Making Electric Motor Brushes

brushes on alternating current?

High speed motor like what power tools, kitchen tools, and vacuum cleaners use.

An AC universal motor does indeed have a commutator and brushes.

AC Split phase induction motors such as those used in washing machines, dryers etc. also use brushes.

That's new to me, can you post details about such AC Split phase induction motors?

They generally have a centrifugal switch if the start phase needs to be removed when running (some leave it running for more power), but I have not seen one with brushes (up to now at least).

Ready to learn something new.......

Sorry, did mean to say AC Wound rotor motor. Incorrect terminology used.

AH!

Many thanks for the explanation......and I was ready to learn something new......

I tried that approach but nothing out there has the correct combination of bits. I was able to search through an old electric motor repair shop but couldn't come up with big enough brushes.

I suspect that brush manufacturers mold the brush and the pigtails into one piece all at one go.

A new motor is $150 which is outrageous. A new brush set in their holders is $58 each, again, outrageous. Nobody just sells brushes.

The front-loading washing machine is a Frigidaire and these are made in Germany so the electrical bits are not standard U.S. including bolts with a small oval head that I may have to make a socket for so I can take the motor apart and turn the commutator.

BTW, to answer the question, "brushes on an AC motor?" Yup, they call them universal motors because they will run on AC or DC. Most drill motors and hand tools are actually universal motors IIRC.

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Do you have the brush dimensions?

Rated current of motor?

What is the make and model of the motor?

You haven't looked around enough as generator and big motor brushes can be huge, far larger than any household motor (what size IS the motor?) needs....

I find all the carbon motor brushes needed through local surplus/recycling centers and ebay. Just recently ordered some new (generic) carbon motor brushes from China that were only about 1mm oversize. Shipping took a bit over 3 weeks and total cost was just over $1 US per brush. They fit very well after light sanding.

The included spring and end connection to the new wire pigtail would NOT fit the old motor assembly, so I just cut them off leaving as much of the embedded pigtail as possible. It was very easy to splice the connection end of the old pigtail onto the new one with a small crimp connector. I reused the old brush holders and springs since these are difficult (but not impossible) to fabricate/replace.

My 2HP shop vacuum worked like new after a light resurfacing of the commutator and installation of the new brushes.

I only have a hobby workshop and basic tools, but have made many similar repairs for under $5 in materials plus my time. I ENJOY repairing (or re-purposing) certain items I frequently use and can easily justify the the 1-2 hours invested in this particular effort. Since new shop vacuums can be purchased for $50, many would have choosen to just discard the old one and purchase a new one. For a high cost item, like a front load washing machine, a DIY repair time investment should be easier to justify. Wish you good luck on the repair effort :-)

There is a company called Graphalloy ( Graqphite Metallizing) inYonkers New York.

www.graphalloy.com

They can make brushes for anything, and have been since 1913. They probolly have what you need on the shelf. I use them for Custom Slip Rings.

BJG

Pic's might help....or at least dimensions...or possibly both...you might try this place...

http://www.mersen.com/en/landing-pages/l/mersen-usa/electrical-solutions-for-motors-and-generators/carbon-brushes.html

video on making your own....

http://www.youtube.com/watch?v=QtzqDkhyWbw

or maybe you could make them out of copper...

Have a look on eBay for "motor brushes". They come pretty big!

File some copper. Take the filings and mix with lead 50/50. Place in square mold, add end of pigtail. Heat with torch until it melts. When cooled file/grind to desired shape.

I suspect that the commutator is not hard enough for a copper/lead brush as it wears fairly rapidly with just carbon.

But that does lead me to wonder if I can drill a hole in the carbon brush and fill the hole with solder. Might do OK although I cannot recall what the shrink factor is for a lead/tin combo, it is significant I think.

I did find SN100C, a lead-free solder alloy developed by Nihon Superior in Japan that is comprised of tin-copper-nickel + germanium. It might work because it does not shrink as it solidifies.

Thanks for all the input, folks. More is always appreciated.

Get youself some brushes that are slightly oversize and have correct length pigtails and then grind them to size on a disc sander. Very easy fix to your problem.

