Basic electrical |
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There are a lot of definitions of what this stuff is that are factually correct but hard to understand. I will attempt to make it understandable.
All substances want to have equal amounts positive and negative charge. If you look at the 2 pics above they obviously show lightning strikes. This is a form of electricity. The weather has caused the sky to be charged with, say a negative charge. The weather has also caused the ground to be charged positive. The lightning is the equalization of the charges. Walk across a carpeted floor in socks. Then reach out to a door knob. Sometimes you will get a small spark from your hand to the knob. The action you took in walking across the floor caused you to be charged differently than the the knob. The spark is the equalization of the charge to make you balanced with both positive and negative charges.
In a chemical battery, there is a positive end and a negative one. The chemicals in the battery create the imbalance between the positive and the negative ends.
If I run a wire between the positive and negative end and place a small light bulb in the circuit, the light will glow. The electricity in the circuit is trying to get from the negative to the positive end to equalize the charge. The electricity, in its hurry to equalize the charge, will do work (light the light). When I leave the light in the circuit for an extended time, the charge becomes equalized. We call this a dead battery.
All substances want to have equal amounts positive and negative charge. If you look at the 2 pics above they obviously show lightning strikes. This is a form of electricity. The weather has caused the sky to be charged with, say a negative charge. The weather has also caused the ground to be charged positive. The lightning is the equalization of the charges. Walk across a carpeted floor in socks. Then reach out to a door knob. Sometimes you will get a small spark from your hand to the knob. The action you took in walking across the floor caused you to be charged differently than the the knob. The spark is the equalization of the charge to make you balanced with both positive and negative charges.
In a chemical battery, there is a positive end and a negative one. The chemicals in the battery create the imbalance between the positive and the negative ends.
If I run a wire between the positive and negative end and place a small light bulb in the circuit, the light will glow. The electricity in the circuit is trying to get from the negative to the positive end to equalize the charge. The electricity, in its hurry to equalize the charge, will do work (light the light). When I leave the light in the circuit for an extended time, the charge becomes equalized. We call this a dead battery.
So much for the simple stuff.
The electricity in the battery is called direct current. That simply means electricity passes from the negative pole (indicated by a - sign) to the positive pole (indicated by a + sign) in a continuous flow if there is a complete circuit.
Before we get any further, we need to do a little defining of terms. Negative and positive poles are the terminals that we connect from the source (battery) to wire that electricity can pass thru to connect to a load. The load can be anything that we want to operate, a light, a motor, a TV set. If we connect the load to the source with wires then the load operates. There is one other device we need in this circuit. A switch. The switch is just an opening in the circuit that stops the flow of electricity. Below we have a schematic diagram. This diagram shows the 4 things needed to make an electric circuit. A source, a load, a switch and the wires to connect all parts. In the circuit below, the light is not on. This circuit is called open. If the switch is moved down to where there is a connection between the 2 dots, it is called closed. The light will glow. Current is flowing. Current is the amount of electricity flowing. This is the basis of all electrical circuits. They will become very complicated but this is still the basis.
The electricity in the battery is called direct current. That simply means electricity passes from the negative pole (indicated by a - sign) to the positive pole (indicated by a + sign) in a continuous flow if there is a complete circuit.
Before we get any further, we need to do a little defining of terms. Negative and positive poles are the terminals that we connect from the source (battery) to wire that electricity can pass thru to connect to a load. The load can be anything that we want to operate, a light, a motor, a TV set. If we connect the load to the source with wires then the load operates. There is one other device we need in this circuit. A switch. The switch is just an opening in the circuit that stops the flow of electricity. Below we have a schematic diagram. This diagram shows the 4 things needed to make an electric circuit. A source, a load, a switch and the wires to connect all parts. In the circuit below, the light is not on. This circuit is called open. If the switch is moved down to where there is a connection between the 2 dots, it is called closed. The light will glow. Current is flowing. Current is the amount of electricity flowing. This is the basis of all electrical circuits. They will become very complicated but this is still the basis.
Voltage is similar to pressure in a water system. All components in the electrical system have resistance to the flow of current. Voltage must overcome that resistance. The higher the voltage the more volume of current passes thru the circuit.
Amperes is the amount or volume of current that passes thru the circuit.
Resistance is the opposition to current flow rated in ohms.
These 3 measurements are related to each other. Increase the voltage against a fixed resistance and the current increases.
Increase the resistance against a fixed voltage and the current decreases.
There is a calculation that allows you to determine one value if you have the 2 others. The law here is called Ohm's law. The triangle below is used by covering the value you do not know.
