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dgr68 12-31-2008 01:06 PM

Unisaw wiring problem
Greetings all! I'm an amateur woodworker and purchased a used Unisaw that dates to around 1970. The saw has a 2hp, single phase, 115v(24a)/230v(12a) Delta(Baldor) motor, an original low voltage controller, and an original magnetic push button switch. I had an electrician configure the motor and lvc for 115v and install a new plug, receptacle, and 30a single pole breaker. Tried it and got absolutely nothing. I asked the electrician about it and he told me that itís probably the motor. Brought the entire saw to motor shop #1(big mistake) and wound up paying $150 for him to take off the motor, take it apart and give it back to me. Told me the motor needed all kinds of work, etc. It looked very good to me so I brought it to the second motor shop and he said it looked fine, put it together, and told me it runs fine. I brought it back home and examined the lvc closely. The wire from the switch to the lvc was bad so I replaced that. All the wiring in the lvc seems be exactly like the schematic and the condition of the unit appears good. I rewired everything as it should be andÖ..nothing. Here is where I have questions. I have a 3 phase service in my building so is this a problem with the single phase motor? From the motor, there is a group of 3 wires and a group of two wires. Iím assuming that the 3 wire group is the hot and the two wire group is the neutral. Iím at a loss and would like to restore the machine with original components. I can take pictures as well. Thanks in advance!!

dgr68 12-31-2008 02:38 PM

Here are the photos..

micromind 01-01-2009 01:36 PM

I'm going to be on vacation from fri (1/2) to next thur (1/8), but we can at least get started.

What sort of test equipment do you have? (A multimeter would be about the minimum). Are you comfortable taking voltage readings in the control box with it plugged in? (this isn't a requirement, it'll just speed things up a bit).

First though, was there any possibility of the black transformer lead terminal touching the metal case when the unit was plugged in? If it did, then the transformer is most likely burned up.

If you or one of the Mods can move this to the electrical section it'll get a lot more exposure.


P.S. The fact that the building service is 3 phase will have no effect whatsoever on the operation of this motor.

dgr68 01-01-2009 07:40 PM

Thanks Rob
Yeah- I pulled out my multimeter- which I have never used but figured it out pretty well. Didn't have much time to go through it as I had the kids but I'm comfortable taking readings. I did read the outlet and the needle spiked to halfway on the 250v setting- which I assume means I have 120 at the outlet. How does that LVC work. I read a manual off the OWWM website but it is for a newer lvc and doesn't explain how the contactor works. I have this posted to a bunch of sites in the hope that someone knows their stuff. A guy has responded at one of them and tells me the contactor needs to be pushed down. With no power attached I did push it and it seems to have some spring mechanism in it that pushes it back up. This makes no sense to me. There is already an overload mechanism(with the red handle) in the controller so I'm not sure why the contactor moves up and down. If you could shed any light on this I'd appreciate it. Thanks in advance. Dave

micromind 01-01-2009 08:27 PM

Here's the lowdown on this type of controller.

Line power (120 volts) goes to one side of the contactor, and the transformer. When the start button is pressed, the coil of the contactor is energized, pulling it in. You can do the same thing by manually pushing the contactor down. (In fact, you did).

Once the contactor is pulled in, all 3 contacts close in (turn on). 2 of these contacts send the line power to the motor. The third one maintains power to the coil through the stop button. When the stop button is pressed, the holding circuit to the coil is broken (turned off), the coil is de-energized, and the springs push the contactor open (off).

The first test, if you're comfortable with it, is to plug the controller in, and manually push the contactor closed. Make sure that you don't touch anything metal. 120 volts can be lethal. Use a small wood stick if needed. Practice this with the controller unplugged first. You'll likely see some blue sparks when the contactor is first pushed in, and again when it is released.

If the motor starts when the contactor is manually pushed in, you've proved that the power circuit and motor are OK. The problem will then be with the control circuit. If the motor is just laying on the floor, it'll jump when it starts.

