Any ideas about planer mag switch problem?

[Marcus Isaacson]

The other night I was planing some 6" wide butternut boards when my 15" shopfox planer w1742 turned off. I can restart the planer if I hold the on switch down and it works perfectly, but as soon as I let the switch go it turns off again. I tried pressing the reset button on the thermal overload relay with no success. I also checked the receptacle by plugging in my 3hp jointer and it works like normal. There was one time where I was able to get the planer going again without have to hold the button down, but as soon as I turned on the dust collector (on another circuit), it shut down again.

So, do you think it is a problem with the start button, the magnetic switch, or something else? If it is the magnetic switch, are there serviceable parts in them? I would rather fix than just replace.

[david brum]

Not that isn't the switch, but my Shop Fox jointer did the same thing when the centrifugal switch came loose on the motor shaft. If that's the issue, it's a very easy fix.

BTW, if you suspect the mag switch and want to isolate it, you can always bypass the switch and directly wire it into the power cord (unplugged). It it works, you know it's one of the switches.

[Ken Fitzgerald]

Marcus,

It isn't caused by the thermal overload as depressing the Start switch doesn't bypass the thermal overload in most cases. Typically, if the thermal overload is tripped, the motor won't start at all.

I will try to find a schematic for your planer and see if I can determine a possible cause and troubleshooting route.

[Ken Fitzgerald]

Marcus, it sure sounds like the "holding contacts" on the motor contactor has gone bad.

Typically, when you press a "start or on" button, it momentarily pulls in the motor contactor. On the motor contactor is a set of "holding" contacts what will provide power to the contactors coil after the "start or on" switch is released. This keeps the motor contactor energized and applying power to the thermal overload which applies power to the motor and the appropriate capacitors (run and start).

The Emergency off switch is in series with power going to the "start on" switch and the holding contacts on the motor contactor. When depress the Emergency Off switch it removes power from the holding contacts and the contactor de-energizes removing power to the motor.

It sure sounds like the holding contacts have gone bad. Unfortunately, it doesn't appear that the motor contactor is a individually replaceable part.

[Marcus Isaacson]

Thanks for the ideas. David, can you describe to me where the centrifugal switch is and how to access it? Also what it looks like? I will check that first. Ken, I take it that is the switch that I can watch move in and out when I press the power button? If so, then I am assuming that the entire magnetic switch box needs to be replaced.

I have to wonder what would make a mag switch go bad? Is there something else I should check that could also cause a replacement to fail?

Thanks for the help.

[Duane Meadows]

I have to wonder what would make a mag switch go bad? Is there something else I should check that could also cause a replacement to fail?

Thanks for the help.

Dust, pitted contacts, most likely. Doubt there is a problem with the planer motor. The centrifugal switch is in the motor itself, not the mag switch. It is to kick out the start circuit after the motor comes up to speed.

Yes, I would just change the whole mag switch. Compared to the price of a planer, they are not that expensive!

[Ken Krawford]

My Unisaw did the same thing a couple of weeks ago. I took the switch apart and blew compressed air into everything. Even though the inside of the switch looked fairly clean - Problem fixed.

[david brum]

The other guys are probably right about a defective mag switch, but here's what a centrifugal switch looks like. Its located on the motor shaft behind the fan, under the fan housing. There are a few screws which hold the fan housing onto the motor. It's the end of the motor opposite the end holding that the pulley is attached to. There will be a fan underneath, probably white plastic. It's attached to the pulley with a set screw. Slide it off and you'll find one of these switches underneath. In my case, the set screws holding the switch onto the motor spindle had come loose and it was sliding free on the spindle. I've had this happen more than once with machines. It doesn't cost anything to check and there is probably some value in knowing what it looks like in there.