Amperes is the amount or volume of current that passes thru the circuit.
Resistance is the opposition to current flow rated in ohms.
These 3 measurements are related to each other. Increase the voltage against a fixed resistance and the current increases.
Increase the resistance against a fixed voltage and the current decreases.
There is a calculation that allows you to determine one value if you have the 2 others. The law here is called Ohm's law. The triangle below is used by covering the value you do not know.
V is for voltage, R is for resistance, and I is for amperes. Example: You need amperes, you have 12 volts, 10 ohms resistance, divide 12 by 10 = 1.2 amperes. Another example: You need voltage. amperage is 5 amperes, 7 ohms resistance, multiply 5 X 7 = 35 volts.
In the HVAC industry, this calculation is seldom used. It is shown here to demonstrate the relation of these values to each other.
In the HVAC industry, this calculation is seldom used. It is shown here to demonstrate the relation of these values to each other.
So, if I increase the voltage (pressure), the amperes (volume), will increase if the ohms (resistance) stays the same.
The Power or the watt
I cannot know the total power of a circuit unless I know both the voltage (pressure) and the amperage (volume). Against a fixed resistance, If I increase the voltage, the amperage will increase. That will increase the total power used by the circuit. So, if I know the voltage or I know the amperage, but not both, I have no idea how much power is being used. What we do to determine total power is multiply voltage by amperage. Thus if I have 12 amperes flow and 120 volts, The wattage is 1440. When we are expressing wattage for metering from the utility, we usually use kilowatts. Which, of course, is 1000 watts.
The load
The load is sometimes called a current limiting device because it is the part of the circuit because it should have more resistance to current flow than any other part of the circuit. It is also called the current consuming device because energy is used when the current passes thru. No other part of the circuit is designed to use energy. It is also the only reason we make up a circuit at all.
One of the attributes of the load is that the higher the resistance of the load, the less current it consumes. When we think of resistance we tend to think high resistance equals more power being used. In electrical, the opposite is true. If you note the ohm's triangle above and how it works, decreasing the resistance increases the amperes (current flow) and increasing resistance reduces current flow.
Examples of loads are motors, light bulbs, heating elements and TV sets.
In most circuits, there is only one load. However, as in virtually all things in electrical, there will always be exceptions.
One of the attributes of the load is that the higher the resistance of the load, the less current it consumes. When we think of resistance we tend to think high resistance equals more power being used. In electrical, the opposite is true. If you note the ohm's triangle above and how it works, decreasing the resistance increases the amperes (current flow) and increasing resistance reduces current flow.
Examples of loads are motors, light bulbs, heating elements and TV sets.
In most circuits, there is only one load. However, as in virtually all things in electrical, there will always be exceptions.
The switch
Any time there is a circuit, we need some sort of control so the load can be disconnected from power. This is usually a switch. In the above circuit, the switch is manually operated, like a wall switch. Unlike the load, there can be any number of switches in the circuit. Switches can be operated manually, in response to pressure or temperature changes, in response to light changes, pretty much anything you can think of. The switch should consume no power, it should only direct it. However, as in all things electrical, nothing is 100%. There will always be some resistance loss in the switch.
The Wiring
The wiring we use to connect the load to the source is usually made from metal. We want to reduce the resistance of the wiring to as low as possible. All materials have resistance to electrical flow. resistance limits the amperes allowed to pass thru the material. This resistance converts electrical energy in to heat. The heat is wasted energy that is not used to power the load. Thus, we want to use the best conductor to minimize the loss. Obviously, cost is also a factor. Which is why silver is not used for all wiring.
In addition to the material used for wiring, the size also determines the resistance to flow. The larger the wire, the less the resistance. Larger diameter wire also will take more heat and not overheat. Below are several metals and their electrical conductivity. The higher the number, the better the conductivity.
In addition to the material used for wiring, the size also determines the resistance to flow. The larger the wire, the less the resistance. Larger diameter wire also will take more heat and not overheat. Below are several metals and their electrical conductivity. The higher the number, the better the conductivity.
The diameter of the wire (we are using copper here) and type and thickness of insulation determines how much amperage (volume) a wire can carry without overheating.
There are ratings for how much amperage can be safely carried by the different sizes and types of wire. In the US this text is the National Electric Code (NEC). It is not the purpose of this book to teach electrical code, so only examples will be given here.
There are ratings for how much amperage can be safely carried by the different sizes and types of wire. In the US this text is the National Electric Code (NEC). It is not the purpose of this book to teach electrical code, so only examples will be given here.
