humming motor

drodgers2252 · Post by **drodgers2252** » Wed Jan 20, 2010 4:36 pm

I have a shopsmith mark V that was given to me by my father. When I received it the motor had a problem. the issue was that when the switch was turned on it would hum loudly and not move. I replaced the motor and the unit worked fine. After 3-4 times using the saw, the same condition returned. I have removed the belt and at best when the switch is turned on, the motor will start to turn 1 out of 5 times. the rest of the time, it will make a loud rattling hum sound and will not turn. Do I need to replace the motor again, is there something I could have assembled incorrectly, or is there just some information I was missing when I assembled the headstock. I am very mechanically inclined and it seems that the motor is just weak or has a starter that is in failure. Any info you can give, will be a help. Thank you

davebodner · Post by **davebodner** » Wed Jan 20, 2010 4:46 pm

Sounds to me like there's something keeping the motor from turning. If it only hums and doesn't turn, turn it off immediately, or the motor will burn out.

Can you turn the shaft by hand?

heathicus · Post by **heathicus** » Wed Jan 20, 2010 4:50 pm

Would inadequate power cause this? Maybe an issue with either the electrical circuit or an extension cord?

------------------------ · Wed Jan 20, 2010 5:14 pm

Thats what happened to my motor and even when the motor did run, all of the metal was electrified. Is yours the sign of a bad capacitor?
Mark

buck50bmg · Post by **buck50bmg** » Wed Jan 20, 2010 6:23 pm

Sounds like a bad cap. But measure your line voltage at the point of use also.

When you replaced the motor, did you replace the cap? If you can, disconnect the cap and measure continuity across it, if its open then you have a bad cap. Also make sure you have the correct cap. Try to spin the shaft when it is humming, does it start to move?

dusty · Post by **dusty** » Wed Jan 20, 2010 6:31 pm

drodgers2252 wrote:I have a shopsmith mark V that was given to me by my father. When I received it the motor had a problem. the issue was that when the switch was turned on it would hum loudly and not move. I replaced the motor and the unit worked fine. After 3-4 times using the saw, the same condition returned. I have removed the belt and at best when the switch is turned on, the motor will start to turn 1 out of 5 times. the rest of the time, it will make a loud rattling hum sound and will not turn. Do I need to replace the motor again, is there something I could have assembled incorrectly, or is there just some information I was missing when I assembled the headstock. I am very mechanically inclined and it seems that the motor is just weak or has a starter that is in failure. Any info you can give, will be a help. Thank you

Do not start the process by replacing the motor. In fact, if you still have it, you should probably drag it back out for a check up.

Readings between the lines, I think that your motor is good. At least it is neither shorted nor are the field windings open.

The failed Shopsmith motor that I have experience with was visually defective and you could smell it as well. The field windings overheated and shorted out.

My approach would be:

Remove the drive belt from the motor. This removes all mechanical drag and instantly eliminates the mechanics of the Mark V as the cause.

Blow all the dust out of the motor. This can best be done with the motor running but that may not be possible. The dust, if it is the cause of your symptoms, is in the contacts of the start switch which prevents power from being applied to the start capacitor and start windings. Dust in the motor will not otherwise cause it to not start. I have worked on some really dirty, dust impacted motors than ran fine. Being excessively dirty reduces the flow of air thru the motor and subsequently causes it to over heat and maybe burn out.

Check the power cord for general condition and measure the voltage across the black and white wires where they connect to the motor. Insure that all power connections are secure. Excessive voltage loss can occur as a result of loss connections (at the switch, at the motor, at the plug).

It is now time to plug it in and turn it on with the drive belt still removed from the motor. It should turn on and come to run speed very quickly. You should be able to turn it off and then back on repeatedly and repeatedly experience the same quick start.

Now turn it on and let it run. It should run with no detectable variance in speed. The speed control does not work with the belt removed. No not change the speed control setting now as doing so can cause serious mechanical damage.

After doing all of this, you should be able to declare whether or not the motor is in need of repair/service based on the observations made.

NOTE: It is possible for a defective on/off switch (high resistance contacts) to cause the symptoms that you are experiencing.

tkhudson · Post by **tkhudson** » Wed Jan 20, 2010 7:02 pm

Is there a chance someone "tested" the speed control while the unit was not running... that is what mine did when I found it.

------------------------ · Wed Jan 20, 2010 8:05 pm

My 3/4 horse motor seems to have the same issue as drodger's. When I flip the switch it humms (no belt on pulley-ER) If I spin the pulley before I hit the switch it comes right on. I can turn it off and on and as long as the pulley is still spinning it instantly comes back to speed and runs great. When the motor is almost ready to stop it emits a clicking sound in the rear of motor. It comes from a part that looks like a phenolic wishbone or something. I checked and all connections are great!
Mark

robinson46176 · Post by **robinson46176** » Wed Jan 20, 2010 9:52 pm

Read this site...
http://us.fluke.com/usen/Community/Fluke+Plus/ArticleCategories/MotorsDrives/Single-PhaseMotors.htm

JPG · Post by **JPG** » Wed Jan 20, 2010 10:28 pm

buck50bmg wrote:Sounds like a bad cap. But measure your line voltage at the point of use also.

When you replaced the motor, did you replace the cap? If you can, disconnect the cap and measure continuity across it, if its open then you have a bad cap. Also make sure you have the correct cap. Try to spin the shaft when it is humming, does it start to move?

I take issue with the 'continuity check' of the capacitor. A good capacitor will always appear open. It will however briefly act 'not open' as it charges due to the applied 'test' voltage. How this appears will differ depending on what type of 'meter' you are using.

What you have described is what will happen if the start switch contacts are not closed during initial startup.

A final SAFETY NOTE!!!!!!! If the capacitor has recently been energized(motor turned on) it may be holding a charge. ALWAYS discharge them prior to accessing the terminals. Shorting across them with an old(conductive) screwdriver shaft or something similar(conductive to the capacitor terminals, yet keeps YOU insulated from them. If the capacitor is fully charged, you WILL notice it discharging!

If a start capacitor IS holding a charge, then the start switch is NOT making!
The 'rattling' noise is of unknown origin.

Comments on other posts above: The 'clicking' sound and the moving thing is the start switch actuator returning to its at rest(not rotating/low rpm) position. This actuator could be operating correctly, but if the start switch points are not making, the motor will not turn. This type motor will run if it is spun as it is being turned on(or turned on whilr still rotating). The start switch in my emerson motor on my mark V moves almost imperceptually and the actual points are not visible. Proper operation can be verified by a continuity check across the points. That requires removal of the end cap

A motor that is 'electrified' while running has a short to the motor frame. If this short is in the windings, it needs to be replaced. It is his type of failure for which the third(ground) wire has been added (and ground fault protection).