Our  12 Volt Battery Reading as 13 Volts why?

All Lead acid batteries (Gel, AGM, Flooded, Drycell, etc) are made up of a series of 2.2 volt cells that are bridged together in series to reach their final desired voltage. For instance, a 6 volt battery will have 3 cells (3 x2.2= 6.6 volts), a 12 volt battery will have 6 cells (6 x2.2=13.2 volts) and so on.That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery. These numbers assume 100% healthy cells, and may vary a bit lower for older batteries.

 Compressor Vs Blower Vs Fan 

Compressor:
Compressor is a mechanical device that increases the pressure of a fluid, either gas or liquid by reducing its volume. The inlet diameter of the pipe will be more than the outlet diameter. This reduces the volume flow rate and thus the pressure of the fluid increases. Thermodynamically, low pressure high volume in the Inlet becomes high pressure low volume at the outlet. Compressor are mainly used for fluid flow at high pressures i.e, the inlet pressure will be low while inlet volume will be high and outlet pressure will be high while outlet volume will be low. There are many types of compressor based on the different principles of working such as 
1. Rotary Compressor
2. Reciprocatory Compressor
3. Centrifugal Compressor
4. Axial Compressor
Compressors are extensively used in refrigerator, air conditioner, pipeline transport of natural gas, petrol refineries, pneumatic compressors are used in industries.

Blower:
Blower is also known as "Centrifugal Fan". This fan increases the velocity of air or gas when it is passed into the impellers. The inlet pressure will be low and the outlet pressure will be high. At constant volume flow rate, the low pressure air becomes high pressure at the outlet. This is mainly due to the rotating blades in the impeller. The kinetic energy of the blades increases the pressure of the air at the outlet. Blowers are mainly used for industry purposes and in climatic control after fan due to its high pressure than fan

Fan:
Fan is a machine used to create a fluid flow. The flow of fluid is increased with the fan. It produces high volume and low pressure than the ambient conditions. It is mainly used as cooling device in computer CPUs and other electronic gadgets apart from climatic condition control.

Main difference between Fan and Blower is blower can achieve more pressure ratio than fan. Blowers can produce more high pressured air than fan. 

Difference between Compressor and Blower - Compressor produces high pressure at low volumes where as blower produces low pressure at high volumes.

Which is more dangerous AC or DC power?

     Alternating current (AC) and Direct current (DC) have slightly different effects on the human body, but both are dangerous above a certain voltage. The effect on a particular person is very difficult to predict as it depends upon a large number of factors - amount of current, duration of flow, pathway of current, voltage applied and impedance of the human body. 

Having said that, I would rate AC as more dangerous owing to the following reasons,

1. To produce the same excitatory effects, the magnitude of DC flow of constant strength shall be two to four times greater than that of the AC. i.e more DC current is required to induce the same harmful effects as AC current.

Why? The main difference between the effects of AC and DC on the human body result from the fact that excitatory actions of the current are linked to the changes of the current magnitude especially when making and breaking the current. Excitatory actions of the current include stimulation of nerves and muscles, induction of cardiac atrial or ventricular fibrillation. To produce the same excitatory effects, the magnitude of DC flow of constant strength shall be two to four times greater than that of the AC.

2. Accidents with DC are much less frequent than would be expected from the number of DC applications, and fatal accidents occur only under very unfavorable conditions, for example in mines. This fact is highlighted in the IEC publication 60479 - Effects of current on human beings and livestock. This reveals that DC is only an 'occasional culprit' compared to the 'serial killer' AC.

3. Ventricular Fibrillation is considered to be the main cause of death by electric shock.The probability of a human suffering from Ventricular Fibrillation is much higher in the case of AC than DC.

Why? For shock durations longer than the cardiac cycle, the threshold of ventricular fibrillation for DC is several times higher than for AC. For shock  durations shorter than 200 milli seconds, the threshold of fibrillation is approximately the same as for AC measured in RMS values.

4. The total impedance of the human body is higher for DC and decreases when the frequency increases. Since the impedance for DC is higher, the severity of electric shock would be comparatively lesser than AC.

Why? The impedance of the human body is one of the factors influencing the effect of electrical current on humans. The total impedance of the human body depends upon a number of factors (including the frequency of electrical supply). Therefore, the impedance of the human body is higher for DC and decreases when the frequency increases.

5. It's comparatively easier to let go of the gripped 'live' parts in the case of DC than AC. This is in contrary to popular belief.

