Looking for info on old Master Electric motor

[1yesca]

outstanding please do keep us informed on your progress

 

[Just a Sparky]

Skipped.

Type 'RA' is a brush-riding type repulsion start induction motor. All four brushes are short-circuited together and bonded to ground via the motor frame. These motors have a short-circuiting mechanism only, as opposed to the brush lifting and shorting mechanism seen in higher end repulsion start motors. Cheaper to make but they're noisy bastards and the brushes wear much faster.

Since this is on a door opener I am guessing it is an electric reversing type repulsion start motor - single voltage with four leads. One inducing coil, one field coil. Both must be connected in series. Reversing the polarity of one with respect to the other will reverse the starting moment of the motor by shifting the magnetic field with respect to the brush cage. Look for 'ELEC-REV' on the accessory field of the nameplate to verify this else ohm the windings and check for two distinctly different resistances.



Try www.carbonbrush.com for brushes. If not an exact match, look for something you can modify easily.

The motor will start as a repulsion motor and then transition into an induction motor by way of a shorting necklace which slides into place within the commutator barrel by way of fly weights and push rods. Difficult to see on these motors but it's in there.

Guessing your commutator is going to have some damage if the brushes have worn to the point the motor no longer operates. It may have to be skimmed and/or ground in a lathe. It should operate with minimal sparking.

 

[Lben]

Hey Sparky, the motor is actually simpler than you describe. No fly weights, no pushrods. Shorting necklace is on the end of the commutator. There is a shallow brass or copper cup that has a bunch of little copper segments held together by a tension spring. When motor shaft hits some rpm the centrifugal force of the copper segments push against the tension spring and they contact the inside of the commutator shorting all of the segments out.

I wish I would have seen the link for the carbon brush supplier earlier - no order minimum with those guys.

I took apart the drive end of the motor shaft - not a happy camper. Trying to decide whether or not to now call it quits in this deal.

The gear on the shaft is only retained by a single 3/32" roll pin. No key, no nothing. It amazes the heck out of me that a roll pin that small, even in double shear can handle the torque.

And then there is the oil seal issue. The seal is axially loaded through some sort of compression mechanism. The compression mechanism pushes against a metal ring, which in turn presses against the front of the seal, forcing the seal into the housing and at the same time putting pressure on the shaft side of the seal. I have no idea where the actual oil leak is, seal to shaft, seal to housing. Finally, I have no idea at all where to source a replacement seal like this. Pictures attached.



Here are all the pieces on the shaft. Dinky roll pin is on the paper.



Parts laid out in order.

 

[Jim Christie]

The Seal looks similar to some I have seen on older centrifugal pumps .
If you have an industrial supply house near you that sells belts and bearings etc. they may be able to match up an equivalent seal if you can go with it in person.
Here is one manufacturer
Home | U.S. SEAL MFG.
that I found in this search .
pump shaft seal - Google Search
Jim

 

[Lben]

Hi Jim,

I'm out in the boonies in Colorado, don't know if there is such a place in Colorado Springs. Used to live in the Houston metro area, I'm certain what you suggested would have been an option there. I've been in touch with a rep from WinSmith who is doing a bit of research on the gearbox. I don't hold out too much chance of success there. I have a backup plan which consists of adding a washer to increase the preload on the old seal - may or may not work - won't be able to tell until I put it all back together.

I did some cleaning on the cases today. Needed to get that done while it was somewhat warm outside. We are gonna get temps below zero a few days down the road. It doea appear that this motor had a manual method of reversing the rotation at one time. There is a notched ramp in the rear motor case where a metal tab may be been used to rotate the brush holder into two different positions. What ever was there is missing and someone used the metal strap to make sure the brush holder stayed in one position.

 

[Jim Christie]

I don't know much about your area but this turned up in a search I tried.
Colorado
1350 Bellprat View Colorado
Springs, CO 80921-7660
T: +1 719.884.9500
Contact Us | Bal Seal Engineering
If they can't help you with a seal ,someone there may be able recommend someone who can .
mechanical seals in colorado springs - Google Search

 

[Lben]

Thanks for the info Jim.

What I thought was the seal, only seals the outside bore. I'm still puzzled about how the shaft is sealed. The original MRC 203 bearing had a rubber seal on both sides. I don't see how that would be the fluid seal - thinking that that seal is only to keep the bearing grease from getting contaminated. I replaced both bearings with 6203 numbers having the rubber seals on both sides. Some how the brass assembly with an internal spring must do the shaft seal. There are seals on both ends that fit with some drag on the shaft. The faces of those seals go up against machined surfaces on both the front and back sides. There are multiple parts that can rotate with respect to each other. The only thing I know for sure that isn't rotating is the outer shell of the bearing. Everything else can rotate or not rotate with respect to its nearby part.

