Looking for info on old Master Electric motor

I'm hoping someone(s) can take the time to help me out a bit on this.

First background. I rent a aircraft hangar from a county and the original motor gearbox assembly was starting to really struggle to lift the door open. The county hired an electrician to replace the motor/gearbox assy. Well long story short, 3 months later and several iterations, the door still doesn't work. Yep, these boys aren't very competent.

So I took the old assy home and now it is in some pieces on my workbench. Confession - I am not knowledgable of electric motors - well I know some of the basics, but that is it. This assy is OLD, probably dates back to the Korean war. Back when it was mounted in the hangar, one of the brush leads was no longer attached to its brush, it was just laying on the brush holder.

Now some details. The data tag says the motor was built by Master Electric Co in Dayton, OH. Style - 123700, Type - RA, Frame - 5825. It is a 1/3 hp, 115v, 60 hz motor. It has an electric brake assy on the back of the motor which has been disabled. This motor is integrated with a Winsmith Speed Reducer right angle drive. The gear box has a bad lubricant leak. The data tag on the gear box is severely damaged. I cannot read the part or reduction numbers on the data tag.

Since I have my doubts that these so called electricians are ever going to get their stuff working, what I would like to do is replace the motor brushes and bearings and the bad gearbox seal. If by the time I get this motor back together and the boys still haven't got their stuff going, we will put the original repaired unit back in. I haven't pulled the motor armature out of the gearbox yet, so I don't know if there is a seal part number that I can use to order a seal. The one bearing I have exposed has a visible part number, but I have not tried to look it up. I'm reasonable certain I'll have to have somebody custom build a brush set. I did some searching, but couldn't find anyone selling the type of brush configuration that this motor is using.

From what little research I've done, I think the motor is a single phase repulsion motor? I don't know how this type of motor works. I see that the line current coming in only goes to the stator windings. What confuses me is the brush setup. The four brushes are wired in pairs and the brush holders are mounted to a common metal plate which in turn sits in a recess in the back of the motor housing. It certainly looks to me like the brushes, mount plate and motor case are all electrically common.

Thanks for reading and if anyone can help out explaining how this beast works - I'd greatly appreciate it. I don't want to turn this into a big project. I would just like to understand the operational basics, obtain the proper parts and put it all back together without letting the smoke out.

Thanks all,
Lowell

From the description it does sound like a "repulsion start, induction run" motor. Sometimes you'll find four stator wires and that will be dual votage capable. The brushes are designed to lift once the rotor comes up to speed, and these motors are typically reversed by shifting the brushes.

Photos ot your particular unit would help for folks to provide guidance.

An example:

Ok, gonna try to attach some images. As a reminder, I have taken the motor partially apart. The front motor case is still attached to the gearbox. I was going to open up an access plate on the gearbox to get at one of the attach bolts, but I got side tracked trying to research what kind of motor this thing is. There is no centrifugal switch and no brush lifting assembly. Mechanically this thing is pretty simple.

This is the gear box with front motor housing still attached along with the armature

Close up of the back section of the armature with the commutator.

Brush plate assembly which shows that one brush has a broken lead

Rear motor casing showing where rear bearing sits in case. Also shows the two brake leads that go back to the brake unit

You just need to repower it with a new motor and gearbox.

the brushes on that motor stay in contact with the commutator all the times running or not. next thing is that plumbers tape that is screwed to the brush bracket is it a lever that allows the brush bracket to pivot ? if so that is how the foreword and reveres work . and from your pic. of the brush wiring you can see that there is a jumper from one brush to the other brush so reconnect the jumper to the brush that is by itself [no jumper on it] and if all the brushes look good there all about an inch or so long and the brush springs all look good there not burned and can push the brushes against the commutator and the bearings are good there not locked up or trying to do so .then put it back together on the bench and try the smoke test will it run will it go forward and reverse with out tripping the breaker and if it dose what you want and you want to put some new bearings and a seal or two in it give it a go . the one place that F-troop may have tripped on there foreskin on there new set up is they may not have put a big enough motor / gear box set up in as far as torque goes . inch / foot lbs or the door itself may have a problum dose it have a separate chain that lets you open or close it manually [ and what kind of door is it a roll up , swing/ tilt up or sliding ]if the door works manually ok by its self then go from there but the first thing is safety yes in a perfect world you tell the land lord to fix it but at what cost well raise my rent or you need to find a new place so yes it not always that ez you can get there just be safe about it and do your home work about the info you need to get the job done .