Except I have not been able to do that over the 3 years I"ve been fighting this motor, that would be good advice.

Send pictures with dimensions and more help will be available.Very vague request otherwise.

A model and serial number of the washer would also be beneficial.

And yes,you are right,the brush and pigtail assembly are pressed together under heat and pressure as a single unit.Not going to be able to duplicate that manually.

Must be a very big motor. There are brushes available for the elevator industry in particular that measure 31.75mm x 19mm x 47.6mm long.

A bit of a look will possibly find even larger ones if you really need them.

I have had very good results taking an oversized brush, with wire attached, and crafting them down to the size I needed. This is usually accomplished with a Dremel tool with an appropriate bit (usually a disc sander bit), a disc grinder (watch the fingers), a file, or some other similar abrading tool. Some times the wires might have to be cut or resoldered.

I have found used brushes to start out with at: electric motor repair/rebuilder shops, junk yards that handle a lot of electric motors, and I always pull them out of any motor I scrap. New ones are available from McMaster-Carr, Graingers and especially electric motor part suppliers (Google "electric motor carbon brush supplier") and the repair shops for electric hand tools. There are some others but I can't jog my mind enough to remember them.

Just be carefull and don't try to remove a lot at one time. They can chip and break very easily if too much pressure is used in the wrong way.

Good Luck, Old Salt

Brushes on motors are made of a composition material something like carbon and graphite. Generator brushes are made of carbon and have more resistance than motor brushes. Brushes made of a mixture of copper and graphite will give better commutation and are self lubricating. I would prefer lead for a binder as you said epoxy disentigrated. If you cannot find larger brushes that you can grind to fit you can make your own, just remember that when melting your mixture to heat the crucible/mold and not the metal itself. Also you must use adequate ventilation as lead fumes are toxic and can kill you. Im sure if you look around you can find some that are larger that you can grind to fit. When doing so wear an appropriate mask to avoid breathing the particles ground off. Then you will have to seat the new brushes by "sanding in" so they will match the curvature of the commutator. This can be done by wrapping some sandpaper rough side out around the commutator and setting the brushes against the paper and turn the motor by hand until the brushes match the curve.

Spring pressure is also very important in terms of continuity.

For high or low current or ac or dc do they use same composition or brush pressure?.

The composition and pressure are specific to each motor design. But, in general there is little difference. Composition is almost identical in all brushes except very small and very large brushes. Pressure is mostly a factor of the area of the brush in contact with the comutator. There are some other exceptions of course, for extremely high speed motors and other such unusual design factors.

The brush spring tension should be strong enough so that when the brush is pulled off the commutator by means of the pigtail and then released, the spring pressure snaps it back freely on the commutator and should have enough tension to press the brush to the commutator and still move freely. Too much pressure will wear things out faster, but is better than too little which will cause sparking and burn the commutator resulting in a full open circuit. At least 50% of the brush end surface should bear on the commutator curve. Motor brushes should be set at the position of least sparking when at full load, and must be set parallel to the commutator segments.

Dimensions, dimensions, dimensions....

Make a non-pig-tailed brush to be placed in front of a shortened down original.

If the guides are long enough, you could try cutting an original brush so short as possible, just leaving long enough so that the pig tail piece remains solid... Then cut a new brush which would be shorter than a new one ( shorter by the length of the pig-tailed piece) and place it in the guide first with the original piece being forced aginst it with the spring pressure. Of cousre, make good flat mating surfaces. Wouldn't last quite as long but easier to replace.

That would work well, good idea.

Why can't you get new brushes. In the past worked on electromotive equipment. I know brushes come in all sizes. In the vast array made, one of them should match up. There are numbers on the brushes to ID them.

http://store.eurtonelectric.com/brushes.aspx?gclid=CP22ha2t77QCFYY7OgodyH8AsA

http://store.eurtonelectric.com/washingmachinemotorbrushes.aspx

Make your brush the size you need, drill an oversized hole where you want the wire to be, make a plug of the same carbon that will fit into the hole .03 -.1mm clearance fit, slot the plug long ways to allow the wire to be stuffed into the hole followed by the plug, mix equal parts of your carbon dust and a quality 2 part epoxy, shove the wire into the hole and allow the wire to bunch up in the bottom of the hole, apply glue and carbon mix to the hole and plug, and insert it. Let it dry and you will have a very permanent wire to carbon fix. I am not sure how much the carbon mixed with glue will help your conductivity but it make for better strength and it holds up well on our EDM electrodes. Good Luck.

