School me on Brush Type AC Motors

Doug W · Mar 7, 2008

I have a Wells bandsaw with a Peerless 3/4hp AC motor with brushes.
Never seen an AC motor with brushes.
Why?
What were the advantages?

Worth rebuilding or just mount a regular AC motor?
It has a unique mount, but I can fab something.

johnoder · Mar 7, 2008

Sure you have

Vacuum cleaners, cord type drills, etc

I think they call them Universal

minder · Mar 7, 2008

There are at least three types of AC motors that use brushes on the armature, Synchronous, wound rotor induction motor for low speed/torque control used on cranes etc and Universal AC/DC series connected motor, I would say you have the latter, if it is on a band saw.
These motors are used in everything from vacuum cleaners to power tools etc.
They run at very high rpm due to the fact they operate in a runaway condition, the only thing that restricts the speed is friction, bearing/gears/fan etc.
This is why if you cover the end of a vacuum nozzle, you will notice the motor rpm climbs.
To replace it with a regular induction motor you are restricted to something just under 3600 rpm, unless you go with the high speed spindle induction type motor run off a Variable frequency drive, but these are very big bucks for 20,000rpm.
For high rpm and cheapness, you probably cannot beat the Universal Motor.
M.
One more advantage, it can be Triac speed controlled.

J.R. Williams · Mar 7, 2008

Motor

Doug
You probably have an old "Repulsion start-Induction run" motor. It was widely used before the capacitor start motors took over The Repulsion start-Induction run motors are excellent for hard starting loads. It probably has four brushes that are on a plate mounting that can be shifted to reverse the motor. They are excellent motors. I have an old unit that ran many years in farm service before bing installed on my old aircompressor. The unit is around 56 years old.

JRW

Doug W · Mar 7, 2008

Yes to all the above.

Now that you mentioned it John, I have seen a power tool or two with brushes.

And it is the 4 brush type.
The commuter is well worn and the entire interior is caked in graphite goo.

I assume the commuter can be turned down and the Mica? recut.

JunkyardJ · Mar 8, 2008

I have a bunch of the repulsion start motors.

They use them in bench grinders a lot, you hear them click when they get to a certain RPM where the brushes disconnect. You can also see a little blue spark when they click. My home made disc sander has one of those on it, and my dad's old table saw motor. I have a few others I picked up at a yard sale that were made in the 30s and 40s. They DO have HUGE torque to start, but they SUCK JUICE to go with it! My 1/4 horse motor on the disc sander DIMS THE LIGHTS when it kicks on.

macona · Mar 8, 2008

The brushes never disconnect from the armature on a repulsion start induction motor. If you are hearing it click than that motor has a centrifugal switch. Standard induction motor.

JunkyardJ · Mar 8, 2008

This is EXACTLY how my disc sander works.

See the link, my disc sander works EXACTLY as that motor in the first post. When the brushes disconnect, it goes click. I've seen motors that don't have brushes that click too, but I thought they had a cap. The motor on my disc sander has NO CAP. I'm pretty sure my dad's table saw motor works the same way, but I'm not sure. It clicks, and you see the blue spark inside it. It dims the lights WORSE than the disc sander, normal induction motors DON'T do that as bad. I KNOW the old motors I got from the garage sale are repulsion start, because they say right on them. I've never plugged them in to see if they work.

http://bbs.homeshopmachinist.net/archive/index.php/t-15273.html

JST · Mar 8, 2008

The induction run motors DO click........ They short the commutator to turn it into an induction motor. There is a centrifugal switch setup that does it.

There are also straight repulsion motors which do NOT change to induction. Those can be plug-reversed on single-phase, and as I understand it were used on some Southbend machines.

chuckey · Mar 8, 2008

J R Williams, I have an old motor on my lathe, its marked "explosion proof"!!. When I first got it it ran in the wrong direction, so I undid a cover and its got 4 brushes and had a mark inside it, so I undid the brush carrier re-aligned it with the mark and then tried it out. To my amazement, as the motor ran up to speed a spring wrapped around the comutator suddenly shot along it!!!!. On switching the motor off the spring jumped back right up against the armature coils. Oh yes the motor now runs in the right direction and has done so for for 22 years. The motor is rated at 1 HP and is about 18" long and 12" diam and weighs an awful lot - 70 lbs? Is this a Repulsion start-Induction run motor, from the books I have seen it seems the "spring" assisted run mode is not listed.
Frank

Doug W · Mar 10, 2008

Update
Stopped by an armature repair shop today.
The cost to turn and cut the commuter is about $40 and it will need new brushes. Will probally have to modify ones to fit.

He also stated it had a centrifical ground switch (something to that effect) that cuts in or out when the motor is up to speed. it is mounted on the tail end of the shaft.
He also said that switch was unavailable, so I hope mine works.