Likely the door has not had a drop of lube since Hiroshima,and the effort to open has quadrupled.....get some Rocol chain lube and give all the moving parts a good bath......And while up there check for flogged out runners,guides ,pulleys etc.

thermite said:

^^^ THIS!!!^^^

OTOH? "Get it right...."

Previous owner warned me the 18-footer on my garage was so finicky it MUST have all rollers & sliding shafts shot with a special silicone lube twice a year lest it de-rail.

F**k me ... what?

Eyeballed it. Aligned the damned track properly. Used a proper stay-in-place lube instead.

Haven't lubed the b**h in 30 years since, and - having also corrected improperly set springs - can easily run it up and down by hand "directly" if the power is out!

HOPE your DOOR is the real source of the problem, too!

They CAN be far the easier to fix!

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18 footer on your garage??? How high? I'm envious as my shop door is only 14'x12' and some machines on the farm have to be serviced outside.

thermite said:

Sorry mate. So close, but yet so far?

The Devil made me do an edit!

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well one thing is for sure its ez'er to read / understand

1yesca said:

the brushes on that motor stay in contact with the commutator all the times running or not. next thing is that plumbers tape that is screwed to the brush bracket is it a lever that allows the brush bracket to pivot ?

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1yesca is hot on the trail.

Before I run along 1yesca's train of thought, I once again must point out that this a county owned building. I'm not allowed to make major changes to the building, I'm not going to assume liability by making changes and I'm not going to give the county $5-6k in new hardware.

This motor appears to be a single phase repulsion motor. The wound armature with the brushes gives the motor additional starting torque. The brushes have to have an angular shift from the stator fields to generate that torque. The brush plate can be positioned in different angular offsets, but only one position will result in max torque. Shifting the plate in the opposite direction would cause the motor to run in a reversed direction, but that aspect is not used here. I guess someone previously wanted to make sure that the brush plate would not move so they attached the metal strap "plumber's tape" to fix the brush plate in one position.

The data plate specs this motor as a single phase, 60 Hz, 120 volt unit. There are three leads coming from the stator, one lead has a white tag on it. From what I have read about similar motors is that applying 120 volts to one of the black wires and the white tagged wire will result in rotation one way, then moving the power to the other black wire will result in the motor running in the opposite direction without having to move the brush plate.

To answer more of 1yesca's questions: It is a swing door that weighs about 1200#. Half that weight is supported by hinges so the motor/gearbox assy has to lift 600#. The cable spools at the gearbox have just under a 3" radius. So I calculate a load of 1800 inlb at the gearbox. If the motor/gearbox don't work, the doordoesn't open - no manual work around. My airplane is in another hangar for now, another airplane is trapped in this hangar.

The old motor was a 1/3 hp unit running at 1725 rpm. I determined the gearbox reduction to be 175 to 1. So when that motor was running at no load speed, the gearbox is turning at 10 rpm. Geared down that much, 1/3 hp will lift one helluva lot.

The boys first installed a 1 hp motor with a gearbox rated at only 1400 inlb. I told them that that wasn't gonna work. That combo would not open the door. It would start to open the door, then the motor would stall. I think I heard a click when that happened. For this combo my concern was that the gearbox would be overloaded and fail. But the undersized gearbox would have no bearing on the motor stalling.

A month later the boys had ordered a higher rated gearbox (2400 inlb) and installed that. Door still doesn't open. Door starts to open, gets about 30% of the way up and everything stops. Pushing the up button makes motor hum, but there is no movement. I don't know what the ratios of the gearboxes are, but when the door was moving it was a heck of a lot faster than the old setup. So I believe the ratio on the gearbox is one problem.

