3 phase problem - need help please

[MinnesotaDave]

I'm trying to fix the thickness planer in the school shop (it's been broken for a year, I guess I'll have to fix it myself).

Last year a board got caught, the motor stalled and shut down. It hasn't started since.

I've tested the stuff I can figure out.

I took the starter apart and cleaned the contacts. Two showed arcing on the plastic cover I removed (possibly from the motor stalling).
The fuse in lower right tests unbroken.
I replaced the overload with one from a working machine, no change.

Lower left, power in.
Lower right, power to motor.
Upper left, wires to switch.



I tested the switch, it works fine.

One problem I noticed, the "on" wire (white) has continuity with the center wire (black) before I push the button. That makes no sense.

I checked the wires and they are not shorted together in the cable. So they must be shorted someplace else?

[homanfab]

Is the contactor closing when you push the start button? Or is there nothing happening when the buttons are pushed?

Are the inline power fuses good (should be one for each phase)? Do all 3 phases have power? Looks like the control transformer is powered by L1 and L2 so a bad fuse would prevent the contactor from operating.

[Virgil5]

There is a way to manually close the Furnas contactor, I believe employing a screwdriver.
Manually close it and determine if the problem is in the motor or the control circuit.


If the motor runs
use a jumper to work thru the control circuit.

Option A- mess with the reset lever on the R side of the green contact cover. Chances are that is the reset for the internal overload heaters.

Option B. use jumper to bypass all controls and bring control voltage directly to the coil of the Furnas starter.

[MinnesotaDave]

Is the contactor closing when you push the start button? Or is there nothing happening when the buttons are pushed?

Are the inline power fuses good (should be one for each phase)? Do all 3 phases have power? Looks like the control transformer is powered by L1 and L2 so a bad fuse would prevent the contactor from operating.

Nothing happens when button is pushed.
I have not seen any inline power fuses, but I will double check up in the ceiling where the shut off box is.

As I recall last week's testing, all three had power coming in, but I will check again.

[MinnesotaDave]

There is a way to manually close the Furnas contactor, I believe employing a screwdriver.
Manually close it and determine if the problem is in the motor or the control circuit.


If the motor runs
use a jumper to work thru the control circuit.

Option A- mess with the reset lever on the R side of the green contact cover. Chances are that is the reset for the internal overload heaters.

Option B. use jumper to bypass all controls and bring control voltage directly to the coil of the Furnas starter.

When I manually push the contactor closed, all I get is a buzzing noise.
Option A - I already replaced the overload with a known good one but got no change.
Option B - I will have to think on this one, not sure if I know which is which to do this direct jump.

[Virgil5]

Plan C.3
Verify incoming voltage to all 3Ø at L1-L3 on contactor

Verify control voltage from transformer

Verify control voltage passing thru overload heater assembly below starter
1 probe on transformer while you walk up line thru the overload assembly.
Red wire from transformer with second probe on transformer output other terminal

Verify control voltage passing thru START button to coil.

[homanfab]

When I manually push the contactor closed, all I get is a buzzing noise.
Option A - I already replaced the overload with a known good one but got no change.
Option B - I will have to think on this one, not sure if I know which is which to do this direct jump.

If you are pushing the contactor closed and it is buzzing either one of the phases doesn't have power or there is an issue with the contactor/heaters. If you turn off the power to the machine and manually close the contactor there should be continuity from the incoming power to the motor wires on all 3 phases.

[MinnesotaDave]

I found a dead leg in the ceiling - now the motor will run when I manually close the contactor.

But, I still have a short somewhere because pushing the "on" button instantly fries the little fuse in the lower right.
KTK 1/4


The machine

[Virgil5]

I got a hunch some little darling named Dindu Nuffin got to the machine while nobody was looking.

What's the control voltage and do you have a light bulb in that voltage?
If you have a bulb it should be easy to locate the problem and clear it.

[MinnesotaDave]

I really don't think any student caused the problem.
It seemed to run fine until the board got caught and stalled the motor.
Immediately quit and wouldn't re-start.

I don't actually know what control voltage means

I'm just muddling my way through like a gorilla pushing random buttons on a typewriter.

And I'm also operating on the assumption that even a blind squirrel finds a nut now and then.

[Virgil5]

Control voltage is the output voltage from the transformer.
Should be either 120 or 24 volts.

Gorillas have solved problems before.

Suspicion of sabotage is derived from experience in schools. Machines that don't run become targets.

[MinnesotaDave]

I'll make a guess that the transformer is the item in the lower left with the little fuse.

I think the problem that is remaining is: the switch "on" wire (white) has continuity with the center wire (black) before I push the button.

That should not be right to my way of thinking. Otherwise there would be no reason to have the switch join them?

[smilindave]

Dave,
The pull coil in the starter maybe fried, the transformer makes the control voltage, it will have multiple taps to allow different voltages. disconnect wires at the coil, apply voltage then you should be able to isolate the control voltage and determine if the pull coil is shorted. The small fuse will be the input current limiter for the transformer, if it still blows, the transformer may be bad. Good Luck
Regards
Dave

[ljdm]

I'll make a guess that the transformer is the item in the lower left with the little fuse.

I think the problem that is remaining is: the switch "on" wire (white) has continuity with the center wire (black) before I push the button.

That should not be right to my way of thinking. Otherwise there would be no reason to have the switch join them?

I have to agree, white and black shouldn't have continuity, if they are both going to a switch. What are those wires, are they power in, etc, cant tell from pic what they are. Again, if they are going to a switch, shouldnt have continuity.

