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Induction motor, capacitor and smoke

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Newbie level 4
Sep 25, 2011
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My neighbor asked for my help with wiring an induction motor that he got for free, despite my lack of experience and knowledge in this field. I didn't even know how to connect the capacitor (which I told him), but he still insisted I should look it up on the Internet and do it (he probably didn't want to pay anyone).

The motor was Croatian made, 6.6A, 1 HP unit. I guess it's capacitor start motor because I saw something that must me centrifugal switch inside of it. It has 6 terminals on it, 1 - 4 and 2 - 5 are connected with jumpers and 3 - 6 read 0 ohms on an ohmmeter. He got the motor with mains voltage connected to terminals 5 and 6 and without the capacitor motor starts up on it's own, but very slowly and it cannot start under load. The resistance measured with an ohmmeter between 5 - 6 and 4 - 5 is about 4 ohms, so after some thinking I decided that the capacitor should go between 6 - 4 (or 1 since 1 - 4 are jumpered). I connected the capacitor as shown in the picture and in the first try the motor started quickly, lights went a bit dim, but came back up when the motor reached full speed, as expected. I kept my hand on the capacitor - it stayed cold. Then my neighbor switched the motor on and off several times, left it to sit for a minute or two while we were talking and then started it again. This time lights went really dim, engine windings were quite loud, motor was running slow and after a few moments the capacitor (125 uF, taken from another induction motor, metal case banged up and stuck with duck tape, also given for free) started smoking and that was the end of it.

I would like to know - was this my error? Was my wiring wrong? There weren't any markings on the motor, but I don't see any other way of wiring it without taking off the jumpers. The motor run well in first attempt and I've tested the capacitor before installing it, it wasn't shorted between plates and it wasn't shorted to the case. Could fault like this be caused by frequent on/off cycling?

Just out of curiosity - what would happen with a big capacitor like this if connected directly to 50Hz AC mains? In theory it would draw about 25A, but shouldn't generate any heat expect from resistive losses, right?

I guess my neighbor shouldn't have expected more from free stuff and free repairman :)


Well it looks like a 3 phase induction motor as it is having 6 terminals...usually the capacitor motors are having 4 terminals 2 for starting and ending of main winding and 2 for starting and ending of auxiliary winding. If its a 3 phase motor as it seems to be, it starts as a single phase when you plug it in, as it is running in single phasing mode, it is running slowly. The bottom three terminals are the three coil ends and the top three terminals are the three coil starts.

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