bench grinder capacitors

[GMR]

I have a Skil 3380 bench grinder that hums at startup. There are 2 capacitors.
One is about 2 1/4" tall by 1" diameter in size 300v 12 micro farads. The other is soldered on a small board that contain the wires for the lights and 2 blue wires that go to the stator windings. It is 1" by 3/8" 16v 1000 micro farads. There is no centrifugal switch.

Been trying to learn but am confused. Is this a split phase induction motor, cap start inductor motor, cap start cap run induction motor, permanent split cap induction motor, shaded pole induction motor?

I've read start caps are greater than 70 mf and 125v, 165v, 250v, or 330v and run caps are in a range of 1.5 - 100mf 370v or 440v.

I know it's a pretty cheap tool to replace but would like to try to at least learn what I have and what the problem is - for next time.

 

[wyliesdiesels]

how many poles on the cap?

Post a pic of the cap and its wiring.

 

[GMR]

each cap has 2, the 12 mf cap has 2 red wires which go to the stator seemingly 180* apart on the stator.

the 1000 mf cap has 2 leads soldered to the green board. The green board also has 2 blue wires, 1 of each seems to pair up with the red wires as they go to the same respective places on the stator. There are also 2 snap on plastic connectors on the green board - one for each light.

The black wire from the on/off switch goes to the same place on one side of the stator as a red and blue and the white wire from the power chord goes to the other side of the stator along with the other red and blue.

 

[LS6 Tommy]

A diagram would be nice, but it I'm almost positive you have a permanent split capacitor motor. Check the 12 uF cap. The 1000uF cap is not for the motor. A 16v cap would blow if you applied line voltage to it.

Tommy

 

[wyliesdiesels]

Do u have a meter with capacitor function to test the cap?

 

[GMR]

thanks fellas

sorry - don't know how to post diagram or picture

do not have capacitance on my cheap Radio Shack meter

as per internet using analog ohm meter - I tested both caps - taller 12mf cap with the 2 red wires tested good (needle moved to the right somewhat then slowly returned to original position - did this a couple times, shorting out the cap before each attempt). This cap is XUFENG CBB60.

the small 1000mf cap failed the test - the needle jumped all the way right and stayed there - repeated this step same way. This is a CHENG X, black with gray stripe soldered to the green board.

So, the motor hums at start up but doesn't run so is the 1000mf cap (CHENG X) the start cap (because it's bad and the motor won't start)? and the 12mf XUFENG the run cap?

I also did this: disconnected both wires from the XUFENG cap. Put my meter on volts and attached it's lead to the red cap wire which goes to the stator (along with the black power wire from the on/off switch and one of the blue wires). Plugged in the chord, turned on the switch and got 120v. Moved my meter lead to the other red cap wire (this goes to the other side of the stator along with the power chord white wire and the other blue wire from the green board). Plugged in the chord, turned on the switch and got 2v.

I put my meter on ohms and with one lead on each of the six wires that go to the stator (black, 2 reds, white, 2 blues) and the other lead on the green ground wire on the case and got infinity on all 6. So I assume I have no shorts.

 

[exmaxima1]

I'm stumped as to the purpose of a 16v cap in a grinder...

 

[wyliesdiesels]

thanks fellas

sorry - don't know how to post diagram or picture

do not have capacitance on my cheap Radio Shack meter

as per internet using analog ohm meter - I tested both caps - taller 12mf cap with the 2 red wires tested good (needle moved to the right somewhat then slowly returned to original position - did this a couple times, shorting out the cap before each attempt). This cap is XUFENG CBB60.

the small 1000mf cap failed the test - the needle jumped all the way right and stayed there - repeated this step same way. This is a CHENG X, black with gray stripe soldered to the green board.

So, the motor hums at start up but doesn't run so is the 1000mf cap (CHENG X) the start cap (because it's bad and the motor won't start)? and the 12mf XUFENG the run cap?

I also did this: disconnected both wires from the XUFENG cap. Put my meter on volts and attached it's lead to the red cap wire which goes to the stator (along with the black power wire from the on/off switch and one of the blue wires). Plugged in the chord, turned on the switch and got 120v. Moved my meter lead to the other red cap wire (this goes to the other side of the stator along with the power chord white wire and the other blue wire from the green board). Plugged in the chord, turned on the switch and got 2v.

I put my meter on ohms and with one lead on each of the six wires that go to the stator (black, 2 reds, white, 2 blues) and the other lead on the green ground wire on the case and got infinity on all 6. So I assume I have no shorts.

As said above, a 12v cap WONT be for starting or running the motor....

U really need to get the proper testing tools to figure this out.

And u could draw up a diagram on a piece of paper and snap a pic of it and then upload it here.

I'm stumped as to the purpose of a 16v cap in a grinder...

for the electronics such as the LEDs perhaps??

 

[exmaxima1]

for the electronics such as the LEDs perhaps??

An LED would run on AC via a simple rectifier so a cap would not really be necessary. But a capacitor would minimize flickering

 

[remauto1187]

I'm stumped as to the purpose of a 16v cap in a grinder...

Its there to oppose a change in voltage.

 

[GMR]

thanks for the replies and suggestions, much appreciated, I will follow up on them

 

[Dingleburry]

low mfd caps are for run. 12mfd would be run, start caps around 80+ mfd. Get yourself a 300v+ 12 mfd cap and you should be in business. As far as i know bench grinders are permanent-split capacitor motors. Another way to check caps is use resistance on dmm. Should start at 0 then slowly goto infinity. Another thing to test is while its humming away spin it with your hand in either direction. Should start up and run like nothings wrong. And in that case its your cap. Or cap circuit.
Im by no means an electrician. Just a dude with tools.