Put the motor back together today, but did not reinstall the brake assembly. I added a little more preload to the brass assembly. Motor runs both directions. Kinda interesting to watch the shorting necklace operate. Within a second or so of applying power, there is a kind of haze of little sparks as the little pieces of the shorting necklace swing out to short against the commutator. Then there are just occasional random little sparks. One can hear the difference when the motor first starts up as repulsion and then transitions to induction.

Tomorrows task will be to bolt the gearbox case to the front of the motor (which is gonna be a pain in the keester) and then put the gearbox all back together. Will be a challenge to get the endplates and bolts all sealed so that they don't leak.

Nothing has been going on with the hangar for over two months. I got on the airport manager's case to get something done. Supposedly the electrician is supposed to come out sometime this week. Rumor has it that the electrician wants the county to buy a larger electric motor. As a taxpayer, I'm pretty pissed. This electrician has no clue what he is doing and is just throwing parts at the problem.

 

[Lben]

So still no electrician.

Since there had been talk of a power issue coming in, I ran another power feed in from a building about 20 feet away - no change.

I put a clamp ammeter around the hot wire and the motor was pulling 34 amps when it stalled. Motor is rated for 12.8 amps.

So I believe the motor pulling 34 amps means motor is undersized, gearbox ratio is insufficient - or - both.

Airport manager will not let me put back in the old motor/gearbox.

 

[Just a Sparky]

Airport manager will not let me put back in the old motor/gearbox.

I mean... it worked for the past 50 years, didn't it? Either something else changed in the system, one of the windings failed open or it just needed some TLC.

Always try the simplest fix first... i.e. replacing the worn-out brushes causing the motor to throw sparks and sputter to a halt rather than replacing the entire opener unit.

By the way... has anyone bothered to check the torsion springs on the door? Broken or incorrectly set springs will cause any door opener to stall - new or old.

 

[Lben]

Door is a dead lift - no springs - just cables and pulleys. Pulleys are not binding when the load is applied, I can pull on the cables one at a time and move the door.

As a refresher, old motor is a 1/3 hp repulsion start, induction run unit. It is attached to a 175 to 1 reduction gearbox. It was struggling to open the door and would occasionally stall. It was gradually getting worse. I had taken the old motor/gearbox home and put in new bearings and brushes and cleaned up the commutator. I believe that the brushes aren't really doing anthing when the motor is operating as an induction unit.

There are few to no skilled tradesmen out here depending upon what kind of work one needs done. A lot of things get done half-assed. Most of them go immediately to the replacement route with no troubleshooting. These guys initially threw up a 1 hp capacitor start motor with an undersized gearbox. Then they put up a stronger gear box. New gearbox ration is 60 to 1. All the time the door is only going up about 30% of the way before it stops. I did a loads analysis and just got a deer in the headlights look when I handed over the paper.

Then there was talk of a power supply issue. So I ran an alternate power feed from another building - no improvement - but last I heard is that the electrician is still gonna look for a power issue.

It is not my building, I just rent space in it. The county is in charge and it has now gone on for about 6 months. I would have fixed the damn thing in a couple weeks if it was my building.

 

[1yesca]

Door is a dead lift - no springs - just cables and pulleys. Pulleys are not binding when the load is applied, I can pull on the cables one at a time and move the door.

As a refresher, old motor is a 1/3 hp repulsion start, induction run unit. It is attached to a 175 to 1 reduction gearbox. It was struggling to open the door and would occasionally stall. It was gradually getting worse. I had taken the old motor/gearbox home and put in new bearings and brushes and cleaned up the commutator. I believe that the brushes aren't really doing anthing when the motor is operating as an induction unit.

There are few to no skilled tradesmen out here depending upon what kind of work one needs done. A lot of things get done half-assed. Most of them go immediately to the replacement route with no troubleshooting. These guys initially threw up a 1 hp capacitor start motor with an undersized gearbox. Then they put up a stronger gear box. New gearbox ration is 60 to 1. All the time the door is only going up about 30% of the way before it stops. I did a loads analysis and just got a deer in the headlights look when I handed over the paper.

Then there was talk of a power supply issue. So I ran an alternate power feed from another building - no improvement - but last I heard is that the electrician is still gonna look for a power issue.

It is not my building, I just rent space in it. The county is in charge and it has now gone on for about 6 months. I would have fixed the damn thing in a couple weeks if it was my building.

sounds like F TROOP