Brush leads are usually attached by molding them into the carbon. Other styles attach brush leads with rivets. Both are mechanical connections.

Your best bets are:

1. As stated above, buy slightly over-sized brushes with leads and cut them down.
2. Make a conductive tab with the lead and place it between the brush and spring.
3. If the brush is large enough, drill a hole through the brush, insert the lead and a length of malleable material/wire (soft copper, lead, tin, solid solder) into the hole next to the wire. The material should be slightly too long so that it can be pressed or hammered to expand it.

Soldering, or filling a hole with the wire and solder alone will not work because the CTE of carbon-graphite is less than that of silver, tin, and lead. Once the solder cools, the slug filling the hole will become loose. But perhaps the slug could be expanded by peening. This would be a variation on recommendation 3 above.

I found a somewhat obscure tag on the motor. All it said was 'fhp motor.' So I typed that into a search engine and I immediately found the 12 by 6 by 35 mm brushes I want (at $40 a pair). Apparently 'fhp' is a classification for a unique motor design (at least in the brush department).

Thanks for all the good advice. This thread should be posted in some permanent location for future reference.

Most of the suggestions I had already tried, some with success and some without. I never could find brushes using the motor part number, the German product number or any other identifying mark on the motor.

I've had good luck replacing broken/disengaged lead wires on brushes by copper plating the end of the brush and soldering the wire to the copper plating.

Clever and resourceful!

You don't say where you are, but over here in England I had some made for a Stanley router that is 50 years old, All I did was gave them the dims of the carbon & the length of the cable by Email and they were delivered within 48 hrs, So if you lookup carbon brush manufactures on the WWW I'm sure you,ll have some within the week.

Bazzer

I need some hard to find brushes and everywhere I looked online they were about $30 a set which I was ready to spend until I found this company http://www.lakeeriecarbon.com/ which had them for $1.75 each and was under $5 for the set shipped to me in the usa.

I've asked them for a quote on the brushes. Guess I'll hear from them next week.

Thanks to everyone for your excellent suggestions.

Their reply was although they make a few thousand at a time, they are out of the brushes.

So I think I'll take the suggestion to drill the backside of shop-made brushes and epoxy them in place. I think the silver epoxy is more conductive than an epoxy/carbon dust mixture and should serve better in this high current application.

The series wound AC motor uses an incredible amount of current when starting and I wouldn't be surprised if the motor exceeds 5,000 rpm when spinning the wash drum. Maybe even higher.

12mm x 6mm is a fairly common size for wheelchair motor brushes. Connection and length will vary of course.

A retired electrician friend of mine finally remembered the go-to place for motor parts and repairs.

http://eurtonelectric.com/ They are in Los Angeles.

They will repair any motor from a sewing machine to big stuff.

They also list the exact brush I need and their prices are reasonable. They also list a new rotor and new field coil setup although the armature is more expensive than a new motor.

I have now gone through the motor and replaced bearings and turned the armature. I'll make my own brushes for now and order a new set from these guys when they get in stock mid-next month.

Since all potential suppliers do not yet have this brush in stock, I built a pair. When I install them, I will evaluate their performance and may replace them with a commercial set when those are available next month.

In the meantime, here are the pictures of the brushes:

Before using silver epoxy to attach the pigtails to the brush. note the tips of the pigtails have been cleaned.

After applying the silver-filled epoxy. As difficult as it was to get the epoxy into the 0.11" bores, I should have drilled cross-holes to allow air to escape.

However, the resistance of the brushes, end-to-end is 1.1 ohms and the resistance of the pigtail to brush connection is 0.4 ohms. I think that will be OK.

Now I just need to wait 5 hours for the epoxy to cure.

