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Single Speed AC Otis

Guest · 2013-07-16T21:23:00Z

We have been called in on a unit and thought that we had it done.Several companies have looked at this and told them they needed a mod.(a whole different subject please)It is a 1958 circa Single speed AC unit, no selector. It was blowing the mainline fuses when it took off. The problem we thought, and still do,was the brake was not releasing fast enough and the motor was trying to pull through it. You can see the brake pick just a little, the motor hums pretty good and then the brake will pick all the way. We first cleaned all contacts, adjusted the resistors, to get full brake voltage from the rectifier. It worked for about a week and then started blowing the fuses again. We then did a complete brake teardown and adjustment. We pulled apart the brake pistons, cleaned them, turned the sleeve, lubed it with graphite and replaced the coil to be on the safe side. The new coil resistance was the same as the old one. It worked this time for two weeks and today it blew one of the mainline fuses. They are 30 amp, with 25 amp fuses inside the controller. The rectifier was supposedly replaced a couple of years ago. The rectifier while not under a load will produce 160 volts. Once under a load it drops to 127 volts, which we are getting to the coil. It will only blow the fuse at take off, once the brake has lifted it will travel the entire 60 foot of shaft with no problem. Any ideas?

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jkh

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21/08/2013 5:02 am

Brett
I will send you an old print from a tear out. Nothing like a print to refresh your memories.

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uppo72

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21/08/2013 3:02 pm

Originally Posted By: jkh

Brett
I will send you an old print from a tear out. Nothing like a print to refresh your memories.

thanks mate.

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uppo72

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21/08/2013 3:05 pm

I would seriously consider bring your motor rewinders in to test the ac machine properly(they can test the motors better than we can with their equipment and knowledge). if they check out ok then at least you've isolated that from your fault finding.

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traction

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21/08/2013 5:50 pm

I second having the motor tested.

When you're done that mod it out 😉

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maine_r

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16/07/2021 11:06 pm

So what was the end result ??

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