To quote the popular belief, one such argument is shown below,

"AC would allow your muscles enough time to pull your limb away from the 'live' part because of the alternating cycles (AC frequency) which pass through zero. DC current, on the other hand, has continuous flow due to the absence of frequency oscillations and therefore you can't pull your limb away from the 'live' part.''

I could see many such 'flawed' arguments prevalent on the internet - especially the science forums debating on this topic. But, this is simply a myth.

Why? The "let-go" current is the best experimental measure we have of the effect of electricity on humans. The "let-go" current is the lowest level of current passing through a human subject through an electrode held in the hand that makes the subject unable to open his hand and drop the electrode. As mentioned in the IEC publication 60479 - Effects of current on human beings and livestock, the let-go of parts gripped is less difficult in the case of DC. This is based on experimental evidence.

Given the above reasons, we can safely conclude that AC is more dangerous than DC. Nevertheless, you should always avoid contact with high-voltage electrical conductors, regardless of the type of electrical current.

            No less important engineers than Thomas Edison and George Westinghouse argued that point ad inifinitum without reaching any conclusions that stuck. while debating the merits of their different power systems (Edison championed DC and Westinghouse championed AC which, as we all know own for its technical merits, safety not being one of them).  A great deal was made about electrocution as a form for death sentence and each one advocated the power of his opponent for this.

For example, are we talking peak voltages or RMS voltages? Different ways of measuring things. For example the AC Mains is 120V RMS. The equivalent DC for the same power is 120VDC. But the AC has much higher instantaneous peaks of 170V.  Its not the power that kills so its very hard to compare AC to DC voltages in terms of killing ability and absolute voltage.

Why 50 Hz frequency Used..?

IT STARTS FROM THE BEGINNING OF ELECTRICITY-
         Early in the history or electricity, Thomas Edison's General Electric company was distributing DC electricity at 110 volts in the United States. 
        Then Nikola Tesla devised a system of three-phase AC electricity at  240 volts. Three-phase meant that three alternating currents slightly out of phase were combined in order to even out the great variations in voltage occurring in AC electricity. He had calculated that 60 cycles per second or 60Hz was the most effective frequency. 
              Tesla later compromised to reduce the voltage to 120 volts for safety reasons.
With the backing of the Westinghouse Company, Tesla's AC system 
became the standard in the United States. 
Westinghouse chose 60 Hz because the arc light carbons(arc lamp) that were popular at that time worked better at 60 Hz than at 50 Hz.

Europe goes to 50Hz and 230V
Meanwhile, the German company AEG started generating electricity and became a virtual monopoly in Europe. 
They decided to use 50Hz instead of 60Hz to better fit their metric standards, but they stayed with 120V.
Europe stayed at 120V AC until the 1950s, just after World War II. 
They then switched over to 220V for better efficiency in 
electrical transmission. Great Britain not only switched to 220V, but 
they also changed from 60Hz to 50Hz to follow the European lead. 
Since many people did not yet have electrical appliances in Europe after the 
war, the change-over was not that expensive for them. 

U.S. stays at 120V, 60Hz
The United States also considered converting to 220V for home use but felt it would be too costly, due to all the 120V electrical appliances people had. 
A compromise was made in the U.S. in that 240V would come into the house where it would be split to 120V to power most appliances. 
Certain household appliances such as the electric stove and electric clothes dryer would be powered at 240V.

India got 50Hz, because it was colonized by England, which when they developed their electrical systems, choose 50 Hz.
From technical point of view operating 50 Hz versus 60 Hz would not make much difference but, to achieve it, either the prime movers - for example steam turbines, gas turbines and diesel engines  would need to be able to tolerate a 20% increase in speed or the alternators they drive - which produce the electricity  would need to be completely rebuilt with extra poles and windings so that they could continue to run at the same rotational speed. 
The costs of doing such re-engineering would be enormous and could not be justified as "economically worthwhile" from the point of view of actual necessity.

We  could have chosen any other frequency other than 50/60 hz but
50/60 HZ is an optimum frequency which keeps the transmission losses to tolerable limits. 
The higher will be the frequency, the more will be the losses.
and lower frequencies would causes the size, weight & hence the cost to increase. Also, more flickers are noticed in lesser frequencies than higher frequencies.

The voltage and frequency of AC electricity varies from country to country throughout the world.
 Most use 220V and 50Hz. About 20% of the countries use 110V and/or 60Hz to power their homes.220V and 60Hz are the most efficient values, but only a few countries use that combination. 

HVDC transmission lines replacing HVAC transmission lines at some places 

       
                  With AC systems the peak voltage is 2^0.5 (1.4142) times the RMS (nominal) voltage.  At transmission voltages that additional .4142 x voltage makes the insulation systems much more critical, lengthening the insulator strings and so increasing the cost of the insulators and poles required to separate the lines.

