Smoking capacitor

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Forum topic by Loren posted 01-13-2015 08:49 PM 1214 views 0 times favorited 9 replies Add to Favorites Watch
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10269 posts in 3615 days

01-13-2015 08:49 PM

I’ve been fussing with getting the table raise/lower gearmotor
on my stroke sander working. It worked before then stopped.

Anyway, once I got it going again, doing a few cycles up and down
the capacitor started smoking. I figure it’s done and I’ll order
another one… but I’m wondering if this is an issue with gearmotors
or just my lucky day that it wasn’t something worse?

9 replies so far

View NoThanks's profile


798 posts in 1496 days

#1 posted 01-13-2015 08:58 PM

I know where you could get a whole used stroke sander pretty cheap (at the moment), it’s closer to you than it is to me. Just to let you know, I decide to pass if your interested.

-- Because I'm gone, that's why!

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10269 posts in 3615 days

#2 posted 01-13-2015 09:08 PM

I don’t want it. One stroke sander is enough. It’s real close
to me though. If you buy it, look me up.

View ElChe's profile


630 posts in 1303 days

#3 posted 01-14-2015 02:50 AM

Smoking capacitor sure seems like it is shot. I’d make sure it is not holding a charge by using a bleed resistor and then hook it up to a multimeter and test its capacitance just for giggles. I bet you it isn’t anywhere near the plus minus percentage of its specs. Not familiar with a gear motor so what does the capacitor on a gear motor do? Is it a start capacitor or a run capacitor? I’ve smoked a couple of start capacitors on some of my machines and I was surprised at how much voltage those suckers can hold even when power is disconnected. I had a buddy that melted a screwdriver tip shorting a start capacitor. It was impressive.

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

View Loren's profile (online now)


10269 posts in 3615 days

#4 posted 01-14-2015 02:59 AM

Well, in this case the motor turns a much slowed
down gearbox and also has to reverse. I’m still figuring
this out. There are a couple of wires in the box that
are shedding their insulations and I think they need replacing.

View Dark_Lightning's profile


3146 posts in 3076 days

#5 posted 01-14-2015 04:13 AM

Capacitors provide a delay across the field windings for starting an AC motor, and are the first thing to fail in an AC circuit; it is just the nature of the beast. If you see failing insulation, replace that, of course. BUT, if the wires aren’t touching anything else, it is advisable to not mess with them. Just don’t touch them when the machine is powered on, shield them from casual touch. Make sure to get the same capacity in the replacement, since the forward/reverse depends on it, unless there is another provision for it.

-- Random Orbital Nailer

View ElChe's profile


630 posts in 1303 days

#6 posted 01-14-2015 01:42 PM

As I was sitting in my shop early this morning smoking a cigar I think you should have a talk with your capacitor about the dangers of smoking. Sorry. Can’t help myself. ;)

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

View Buckethead's profile


3194 posts in 1835 days

#7 posted 01-14-2015 02:39 PM

Lol Che!

Anywhoo… Love reading this type of discussion. Inner workings and such.

-- Support woodworking hand models. Buy me a sawstop.

View Planeman40's profile


1153 posts in 2728 days

#8 posted 01-14-2015 03:48 PM

Hello Loren,

I had a similar problem with the motor of my milling machine after the tool bit hung up during a cut. I called Digi-Key Electronics ( and asked to speak to a technician. I read him the info from the 40 year old capacitor and he fixed me up with a modern equivalent. It was a cheap and simple fix and I was up and running in no time. You might want to give Digi-Key a call.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View rushjosh's profile


1 post in 259 days

#9 posted 08-07-2017 10:23 AM

They get old, electrolyte degrades, resistance increases, this causes capacitor current to generate more heat, capacitor swells and can pop. For very large currents, you can pop a fresh capacitor (if you are over the current rating of the cap). you might possible be able to search new capacitors for your need.

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