Old GE Motor Problems

[Cozumel]

By the JS thread, I assume you mean the one hot-linked in your post # 13. I found that thread some time ago and that's what got me started on this board.

Sadly I'm no longer in a position to take resistance readings. Will have to wait for next season.

FYI, here is detailed info on the two 4PDT relays. In the photo it's just hard to see the layers of contacts. I just replaced the Up relay (top one) due to a failed coil, so I know it is the correct device:

PM-17AY-24VAC-PMSeries-OpenStylePowerRelays.pdf

BTW, I think I understand your diagram in post 18, including your edit, but I can't get it to square with the fact that there is a capacitor connected to wire 1 and 2, and nothing else.

Following is a verbal description of what I think the path is for power to the motor:

L1(+115 VAC) and L2(-115 VAC) connect to two of the unmarked wires and presumably power the main windings.
Somehow inside the motor, L1 and L2 tie back out to the two heavy yellow leads via wire 4 and 5 with a capacitor in series on wire 4.
With a "Down" button push the Down relay (normally closed) opens and returns power to the starting coil(s) with no phase change relative to L1 and L2
With an "Up" button push, power flows up the parallel yellow leads to the Up relay which opens and transfers reversed polarity power back to the starting coil(s).

Don't know where the centrifugal switch fits or the other capacitor.

I'm sure I'm not using the correct terminology, but hope you can decipher what i'm saying.

With regard to the four power contactors, I believe two of them close for one direction and the other two for the reverse (and they chatter quite a bit if the control relays don't behave cleanly, such as with a failing coil). That threw me for a long time before I figured out that it's the relays that are the problem. I still don't understand why or how all these contactors are needed when all they are doing is switching L1 and L2 on or off. The motor, and therefore the tram, would simply stop if the contactor fails since that also kills power to the electric brake.

 

[Les Jones]

Thank for posting the link to the relay data. I see the coils are 24 volts AC. Are the coils on the contactors also 24 volts AC ? I suspected that there may have been some connections hidden from view as the pictures were taken directly from above. Does the transformer near the bottom right in post #19 just supply the 24 volts AC for the relays or does it have any other function ? Just to get a better picture in my mind of the tram does the motor drive the wheels or does it drive a winch to pull the tram up the incline ? Also are the two sets of push buttons situated so the passenger has to lean out of the tram to operate them ? I have been looking at the JP thread again to try to work out exactly how he had the motor connected at the end. I can't be sure but I think he had it connected like the lower schematic in post #7 of that thread

Les.

 

[Cozumel]

Yes, the coils of the contactors are also 24 VAC. The transformer provides power for all the coils and energizes all the control wiring. The low voltage wiring within the control panel is quite complicated and difficult for me to sort out. With luck I will sort it out over this winter. I've found a schematic of the control wiring that looks like it may be close to correct for the current system. It only deals with wiring of the two right hand legs of the 4PDT relays and doesn't show the contactors or the left two legs of the 4PDT relays. I'll try to scan it and post it.


The motor is coupled to a gear box which in turn drives a winch spindle with 1/4" steel cable that pulls the tram cart up and down the hill at about walking speed (about 100 m and a 20 degree slope). The pushbutton consoles are next to the track and easily reached when sitting on the cart.

Incidentally, addressing one of your initial comments, my interest in ultimately replacing the control panel is due to the fact that the contactors and relays are getting increasingly difficult to find and the whole thing is difficult to diagnose when there is a problem. The system was originally installed in the late 1960's. I would also like to replace the pushbutton consoles with a wireless system that allows a passenger to start and stop the cart anywhere along its track, not just at the top and bottom limit.

 

[Cozumel]

Am back home in California and have created an album in Google Photos of the various pictures that I've taken over the past few years. The individual photo files are too large for the Electro-Tech server to digest and if I crop them to reduce file size, too much useful image can be lost. So here is a link to that album (keeping my fingers crossed that this works ):

https://photos.google.com/share/AF1...?key=V3NQN09aMFlMMFpGLWprWGZBM0VPbER2bFF1TnR3

I have not figured out how to add descriptive text yet, but I think the photos speak reasonably well for themselves.

You are correct about the contactors being wired to act as pairs of single throw switches. If they don't get clean activation signals from the relays, as when a relay coil is not activating solidly, there is a lot of contactor chatter before they finally engage. This is one of the reasons I want to ultimately switch to SSR's of appropriate values.

There are no SSR equivalents to the 4PDT relays, but I think I can make it work using six appropriately rated individual SSR's triggered by an Arduino microprocessor.......but only if I know how to wire properly into the motor.

