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03-07-2008, 08:48 PM #1
School me on Brush Type AC Motors
I have a Wells bandsaw with a Peerless 3/4hp AC motor with brushes.
Never seen an AC motor with brushes.
What were the advantages?
Worth rebuilding or just mount a regular AC motor?
It has a unique mount, but I can fab something.
03-07-2008, 08:54 PM #2
Sure you have
Vacuum cleaners, cord type drills, etc
I think they call them Universal
03-07-2008, 09:03 PM #3
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.
One more advantage, it can be Triac speed controlled.
Last edited by minder; 03-07-2008 at 09:25 PM. Reason: Addition
03-07-2008, 09:29 PM #4
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.
03-07-2008, 10:16 PM #5
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.
03-07-2008, 11:17 PM #6
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.
03-07-2008, 11:31 PM #7
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.
03-08-2008, 12:00 AM #8
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.
03-08-2008, 12:47 AM #9
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.
03-08-2008, 07:06 PM #10
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.
03-10-2008, 07:32 PM #11
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.
03-10-2008, 11:23 PM #12
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?
03-12-2008, 03:24 PM #13
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.
03-13-2008, 06:08 PM #14
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.
03-13-2008, 11:09 PM #15
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.