You don’t come across DC motors face to face in your every day life. Let me give you some common applications of DC Motors.

1. Electric Train.

A kind of DC motor called the DC Series Motor is used in Electric Trains. The DC Series Motors have the property to deliver more power when they are loaded more. So the more the people get on a train, the more powerful the train becomes.

2. Elevators.

The best bidrectional motors are DC motors. They are used in elevators. Compound DC Motors are used for this application.

3. PC Fans, CD ROM Drives, Hard Drives.

All these things need motors, very miniature motors, with great precision. AC motors can never imagine any application in these places.

4. Starter Motors in Automobiles.

An automobile battery supplies DC, so a DC motor is best suited here. Also, you cannot start an engine with a small sized AC motor,

5. Electrical Machines Lab in Colleges.

Ofcourse, if the motors are not here, where else would they be?

Let me tell you the types of DC motors that are there.

1. DC Shunt Motor,

2. DC Series Motor,

3. DC Long Shunt Motor (Compound)

4. DC Short Shunt Motor (Compound)

The rotational energy that you get from any motor is usually the battle between two magnetic fields chasing each other. The DC motor has magnetic poles and an armature, to which DC electricity is fed, The Magnetic Poles are electromagnets, and when they are energized, they produce a strong magnetic field around them, and the armature which is given power with a commutator, constantly repels the poles, and therefore rotates.

The DC Shunt Motor

For example in a 2 pole DC Motor, the armature will have two seperate sets of windings, connected to a commutator at the end of the shaft that are in constant touch with carbon brushes. The brushes are static, and the commutator rotate and as the portions of the commutator touching the respective positive or negative polarity brush will energize the respective part of the armature with the respective polarity. It is usually arranged in such a way that the armature and the poles are always repelling.

The general idea of a DC Motor is, the stronger the Field Current, the stronger the magnetic field, and faster the rotation of the armature. When the armature revolves between the poles, the magnetic field of the poles induce power in the armature conductors, and some electricity is generated in the armature, which is called back emf, and it acts as a resistance for the armature. Generally an armature has resistance of less than 1 Ohm, and powering it with heavy voltages of Direct Current could result in immediate short circuits. This back emf helps us there.

When an armature is loaded on a DC Shunt Motor, the speed naturally reduces, and therefore the back emf reduces, which allows more armature current to flow. This results in more armature field, and therefore it results in torque.

When a DC Shunt Motor is overloaded, if the armature becomes too slow, the reduction of the backemf could cause the motor to burn due to heavy current flow thru the armature.

The poles and armature are excited seperately, and parallely, therefore it is called a Shunt Motor.

The DC Series Motor

A DC Series Motor has its field coil in series with the armature. Therefore any amount of power drawn by the armature will be passed thru the field. As a result you cannot start a Series DC Motor without any load attached to it. It will either run uncontrollably in full speed, or it will stop.

When you load it, its effeciency increases with load. Thats why they use it on Electric Trains and elevators.

DC Compount Motor

A compound of Series and Shunt excitation for the fields is done in a Compound DC Motor. This gives the best of both series and shunt motors. Better torque as in a series motor, while the possibility to start the motor with no load.

Above is the diagram of a long shunt motor, while in a short shunt, the shunt coil will be connected after the serial coil.

A Compount motor can be run as a shunt motor without connecting the serial coil at all. But not vice versa.

B L Theraja is an Electrical Engineering Professor, and he has written a huge 4 Volume Book called Basic Electrical Engineering, Read that and you will get the derivations, calculations, formulae, and anything that you need to become an electrical engineer.

By becoming an electircal engineer, the best you can do is to work at some power station, or at the Power Department, or as a foreman at the Electric Train Station or as a lift mechanic. But I for some reason really feel bad that I did not make a career out of Electrical Engineering. I was keen on computers when I was learning Electrical Engineering, But right now, I find my passion for Electrical Machines growing more and more than it is for computers.

When you are old, you start worrying. Even if you are filthy rich, if you dont have some one of your own around you, you are scared. If there is an emergency, who could help you from their hearts, and who would remain with you for your money. And who would try to take advantage of this situation and get you killed, and take some money away from you?

This problem is there around the world. Even for small families, the worry about health is always there. The best way is to do preventive maintenance. You need tips about caring for yourselves. Or professionals who would do that for you. Not for the money, but as a service, from the heart.

A nursing home that gives you all that you need. Answers to crucial questions when it comes to self or your loved ones.

