Myford Capacitor problem?

Thanks for the offer. I was 50/50 whether to go to Harrogate but unfortunately can't really spare the time. I'm in Kent. However, I did a meter test. I'm getting a reading of 17 with the meter set on 2000 across P and Z2. I'm getting no reading at all on any setting across U1 and P or U1 and Z2 i.e. the meter value of 1 remains unchanged.

Edited By Chris Trice on 09/05/2014 13:36:18

Between U1 and U2, I'm getting a reading of 2 (which is good I think).

Hi Chris,
Harrogate would be a long journey for you. I am much closer as you will see from my profile. The reading you are getting (Assuming the units are ohms.) are near to what I would expect. The main winding resistance is a little lower than I would expect and the start winding in series with the centrifugal switch is a little higher than I would expect. (The main winding on the 550 watt motor on my lathe is 4.4 ohms. I could net get at the end of the start winding without taking the motor apart.) When I get time I will see if I can measure the start winding resistance on my pillar drill. I am puzzled by this sentence "I'm getting no reading at all on any setting across U1 and P or U1 and Z2 i.e. the meter value of 1 remains unchanged." It is the value of 1 (ohm?) I do not understand. The reading should be infinity. (Or at least sever megohms.) Up to the" value of 1" bit I understood the reading was infinity.

Les.

Edited By Chris Trice on 09/05/2014 16:49:59

Hi Chris,
It looks like the 1 display is your meters way of indicating over range. ((Very high resistance value.) I tried to check the start winding resistance on the motor on my pillar drill. Only two wires come into the connection box from the inside of the motor so I could not check the resistance without taking the motor apart. All your readings are reasonably sensible values so I do not know what the fault is. I was expecting the "P" and "Z2" to be higher indicating a fault with the centrifugal switch. It is just possible that the centrifugal switch has slightly high contact resistance but this is very unlikely. If your other motor is identical you could compare the readings. It is looking like there is a fault with one of the windings.

Les.

I'm coming to that conclusion. I feel another strip down coming on and a more detailed check for swarf or burning/pitting somewhere in the motor. The frustrating thing is it's worked perfectly for years with no failures or hiccups then suddenly, doesn't work with no warning or indicators of what the problem is.

My motor had problems back in 2005. I thought it was a cap problem, so took the motor off and to a place to check it out. The man un soldered the cap,tested it and said it was all fine. I took it apart, he looked at the brushes in the switch, although not perfect he said that it still should have been working. I put it all together, he soldered back on the cap, connected some wire and worked fine. He said that sometimes over time, the soldered connection of the wires to the cap need re soldering. I took it all apart as I thought that there was a problem with the centrifugal switch. I was wrong.

It worked faultlessly until 2012, when everything stopped again. This time it was the forward and reverse switch that went. So I retired the motor and put on a 3phase motor with a VFD drive. The motor still works fine, and is sitting on the shelf as a spare for something one day.

The motor on my sawbench started to get hot and sometimes stopped mid run, I could not get a replacement as it was a double ended shaft type with pulleys at both ends. I took it to a local rewind place, just 2 chaps and quite a lot of test gear. They set it up and ran it for a moment and it showed that the start windings were not switching out. They rewound it and put in a new switch and it works fine, a bit expensive but as there was no hope of a replacement motor justified. Put it in the hands of a qualified motor rewind service, they will fix it or supply a new one.Wondering whether its a capacitor or a winding, is a fault waiting to come back and bite you later.

Clive