                With DC systems the peak voltage is the nominal voltage, so the insulator strings need only deal with the nominal voltage reducing capital and maintenance costs (washing from helicopters etc.).

                With very high voltage transmission where maximum voltage is limited by available technology, this fact is used to increase the nominal voltage on a given insulation type, resulting in a system which would be operated at 750,000 volts nominal (RMS) AC being used for 1,000,000 volts actual DC with 25% additional capacity for the same amperage (cable) design.

The other factors are,

1. In HVDC no corona loss is there as incase of HVAC.
2. For longer distance,HVDC system is very economical as compared to the HVAC system.
3. Allowing power transmission between unsynchronized AC distribution systems.
4. HVDC increases the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
5. For  DC  frequency is 0.Therefor there is no inductive reactance drop, result of it is improve voltage regulation.
6. There is no problem of stability as in AC.
7. There is no skin effect in DC.
8. AC require 3 wire for transmission but DC require only 2 .
9. There is no ferranti effect in DC{it doesn't  mean that capacitance is absent in DC,capacitance act as open CKT for DC}

Why do we hear a noise while passing a high voltage line?

   This is because of corona effect..

            When an alternating current is made to flow across conductor of the transmission line, then air surrounding the conductor (composed of ions) is subjected to di-electric stress. At low values of supply end voltage, nothing really occurs as the stress is too less to ionize the air outside. But when the potential difference is made to increase beyond some threshold value of around 30 kV known as the critical disruptive voltage, then the field strength increases and then the air surrounding it experiences stress high enough to be dissociated into ions making the atmosphere conducting. This results in electric discharge around the conductors due to the flow of these ions, giving rise to a faint luminescent glow, along with the hissing sound accompanied by the liberation of ozone, which is readily identified due to its characteristic odor.
         This phenomena of electrical discharge occurring in transmission line for high values of voltage is known as the corona effect in power system. If the voltage across the lines is still increased the glow becomes more and more intense along with hissing noise, inducing very high power loss into the system which must be accounted for. 

Corona Effect is the phenomenon of purple glow, hissing noise and production of ozone gas in a transmission line.

Representation of Waveforms..?

Electronics

                 In Electronic Circuits we need to produce many different types, frequencies and shapes of Signal Waveforms such as Square Waves, Rectangular Waves, Triangular Waves, Sawtoothed Waveforms and a variety of pulses and spikes.

These types of signal waveform can then be used for either timing signals, clock signals or as trigger pulses. However, before we can begin to look at how the different types of waveforms are produced, we firstly need to understand the basic characteristics that make up Electrical Waveforms.

Technically speaking, Electrical Waveforms are basically visual representations of the variation of a voltage or current over time. In plain English this means that if we plotted these voltage or current variations on a piece of graph paper against a base (x-axis) of time, ( t ) the resulting plot or drawing would represent the shape of a Waveform as shown. There are many different types ofelectrical waveforms available but generally they can all be broken down into two distinctive groups.

• 1. Uni-directional Waveforms   –  these electrical waveforms are always positive or negative in nature flowing in one forward direction only as they do not cross the zero axis point. Common uni-directional waveforms include Square-wave timing signals, Clock pulses and Trigger pulses.
• 2. Bi-directional Waveforms   –  these electrical waveforms are also called alternating waveforms as they alternate from a positive direction to a negative direction constantly crossing the zero axis point. Bi-directional waveforms go through periodic changes in amplitude, with the most common by far being the Sine-wave.

Whether the waveform is uni-directional, bi-directional, periodic, non-periodic, symmetrical, non-symmetrical, simple or complex, all electrical waveforms include the following three common characteristics:

• 1). Period: – This is the length of time in seconds that the waveform takes to repeat itself from start to finish. This value can also be called the Periodic Time, ( T ) of the waveform for sine waves, or the Pulse Width for square waves.
• 2). Frequency: – This is the number of times the waveform repeats itself within a one second time period. Frequency is the reciprocal of the time period, ( ƒ = 1/T ) with the standard unit of frequency being the Hertz, (Hz).
• 3). Amplitude: – This is the magnitude or intensity of the signal waveform measured in volts or amps.

Periodic Waveforms

Periodic waveforms are the most common of all the electrical waveforms as it includes Sine Waves. The AC (Alternating Current) mains waveform in your home is a sine wave and one which constantly alternates between a maximum value and a minimum value over time.

