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?
We received a call back out this weekend. Two of the fuses in the disconnect were blown. This is the first time we have been back since my posting. When we replaced the fuses it ran fine while we were there. Got a call yesterday and the fuses were blown again. This time we changed the oil in both bearings of the motor, and the repair tech noticed that the contacts were arching, spent about an hour filing and adjusting the contacts to keep it from arching and not blowing the fuses again. (it blew several times while they were there) No call today. I guess we will keep on it until we get under control. They are not calling anybody else, and seem to be happy with us.
How many amps are you showing in each direction with a empty car? With capacity? With a balanced load? You should see a balanced load between 40 and 50 % capacity. Remember when checking for a balanced load that your amps and your car speed should be the same in both directions.
Also have you meggered out the motor? Have you opened up the motor and checked the rotor. Broken bars will cause problems.
I've bumped this up as I think this should be your start maybe after you have tested the motor like JKH just stated. It appears that you have 2 phases shorting or overloading and those 2 are the ones id look at. Also make sure your arc shields are in place as they can track across them.
Check and see that the carbons are even and the copper paddles have plenty of wipe.
Is this a 2 of 3 phase unit?
I was trying to ask is this unit a 2 OR 3 phase unit...
Any conclusions?
We have opened up the motor and looked at it. We have made sure the contacts are even, wipe good, and the shields are in place. Your comment about the material is a likely possibility, did not even consider that.
When we go back out there again, we will look at the contact material, check the amps with a loaded car, and try uppo's suggestion about the brake wires.
Thanks for the follow up.
Have the overloads ever tripped? Are you sure they work? Are they adjustable? I would think if your brake doesn't open the overload would trip. You could do a current injection test. Although most of us probably don't have that type of equipment. You could ask you local motor repair shop if they can test the overloads. But it would be less expensive to just replace them with solidstate overloads.
Here's my concern...
If you block out the break from lifting and the overload doesn't trip then the motor will take a big hit.
How do the stator windings look? What have they meggered out too?