I looked at the design specs of the new 1 hp motor. It has a run and start winding. The start winding gets disconnected by a centrifugal switch. I'm wondering if the motor can start moving the door cause the start winding is engaged and then when the motor speeds up enough to disconnect the start winding that the motor can not pull the load due to a bad gearbox ratio? Thoughts?

I cannot repair the broken brush lead, so my only option there is to replace the brush sets. There are at least two companies that will custom build brushes. Shipping cost will probably be more than the cost of the brushes. Also the brushes are just about worn out. One of the brushes is worn enough that the spring is almost touching the brush holder.

All though I believe I understand the role the brushes, commutator and wound armature play - I don't understand the implementation. The brushes ride in metal brush holders, those brush holders are part of a large metal plate that touches the motor housing. All of the parts are electrically common. Brush pairs wired together would seem to have no purpose as they are electrically common through the brush holders and mount plate. Can anyone explain what is going on with this setup?

Thanks,
Lowell

Its likely the new gearbox doesnt have sufficient reduction.....175/1 is a lot for a single reduction worm,and I doubt its correct......never the less ,if you look around ,pallets of used reduction/motors can be bought for scrap price ,but IMHO ,for anything like 175/1 ,you will need multiple gear reduction....these boxes at around 1 to 2 hp are commonly used on small bucket elevators ,small conveyors....any food factory will have dozens of spares ......you will also need a travel cutout,or someone will bust the door .

john.k said:

Its likely the new gearbox doesnt have sufficient reduction.....175/1 is a lot for a single reduction worm,and I doubt its correct.

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Determining the gear ratio was straight forward, but kind of tedious. I attached a vise grip to the free end of the motor shaft and used a sharpie to put a mark aligning the output shaft with its case. Having only 20 toes and fingers gave me a challenge in keeping track of the count. But anyway, it took 175 rotations of the motor shaft to complete one full rotation of the gearbox output shaft.

Master Electric is long gone, I have a little generator they made in the 50's-60's, and have seen a few others. WAG says they might have been a predecessor of Dayton Electric???

From your description it sounds like a bi-fold "suicide" door. Since you do not own the building, I'd recommend letting county fix it, and assume the liability.

P.S. Its probably time to replace the 1/8" wire cables too.

thermite said:

If you be (s)he who is County Engineer, Safety, Fire Marshal, head of Code Enforcement, or "whatever" they do in your jurisdiction...you need a more aware contractor.

If you are NOT (s)he?

You have gone as far as you should.
And then some.

Wrap up what has been learnt ... or suspected.. drop it on his desk. At the very least, approval for a course of action is required.

Lose-lose situation in the making otherwise.

"Rules" not torque. Not your rules. Not your football.

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I'm just a guy who rents space from the county to hangar my airplane. My only interface is with the airport management. I did make the airport management talk to the county engineer about reviewing the contractor's work. The airport management solicited two bids. They went with the cheaper one (by a factor of 3).

The ratio for the latest gearbox they installed is 60, different by a factor of three. Latest rumor I heard is that they are going to rewire the motor supply for 240 - still not gonna lift the door.

The original setup was struggling to lift the door. Occasionally the motor would stall. I had complained to the management for several months before they finally tendered bids. When the crew came out to do the repair I looked at the rating tag on the gearbox and told them it wasn't gonna work. Electrician looked at me like I was a dumbass. So I calc'd the door weight and computed the amount of torque that the gearbox had to deliver. Airport management just looked at the numbers and said hokay. I also pointed out that the way they were fastening the cable spools to the gearbox output shaft was unsafe and that if either the spool attachments or the gearbox would fail with the door up that it would kill someone and/or destroy an airplane.

After several iterations on spool attachment methods and now a higher rated gearbox - the door still won't open. This airport is in a rural county and the quality of contractors and the willingness of the county management to do things the right way is severly lacking. Yes, there are building codes out here - but the county enforcing code compliance on themselves - probably not gonna happen.