The amount of time it takes between each individual repetition or cycle of a sinusoidal waveform is known as its “periodic time” or simply the Period of the waveform. In other words, the time it takes for the waveform to repeat itself.

Then this period can vary with each waveform from fractions of a second to thousands of seconds as it depends upon the frequency of the waveform. For example, a sinusoidal waveform which takes one second to complete its cycle will have a periodic time of one second. Likewise a sine wave which takes five seconds to complete will have a periodic time of five seconds and so on.

So, if the length of time it takes for the waveform to complete one full pattern or cycle before it repeats itself is known as the “period of the wave” and is measured in seconds, we can then express the waveform as a period number per second denoted by the letter T as shown below.

A Sine Wave Waveform

Units of periodic time, ( T ) include: Seconds ( s ), milliseconds ( ms ) and microseconds ( μs ).

For sine wave waveforms only, we can also express the periodic time of the waveform in either degrees or radians, as one full cycle is equal to 360^o ( T = 360^o ) or in Radians as 2pi, 2π ( T = 2π ), then we can say that  2π radians = 360^o – ( Remember this! ).

We now know that the time it takes for electrical waveforms to repeat themselves is known as the periodic time or period which represents a fixed amount of time. If we take the reciprocal of the period, ( 1/T ) we end up with a value that denotes the number of times a period or cycle repeats itself in one second or cycles per second, and this is commonly known as Frequency with units ofHertz, (Hz). Then Hertz can also be defined as “cycles per second” (cps) and 1Hz is exactly equal to 1 cycle per second.

Both period and frequency are mathematical reciprocals of each other and as the periodic time of the waveform decreases, its frequency increases and vice versa with the relationship betweenPeriodic time and Frequency given as.

Relationship between Frequency and Periodic Time

Where:  ƒ is in Hertz and T is in Seconds.

One Hertz is exactly equal to one cycle per second, but one hertz is a very small unit so prefixes are used that denote the order of magnitude of the waveform such as kHz, MHz and even GHz.

Prefix	Definition	Written as	Time Period
Kilo	Thousand	kHz	1ms
Mega	Million	MHz	1us
Giga	Billion	GHz	1ns
Tera	Trillion	THz	1ps

Square Wave Electrical Waveforms

Square-wave Waveforms are used extensively in electronic and micro electronic circuits for clock and timing control signals as they are symmetrical waveforms of equal and square duration representing each half of a cycle and nearly all digital logic circuits use square wave waveforms on their input and output gates.

Unlike sine waves which have a smooth rise and fall waveform with rounded corners at their positive and negative peaks, square waves on the other hand have very steep almost vertical up and down sides with a flat top and bottom producing a waveform which matches its description, – “Square” as shown below.

A Square Wave Waveform

We know that square shaped electrical waveforms are symmetrical in shape as each half of the cycle is identical, so the time that the pulse width is positive must be equal to the time that the pulse width is negative or zero. When square wave waveforms are used as “clock” signals in digital circuits the time of the positive pulse width is known as the “Duty Cycle” of the period.

Then we can say that for a square wave waveform the positive or “ON” time is equal to the negative or “OFF” time so the duty cycle must be 50%, (half of its period). As frequency is equal to the reciprocal of the period, ( 1/T ) we can define the frequency of a square wave waveform as:

Electrical Waveforms Example No1

A Square Wave electrical waveform has a pulse width of 10ms, calculate its frequency, ( ƒ ).

For a square wave shaped waveform, the duty cycle is given as 50%, therefore the period of the waveform must be equal to: 10ms + 10ms or 20ms

So to summarise a little about Square Waves. A Square Wave Waveform is symmetrical in shape and has a positive pulse width equal to its negative pulse width resulting in a 50% duty cycle. Square wave waveforms are used in digital systems to represent a logic level “1”, high amplitude and logic level “0”, low amplitude. If the duty cycle of the waveform is any other value than 50%, (half-ON half-OFF) the resulting waveform would then be called a Rectangular Waveform or if the “ON” time is really small a Pulse.

Rectangular Waveforms

Rectangular Waveforms are similar to the square wave waveform above, the difference being that the two pulse widths of the waveform are of an unequal time period. Rectangular waveforms are therefore classed as “Non-symmetrical” waveforms as shown below.

A Rectangular Waveform

The example above shows that the positive pulse width is shorter in time than the negative pulse width. Equally, the negative pulse width could be shorter than the positive pulse width, either way the resulting waveform shape would still be that of a rectangular waveform.

These positive and negative pulse widths are sometimes called “Mark” and “Space” respectively, with the ratio of the Mark time to the Space time being known as the “Mark-to-Space” ratio of the period and for a Square wave waveform this would be equal to one.

