Electrical Wiring in the Home/Book or books?
QUESTION: Mr. Babbitt,
I am trying to improve my knowledge on electrical motors such as A.C. and D.C., specifically A.C. I am having trouble trying to find information on a breakdown of just very basics leading up to what is a single phase or poly-phase is and so forth almost elementary.
Slip rings and commutators too. The windings too, such as in which direction is a coil wound and if too if the opposite coil is wound in the same direction. These are my questions that I would like get cleared by a good book or books.
Do you recommend any good book(s) with an easy reading along with good pictures or schematics? I would appreciate your help on the matter.
Joel T. Gonzalez
ANSWER: Joel, in these days and times knowing about electric motors can be very beneficial, sounds like because you want to know about single and three phase, you might be working as a maintenance person or HVAC person,
EASA.com is probably the world's largest electric motor and apparatus association. Some of their white papers and other documents are free, they publish a monthly magazine, if you work it right you can get it for free,
I would suggest asking a local motor shop for a tour, now they may be busy, but if they think for one minute you are in a business that could be a customer, or you would advertise by word of mouth for them, they will find a way to give you a tour,
That is my best advertising, I put on classes depending, monthly or quarterly and bring in maintenance people, HVAC techs, anyone having to deal with motors, transformers, mechanical devices, gearboxes so on,
You will learn a lot if someone near you has the same type of classes, I do mine free, and we provide some simple snacks, then after the tour and and QA we have sodas and beers for those who want to hang out and get more detailed info, a two hour tour barely gets the surface covered there is so much to it, now with automobiles powered with motors, even more interest,
Right now if I knew two people who could wind a simple three phase motor the starting pay would run from a min of $15 an hour to maybe $25 plus, and they have a job for life,
So you are doing the right thing,
A couple answers to some of your examples, a coil is wound in really NO direction, a motor coil has a start and finish and is wound around or inserted around a section of laminated steel, the steel is laminated with insulation between the very thin sheets, making up the stator core, this prevents induction into the laminated core. If the core is shorted, then current can flow, this creates hot spots, and all kinds of issues, versus the electro magnet coil interacting with the rotor, or many coils would around the core acting on the rotor,
So the physical coil really has NO direction [as far as setting a north or south pole].
Because AC motors are fed alternating current, the coils goes neg then pos, depending on the cycles per second the voltage is generated at, if 609 cycles it changes 60 times a second from pos to neg, so the coil is neg then pos, neg then pos, so how do you create rotation?
The simple example is this three coils wound physically side by side, it is the timing of the three phase where coil 1 is pos while coil 2 is neg, and coil three is pos, for that brief period of time based on the cycles which is determined by the generator or frequency drive,
That is why frequency drives are so popular, they can control the cycles fed to an ac motor, at 60 which is common US voltage, 4 poles is 1800 RPM synchronous, the motor will run just shy of 1800, due to windage and friction, the windage is the restriction caused by internal or external cooling fans, and the friction is from the bearings.
That last one is hard for many to grasp, but rolling element bearings are technically titled ANTI FRICTION BEARINGS, not friction PROOF bearings, there is friction in the bearings and the best a design can do is to put the bearings in line, with the end housings bored in line, so there is no ADDED friction from the shaft being out of center and pulled or pushed one way or the other,
Now take a plain or sleeve type bearing, you hear stories that once a motor is up and running the plain bearings could be removed and the rotor would spin in the middle of the magnetic field around it, that is so bunk,
Plain bearings also must be aligned within thousandths of an inch, the rotor has journals which ride inside the sleeve, [Babbitt, babbit, Babbit, bearings, or cast bronze or many combinations of metals to make a sleeve bearing]
Then the bearing is sized with enough clearance so the oil film can form on the internal sleeve, the shaft actually rides on the film of oil, the oil rides on the bearing surface, thereby no problems with gravity,
Now there are special applications or motors that can spin inside a magnetic field but that is way beyond what you want to know,
Another trick to windings, is what is called a salient pole, because we do not understand magnetism, if two coils are side by side in a poly phase motor, and versus the standard connection where one phase has coil one starting on a finish, then connected to a start of the next or if you want to look at the coils as having rights and lefts, as far as the two ends that is common, so most motors go right as a lead, left to a right, right to a left, so on depending on the number of poles designed in the motor, remember at 60 cycles four poles gives you 1800 RPM sync, less windage and friction, for the RPM.
So in an instant the four poles are changing form pos to neg, but at that single point in time each pole is starting from pole one either neg or pos, then the next because the connection is from a right to a left, the opposite, so around the motor you have neg, pos, neg, pos, three times for a three phase motor with phases abc laid in the motor just like that
Now back to one phase of the three, all the same, all laid next to each other, first a phase, then b then c, each starts with power to the right of the coil, so you have that instant neg pos neg pos for 1/60th of a second, then they change to pos neg pos neg, then back 60 times A SECOND
But what if you connected the poles or coils right to left versus right to right, so each pole at that given period of time are the same polarity?