Meanwhile, my airplane sits in a crappy hangar that fills with dirt when ever the wind blows (and we have had nasty winds out here, sometimes up to 100 mph this winter). I need to do an oil change and replace an accessory drive gear on the engine - but don't really want to open up the engine cause there is no way I can reasonably keep dirt from blowing around.

I don't know how old this hangar is and it was hacked together when it was built. Most of the county owned hangars are poor. There are no other airplane storage options out here as everything is 100% occupied. Way back when the old motor started having problems, a visual inspection showed the broken brush lead and I thought that that may be the problem. Both contractors that bid only wanted to put a new motor and gearbox in. So now as the contractor they hired is having major issues and I haven't been able to use a cleaner hanger for almost three months - I figured to spend some of my time to see if I could do a repair on the old unit.

Before I spend the money on parts though, I need to understand how the brush plate is actually working. Electrically, the brushes, brush holders, brush plate and motor case are all common. Why are the brushes wired in pairs since they will conduct through the brush plate? What am I missing here? I've got an ex - Air Force bud who worked as a master electrician in a Wisconsin paper mill. There were hundreds of all sorts of different electric motors in that place. Gonna give him a call tonite to see if he can provide some insight.

Lowell

I have a 1/2 hp Master motor very similar to yours. Brushes are wired in pairs too. I did read somewhere at the time why this worked but can't recall it at the moment. Sorry I didn't take more pics of it disassembled.

Spent most of the afternoon doing more research and looking at videos. This thing IS a repulsion start - induction run motor. One of the vids showed a breakdown of the shorting necklace. An additional look at this motor and I now see what I had thought was just a bearing grease shield was actually the outside of the shorting necklace housing.

So still want to understand how/why the brush pairs are interconnected when electrically, everything is essentially shorted together. Must be some weird electrical chit going on. Tomorrow I'll call one of the companies that can custom build brush sets to see how much they want.

Once again, thanks guys for helping out. I'm learning more than I ever wanted about AC motors.

Lowell

A word to the wise: many local ACE hardware stores have the plastic boxes with various types of parts commonly needed. I know that our local one has a selection of carbon brushes. If the brush is too LARGE that's not a problem as they are easily machined to size. Ideally you would want to get one with the copper pigtail on it. I don't know the exact method for securing copper braid into a carbon brush but I bet a few minutes seaching online would show you a way to repair the single brush that is broken.

thermite said:

Helwig Carbon will have the ability to make brush holders, tampers, and brushes.

Helwig Carbon | American Carbon Brush Manufacturers Since 1928

They are not likely to have shelf stock, but one could ask.
Their published info alone is a treasure trove.

You can reshape a larger brush by hand, but the materials are NOT all the same. See Helwig pubs and not-only.

A(ny) shop that does custom brushes as part of "Day Job" would be the wiser choice for a DURABLE fix.

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Thanks, I'll be checking those guys out.

jim rozen said:

A word to the wise: many local ACE hardware stores have the plastic boxes with various types of parts commonly needed. I know that our local one has a selection of carbon brushes. If the brush is too LARGE that's not a problem as they are easily machined to size. Ideally you would want to get one with the copper pigtail on it. I don't know the exact method for securing copper braid into a carbon brush but I bet a few minutes seaching online would show you a way to repair the single brush that is broken.

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Ok, I will do both. Dammit, I was just in town today and stopped in at the local ACE. Didn't think to check. This Ace has quite a bit of stuff, but I have had to special order some things from them before.

Chatted with my Air Force bud tonite. Bummed that he was no help. The lowest voltage in the mill running equipment was 480 volts and I think he said that the smallest motors were in the 500 hp class. After we ended the call, I remember him telling me that this paper mill used to generate electrical power for the local town back in the day. Yes, it was located next to a river and the old generator station was still present. I say "was" cause the mill is now shut down.

that carbon brush that is missing its wire lead is soft enough to dill and tap so drill and tap it to 6-32 and screw a brass screw

in to it to connect / hold the wire lead to the brush