I used a 3D CAD program to draw the brushes as they would appear in the 1" diameter bar of carbon I started with. I used the dimensions to set the mill up for the cuts. I still have about 8 inches of bar left so if the motor had more life in the commutator (which it does not) I could keep going.

The motor reassembled except for the brush holders.

Commutator looks pretty good to me from what i can see.Color looks good.A slight discoloration is normal and healthy.Commutators can be turned down in a lathe and undercut to extend service life.You need to radius the brushes to match the commutator at contact point.Tape a piece of flint paper(not emery cloth)to the commutator and press brushes into it while turning the commutator by hand.This will radius them properly and reduce arcing while they seat.A brush-seater abrasive stick is a professional method of getting a perfect match, but cost too much for a single job.

Here is a link to learn more about commutators and brushes from a company that has made millions of them.

www.morganamt.com/us/files/Morgan Carbon US/GuidelinesForSuccessfulcommutatorAndBrushOperation.pdf

Good luck.

It LIVES!

No arcs or sparks, quiet operation. A little bit of brush noise at the fastest spin speed but that will probably disappear with a little more break-in.

I filed and sanded the brushes into an approximation of the commutator radius.

Thanks for all the input.

Six months later the motor is working well and has been well worked!

This is a great find . I have a toe kick saw that is used in the flooring business. I cannot buy brushes for it as I'm told you have to buy the entire motor head assembly. might was well buy a new saw . It basically has a skil saw motor on it, so I'm going to look for brushes that can be made to fit, or hopefully find brushes that fit already

couple questions,

1. how accurate of a fit do the brushes need inside the holder? I realize if they bind that's no good, but if they're not 100% accurate fit is that OK? is it better to hand file or use a belt sander
2. should I get the armature turned? it's slightly grooved and blackened , I can get a buddy to turn it on his lathe

Thanks to this great knowledge base!

If possible, go to that brand's parts dealer and see what they have. Also can you get, probably off the manufactures web site, a parts diagram and list (preferably with illustrations)? Milwaukee has these and they are extremely helpful in spec'ing replacement parts. Most mill supplies could then order them for you. This will probably save a lot of work and possibly frustration.

1. The accuracy needed is the best that you can make them. Oversize won't fit in the holders and undersize will fall out of the holders. Try to make them as best as you can. Try "fitting" then in the holders very frequently and take as good a "bite" each time as you think you need. Go in small steps reducing the depth of cut as you get closer to the "good fit". I always use a file, reducing the cut (1st, bastard and then up to smooth) as I progress. I wouldn't use a belt sander for several reasons: 1. If my fingers get too close to the belt while holding the brush, I then have to clean all the blood off of everything. 2. Belts on belt sanders are not tight enough to give a constant position of the belt, too much slop between the belt and the sander surface. 3. Even with a very fine belt on, it will probably be difficult to get an accurate cut each time. 4. If you want to sand, use sand paper on a sound flat surface and hold the brush in your fingers, better feel, more control and you can change the depth of cut by using finer and finer sand paper.

From what you indicate, the armature is still sound but not brand new. If convenient, get it turned down. Before doing this, show it to someone who really knows the difference. How accurate is your buddy's lathe? Does it have much slop? how smooth and aligned are the beds?

Lastly, if you buy some and plan to alter them, buy as many as you think you will need for your trial and error modification. Then add 1/2 more to your purchase.

Give it a good try! Worst that can happen is having to do it another time.

Good Luck, Old Salt

"how accurate of a fit do the brushes need inside the holder? I realize if they bind that's no good, but if they're not 100% accurate fit is that OK? is it better to hand file or use a belt sander"

Use a power sander until you get close, then hand sand/file for final fit. Carbon brush is "slippery" by nature and should slide easily in holder. Excess "wobble" from being undersized will cause excess wear and reduced life.

"should I get the armature turned? it's slightly grooved and blackened , I can get a buddy to turn it on his lathe"

Copper commutator is VERY soft and will smear if you use a lathe without practice. I usually just spin the motor shaft with a power drill and lightly sand/file the commutator surface until the copper shines through. Don't forget to clean the grooves between commutator segments so that any conductive junk that gets stuck in there doesn't short out the segments.