Electrical Waveforms Example No2

A Rectangular waveform has a positive pulse width (Mark time) of 10ms and a duty cycle of 25%, calculate its frequency.

The duty cycle is given as 25% or 1/4 and this is equal to the mark time which is 10ms, then the period of the waveform must be equal to: 10ms (25%) + 30ms (75%) which equals 40ms (100%) in total.

Rectangular Waveforms can be used to regulate the amount of power being applied to a load such as a lamp or motor by varying the duty cycle of the waveform. The higher the duty cycle, the greater the average amount of power being applied to the load and the lower the duty cycle, the less the average amount of power being applied to the load and an excellent example of this is in the use of “Pulse Width Modulation” speed controllers.

Triangular Waveforms

Triangular Waveforms are generally bi-directional non-sinusoidal waveforms that oscillate between a positive and a negative peak value. Although called a triangular waveform, the triangular wave is actually more of a symmetrical linear ramp waveform because it is simply a slow rising and falling voltage signal at a constant frequency or rate. The rate at which the voltage changes between each ramp direction is equal during both halves of the cycle as shown below.

A Triangular Waveform

Generally, for Triangular Waveforms the positive-going ramp or slope (rise), is of the same time duration as the negative-going ramp (decay) giving the triangular waveform a 50% duty cycle. Then any given voltage amplitude, the frequency of the waveform will determine the average voltage level of the wave.

So for a slow rise and slow delay time of the ramp will give a lower average voltage level than a faster rise and decay time. However, we can produce non-symmetrical triangular waveforms by varying either the rising or decaying ramp values to give us another type of waveform known commonly as a Sawtooth Waveform.

Sawtooth Waveforms

Sawtooth Waveforms are another type of periodic waveform. As its name suggests, the shape of the waveform resembles the teeth of a saw blade. Sawtoothed waveforms can have a mirror image of themselves, by having either a slow-rising but extremely steep decay, or an extremely steep almost vertical rise and a slow-decay as shown below.

Sawtooth Waveforms

The positive ramp Sawtooth Waveform is the more common of the two waveform types with the ramp portion of the wave being almost perfectly linear. The Sawtooth waveform is commonly available from most function generators and consists of a fundamental frequency ( ƒ ) and all its integer ratios of even harmonics only, 1/2, 1/4, 1/6 1/8 … 1/n etc. What this means in practical terms is that the Sawtoothed Waveform is rich in harmonics and for music synthesizers and musicians gives the quality of the sound or tonal colour to their music without any distortion.

Triggers and Pulses

Although technically Triggers and Pulses are two separate waveforms, we can combine them together here, as a “Trigger” is basically just a very narrow “Pulse”. The difference being is that a trigger can be either positive or negative in direction whereas a pulse is only positive in direction.

A Pulse Waveform or “Pulse-train” as they are more commonly called, is a type of non-sinusoidal waveform that is similar to the Rectangular waveform we looked at earlier. The difference being that the exact shape of the pulse is determined by the “Mark-to-Space” ratio of the period and for a pulse or trigger waveform the Mark portion of the wave is very short with a rapid rise and decay shape as shown below.

A Pulse Waveform

A Pulse is a waveform or signal in its own right. It has very different Mark-to-Space ratio compared to a high frequency square wave clock signal or even a rectangular waveform.

The purpose of a “Pulse” and that of a trigger is to produce a very short signal to control the time at which something happens for example, to start a Timer, Counter, Monostable or Flip-flop etc, or as a trigger to switch “ON” Thyristors, Triacs and other power semiconductor devices.

Function Generator

A Function Generator or sometimes called a Waveform Generator is a device or circuit that produces a variety of different waveforms at a desired frequency. It can generate Sine waves, Square waves, Triangular and Sawtooth waveforms as well as other types of output waveforms.

There are many “off-the-shelf” waveform generator IC’s available and all can be incorporated into a circuit to produce the different periodic waveforms required.

One such device is the 8038 a precision waveform generator IC capable of producing sine, square and triangular output waveforms, with a minimum number of external components or adjustments. Its operating frequency range can be selected over eight decades of frequency, from 0.001Hz to 300kHz, by the correct choice of the external R-C components.

Waveform Generator IC

The frequency of oscillation is highly stable over a wide range of temperature and supply voltage changes and frequencies as high as 1MHz is possible. Each of the three basic waveform outputs, sinusoidal, triangular and square are simultaneously available from independent output terminals. The frequency range of the 8038 is voltage controllable but not a linear function. The triangle symmetry and hence the sine wave distortion are adjustable.