[OP]
Member
Do I really need the contactor on my saw (1972 Cabinet saw)? It quit working yesterday, contactor wont draw up, and I'm not sure what to look for.
I have power to the top of the contactor and power to the on-off switch, The only thing is the contactor wont draw up to start the saw.
Any suggestions?
Member
The reason they put a magnetic switch on the saw is because they are often used in an industrial location. If it had a regular switch and the power goes off one person might go across the building to turn the breaker back on where another person not knowing about the problem might go to change the blade or something where they might get hurt when the breaker is re-set as the saw would come on. A magnetic switch wouldn't come back on without pushing the on button again. For the home shop use you wouldn't have that problem with other people getting around the saw so you could use a toggle switch.
Contributor
Not to be a smart horses butt, did you press the reset button to reset the overloads?
Contributor
Most likely the stop switch has dirty contacts. Take off the cover and blow out the sawdust. Do the same for the contacter contacts. While it is open close the contacts with a dry piece of wood and see if the motor turns on.
Bil lD
Contributor
I've gone to magnetic switches on all of my stationary tools (and the router tables). Even though it's a hobby shop and i don't have to worry about a second person stepping in--when we have a power outage in our area, the typical sequence is two or three flickers as the delivery lines try to reset themselves (i don't know the technical terms-so feel free to clarify what i'm trying to say). Without a magnetic switch/contactor, when the power drops out and restarts--if it happens in the middle of a cut the restart would be a ripe time for a kick-back. The magnetic contactor would drop out and allow for safe removal of the work piece from the tool. Doesn't happen often, but it's good insurance against the tool restarting at a bad time.
earl
Member
If you hear the starter ‘thunk’ when Start is pressed, use a multimeter to (safely!) check voltage on the output of starter. If none, it’s probably dirty or burned contacts in the starter. Open and clean, or replace.
If no ‘thunk’, use the meter to check voltage across the A1-A2 coil contacts. If you find proper voltage, you probably have a bad coil (and it is usually available as separate item). If no voltage when Start is pressed, then use meter to start checking the Start/Stop buttons, overloads, and/or reset. If you ID a device as culprit, open and clean, or replace.
....A schematic helps tremendously. As does a 2nd set of hands.
Last edited by Malcolm McLeod; 11-11-2019 at 7:26 AM. Reason: Clarity
Contributor
Often along with the contactor there will be an overload inside the box. The overload will stop the current going to the coil for the contactor shutting off the motor. If the motor doesn't have a thermal switch on the motor itself I wouldn't replace it with just a switch. If you have the cover off and measured voltage at the top of the contactor then usually you can use something insulated to push in the contactor. If the saw runs then the problem is the coil or the coil circuit. Again if it has an overload that can't be tripped. The coil will need to have both the power that goes to it when the start button is pushed and a path to ground or the other side of the 240v circuit depending on what the coil is rated for. Either mapping out where all the wires go or a schematic would be very useful.
Member
All pretty good responses so far. There are several reasons why a contactor is used for these saws -
The motor requires more power than most on/off switches can handle, and the electrical contacts of the contactor are large enough to handle this.
A motor starting circuit like this will not restart on it's own should power go off, and then come back on later - a great safety feature.
The contactor contains motor overload protection that will turn off the motor should it draw more than it's rated power.
The circuit design involving the contactor allows for multiple small contact start and stop button stations, not so important for Unisaws, but the design can be very beneficial for large dust collectors.
You most likely have tripped one of the overload detectors on the side of the contactor (the small wire connections), or for some other reason the circuit running through the overload detectors and the stop button is open somewhere. In many cases, the stop button contacts fail to close completely after the button is released. Make certain that the switch is clean and these contacts are going back together when the button is released. Some variations of the Unisaws will start and run only while holding in the start button, if there is an open in the stop circuit. Others will not run at all if the stop circuit is open.
Charley
Last edited by Charles Lent; 11-11-2019 at 8:25 AM.
Contributor
If the old switch is truly dead, Grizzly sells replacements for around $100. I've got one my 1986 Unisaw. Personally, wouldn't have a toggle on a Unisaw, I like it to be totally off when it is off with no chance to restart, even though I do unplug it to change blades.
Contributor
Andy, I've a similar vintage Unisaw but there isn't a contactor on it. Did you put the contactor on? What's the part number you used? Seems like a good safety feature.
Originally Posted by Andrew Seemann
[OP]
Member
Gentlemen; please let me apologize for the delay in responding. Everyday life took precedence so I just took the power off the contactor and connected it straight through and the saw will run but wont shut off. Guessing the switch is bad? Thanks for all the replies, they helped me understand a great deal about my saw and the kinks it may have. Think I will try a new switch and see if that helps. I tried to make the contactor work with a piece of wood and there was no click bump or other noise from it.
Contributor
My saw is actually a bit of a hybrid of my old 1968 and a 3 phase 1986 I picked up as a parts saw. It is now a 3HP, single phase, 240V, mostly 1986 saw. The equivalent I switch to what I used looks like "Grizzly T24101 - Magnetic Switch, Single-Phase, 220V Only, 3HP, 21-25A" The one I used might have been branded Shop Fox when I got it, since it was retail from someplace locally.
You'll need to match your voltage, phase, and HP to the switch. Wiring was pretty easy; wire the cord to the switch (line side), and then the motor to the switch (load side). Because of the aftermarket Biesmeyer, I did have to make a special bracket (out of wood) to mount it, which wasn't too hard. Photos below.
IMG_7146.jpgIMG_7145.jpg
Contributor
If you do have to make a wooden bracket to mount a new magnetic starter, I'd consider a hinged board in front of the starter with a hole above a dowel or small square of wood. The hole is over the start button and the dowel or square is over the stop button. To power up the saw stick your finger through the hole and push the green button. To turn off the saw just bump the board with your knee. That way you can keep both hands on the work while turning the saw off. Safer and more convenient.
Member
How do I access the contacts? I have a 36-825 Unisaw with a single phase, 3hp motor. Thanks!
Contributor
The magnetic starter has to be disassembled some to access the contacts. You would need to have access to the manufacturer's information on the exact starter used to see how to disassemble it without damaging it. That being said, starters are generally pretty simple, with the control wiring configuration being the only complex part (and it's simple if you understand motor control).
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