[Virgil5]

OK Dave, we have a little problem here.

EXACTLY where on the machine did you find the black plastic contact set you're holding in your left hand?

The control transformer is the object with the fuse on it in the housing with the contactor and overloads. It takes line power at whatever voltage (240 / 480) and reduces it to control voltage. The fuse on top of the transformer protects the transformer from loosing smoke in the event of a problem in the control circuit.

Best I can see in the picture, the red wire leaving the low voltags side of the transformer is connected to one side of the coil of the contactor.
The BLACK wire leaving the transformer is probably going out to the Start/Stop button on the machine. Red and white returning from the button in the same cable.

I don't have a cut sheet for that contactor handy so I'm not sure how the coil of the contactor connects up.

Now, it gets sketchy since I ain't there putting test leads on wires and I can't see exactly where red and white from the Start/stop buttons connect.

We also need to get on the WHY THE FUSE BLEW issue first, and the easiest way to solve that is with a lightbulb of appropriate voltage temporarily replacing the fuse.

PLEASE, look at the nameplate on the transformer and tell me what the voltage leaving the transformer is.
If you can't see that number, you can meter the voltage from the terminal where the black wire going to Start/Stop and one side of the fuse clip. It should be AC and below 250 volts.

Bear in mind, I am taking your Gorilla assertion very seriously in this situation.
If your line voltage is 480, we will be going very S L O W.

[MinnesotaDave]

I did some Googling on the coil. Seems like 10-100 ohms means it would be ok?

I'll take off the wires coming off the left side of the transformer (where the fuse is) - hook leads to those wires and see what the meter says about the coil.

[Virgil5]

PLEASE STOP!

Did the black plastic block in your hand come from the Start/Stop button?

The coil isn't even in the circuit until the Start button is pushed.

If the coil is in circuit the only way that can be happening is if the internal holding contacts in the contactor are malfunctioning.

[MinnesotaDave]

Coil tests at 1.8 to 1.9 ohms.

[MinnesotaDave]

Transformer

[MinnesotaDave]

PLEASE STOP!

Did the black plastic block in your hand come from the Start/Stop button?

The coil isn't even in the circuit until the Start button is pushed.

If the coil is in circuit the only way that can be happening is if the internal holding contacts in the contactor are malfunctioning.

The black plastic thing is the stop start button.
When assembled and the start is pressed, it blows the little fuse instantly.

[MinnesotaDave]

I'll have to table this for now, I live an hour away and still have to feed the kiddo

You guys have been great and I'll be able to work on it again in the morning.

[Virgil5]

With POWER OFF

Disconnect white wire coming from S/S button from the contactor.

Put ancient meter on ohms and red wire leaving transformer and check for continuity between those points with Start button depressed.

[Willie B]

I can't see all the wires.
The transformer is there because relay coil voltage doesn't agree with power supply.

Break it down into compartments.

Three phase is pretty simple. Three wires power line 1,2,3. A contactor lies behind the nameplate. It closes when a magnetic field pulls it closed.

The three springs are heaters.

At the bottom are terminals T1,2,3. They are the load terminals for the motor.

2, and 3 on the left are a forth set of contacts that function simultaneous to the other three. These are the latching contacts.

95, and 96 are the overload relay contacts.

Overload relay senses heat, opens 95-96 which must be manually reset after a cooling period.

Transformer primary gets power from L1 and L2, creates a magnetic field, inducing a lower voltage in transformer secondary.

One leg of secondary coil connects to 96. 95 connects to the big contactor magnet. If 95-96 contacts are closed, this provides power to one side of the contactor magnet.

The other leg of transformer secondary passes through a fuse, and goes to a stop button. A stop button is a normally closed set of contacts opened by pressing ones finger on said button.

Power passes through stop button. two wires leave the stop button from the other side. One goes to 2 on the left of your control. The other goes to one side of the start button.

Terminal three connects to the remaining side of the start button, and to the other side of the magnet.


If all is well, power flows from the transformer secondary to the stop button. If no one has their finger on the stop button, it passes through to the start button. Push the start button, power arrives at terminal 3. from there it enters the magnet coil, through the magnet coil down to 95. If thermal contacts aren't overheated electrons pass through to the other side of the transformer secondary.

The magnetic field created closes all four contacts. The motor starts, and power originating at the stop button flows from terminal 2 to 3 where it also supplies a redundant path other than the start button.

If the stop button is pressed, or 95-96 opens the flow stops, and the magnet dies. opening all four sets of contacts.

Check the bridges. Stop button must be closed, start button must flow current when pressed, 3 must connect to the magnet coil. coil must be intact. 95-96 must be closed, carrying to full circuit at the control transformer.

Most common failure is in start/ stop buttons, (sawdust) or 95-96 (burned, or failure to reset. Confirm that reset mechanism is latching. Most common are solder pot mechanism, where a trigger mechanism is dogged onto a star wheel. The shaft of this star wheel carries at its other end another cog wheel. This second star wheel is surrounded by solder. When the heater sized for motor nameplate gets hot, solder melts allowing the shaft to turn, triggering opening one of three switches in series controlling terminals 95-96.

Your overload relays seem to use some bimetallic trigger.

Willie

[Willie B]

[farmshop]

The fact that manually closing the contractor just creates buzzing of the motor probably means you are not getting full voltage to the motor or the motor was damaged in the previous incident. I would continue to check power supply coming in as well as power to the control transformer. Your stalled motor could have burned a connection somewhere in the the line. A disconnect or wire nut is a likely place to look. Being your controls are not working I would start with the phases that the transformer is powered off