Removing a motor starting capacitor from an old 1 HP Craftsman electric motor

[Wrenchmensch]

Tomorrow a.m. I will be removing a starting capacitor from a Model 113.19092 Craftsman 1 HP motor.  The motor is connected by twin belts to an old but fine Craftsman table saw. The price is right, but the saw did not start when I threw the motor's toggle switch last Friday.  It didn't even hum.  Knowing the motor uses a starting capacitor (Part 24443 - permanently out of stock), I figured the conservative thing to do is to start by replacing the capacitor with another new one.  The only thing is, I have to remove the old capacitor to determine its micro farad specification.  I am taking my Greenlee multimeter along, and I will check the mfd (if any) of the old capacitor before I take it out. Am I risking a shock if I don't drain the capacitor before removing it???  Anybody care to give advice?

[rusty]

In theory.....the start winding shorts the capacator into the run winding after the motor runs...
But in practice...your motor doesn't run....so stick a screwdriver across it before you go grabbing the terminals ;P

Oh,yeah, good idea to unplug the saw first...I'm just saying...

Check if there is a centrifugal switch first tho, they get sawdust in the contacts....

PS: It's probably 161mfd

[Wrenchmensch]

Thanks, Rusty!!!!

[scottg]

Yeah, short it if concerned, and just find a capacitor that has the same rating.
 I have a Jet table saw. They offered me a replacement cap for like,  $48!
  Yeah right, that's going to happen.
 I got one for about 4 dollars shipped, and I think I got ripped off on the price!
 I had to vandalize and redesign the little sheet metal bullet cover to fit some,
  but it all worked fine and now I can always get another cheap.
 
   Just match the rating, same volts and microfarad rating.
 yours Scott 

[ray]

If the motor does not hum, you might not be getting any power to it.
check for power first before you go through all that work. if you have power then check the resistance of the windings, that size motor should be 5 to 25 ohms.

Ray

[Wrenchmensch]

Guys:

The in-place capacitor rates 161-193 microfarads (kudos to Rusty!).  When I checked its capacitance on my Greenlee Multimeter, it checked out at 173.4 microfarads.  To me, this says the capacitor is still good.  Am I correct in this?

I will check the resistance in the windings next.

[Wrenchmensch]

Ray:

I think I checked the resistance of the windings.  My method may have been incorrect. I put Greenlee Multimeter probes on two points along the windings. The readout was zero ohms. Was my method correct?  If so, should I spring for new windings?

[johnsironsanctuary]

The best way I know of to unload a capacitor is with a regular light bulb in a socket with two bare wires. An old electrician showed me this after I zapped a screw driver in half unloading a big one.

[Wrenchmensch]

Ray et al.,

I checked the windings resistance, and came up with 0.3 ohms, well below the range Ray specified.  The contact points were the leftmost large white wire and the large black wire on the reset button to the right in the photo below.

It's my conclusion that the capacitor is OK, and that the windings are shot.  Do you guys agree?

Bob

[rusty]

The capacator is probably ok.

That motor can be wired for either 110 or 220, I would check that the last guy wired it right, it could be it is cross wired, look on the inside on the cover plate for which terminals go where (vintagemachinery web site has the manual for that motor btw)

Your meter might not be able to measure such low resistance, many of the cheap ones can't...

PS: The motor does spin freely, right?

[Wrenchmensch]

Rusty:

My Greenlee Multimeter DM110 is pretty sensitive (and not a cheap meter).  The guy who changed the wiring from 230 v. to 115 v. did so in the 1960s when he bought the saw. He continued to use the saw until 4 years ago when he died. Today, I blew out more a cup or more of very fine sawdust from inside the motor. This dust probably compromised the windings over time. The windings look unburned, but the insulation looks as if it got hot some time ago. We are giving up on this saw table, returning the motor to the widow, and setting out to find something better.

Thanks for all the input Rusty and all you other guys!

Bob

[ray]

I think that I see a thermal safety overload ( round thing ) check that.

It would cost more to have the motor rewound then buy a new one.

Ray

[Wrenchmensch]

Ray,

The round thing is an optical illusion.  It's the hole through which the rotor shaft goes.

Thanks, anyway!  The resolution has been for me to throw the motor away, and for the widow to throw the table saw away. The saw was too heavy for my wife's use, e.g. to cut quarter inch masonite rectangles to paint her pictures on. We are considering getting a reconditioned Riyobi table saw for that purpose, circa $90.  She can move it upstairs to her studio by herself.

Bob

[scottg]

Bob
 Resistance is resistance. You should have open line if the windings are cooked.
 I would still risk the $5 capacitor. 

   The sliding collar on the rotor? with the springs? has to move freely.  Make sure it does. 
Also that contact block had to move as well.

 Lightness is never a bad thing in a table saw. In fact, my own TS rule is,
  If I can pick it up? I don't want it.  At all.
 
 Build the girl a rolling dolly/stand.
  yours Scott
   

[Wrenchmensch]

Scott:

As I understand it, the fundamental check for a bad motor starting capacitor is: if the motors hums but does not spin when it is turned on, then the capacitor is bad.  No hum was heard in this motor. Furthermore, the capacitor looked and smelled fine, and it's capacitance checked out on the multimeter. 

http://liutaiomottola.com/Tools/Motor.htm

The rest of the relevant variables everybody presented all checked out except for the measured resistance across both ends of the windings.