Table Saw Motor Humming? Bad Start Capacitor?

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Forum topic by John posted 06-14-2016 02:59 AM 4387 views 0 times favorited 19 replies Add to Favorites Watch
View John 's profile


100 posts in 4061 days

06-14-2016 02:59 AM

I was using my table saw today and it just quit, sort of….
I was using it to rip some 3/4 inch oak shelving for about a half hour or so.
I was turning it off and on, as needed, when suddenly it wouldn’t come on?
It would only hum? I had a saw once that would overheat, so I let it cool for about 15 minutes and it started right up again. However, that was only short-lived, since it went back to its humming ways about 10 minutes later.
Now what?

I looked around on the internet and found that it could be the start capacitor???
So, I took it off and tried to find a replacement on the internet, but have failed thus far.
Now it’s late, I’m tired, and hoping you guys can help.

Is the motor fried? Would it hum if it was a bad start capacitor?

The guy I bought the saw from, about 6 months ago, had replaced the 1.5 hp motor with a Leeson 2.0 hp motor.
It is belt-driven and boy what power! However, I bumped into on the net that it should have a closed motor, and it appears the Leeson 110363.00 was made for low dust environments – doesn’t sound like it should have been used on this saw. Cheapest I could find a replacement is on Amazon for $188.

Now what? Please help. I don’t want to order a motor if it’s just a bad capacitor.


-- Thanks!

19 replies so far

View TheFridge's profile


10308 posts in 1631 days

#1 posted 06-14-2016 03:16 AM

I’d say capacitor or the centrifugal switch is hanging up.

If your motor didn’t start smoking then the odds are it is still fine.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View tomd's profile


2167 posts in 3915 days

#2 posted 06-14-2016 03:20 AM

Try this blow the motor out with compressed air, just give it a shot it worked for me once.

-- Tom D

View distrbd's profile


2252 posts in 2591 days

#3 posted 06-14-2016 03:43 AM

The same thing happened to my bandsaw, everyone advised me to check the capacitor first, I did ,it looked good to my untrained eyes so I asked what else could cause the hum, there are a few but I took the motor to a shop nearby and the electrician working there went straight to the capacitor, checked it and it was burnt.

The bandsaw in now working like it should with the new capacitor.

-- Ken from Ontario, Canada

View Lazyman's profile


2525 posts in 1532 days

#4 posted 06-14-2016 04:18 AM

Is it 220v or 110v? If it is 220v, you might try cleaning out the switch to makes sure it doesn’t have a bunch of saw dust preventing one of poles from engaging. If you have a multimeter and are comfortable using it, you can also test that the switch is working correctly on both poles. Safest way would be to do a continuity test with saw unplugged.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View runswithscissors's profile


2843 posts in 2170 days

#5 posted 06-14-2016 04:47 AM

Open motors can ingest a bit of sawdust and prevent the start contacts from closing. I used to have that happen periodically on a Sears 1.5 hp motor (wired for 220v). I’d have to do a partial disassemble to get at the contacts. Compressed air should do it also.

Yes, TEFC motors are better on a saw, but I got by for years with that open motor.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View MrUnix's profile


6931 posts in 2344 days

#6 posted 06-14-2016 06:52 AM

Test the cap so you don’t go out buying one you might not need. If it’s bad, then get a new one. If not, you need to dig a bit further (sawdust in switch, bad or loose wiring, centrifugal switch, etc..).

You only need a cheap multimeter to test the cap. And if it’s bad, get the numbers off the side and googe them. 99 times out of 100, you will find an exact match. Usually it’s the weird model or part number that will get you there, not the rating.


-- Brad in FL - In Dog I trust... everything else is questionable

View John 's profile


100 posts in 4061 days

#7 posted 06-14-2016 11:35 AM

It is 110v. There was not smoke or smell of any kind.
I’ll give blowing it out a try.
I see no visible damage to the capacitor.
Where can I find the centrifugal switch? Inside?
I’m going to ask the guys at our campus physical plant services if they can test the capacitor for me :)
I did try googling the capacitor numbers, but can’t find an exact match. Quite frustrating actually.
Sounds like it may just be dirty inside, but that the motor being open is not as big an issue as I was thinking.

Thanks guys!


-- Thanks!

View CharleyL's profile


223 posts in 3509 days

#8 posted 06-14-2016 12:35 PM

Your problem could be either the capacitor or the centrifugal start switch, or a broken wire inside the motor, but I would believe that it’s the switch, based on your description of how it suddenly wouldn’t start. This is true as long as you haven’t let the magic smoke out of the motor. If you have, it’s new motor time.

The centrifugal switch is inside the rear cover of the motor, the end without the shaft coming through it.
There are long bolts running completely through the motor that need to be removed. Put a scratch mark across the joint between the end cover and the side of the motor so you can line up the two when you re-assemble it.

The centrifugal switch is just an open style single contact switch in the end cover. Clean up the contacts and make sure the spring tension is right to make them go together and separate correctly. They need to open as the motor comes up to speed and close as the motor slows down. Anything that prevents their re-closing could cause your problem.

Next, check the mechanical centrifugal mechanism on the motor shaft. It is what actuates the centrifugal switch. There are two weights and cams, spring loaded to swing in close to the shaft when not spinning.
They move a plastic collar on the shaft as they swing out. The usual problem is that the area where this collar slides back and forth on the motor shaft gets dirty or rusty. Clean the collar and this area. Use a strip of fine emery cloth and buff the area of the shaft as you would do when polishing shoes. Rotate the motor shaft as you do this to get it shiny all the way around. A very light wipe of the shaft area with thin machine oil, just enough to fill the pores of the metal, will protect it and keep the collar sliding well for years.

