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Thread: Unisaw 34-450 won't start/stay running

  1. #1
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    Unisaw 34-450 won't start/stay running

    I'm hoping to lean on the expertise of some electrical gurus here to help troubleshoot, or at least give advice for the best direction for repair.

    I have a vintage Delta Unisaw 34-450 (year unknown) that has had some occasional failures to start before this, but repeatedly jamming the 'off' button or unplugging the machine allowed it to start eventually. It's 1.5hp, running on 230v.

    Yesterday after using it briefly, it decided not to start again.

    I took apart the physical switch, and blew it out; there was a fair bit of sawdust inside. I did the same with the control box, again it had some sawdust inside. Once reassembled, I plugged the machine back in and: the saw fired up, but only as long as I depressed the switch. It shuts off again when the 'on' switch is released.

    I can recreate the above scenario by repeating the same steps, but only briefly. After one or two 'on' cycles, the motor will refuse to start again. I did find a loose wire in the control box. The red wire (see attached control box photo) connected at bottom right of the [coil?] was loose. I removed it, reshaped the wire strands (it was flattened), and tightened it again. Same result as before.

    Electrical repairs in machinery is not my forte. If there are available parts that I can replace with like-for-like, I'll do that. Or if I can replace the entire switch assembly to an updated version, I could maybe do that.
    Alternately, if necessary, I guess I could find an electric motor shop that is willing to work on it. The latter is not my favorite option, not because I'm money-shy, but because I don't relish the task of disassembling and transporting my ~300lb saw. Are there repairmen for this kind of thing who will come on-site?

    Thanks for any help.
    control box.jpg
    switch-cover removed.jpg

  2. #2
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    Power is getting to the motor. The running circuit is good, coil is good, heaters are good. transformer, if present, is good. The problem is the off circuit is open. either bad wire or bad switch.
    Tighten the red? wire at both ends. jump it with a wire from end to end. Last jump the off switch and see if that will let it run.
    Bill D.

    https://twcontrols.com/lessons/contr...t-stop-circuit

  3. #3
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    If you're not familiar with how these circuits work, you could start with bypassing the controls and directly wire the motor power to the plug to see if it will run ok this way.
    An easier to understand replacement would be to buy a manual motor switch rated for the 1.5 hp and use dual element fuses for overload protection.

    You can buy magnetic motor starters to replace the unit you have as well that would have diagrams to help you connect it. If this is beyond your skill range maybe you would be best to find someone who has the skills for troubleshooting your hardware.

  4. #4
    From your description, it sounds like the contacts on the starter need some attention. If the saw runs while holding the start button in and quits when released indicates the holding/latching contacts aren't making. Possibly all of the contacts need a little cleaning/dressing.

    Phil

  5. #5
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    Clean the contacts in the Stop button. If that doesn't fix it, clean the Aux contacts of the relay in the control box (behind the saw). The Aux contacts are smaller than the power switching contacts and attached to the side of the relay. These contacts (both the stop button and relay Aux contacts) hold the relay on after the Start button is released. If not making good contact, the relay, and motor will only run when the Start button is held in.

    Charley

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    Where do you live?

  7. #7
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    I am located in Denver.

    Quote Originally Posted by Charles Lent View Post
    Clean the contacts in the Stop button. If that doesn't fix it, clean the Aux contacts of the relay in the control box (behind the saw). The Aux contacts are smaller than the power switching contacts and attached to the side of the relay. These contacts (both the stop button and relay Aux contacts) hold the relay on after the Start button is released. If not making good contact, the relay, and motor will only run when the Start button is held in.

    Charley
    Thanks for the input, all. I'm going to take apart the switch and relay and do a more in-depth cleaning tonight, as suggested. Just to be certain: what you're calling the relay is the black module with six terminals at the top of the control box, correct?

    If that fails, I may try what Eric Arnsdorff is suggesting. Is something like this appropriate? (presuming I find one that matches my motors amp rating) I would replace the existing control box with this new magnetic switch; and possibly wire a new on/off switch to that as well. Am I heading in the right direction?

