Unisaw Overload Switch

[Kyle Amstadter]

I have a 220V 1 phase Unisaw that I just bought used. When I press the start button, the saw runs, but stops when I release the button. After some time troubleshooting I found that if I held down the blue switch in the image below, the saw would run as normal. I now have the saw up and running, with the blue button depressed with tape, but I am concerned that I am over-riding a safety function. Has anyone run into this problem before? Is there a trick to getting the blue button to stay depressed without tape?

I'm having trouble uploading the picture of the switch, so I'm posting sans photo for the moment.

Thanks in advance for the help,

Kyle

[Kyle Amstadter]

Switch.jpgHere's the photo I failed to upload earlier. The pop-out button I am referring to is the blue one in the center. Thanks!
Kyle

[Leo Graywacz]

The dial with numbers on it is a variable circuit breaker within the magnetic starter. It is set at 12 Depending on what your motor is rated at it may be set to low. Raise it up a bit and see if the motor keeps running. Go all the way to max if you have to.

[Mike Cutler]

The dial with numbers on it is a variable circuit breaker within the magnetic starter. It is set at 12 Depending on what your motor is rated at it may be set to low. Raise it up a bit and see if the motor keeps running. Go all the way to max if you have to.

Pretty much what I was thinking. The Contactor is above the thermal/time delay circuit. I have replaced them before. It looks very familiar, even the wiring designators and colors.
If you keep it taped down you have no overload protection. It's good that it works with it taped down though. It's the reset switch, so the mechanism is capable of resetting, but if you keep doing it, it will eventually fail.
If you have to source one the info is printed on the bottom,or side. It also can be an integrated assembly with the contractor which will have the part numbers on it for both. They're all over ebay. It looks like a Seimen's part. ( I probably have one or two in my desk at work)

[Charles Lent]

Your problem is most likely that the Stop switch has sawdust in it and did not close it's contact the last time you released it. If this happens, the Start button can start the saw, but as soon as you release the Start button the saw will stop. If it isn't sawdust in the Stop switch you have an open connection somewhere in the Stop button circuit, but my bet is the sawdust.

Charley

[Steve Baumgartner]

Switch.jpgHere's the photo I failed to upload earlier. The pop-out button I am referring to is the blue one in the center. Thanks!
Kyle

In that photo the red switch at the right (which is the stop switch) seems to be mis-located and perhaps stuck under the wire leading down? If so, it is as if the stop is being continuously pressed, which will break the circuit as soon as you release the start!

[Leo Graywacz]

As someone else said. Blow everything out. If the stop switch is dusty it will prevent the relay from locking in the on position. I guess that the 1st thing you should do.

[Kyle Amstadter]

Thanks for all of the suggestions. The first thing I did was clean out all of the sawdust in the switchbox and tighten a couple of loose wires. I also tried changing the current setting to the max, but that didn't change things, so I put it back at its original setting, which seems right as it is a 12 amp motor. Note that the red stop switch was disconnected from the box in the photo as I was troubleshooting it with a continuity test (switches are fine).

So, if the reset button won't physically latch back flat with the rest of the thermal overload circuit, is there any fix other than searching ebay for another overload circuit? Any other tests before I go for a replacement?

Thanks for all the help!

Kyle

[Charles Lent]

Kyle,

I truely believe that your problem isn't the overload switch. It's the Stop button or the wiring to it. When the stop button is pressed it opens the circuit that supplies power to the relay that operates the motor. When you release the Stop button it's contacts must close or you will have this starting type of problem that you are experiencing. Please take the Stop button apart, clean out the sawdust and make certain that the switch contacts on the Stop button are closing when the button is not being pressed. Anything that prevents these contacts from connecting when the button is released will cause the exact problem that you are having. It's usually sawdust, but can be dirty contacts or a broken wire. The Start button will start the motor, but as soon as it's released, the motor will stop. PLEASE CHECK THE STOP SWITCH. Leave the overload alone. Your problem isn't the overload circuit.

Charley

[Steve Baumgartner]

I did a little reading up and experimenting, and here's what I found:

First, if the stop button is not closed, the saw will not start at all (I was wrong!). This switch supplies the power for the contactor coil! If the contactor can't pull in, the saw won't even burp! Try holding in the stop button while pressing the start button to confirm this. Nothing at all will happen.

Second, the little blue thingy you discuss is the reset button for the overload protector. It is normally popped out - you press it in to reset the overload protector, then it pops back out. It works by pushing the overload contacts back together, where they are supposed to latch. The fact that you have to hold it in to make the saw run says that the overload contacts are touching when you push, but are not latching. You might try pushing more firmly just to see, but the strong implication is that the overload protector is shot.

Steve

[Charles Lent]

Steve,

Not all Stop circuits are wired this way. Most, if not all Unisaws have the stop button interrupting the holding circuit of the contactor. With the stop button held pressed, you can start the saw with the start button, but it will stop as soon as you release the start button. An open circuit at the stop button will do the same thing without pressing the stop button.

Kyle,

Do this test. Put a small jumper across the contacts of the stop button, then plug your saw back in, but keep the plug connection where you can get to it easily. No press the start button. Does the saw start and keep running? Now unplug the saw to stop it. If the saw started and kept running the stop button is the problem. Remove the temporary jumper and fix or replace the button.

If it still only runs with the start button pressed the problem is likely the small contacts on the side of the motor contactor. These contacts close when the contactor pulls in and they complete the ccircuit to hold the contactor on after the start button is released. If the problem isn't the stop button, it's most likely a problem with these small contacts on the side of the motor relay. If not this you have a broken wire or connection in the circuit.

If I was near you, this problem would likely take me less than 10 minutes to find and fix, but you haven't updated your profile to show where you are. Are you near me?

Charley