You would have four poles of each phase connected, in a manner when energized that would form pos pos pos pos, or neg neg neg neg all around the circumference of the motor.
The rotor develops rotation by the interaction of the rotor bars and the stator poles, so at first glance, you would think if connected all neg neg neg neg, no rotation,
Not so, because magnets as and as far as we know about magnets, always develop an opposite pole, you cannot find a natural or man made magnet that is just one pole north or south, that you could hold in your hand, that is part of the mystery of magnets, this phenomena of always developing both a north and south be it on ends, or sides, or whatever geometric pattern, you will find both a north and south,
So back to the motor physically connected to make a electro magnetic pole, when energized, all the same, what happens is the properties of magnetism creates a salient pole between the two like poles, and this happens, if you use the example of a four pole motor 4 times.
Now you have under power a physical pole creating a north, then a north, then north, then north, but that is a physical set or routine of connections, again most motors [AC VANILLA typical three phase induction motor] are connected in each phase right to right or finish to finish or start to start whatever term you want to use, the coil is nothing more than magnet wire wrapped around a laminated core, that simple, it makes an electro magnet inside that area of the wire is wrapped around, and it changes from neg to pos 60 times every second, but when connected to the next pole depending what side or left or right or start of finish, you can START with the same polarity for that first 1/60th of a second,
This is repetitive but digging this out of any book is going to take a while, so hopefully I am providing you a shortcut to understanding the complexity of all this neg to pos, and so on then with poly phase, the confusion of how the phases interact.
So I take a typical motor, and connect the poles of one phase, instead of typical right to right to right, or finish to finish, I connect them with the physical ends of the coil finish to start, finish to start, again four times, for each phase,
What happens is this magnetic phenomena that creates that salient pole, and you now have four physical poles, and four invisible poles that are opposite, just like a magnet in your hand, and now when energized, you have 8 poles,
Because four at 60 cycles is 1800 RPM, then what do get with 8 poles?
This is how they engineer and design single winding two speed poly phase motors, or at least one very common method.
They engineer enough of the leads to come out externally so the user can configure the poles all opposite or all the same, giving the user two speed choices with one winding.
It is often economical and simple, but that is going away with the advancement of frequency drives, now you can take any induction motor and get infinite or almost infinite control from the use of the manipulation of the applied frequency.
Now instead of two choices, we have 1800 as a base speed, if we lower the cycles to 30 we have half the 1800 or the 900 WITHOUT changing the physical pole connections.
Plus we can now pick and use any frequency and if we were to split the difference, at say 45 we would have 1350, but we have choices all through the spectrum so we can use 34 cycles if need a shade above 900, or we can use 57 cycles if we need a shade below 1800.
No longer bound the physical pole connections giving us only two speed choices,
But even with the physical pole changes giving us two speeds, there are some issues, in some two speed physical pole connection motors, you can have a choice of constant HP or constant torque, or variable torque, it depends on what the motor is driving to determine which motor is most suited to needing either constant torque or HP< so there are physics laws that get in the way, even with the frequency drives, the torque and HP have to be calculated, as you will loose HP or torque or both,
If we use an 1800 base speed at 60 cycles, we can get away with maybe 20% above 60 cycles, then our concerns are structural, can the rotor withstand the new centrifugal demands?
I have read books and own books going back into the 1900s and prior, and some of those are hundreds of pages trying to explain the relationships of poles and cycles and coil connections,
You realize that Edison and Tesla had a huge competition over the use of AC which was TESLA's push, and of course Edison with DC.
Luckily Tesla won out, I am sure along way, we would have discovered that for general electrical supply, alternating current was way more manageable.
In modern electronics you can reduce DC by transforming, but in real life trying to shoot thousands of volts of DC many miles with conductors large enough to carry the current would have been impossible,
With AC being so easy to transform, we can shoot thousands and thousands of volts down a 1/2 inch line and when it terminates at a switching station, it is transformed down, then distributed, keeping thousands of volts from hanging over our heads.
Slip ring motors, where and option that could satisfy speed control and hold some torque, and was developed as in between option of straight AC or DC,
But worth understanding, most slip ring motors are obsolete, but slip rings are used in many other situations where something is spinning, and the rotating element needs to be supplied electrical power.
Take a simple carousel, the devices on the ride need to move in up and down directions, so how do you supply power to the motors driving the various horses and buckets on the rotating platform? Simple, feed power to a set of conductive rings, sets of carbon composite brushes are then fixed to the rotating platform, and power is brought through the brushes and routed to the lights, and devices that need to move on the platform,
There are hundreds of examples, but slip ring motors served a very important service for many decades until the invention of multi speed motors AC_DC type motors, where a faux DC winding is interwound under the induction winding for speed control at low speeds with adequate torque.
You need to read and understand the difference between torque and Horsepower, it confuses most,and if studying electric motors, you have to understand the differences.