    Bill Dufour
    Power is getting to the motor. The running circuit is good, coil is good, heaters are good. transformer, if present, is good. The problem is the off circuit is open. either bad wire or bad switch.
    Tighten the red? wire at both ends. jump it with a wire from end to end. Last jump the off switch and see if that will let it run.
    Bill D.
    To jump the off switch do I just disconnect the wire at 'N.C.'?

  8. #8
    Given your experience with electricity, I'd recommend wiring the motor directly to a cord that you can plug into a 240 volt outlet. If the motor runs properly, the problem is in your switch.

    If the motor doesn't run properly under that condition we can work on diagnosing the motor.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  9. #9
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    I'm in a north suburb of Denver Colorado.

  10. #10
    As mentioned above, I wonder if there are some corroded/oxidized contacts in the switch that need to be cleaned? Also, is there a way to seal the electrical box so that sawdust doesn't get in?

  11. #11
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    Buck you had asked about removing the wire to bypass the off. It is actually
    The opposite. The off button disconnects the circuit which is latched in once the on button is pressed. Pressing the off button opens the circuit and unlatches it to turn it off. Effectively, the off button disconnects the wire for the magnetic starter.
    One of the suggestions of cleaning it is referencing that you sand or otherwise smooth the contacts in the relays and switches as they may have arced and have build up on them. This may work. I wanted to make sure you understood what was meant by cleaning them.
    One further note is that if you do change the hardware/contactor you will need to set the overloads to the appropriate current limit value for your motor. This isnít difficult but wanted to mention it. The easiest thing to do would be see what is set on the existing overloads and set it at the same value. Otherwise, hopefully your motor nameplate has the motor current values and you can set it based on the nameplate ratings.

  12. #12
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    If the above solutions don't work, there are replacement magnetic switches available. Here is an example for a 2 h.p. motor:

    https://www.grizzly.com/products/gri...nly-2-hp/g4572

    The overload protection looks selectable from 8.5 to 12 amps @220 volts. If you end up installing a new switch, be sure to keep the existing one. A future purchaser may want it.

  13. #13
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    Thanks for linking that Curt; that switch has the best wiring diagram I've come across. This appears to be same switch, if I'm not mistaken.

    Update: I took apart the existing physical switch, and wire brushed all the contacts. I did the same with all the contacts in the control box that were easily accessible. I also burnished the stranded wire ends that were soldered, which was most of them.

    There was only minor corrosion on a few contacts. The end result was the same as before: motor starts upon depressing 'start' button, then shuts off when button is released (after two on/off cycles, it fails to run again, period).
    So on to plan B: replace the switch. I'm going to to some shopping around to find a better price; if I don't find anything, the Grizzly switch Curt has referenced may be what I end up ordering.

    Eric: Based on the notation on the motor plate ("22/11"), I would set the overload dial to 11, correct?
    Also: I was wrong, my motor is 2HP, not 1.5hp. motor plate.jpg
    Last edited by Buck Beymer; 10-13-2021 at 4:11 PM.

  14. #14
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    Quote Originally Posted by Buck Beymer View Post
    Thanks for linking that Curt; that switch has the best wiring diagram I've come across. This appears to be same switch, if I'm not mistaken.

    ...................................
    Eric: Based on the notation on the motor plate ("22/11"), I would set the overload dial to 11, correct?
    Also: I was wrong, my motor is 2HP, not 1.5hp. motor plate.jpg
    It looks like the same switch, just be sure it's a 2 h.p. the 3 h.p. looks the same. Yes set the overload protection to 11 amps. The guy that owns Grizzly also owns Shop Fox AFAIK. Grizzly and Shop Fox machines are often fundamentally the same, maybe different hand wheels or accessories but very similar.

  15. #15
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    Good news chaps: I received the new switch and installed it last night. Went together easily with the included wiring diagram and it works a treat. Saw turned on immediately and stays on.
    I made a quick plywood mount and screwed it into my extension table; as an added bonus for all my troubles, this is a much better location for a switch than the original.
    I'm leaving the original switch and control box in place, in case I ever sell it and the buyer wants to use them for some reason. I would have liked to put in a paddle switch, perhaps someday, but one fix at a time. Sawdust to make and all that.

    Thanks for all of your input.
    IMG_1817.jpg
    IMG_1816.jpg

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