If the above test is OK, the next thing to test is the control transformer. With the power on, check for 24 volts AC across the two brown leads coming from the transformer. If the voltage is zero, the transformer is bad. If it's OK, we need to look further, and it'll get more complex.

Not to worry though, there are several of us around here that troubleshoot stuff like this every day.


dgr68 01-01-2009 09:01 PM

Thanks Rob- I'll give it a shot in the morning and let you know what happens..

dgr68 01-02-2009 08:51 AM

Rob- I pushed in the contactor with a stick and the motor started. I also tested the two brown leads out of the transformer and it reads 25-30v. Not sure if you are gone already but I am curious to know what is wrong with this thing. Thanks again..

buletbob 01-02-2009 11:23 AM

for what its worth I have the same unasaw but with the 3hp 220v motor and had a similar problem where I had the 24volts comeing to the contact or but would not pull it in. and when I pushed it in with a screw driver it started. So I replaced the contact or and it has been working fine. It could be your contact-or, Good luck BOB.

dgr68 01-02-2009 11:52 AM

Bob- Where did you get the contact? Also, did you think of just switching to a new switch with overload- a la the Grizzly ones? I'm chasing this around because I'm curious and would like to keep the machine true to original but I'm getting near the end of the rope.

micromind 01-02-2009 12:37 PM

A few more tests; these will be with power off. Since you stated 'the 250 volt setting' on the meter, I'll assume you have an analog (not digital) type of meter. It'll work just fine. I'll also assume that when you pushed the contactor in manually, and the motor started, the contactor didn't stay latched in.

Set the meter to RX1 (resistance). Short the two leads together. The needle should move to the far right. If it doesn't, the batteries need to be replaced. Sometimes, you need to remove the back of the meter to get to them.

Next, read resistance between the 2 and 3 terminals on the contactor. If the needle doesn't move, use the RX10 or RX100 scale. If it still doesn't read anything, go back to RX1. We'll need to check individual components.

Now test the overload relay. It's the thing with the thick coil and red reset button. Test across the two lower screws. The needle should swing to the right. If it doesn't, this relay is bad.

Next, test the stop button. It's in the smaller box that has the start-stop buttons. Test across the terminals marked N.C. The needle should swing to the right. While holding the probes on the terminals, press the small red button. The needle should go back to the left.

The contactor coil is next. It's kind of hard to see in the pic, but it looks like the coil terminals are down below the 3 and T2 terminals. It might be hard to get the probes on the coil screws, if you test between 3 and the red wire on the overload relay, it'll give the same results. You might need to use the RX10 or RX100 scale here. If the needle doesn't swing, then the coil is bad.

If all of these tests are OK, the problem is either a broken wire, a loose terminal, or the transformer might not work under load (even though it reads voltage when it's not loaded).


P.S. Insulate the black wire from the transformer. If the terminal touches the metal case, it'll burn up the transformer. Tape will work.

dgr68 01-02-2009 01:35 PM


Put a new battery in the multimeter but it doesn't spike on RX1. This is the one I have. Do I need to mess with the OHM screw?:

micromind 01-02-2009 01:58 PM

A lot of times there is a fuse of some sort in the back of the meter. This fuse will blow if power is applied to the test leads when the switch is in one of the resistance positions. (It happens on a regular basis!!)


P.S. The ohms screw is to get the needle to zero for accurate measurements. Even with it turned all the way down, the needle will move some.

williswires 01-02-2009 02:45 PM

I noticed you have a 2HP motor, but the contactor wiring diagram specifies a 1.5HP max HP. Is this a replacement motor?

dgr68 01-02-2009 03:48 PM

Rob- The multimeter still doesn't move in that setting. Not sure what to do. I'm pretty sure the fuse works- as the think works in AC..

micromind 01-02-2009 04:27 PM

The fuse is only in the circuit when the switch is in the resistance or amps (250m) range. It doesn't need the fuse or batteries to read voltage.


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