Blow out and clean the inside of the motor of all loose sawdust, dirt, etc.. Then re-assemble it, lining up your scratch mark as you put the end cover back on. If it’s lined up well, the long bolts should go through the motor case easily. Plug it in and try starting and stopping it several times before installing it back into your saw.

If this doesn’t fix your motor, take it to a motor repair shop. Their charge to diagnose and repair any minor problems with it will be significantly less than buying a replacement motor. If they say it can’t be fixed, they can probably sell you a replacement for less than you would pay elsewhere for a new motor.


View woodworkerguyca's profile


30 posts in 1189 days

#9 posted 06-14-2016 11:48 PM

Wow, I did not expect to find this much electrical knowledge in a woodworking forum.
I have had a pool pump motor sitting in my garage with some stuck bolts that I haven’t had time to free. I was going to open it up and see if I could find anything amiss, but it sounds like first I should check the capacitor because my symptoms sound just like that.

I think this post might have randomly saved me a few hours of work.

View crank49's profile


4032 posts in 3116 days

#10 posted 06-15-2016 01:17 AM

Caution. The humming is a common symptom of a bad capacitor. However, the capacitor can be good and the centrifugal switch that switches the capacitor into and out of the circuit can be stuck, or mucked up with saw dust (open motor) and it will still act like this.

Blowing out the saw dust might get it running, but you should really break it down and clean it properly.

View TheFridge's profile


10308 posts in 1631 days

#11 posted 06-15-2016 02:58 AM

You can tell some caps with a metal can are bad because the ends will bulge out a bit. Mainly in smaller ones but a meter is the way to go.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Planeman40's profile


1256 posts in 2906 days

#12 posted 06-15-2016 02:10 PM

Like everyone says, likely a bad motor capacitor or stuck motor centrifugal switch. I had this happen with my milling machine (metal work). Capacitors can ordered by mail from DigiKey ( Just remove the capacitor being careful to make sure the capacitor is discharged by grounding the leads before touching. These things can give you a good electrical shock if still holding a charge. Call DigiKey and ask for a technician. Tell him what you are doing and read him off the information printed on the capacitor and ask him for a replacement.


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

View John 's profile


100 posts in 4061 days

#13 posted 06-15-2016 03:17 PM

Wow, you guys are great. Okay, so I had the capacitor tested at work and it is fine. Now I’m out to the shop to take it apart and check the centrifugal switch. Stay tuned…..

-- Thanks!

View CharleyL's profile


223 posts in 3509 days

#14 posted 06-15-2016 03:18 PM

When you order a replacement capacitor for a motor you need to find an AC capacitor designed for use in electric motors. Capacitors from Digi Key are typically DC capacitors and are not suited for motor starting needs. Electric motor repair shops, industrial suppliers like Grainger, McMaster Carr, etc. should be good sources for these capacitors, but also search Amazon and the internet if you can wait a few days for it. Be sure to match the MFD and AC Voltage values, as well as the physical size of the original capacitor, since what you buy will need to fit inside the cover on the side of the motor. Don’t buy one of a larger physical size unless you are prepared to mount an external box to the motor large enough to hold this larger capacitor. Leaving it without a cover will pose serious safety risks and the possibility of a fire.

To determine if your original capacitor is bad, an ohmmeter check will find a shorted capacitor. On the X1 or X10 resistance scale, the capacitor should initially have a low resistance value, but should increase in resistance rapidly to nearly full scale, if it isn’t shorted. A reading that doesn’t eventually go to full scale is a shorted capacitor and needs to be replaced. You also need to check the capacitor for bulging and liquid leakage. If you find bulging or leakage, usually from the end around the terminals, you have a capacitor that is bad, or going bad, and it should be replaced.This ohmmeter test is only to determine if the capacitor is shorted. It may still be bad, since these capacitors can occasionally change in value. Only a capacitor tester can determine this, and they aren’t cheap or easy to find. An electric motor shop is the best place to have it tested if you suspect this, but a new capacitor isn’t that expensive, so I would just replace one if I suspect that it has changed in value.

Some motors (very few) have two capacitors in one physical container. You may find these on motors that have both start and run capacitors. These will have three electrical terminals instead of the usual two. One of them is the common terminal. Test each of the two sections by testing between this common terminal and one of the other terminals, then do the same test between the common terminal and the third terminal. Since the two capacitors will be different sizes, the meter will move at different rates for each, and you need to keep track of which wire was connected to each terminal when you make the replacement. These two section capacitors also tend to be harder to find exact replacements for. Fortunately, most dual capacitor motors made in the last 50 years use separate start and run capacitors. In a motor with separate start and run capacitors, the larger of the two capacitors will be the start capacitor, and the one that may be causing the starting problems.

Be sure to also check the centrifugal start switch if you don’t find anything wrong with the capacitor, as noted in my previous post, because it is more frequently the cause of starting problems. However, but most times it’s easier to test the capacitor before removing and dis-assembling the motor to inspect the switch.


View Planeman40's profile


1256 posts in 2906 days

#15 posted 06-15-2016 03:57 PM

Good information Charley, but digiKey does carry capacitors for 115 V electric motors. As I said above I repaired my milling machine 115 V motor using DigiKey. I also explained to talk to the technician and tell him what you are doing. He will then know you are dealing with AC voltage. Also, the information on the capacitor that you relay to the technician should note the capacitor is for AC voltage. As to the technical information above, I believe the vast majority of the members of LumberJocks are unschooled in electronics and it would be better to have a knowledgeable technician make the choice of a suitable replacement capacitor.


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

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