Basically HP has many ratings, all related to available power, for example watts is power, KW is watts in multiples of thousands, but all power,
torque is in turning force, example hold out your arm [let's say a distance of two feet straight out horizontally] with a 1 pound load of some kind, to twist it, it takes x from your shoulder to twist it,
in this simple case it is 2 feet of arm length, times 1 pound of load or 2 foot pounds of TORQUE if you increase that load you are holding to 10 pounds you now need 210 foot pounds of torque to twist the load,
This subject is going to one of the more difficult, compared to the other answers you need, but you need to study it,
I am not sure what or why or how basic or elementary you need to improve your knowledge of motors, you can be as simple as just identification, so suggesting what to read that is elementary is tough, because I am not sure where you are headed.
I own two shops in the Kansas City Missouri Area, EMR Repair Inc, MEAR services Inc, the e-mail addresses are first email@example.com, and then firstname.lastname@example.org, feel free to write me there if you need something specific, the websites are also emrrepair.com and mearservice.com if for some reason you need to speak with someone to help guide you the phone numbers are 816-587-3930, and 816-650-4030 most anyone can get you an answer to most things or depending if I am in or out, I am happy to help,
It is long bridge from photos to schematics on an elementary level,.
I would suggest getting or building a simple kit that comprises of several feet of fairly small magnet wire, a foot or two of larger magnet wire, a battery at least one double A, and some tape or holder, a few feet of connection wire,
You can get it all at most pure hobby shops for a few bucks, there are many instructions available on the net that show how to build a simple motor from very little,
The tick is magnet wire is insulated, but doesn't look insulated, it almost looks like bare copper, but it is not, is the modern replacement for cloth or other insulation coverings on magnet wire to build motors and transformers, but it is so thin and the color so close to copper it is almost impossible to tell.
In making this simple motor, you will understand commutation as about as well as anyone, the trick and there is a trick, the magnet wire being round, has to do the commutation,
If you can imagine this round wire having "sides" one end you will scrape the insulation off one side, and to scrape the insulation off the other or opposite "side" then when finished you will see how commutators work,
above is a more elaborate version from wiki, in the simple version you make your coil by winding it around the AA battery, using the battery as your winding mandrel
Video version above
a more complex version, above, I suggest NOT using a magnet and nail it is more visual than a tool to understand concepts. but the very first page shows the two wires from the "slip ring rotor" or "armature" and you see the coil has two ends, however because of alternating current the single strand of magnet wire has to be looked at as having two sides one side is one post, the other side and other end on the other post of the rotating element,
I can mail you the magnet wire, if you want to send me an address, I cannot do this for everyone, as magnet wire has reached nearly $10.00 per pound, but for those trying to learn we will do what we can from scrap new magnet wire, lengths we have cut from forming large coils, and the rest are components you can easily get anywhere,
Radio shack used to carry a small supply of magnet wire but way more than you need for one experiment, and costly,
The cool thing about building your own motor is the ability to make the armature with more or less turns, the permanent magnet stronger, or your can actually use a stronger hobby battery, and wind the stationary field around an iron core, not using a permanent magnet,
You can also use two batteries and control the voltage to the stationary coil, and control the voltage to the rotating element, this is called separately excited and is used in thousands of applications today,
or you can power the rotating and stationary in parallel, put them in series, so many options to understand electric motors, and a very interesting display when you are finished,
As far as books from my library, and thinking simple or elementary, not sure what to tell you, I think you would be better off goggling for free, you tube has thousands of examples,
I really need to your goal, elementary with photos and schematics are polar opposites,
this site is free:
you need to have an understanding of basic electricity, first, magnets and properties, second, power and torque third, motors last,
PROBABLY THE BEST FROM YOUR QUESTION
free book in .pdf format above,
also free for download or available for purchase
If these do not get you where you want to go, send me a note by e-mail to either shop or my home e-mail and I will get you to Amazon to buy a book or two, but I am sure with some simple browsing you can find all you need in an elementary sense from the net,
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QUESTION: Hello Mr. Babbitt,
Thank you for the detailed e-mail. As always, knowledge is power! I am currently taking an electric motors class and right now we are still on the first phases of recapping theory. Hopefully within the next couple of days we will actually be looking and testing to the internals of an A.C. motor. I know the parts and such but it is just the theory trying to envision how the winding(s) is doing its individual job. I will learn/grasp it eventually when I have my eureka moment. I do have some questions but maybe these are questions that I will be able to ask my teacher here of course within the city.
All in all, thank you for your help and your willingless to help out. So yeah, basically a book that maybe has more pictures/schematics of an A.C. and D.C. with rotation and switching of the poles I would grasp the idea a whole lot faster. This means, very basic to just basic theory leading into the idea as to how it affects a motor or how a motor is made to be.
Joel T. González
Free to download in pdf format,
A fairly pricey book, but is owned by nearly every motor repairman,
A book for non professionals, covering the basics of all motor types,