Rotor and Collector Of Electric Motor / Armature Winding / Collector Armature Electric Motor

Most home sewing machines, even some industrial ones, use electrimotors with brushes, they are also called collector electricmotors. Electromotors are also used in all hand-held power tools (drills, grinders, milling machines, hand saws, jigsaws ... etc). With collector electricmotors, the most common problems and failures occur on the rotor, rarely on the stator. The most sensitive part, so to speak, is ... 

rotor collector. The collector itself is cylindrical and of many different sizes, it mostly depends on the power of the motor, its predicted speed, load, etc. The so-called brushes rest on the collector, they are made of graphite which is an excellent conductor, not very hard and tolerates temperature which is created on the collector. The collector and brushes are subject to wear, this problem is related to the quality of the electric motor as well as the collector, the longevity of the use of the machine (apparatus or power tools). The collector consists of a larger or smaller...

the number of copper plates (lamellae) that are separated from each other by insulating material. The basic sign that something is wrong with the collector is a large sparks with spreading of sparks over the edge of the collector, when this appears to you, the machine needs to be stopped and further work stopped. Working under these conditions can permanently and irreversibly destroy the rotor and thus eliminate you from unnecessary servicing and repairs, which service technicians know how to charge well. Our today's topic is the inspection of the collector, the change of the brushes and its eventual alignment.

The rotor on a hand tool is usually mounted on two roller bearings, while on household sewing machine motors the bearings are usually of the sliding type, meaning that the bushings themselves, the rotor shaft are also part of the sliding bearings. Our example today is the electric motor of the Pfaff 1222 sewing machine, one restoration is in progress, so I took the opportunity to take some, I hope, interesting photos. The engine is running, but one additional collector cleaning will not bother it.

So we have a situation where the engine heats up a lot, sparks on the collector, it is necessary to build the engine from the device or machine, disassemble the engine to the extent that the rotor can be completely built. The brushes need to be inspected first, usually if the engine is running poorly and the brush tips are irregular and not as smooth as in normal situations. They are usually worn out (shortened) and need to be replaced with new ones. Now we take the rotor and clean it with a cotton cloth in the kit, possibly dust it well with compressed air. The examination is good to do under a magnifying glass if you have it, the distance between the slats must be identical, the appearance of a greater distance between ...

individual lamellae is a bad sign and usually there is no help for such a rotor. If the collector surface is partially damaged, it must be leveled. Sewing machines have relatively small motors and the processing of the collector can be done on an ordinary drill that is fixed to a special holder (see picture), it can be done without it, but it is much more difficult. At a given diameter the collector was only partially greasy and dirty, there were no special dents. Old brushes can wear out the collector blades and by installing new ones, their fitting will not be good, which is why it is necessary to align the collector. For that we need: a small fine file, a protective crepe tape and a small sandpaper.

We protect the windings around the collector and the ends with crepe tape so that they are not damaged. On longer rotors, fixing is required on both sides, in this case it is a shorter rotor and it is not necessary. Turn on the drill, but reduce its speed to a minimum using the regulator on the switch, start the drill and lightly remove the collector surface with a fine file, moving the file is the same as with standing objects, do not press much unnecessarily. The surface will soon begin to level. The depth of removal of the collector is quite variable, usually about 0.1 mm is enough, and on larger motors (electric starter 12 / 24V) it can be removed up to 0.5 mm and even more.

Mostly on sewing machine motors, it is usually up to 0.15 mm. As soon as we notice that the whole surface is clean, stop with a file and take fine sandpaper, say fineness no. 500, maybe some smaller fineness, repeat a couple of times. The final polishing can be done with a piece of stronger felt or soft leather, we also clean the ends of the rotor shaft, but with the addition of a little oil. In the case of cleaning the pins, the goal is not any thinning, but only repairing the bearing enamel.

After all, assemble the motor, since the bearings are of the sliding type, do not forget the sleeves and add a little special bearing grease to the sliding bushings, finally return the brushes and start the motor (machine). Initially, sparks are possible, but briefly, in the event that even after a given intervention, the collector sparks a lot and creates a high temperature, the rotor is for repair (winding). There are also small devices that can test the correctness of the rotor, some electricians make them, nothing special but quite efficient.

WARNING: Danger of electric shock !! Since these are devices that are usually under 110-220V voltage, do not work around this if you are not 100% sure of your knowledge. !!

Since masters of all profiles come to our site, I ask electromechanics: Is there any mistake in the above post, should I correct it? ☺