It is now the first of August and in spite of much use, the motor is still spinning away with no problems.

Just for grins, when the copper finally wears to the point it causes problems, I am going to epoxy heavy copper foil rectangles to the commutator segments using conductive (silver-bearing) epoxy to hold it to the underlying copper segment remnants. I'll wrap the entire assembly with heavy twine to hold the new segments to the commutator until the epoxy cures. Cutting the new segments slightly wider than the existing commutator segments will allow me to smooth the edges down into the grooves between the segments without shorting between them. This will avoid sharp edges reducing the brush life.

I think I can keep this motor working forever (or as long as I want).

BTW, if you don't have a milling machine to cut the new brushes, I would hold the brush by hand and hold the file in a vise or on the workbench. This should give you a flatter filing job and more control of final dimensions and shape. Do the same thing for any abrasive paper you use.

Well, one of the brushes wore until the pigtail held it short of the commutator. Made another set of brushes and it is spinning again. I had lengthened one of the pigtails but not this one. Next time it will get an extension.

The commutator is still shiny and without any significant scratches.

The silver bearing epoxy I used to attach the pigtails to the brush looked as good on the old brushes as the new epoxy does on the new brushes. I think that stuff is pretty good.

When I was milling the supposedly super-quality carbon rod, I noticed a few sparks flying off with the carbon swarf. Not more than one or two per cut but noticable against the small black cloud of carbon. I had put the vacuum cleaner hose down to increase the table feed on the mill when I saw the sparks.

The brushes that you were looking for are listed on KIJIJI under p/n 131276200 for 24.00 a pair and 5.00 for shipping, maybe make a note of it for next time you replace them.

Same again. The short pigtail stopped the motor again.

I am going to machine new tabs for the pigtails and make new and longer versions as the brushes are a long way from being worn or tipping in the brush carrier.

Given that brushes are cheaper than armatures, I would not put in much effort to smooth the armature to prolong the brush life. If there is a great desire to smooth the commutator, I would not attempt to cut the commutator bars until they are perfect, I would just remove the high spots with a flat file with the armature spinning and then polish with 400 grit sandpaper.

I would also, make sure that the insulators between the commutator bars are cut slightly below the surface of the commutator bars. (If the insulators come in contact with the brushes, they will reduce the contact between the brush and the commutator and both will burn causing pits in the commutator bars.)

After the brushes are replaced, I would run the motor without a load a few minutes and let the brushes wear in and make good contact. (When the motor is first turned on, all the current will pass through the high spots. After a few minutes, the high spots will wear into the brushes and the current density will drop as more and more of the brush comes into contact with the armature. Watching the sparking on the armature while it is running is a good indicator of how well the brush is making contact. At first sparks will only be present on the high spots, then as the brush wears, the sparks will spread until they are across the full width of the brush.)

Wow, thanks everyone.

I would buy the factory brushes but I'm told they aren't available. No parts are available for the motor body . . Upon further research the motor body ( not the entire tool) apparently made by Skil , so perhaps they are available .

I am just getting into this project so will keep everyone posted . We do have another saw but I like to have spares in the event of a breakdown

Great FOrum, thanks for the replies & the information

Update on the brushes.

Wasn't able to track down a model number for the Skil saw body and looked at several brushes that weren't the same , and the manufacturer of the saw only sells the complete motor assembly which is almost the same price as a new saw. but I ended up going to an old timer electric motor repair shop and got some brushes that I was able to file & make fit.the armature radius was the same( or very close ) had to also change the connection but I just soldered on the old connectors to the brush lead. so far so good. thanks guys!

Well, the motor finally wiped out the commutator as I knew it would. I thought for about 5 minutes of machining a new one and then said nah!

Turns out the motor price dropped to $116 from $150 or so.

The new motor, which looks identical to the old motor does run the washer faster in spin mode. So the conductivity of the brushes and the silver-bearing epoxy were apparently not as good as new brushes.

But new challenges have arisen with an over-the-stove microwave that stopped operating and a gas oven that will not ignite. Never boring, is it?