Unisaw not starting

[Jill Magill]

My husband was given a 70's era Unisaw by his father. Someone had tried to rewire it for 110 and smoked some stuff. We have had the motor checked out and it is fine. We replaced the Controller and the overload relay. Now when we press the start button the Magnetic contactor makes a noise like it is trying to work ( vibrating ) but nothing starts. We have checked wire connections and believe it is all wired right.

Any suggestions on what could be wrong or what we could try next?

[Cody Jensen]

I'm a little out of my expertise here, but if the motor is humming when you try to start it, I would check the starting capacitor (assuming its single phase).

[Jill Magill]

I'm a little out of my expertise here, but if the motor is humming when you try to start it, I would check the starting capacitor (assuming its single phase).

The motor is not making a noise the magnetic contactor in the control box is. We had the motor checked out by a professional and it works fine. I believe he would have checked the capacitor at that time or I hope so.

[Eric Commarato]

My husband was given a 70's era Unisaw by his father. Someone had tried to rewire it for 110 and smoked some stuff. We have had the motor checked out and it is fine. We replaced the Controller and the overload relay. Now when we press the start button the Magnetic contactor makes a noise like it is trying to work ( vibrating ) but nothing starts. We have checked wire connections and believe it is all wired right.

Any suggestions on what could be wrong or what we could try next?

Jill, check the voltage to the magnetic contactor and verify it is the proper current to pull the contactor in. If the contactor is chattering, there may not be sufficient voltage to pull the contactor in during motor starting. If someone wired the saw for 110 V. and the coil is a 240V coil, there isn't enough current to pull the contactor in. Just my guess.

[Jill Magill]

Jill, check the voltage to the magnetic contactor and verify it is the proper current to pull the contactor in. If the contactor is chattering, there may not be sufficient voltage to pull the contactor in during motor starting. If someone wired the saw for 110 V. and the coil is a 240V coil, there isn't enough current to pull the contactor in. Just my guess.

Thanks will check that tonight. That is exactly what it is doing, chattering. I believe the wiring is correct right now for 220/230 but will also go over that once more.

[Rod Sheridan]

My husband was given a 70's era Unisaw by his father. Someone had tried to rewire it for 110 and smoked some stuff. We have had the motor checked out and it is fine. We replaced the Controller and the overload relay. Now when we press the start button the Magnetic contactor makes a noise like it is trying to work ( vibrating ) but nothing starts. We have checked wire connections and believe it is all wired right.

Any suggestions on what could be wrong or what we could try next?

Wrong coil voltage on the starter?

Regards, Rod.

[Jill Magill]

Okay, stopped the chattering. Found a bad connection.
Press start and the magnetic contactor closes. Press stop it opens. Motor does nothing. No sound what so ever. Is there something else we can try or rule out? Thanks.

[Mike Henderson]

I'd wire the motor directly to the line (with a plug, of course) and make sure the motor works. If so, I'd work back from the motor to find out what's going on. If the motor works when you directly wire it, power is probably not getting to it from the contactor.

Mike

[If the motor doesn't run when you wire it directly, you have a motor problem.]

[Thomas Bank]

Someone had tried to rewire it for 110 and smoked some stuff.

I believe the wiring is correct right now for 220/230 but will also go over that once more.

What was the original voltage (and possibly phase) for the motor? 110V or 220/230V?

[Malcolm McLeod]

The simplest way to troubleshoot is to use a volt meter: Like this. ($8 - a throw away, but good for x1 use & worth it.)

Its important that you know what voltage the saw is wired for and what you are supplying it (...you didn't indicate in OP).

I recommend a qualified electrician do testing, but if you're comfortable around bare wires:

Remove the feed wires to motor at the motor termination box; tape them away from any possible ground or skin contact.

Set meter for AC voltage and check the line side of the contactor (from plug). Should read voltage that motor is wired for.

With the switch 'off', verify load side of the contactor is at 0V.

'Start' the saw (it won't run, since wires are pulled). Verify that the wires feeding the motor now have correct voltage.

If the voltage at the motor wires is 0V when contactor in 'on', then there is a contactor problem.

If the voltage is correct at the motor, there is either a wiring termination issue at the motor, or the motor is defective.

If the supply voltage doesn't match the motor (wired) voltage at any step , rewire the motor to match the supply. Or, change the supply.

[Charles Lent]

When you replaced the motor starting contactor, did you install the overload heaters? There should be two, one on each side of about where the coil is located but closer to you, or they can be located below the coil on some motor starters. Look carefully at the old motor starter and the new one and compare them. These are just a kind of a metal jumper between two screws, one above the other, with a low resistance portion in the center of them. If they are not there, the power won't go past this point. These overload heaters are designed to measure the current flowing to the motor and heat up enough to trip a bi-metalic switch under them and turn off the motor starter if the current flowing exceeds what the motor is designed to run on. If your old motor starter is the same brand/model as your new one, the overload heaters can be moved from the old one to the new, since it's quite unlikely that they are bad. If not, you should be able to get the number and brand name off of one of them and buy the correct equivalent in your new motor starter's brand. These don't come with new motor starters. You have to purchase them separately, based on your motor's requirements. If you can't use the old ones, you will need to take the information from the name plate on the motor with you to where you bought the motor starter, so they can select the correct ones for you.

Charley

[Lee Schierer]

Post some photos of the contactor, plug, motor wiring diagram, motor wiring, switch wiring.

[Jill Magill]

Sorry, been busy I will respond in the next few days, don't want you to think We are not thankful for your help.

[Michael Dye]

I'm with Charles on this one. I buy a lot of saws at auction and have had several of the Unisaws that have had failed heaters. If you want to do a quick check, just jumper the heater contacts and see if the motor starts. There won't be a safety issue doing it this way as the heaters are there more for a thermal overload as opposed to an electrical overload. At least that is what I convinced myself of. Have fun. Those old Unisaws are fabulous machines.

[Jill Magill]

Sorry , it took me so long to get back to you.saw 1.jpg