Film-Tech Forum ARCHIVE: Century Motor Burn Out

This is topic Century Motor Burn Out in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009144

Posted by Jim Cassedy (Member # 4115) on 02-25-2008, 10:20 PM:

Theater staff said they "thought" they smelled something burning in one of the projection rooms. I could smell obvious trouble as soon as I got near the stairs.

I found the drive motor on a Century SA seized up and humming loudly and was so hot I could not put my hand on it. I told them I'd have a look at it after lunch when it had time to cool down enough for me to work on.

I'm still not sure what happened. The data plate on the motor says it's thermally protected, so I'm not sure why it didn't shut down or why the breaker on that circuit didn't trip long before things got as bad as they did.

Below is a picutre of the junction box on the side of the motor. The large resisitor was part of the "soft start" circuit and it was burned up.
The wire nuts have roasted themselves into plastic globs, and the insulation on the feed wires is singed. The arrow points to the spot where the insulation totally burned off the wire and this finally tripped the breaker when the conductor got grounded.

I could find no problem with the projector mechanism itself. Everything is turning smoothly and nothing is binding.
I replaced the motor this afernoon. Ironically, just as I finished making the electrical connections to the new motor, EVERYTHING went dark. All the other projectors stopped. I looked up and saw that all the emergency lights were on. I KNEW it wasn't anything I had done. The breaker was turned off on the circuit I was working on, and even if it wasn't I wouldn't have taken out the whole building! Fortunately I've been working in theaters long enough to know to always carry or wear a flashight! I went downstairs and discovered that power was out eveywhere for about 10 city blocks in an east-west direction from where I was. It was out for about 90min, but I don't know why. My boss still isn't convinced that I somehow wasn't the cause of it! [Big Grin]

hahahha

> I ran several reels of film through the projector after I replaced the motor and everything is running normally. <

Posted by Mark Gulbrandsen (Member # 72) on 02-26-2008, 08:24 AM:

Dismantle the old motor and see if it has a start switch... it is not uncommon for start switches to weld themselves together or for the plastic pieces that run against the start switch to wear out allowing an always on sort of condition to happen to the start windings. Yes it stinks! I see this happen several times a year, typically with the Strong/Bodine sync motors used on Simplex projectors but with others as well...

Mark

Posted by Jim Cassedy (Member # 4115) on 02-26-2008, 09:24 AM:

Thanks Mark-
I know that motor does have an internal centrifugal start switch, and I'd considered that it had perhaps gotten stuck.
But it also looks like some of the motor windings are fried so I just replaced the whole thing. I'm going to try & find a place to recycle the old motor for the copper or something.

My supplier was out of the "stock" Century motors so he got me one from an alternate supplier. When I first put it in and powered it up (before connecting the drive belt to the projector) I realized it was rotating in the wrong direction.
I could not find a wiring diagram in the box ot on the motor, but I was able to figure out which connections to change to get it to rotate the proper way. I confirmed the connections on the manufacturer's web site when I got home to make sure I wasn't going to muck-up my new motor.
I need that machine for a big change-over show Wednesday night.

Posted by Tim Reed (Member # 137) on 02-26-2008, 06:13 PM:

Wow, Jim! That sure looks like a stuck centrifugal switch. [Wink]

The red-hot start winding probably damaged the insulation of the run winding, causing it to short as well.