This grinder hums and will not turn when plugged in unless you give it a spin. i dont have a wiring diagram and the wiring had been disconnected for years. the motor has no capacitor and no centrifugal switch but it does have a black rectangual looking item . i think it is a starter relay switch but i have no way of knowing how to test it or to hook it up. the windings coming off the motor consist of two larger wires and two smaller wires.the two larger wires are yellow and red and the two smaller wires are black and white. i have heard of two other grinders having this problem but i have no other like item to compare this grinder with to know how to correctly attach the wires. any help would be appreciated. a wiring diagram would be helpful. thanks
Hi again, OK, Well since I don't have a wiring diagram and the colors don't help. I am also going to assume it is 110VAC. The larger wires are probably the run or primary, it you remember which ones were connected it will help with polarizing. ( getting it to run in the right direction as well as the start and primary working together). You can use the two terminal switch but you should use a three wire cord. Use the switch to break the neutral and ground the case. The connections should be as follows: Connection 1, would have one of the primaries and one of the starts to neutral. Connection 2, the other start to the relay. Connection 3, the coil side of the relay to the remaining primary. ( if the relay has two connections on one end and one on the other it would be the single) Connection 4, the 3rd position on the relay to hot. That is how a split phase is wired. You may find a simple wiring diagram on the net if you type split phase motor wiring diagram. Good Luck to you, this should Fixya!
SOURCE: older sears bench grinder wont run 1/3 hp model 397 19581
Can you get a replacement? If not, we could probably figure out some suitable substitute.
Charlie
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on the bench grinder , i removed the messed up remaining wires a few
days ago. the wires had been taken off the bad off/on switch and
operated by a two terminal house type light switch. it should have
been a three terminal original on/off switch. however, some terminals
wire ends broke off and i can,t tell where they went. by the previous
messed up wiring, i could spin the motor after the hum sound and it
would gradually pick up speed. i may could clean the rust off the
terminals of the starter relay switch and wire it correctly with a new
original off/on switch and get it to work. it,s sorta like, you can,t
fix something unless you know how it works, or at least the general
operating principals. a wiring diagram would really help. thanks for
info
I have same model grinder and the same problem., of no switch.
sears-roebuck 397.19581 by reading grsmith's
post and the various replys i was able to fix mine today. thanks a bunch for the help everybody. i'll try to describe the wiring in mine.
my relay was labeled klixon 4CR-20-724, had 3 terminals.
motor has 4 wires coming from it. red,black,yellow,white
input is 110/120v ac black,white,green.
green ground to ground screw inside grinder base.
relay has one terminal on one edge, two on the other.
white 110v neutral goes to single terminal on relay.
black and red motor wires go to the other two on relay. the black was connected to terminal on relay that is even with the white terminal on the opposite edge.(i'm not sure if red/black are interchangeable?) red went to the other terminal on same side.
black 110v line goes to one side of on/off switch,
the yellow and white motor wires go to other side of on/off switch.
runs fine. double checked with meter for any shorts etc.
mine also has a gooseneck light that is wired thru same on/off switch,
one wire to white 110v neutral coming in and other to the on/off switch
on same terminal as white n yellow motor wires.
hope this helps.
Usually, this type of motor has to sets of windings. One set is "Start" windings and the other are "Run" windings. Basically, it works like this. Upon start, the "Start" windings are in the circuit along with the "Run", they are wired parallel to each other but in series in the circuit. When the unit reaches it's running speed, usually in about one to one and a half seconds, the "Start" windings drop out of the circuit and the "Run" windings keep things going. The way you can tell which is which is to take resistance readings of the windings. The higher resistant set is the start windings, generally. The higher the resistance, the higher the starting torque.
As far as the black, rectangular items is, you could very well be right. Makes sense. Some how, it would have to energize both sets of windings and when you let go, the start windings drop out of the circuit but the run windings stay in the circuit.
Hope this helps.
Good Luck
Hi again, I answered your other post on this subject and since you have included a model number I have something to go on. As I told you before it had to be a cap or starter windings. This old motor has starter windings. I am confused however on your description. First you say it will spin if you help it but then you say the wiring has been disconnected for years. I would like more detail as this is important in helping you reconnect it. The black box is indeed a starter relay and that part is still available for $22. There are no wiring diagrams that I can find but it is not much different than newer ones. The fact that you say it runs is helpful. Can you get back to me with any more details, please.
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