Electric motor start capacitor

[yota]

while I'm looking for another motor for a VFD on my Delta drillpress, decided to start the resto on the South Bend drill press I picked up months ago. it has an old 1/2hp Singer motor. I didn't know until I did some googling that a number of manufacturers used Singer motors on their equipment. when I turn the motor on, it buzzes, and I have to spin the motor pulley to get it going. runs quietly and smoothly until shut off. I don't know that much about electrical but from past experience that is usually an indication of a bad start capacitor.

I un-soldered the capacitor (attempted to discharge it first and got no reaction, which is a bad sign) and ran a test on it. got a big zero on the meter. other capacitors I've tested in the past have at least a low reading but never got zeros before. other capacitors I've checked have also had a range printed on them that the test meter should be in if they are good, this capacitor has no range data on it.

I also haven't had a capacitor before with a transistor (or maybe a fuse?) on it either, maybe that is skewing my reading. any ideas? hard to look for a replacement not nowing what range it needs to be in. thanks.

 

[markba633csi]

There is a bleeder resistor attached to the cap- looks like around 16 K ohms- need to unsolder one end to get a proper cap reading
If you still get zero then it's bad
Should be somewhere between 341 and 409 microfarad
Here's the manual, looks like it reads to 10000 uF

 

[yota]

I was wondering about that. will do that. thanks!

 

[yota]

There is a bleeder resistor attached to the cap- looks like around 16 K ohms- need to unsolder one end to get a proper cap reading
If you still get zero then it's bad
Should be somewhere between 341 and 409 microfarad
Some meters won't go up that high- does yours?

don't know if it goes that high, have only ever checked a few. 300-400 seems a lot. I check a cap for a pressure washer motor the other day and it said it was rated for 90, plus or minus 5%. will find out in a few minutes.

 

[yota]

unsoldered one end of the resistor, still getting zeros. I found 2 other capacitors I've saved. one is off a baldor electric motor, its rated for 270-320 UF and test at 295 so it's good. the other one is only rated for 40UF plus or minus 6% and test good also but I cannot remember what I took it off of and it's a much lower rating than the Baldor one.

the baldor capacitor is to large diameter to fit in the housing on the motor but do you think I could use it just to test the motor starting? it says it's for 250V though and the motor is 115V so not sure if that's a good idea.

 

[yota]

also, does it matter which wire is connected to which pole on the capacitor? the wires coming out of the motor look almost the same though one may have a somewhat greenish tint. I took a picture before I unsoldered the original capacitor so could put it back the same if it were working but there are no markings at the poles of the dead original capacitor. thanks!

 

[markba633csi]

Higher voltage is always ok with start caps. And these are non-polar caps, they work either way. A smaller microfarad value will still start
the motor, it will just be slower to spin up and have less starting torque
Sounds like the original one is indeed bad- try the Baldor one to test

The bleeder resistor is just for safety- it drains off the charge so you don't get a shock when handling it- doesn't affect the start up

 

[yota]

really appreciate your help and knowledge. love learning this stuff.

 

[yota]

and thanks for taking the time to look up the manual for my clamp meter. I saved it for future reference.

 

[markba633csi]

What did we do without the internet! Medieval times