How many know that I have been a good builder of audio amplifiers? I’m not talking about the easier way, something like assembling your computers. But the hard way. Getting printed circuit boards, buying each and every component seperately, placing them on the pcbs, soldering them, and getting them to work. Actually, I have been doing this since I was 15 yrs of age. Is any one surprised? Well, kids these days are building robots at the age of 10.

Anyways, let me talk about the amplifiers. When I was 15, I could only play with audio cassettes, since CD Players were a bit expensive. So, I broke an old tape recorder that we had, a very old National Panasonic tape recorder and took out the cassette mechanism or the cassette deck. That had already served for about 15 years, as the tape recorder was bought in my family the year that I was born. And after it died out, the mechanism served me for 3 more years. I dont know where I threw it after that.

I replaced the mono playback head with a stereo AX head, and removed the recording head from it. Changed the pinch roller, and bought a new motor and a set of belts and fly wheel, and the mechanism was ready.

Next thing I needed was a pre amplifier. A Pre-Amplifier is an amplifier that boosts the very weak signals that comes out from the coild of the head, which are induced by the magnetic variations on the tape, to such an extent that it can be fed to the amplifier.

The design of a Pre Amplifier can be very tricky. If you use one mismatching component, all that you will hear is noise, and not the actual music thats recorded in the cassette. And if you dont bias the transistors properly in the pre amplifier, you will end up recording noise in the cassette that you are playing.

I always prefer transistors to those stupid ICs. ICs consume a lot of energy, release a lot of heat, and are stupid. You cant do a single alteration in the circuit thats inside the IC. Its not open source

A Japanese transistor, with number C 138 is my favourite first stage pre amplifier transistor. a Its an NPN transistor, and the boost that it gives to the signals that come in microvolts from the head, are simply awesome. This is usually a single transistor stage, which just boosts the signal and gives a 180 degree phase-shift as well to the signal. We usually try to make it a Class C amplifier to improve the effeciency.

The second stage is a Class AB amplifier, with 2 transistors, and both of them biased thru a preset, thru which the amplitude of the signal can be controlled. But this is a stupid idea that most disagree with. If the values of the components are chosen incorrectly, we would end up creating a low pass or a high pass filter with it.

The 2nd stage amplifies the signal to a better leve. I usually prefer amplifying the signals thru 4 stages of amplification before it gets into the power amplifier, while most do it right from the first stage of the pre amplification process, and thereby get a very poor sound reproduction.

After the pre amplifier stage, the signal is passed on to an equalizer.

People of these days, electronics hobbyists if any, can ignore the above preamplifier section, since thats history now. These days you get CD ROM drives for about Rs 800, or $20, with a built in pre amplifier.So, all you need to do it is to connect the ourput of the drive to an equalizer or the poweramplifier as desired.

The equalizer is a circuit that gives the signal a +10 DB boost or a – 10 DB buck, and this can be done for each and every band of the signal. The most common equalizers come with 5 or 10 bands. If you see winamp, you will find a 10 band equalizer in it.

The equalizers are usually made with Op Amps. IC 741. Any engineer cant have passed out from engineering without hearing about this IC. On a 5 Band equalizer, there are 6 OP Amps, or Operational Amplifiers. The first OP Amp boosts the entire range of Singnal to +10 DB, and this signal is fed thru potentiometers to the other Op Amps. which would be tuned to a particular band of frequency.

The level set by the potnetiometer will be again amplified by the corresponding OpAmp, and we get to tune the sound wave t the perfect style we like. Pop, Jazz, Rock, anything.

The Output of the equalizer is then fed to a noise reducing circuit, which will reduce the noise caused by the 50Hz applications around the amplifier. If you think any other freuqency is noise, you can designer a noise reducing filter for that too.

Then comes the power amplifier. I build power amplifiers only with transistors. And that too, only with British Transistors. I dont trust any other transistors. British Transistors start with the series BC and BD, where BC is the series of low power transistors, and BD High Power. There is a german series called SL, but unfortunately, though I admire German effeciency, I dont like this series.

For a power amplifier, I would use a BC547 to boost the equalizer’s output of 5 Volts to 15 volts. This 15 volts is boosted to 45 volts, and at the last stage, the 45 volts is amplified to 150 volts.

The output of the amplifier should usually be with an impedence of 8 ohms, so as to get optimum deliver of sound and compatiblity with speakers. This particular amplifier could deliver an RMS of about 1500 watts, if, suitable speakers were connected. But I was confined to 2 x 8 inch woofers, and 2 tweeters. And still I had fun.

I still have a big bag full of circuit diagrams here, and I am planning to scan them and put them online for display. So wait for it.