent below. Strange thing is I get different readings on 3 different meters. The Klein refused to give a value; just indicated it’s bad. The Agilent gave a value at the low end of the rated range, which is 540-648 uF. The DER EE gives a value below the rated range. But with the leaking crud and motor refusing to start, there’s no doubt it must be replaced. It's irritating that motor manufacturers (at least two of these have been WEGs) don’t use a 250V capacitor in a motor that can be wired for 120V or 240V. Also irritating that the metal compartment for the 110V-rated is too small for a 250V-rated capacitor. So, I must fabricate a new compartment too. End of rant. Mike |
| Gyro:
That's pretty crappy underrating of a bipolar electrolytic. I suppose it's possible that the cap might only see 110V during start (the rest being dropped across the start winding) but I certainly wouldn't bank on it. That drop might be factored into the rating anyway. Even if the value is still reading somewhere near, the ESR will have gone through the roof. EDIT: If the motor can be wired for 240V or 110V, I wonder if it is possible to use a lower value cap in the 240V configuration. |
| timeandfrequency:
Hello calzap, I agree with Gyro : what you describe is really of bad choice due to such a blatant underrating. The capacitor failure that will result may even fry the motors' windings. AC Service Tech LLC produces a bunch of videos about motor capacitor. Check out at least this one ... where the influence of the incorrect capacitance value is measured, and a basic formula in run conditions (60 Hz) is provided. In AC systems, many of the small to medium sized motors or compressors are PSC (Permanent Split Capacitor) motors that require an external capacitor. As you have to replace the capacitor for 220 - 240 VAC mains, you may find these these sites/products interesting : - Capacitor boots and also here - Capacitor housings - Capacitor mounting brackets - 'Universal' capacitor for quick repair or motor testing (contains 6 different and combinable capacitance values in one part). --- Quote from: Gyro on October 28, 2024, 09:15:26 pm ---EDIT: If the motor can be wired for 240V or 110V, I wonder if it is possible to use a lower value cap in the 240V configuration. --- End quote --- You are probably right : usually the current in both windings of a PSC motor should be about the same. |
| calzap:
Thanks for the info. New capacitor should be installed 31-Oct. As expected, the 250V capacitor will need a bigger housing. Hopefully, motor windings are OK; the overload protector did trip and there was no burning smell. I’ll do a post to let you know the outcome. Mike |
| timeandfrequency:
Hello calzap, The motor might rotate firmly without load even if it suffers from a single shorted turn. Only a ringing test... ... of each motor coil will dispel any doubts. With a shorted turn, the motor has actually lost its' torque : you can truly stop it by hand, just with a piece of wood pushed againt the shaft. If the motor draws an abnormal amount of current by reference of what's written on the motor plate, this means also bad news. But of course, I hope the best for your motor. |
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