JST · Mar 11, 2008

Chuckey:

Sounds like an induction-run motor, alright.

The spring arrangement is a shorting switch to short out the commutator (and lift brushes) turning it into an induction rotor.

Do the commutator segments have a radial surface for that contact/spring setup?

Lloyd H · Mar 12, 2008

repulsion induction motors

They made R-I motors in a lot of different styles, most were brush lifting, ie. a centrifigul mechanism lifted the brushes off the commutator and at the same time moved a shorting necklace of little copper bars to short out all the commutator bars making it an induction motor. These usually had radial commutators. Also common in smaller sizes were brush riding models, they had a shorting necklace with a garter spring around the shorting segments that would hold them away till the motor got up to speed then they would short the commutator. the shorting necklaces fit inside the commutator on both types, part of a good rework on an old motor involves taking them out and cleaning the inside surface of commutator bars, but be careful especially on the brush lifting ons they are on a little wire that sometimes is broke and allows the whole string to fall on the floor accompanied by foul language.

chuckey · Mar 13, 2008

Never noticed any radial segments, I was amazed that the "spring" moved horizontaly along the commutator that did not seem to be tapered, though in retrospect, the commutator was excessively long for the brushes 2 1/2" long with the brushes only about 1/2" wide and at the extreme back end.
Frank

Lloyd H · Mar 14, 2008

R I motors

I've seen a lot of R I motors but never anything like what you are talking about, most of the ones across my bench were refrigeration compressor drive motors (Wagner and Century mostly) and Hobart in large and small meat grinders and meat saws. Just goes to show no matter how much you pay attention you still miss a lot.

tonyscrimenti · Monday at 11:28 AM

I have an A/C motor that we use as a grinder and wire brush machine. It's old and does not have a label/plate on it. It works well and we'd really like to keep going. The problem is the brush. I never saw a motor with one single brush that is circular and sort of "U" shaped. It has a commutator, not slip rings. I was able to reproduce another brush from a block of carbon ferrite that I purchased from Amazon but the motor does not run as well as it did when we started using a few years back. Sometimes we need to open the door that covers the commutator and goose it a bit with a screw driver to move it from start to run mode. I'm guessing but I thing the contact pads on each end are either too long or short. I'm attaching a sketch of the brush. Viewing from the top, the brush is about 1cm wide (about 3/8"). Viewing from the side the brush is curved with a straight line length (tip-tip) of about 5 cm (about 2") and about 1 CM (about 5/8") of each end is thicker where the brush contacts the commutator. The commutator has segments that appear to be attached to various windings in the rotating core. I have never heard of a motor like this but would I'd really like to get it fixed. Any help on pointing me to a supplier that can replace the brush would be great. I'll also attach pictures of the motor with the commutator showing along with the brush.

michiganbuck · Monday at 1:33 PM

We used to take them apart to crocus cloth the commutators. scrape the mica down a little.
One that I just fixed, a big horseof a 3/4 hp drill motor I just stuck an Allen wrench in the brush hole and turned the spindle a few times by hand.

tonyscrimenti · Monday at 1:52 PM

Thanks for the reply. I've cleaned the commutator a few times and I'll do it again but from the looks of it I think my poor workmanship fabricating the replacement brush is causing the larger than typical sparking and fouling up the commutator faster. At first I thought there were two brushes but opening the doors on both sides of the motor clearly proved there was only one.
What I'd really like to know is if someone has any info on the make, model or has seen a source for a brush like this.

tonyscrimenti · 2024-05-08T06:53:32-0500

Doug W said:
I have a Wells bandsaw with a Peerless 3/4hp AC motor with brushes.
Never seen an AC motor with brushes.
Why?
What were the advantages?

Worth rebuilding or just mount a regular AC motor?
It has a unique mount, but I can fab something.

I've seen this motor run when there was no problem and there is only one long curved brush, it's always in contact with the commutator. It's cut such that only about 3/8" of each end contacts the commutator so it's like two commutators? Those paddle looking things on the right side of the picture are weights that must connect to a centrifugal switch - They are loose and I can see them move as the motor spins and hear a switching sound when it comes up to speed. I'm starting to think that when I made the brush I may have made it too long or too short which is what is causing the sparking. I'll clean the commutator today and let you know what develops but I've never seen one of these and I may just end up getting another motor. This motor came to our shop before I did and no one knows where it came from. Thanks to everyone for their responses though.

tonyscrimenti · 2024-05-08T09:02:03-0500

Another update: I triple checked and there is only one brush in the motor. I took it out and filed the section between the ends so they could not touch the commutator and cleaned the commutator with mild emory. It's running much better now with little to no sparking when it comes to full speed. I'm convinced now that the brush and commutator are there just for start up and once at speed the weights handle the switching from a start to a run winding. I've been through this before but I never shortened the pad at each end of the circular brush. I'll see how long it lasts but given

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