 

[Les Jones]

Your last 2 posts (#23 & #24) give some useful information. The pictures of the connector box on the motor which shows that that the capacitors are part of the motor could explain why they are not shown on the motor information plate on the JP thread. Before seeing the picture I had assumed that the capacitors were in a box near the control panel. I don't think we can be sure how the motor is wired until you return to NY (I assume this will be spring next year.) to take some resistance measurments. I suspect two of the contactors switch the power to the motor and the other two switch the power to the brake. I think this is to ensure that there is no single point of failure that cause the motor to run when it should not. I think this is also the reason the two sets of contacts on the contactors are connected in series. I think you need to verify that th cause of the contactors not closing properly is due to the contacts on the relays. You will need to measure the voltage directly across the coils on the contactors. If it 24 volts then the contactor is at fault If it is less than 24 volts then it is probably high resistance contacts on the relays. I would advise not to replace the contactors and relays with solid state relays. It will make the system more complex and it may not comply with regulations. I would not trust a SSR to isolate something I was working on. Thinking about the wireless remote control I do not think it is as simple as I first thought. I think it should be designed so that a loss of the radio signal should stop the motor. I was initially thinking of a three button remote (Up, Down, and Stop.) but that would not be fail safe. I also imagined the "tram" would be more than just a platform.

Les.

 

[Cozumel]

Les:

Thanks you for all the time you have spent on this. It has certainly helped me sort through some of the issues.

I agree that understanding the motor wiring will have to wait 'til next year. I do have some questions/comments regarding your last post.

Have spent time going through my notes and the various photos and at the end of this post have scanned a drawing of how I believe the four contactors are wired for high voltage. I'm pretty confident I got it right, especially since the wiring for the coils looks like it activates all four coils at once.

Am a bit surprised by your comments about SSR's. All the ones I've looked at optically isolate the control signal from the high voltage circuit and there are devices available that handle inrush currents over 100 amps, so a pair of SSR's could replace the four contactors.

Regarding the wireless control idea, I've found a company that makes a long-range system that I think could do the trick including a three-button transmitter. It would still require limit switches at each end for positive stopping. Here is their website:

https://www.appliedwireless.com/shop/remote-control-products/

And here is my drawing (please excuse any incorrect symbolism). Can't figure out how to rotate it -- it's correctly oriented on my desktop :

 

[Les Jones]

I am surprised the way the four contactors are wired. This seems to be taking redundancy too far. All four of the contactors would have to fail with welded contacts to prevent the motor from stopping. Any one of the eight contacts working would be enough to stop the motor. It is not the optical isolation that I don't trust between the "contact" and the "coil" . (I used the quotes as there is no real coil or contact in an SSR.) It is the SCR or triac that I do not trust as much as a mechanical contact.

I have rotated the image using Corel Paintshop Pro X3.
I assume that the item I have marked with the arrow is the 220 to 24 volt transformer. (If it is not then you have the 24 volts connected directly to the 220 volt supply. I assume you did not know the symbol for a transformer.)
I initially thought about just using a three button remote but the stop would not be fail safe if the was a failure of the radio link which is why I think a signal must be being received from the remote for the motor to run. I thing it might be a good idea to post a message on this thread a short time before you return to NY in case I have had any more thoughts on the subject.

Les.

 

[Cozumel]

Les:
Again, thanks for your efforts on this and I will rekindle the thread when I'm headed back to New York next year. Don't know what I was thinking with the battery symbol -- you are correct it was supposed to show the 220 to 24 VAC transformer.

To allay some of your safety concerns: The gear ratio for the pinion and radial gear in the gear box is such that if the motor loses power the cart simply stops, even with a heavy load. I've tested that! A simultaneous failure of power and the electric brake results in a very gradual speed increase of the cart when heavily loaded. The worst that would happen with a lost radio link is that the cart would continue to the end of the track where the limit switch turns things off.

Until next year..

Jack Seitz

 

[Les Jones]

I was not concerned about the motor loosing power I was concerned about stopping the motor in the event of someone falling in front of the tram. I could see from you picture of the winch that the gearbox is a worm reduction so it would not be possible for tension on the cable to rotate the motor even if it was free to rotate. (I.E no power to motor and the brake off) The contactor arrangement will make it more likely for the motor to stop as any one of the 8 contacts failing open circuit will stop the motor. The way it is designed is to be very sure that the motor does not run when it is not supposed to.

Les.