Silver 105
Copper 100
Gold 70
Aluminum 61
Nickel 22
Zinc 27
Brass 28
Iron 17
Tin 15
Phosphor Bronze 15
Lead 7
Nickel Aluminum Bronze 7
The source
The source could be a battery or a generator. The source determines the voltage provided and it also determines the amount of current available. As an example, a generator powered by a 5 hp gasoline engine will have less current available at a specific voltage than a 10 hp engine.
Electricity and magnetism
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Above on the left, is a permanent magnet. On the right, the permanent magnet is placed below a piece of paper with iron filings placed on top. If you look at the center portion of the filings, you can see the 2 poles of the magnet. the filings have arranged themselves around the poles lining up with the magnetic lines of force. These lines of force are very strong close to the poles of the magnet and reduce in strength very quickly as you move away. All permanent magnets have 2 poles. The north and the south. If 2 magnets of the same strength are placed close together with their poles placed north to south, they will attract. If placed with their poles north to north and south to south, they repel.
Electricity and magnetism are closely related. When electricity passes thru a wire, a magnetic field builds up around the wire. This makes the wire a magnet. If I coil the wire, the magnetic field is more concentrated. If I wind the wire around an iron core, it concentrates more. So we often use electricity to make electromagnets. Turn on the power and you have a magnet.
We use this to do work with electricity.
We use this to do work with electricity.
Direct current
In the diagram above, a battery is the power source. Batteries deliver direct current or DC. All this means is the power delivered is a steady voltage. Kind of like a faucet being turned on. The water runs continuously. When we energize a circuit with an electromagnet as its load and the power is DC, The magnet is similar to a permanent magnet. There is a continuous north and south pole. However, electricity delivered to most homes and businesses is AC. This brings us to the next type of power.
Alternating current
Alternating current is quite different from direct current. Instead of a steady flow of current, the voltage and current rises, falls and reverses polarity to rise again.
Look at the sine wave below. This image is seen on an oscilloscope. The oscilloscope gives a picture of the rise and fall of the voltage in the alternating current circuit.
The zero volts line is to the right of the number 2. The voltage rises in positive polarity, drops to zero then drops in negative polarity. It makes a complete cycle 60 times a second in the US. This is called 60 hertz or 60 cps. So, why do we use this type of power? Well read on, I will try to explain.
Look at the sine wave below. This image is seen on an oscilloscope. The oscilloscope gives a picture of the rise and fall of the voltage in the alternating current circuit.
The zero volts line is to the right of the number 2. The voltage rises in positive polarity, drops to zero then drops in negative polarity. It makes a complete cycle 60 times a second in the US. This is called 60 hertz or 60 cps. So, why do we use this type of power? Well read on, I will try to explain.
Electromagnets have a peculiar property. When the power is turned on, the magnetic field builds up and increases in power. When the power is shut off, the field collapses. When this happens, the magnetic lines of force that were built up collapse across the wires that made up the electromagnet. When the wires are crossed, power is induced in the wires. So when power is turned off you get a pulse of power in the wires. This type of power is called induced. This means that there is no physical connection between the induced power and the power that original traveled thru the wires. Now this is interesting, but who cares?
lets take this a little farther. Remember when I said that you could concentrate the magnetic field by coiling the wire around an iron core?
Well, what if we coiled 2 separate coils around that core?
One that carried the original current from a power source and one that was connected to a load.
Now, if I powered up the circuit, then shut it off, when the field collapsed, power would be induced into that second coil of wire. Well, I guess that would be interesting also, but again, who cares? Well, let's start fooling with these windings.
Let's take that original coil that we ran power thru. We will call that the primary coil. Let's coil the wire around the core 100 times. Then let's take the other coil, we will call it the secondary coil. Let's coil this one 10 times around. If I powered up the primary coil with 120 volts, and I checked the voltage coming out of the secondary what do you think you would get?
It would get 12 volts. One tenth of the voltage.
If I energized the secondary with 120 volts, I would get 1200 volts in the primary.
So why? Each wire has become a magnet. If there are 10 coils in the primary, there are 10 magnets. Each wire(magnet) has its own magnetic field. When they collapse, they collapse 10 fields.
If the secondary has 100 coils, those 10 fields cross 100 secondary coils. This induces 10 times the voltage.
So what wonderful result do we have? We were able to easily change the voltage.
This part is called a transformer.
So, again who cares? Why do we want to change the voltage?
Remember volts times amps?
If we want to move a specific amount of watts, we need to know the voltage and the amps required by the circuit.
Example: let's say the circuit requires 20 amps at 120 volts.
When we look up the wire ampacity in the NEC, we see that #12 wire will handle this load.
But if the load is 35 amps at 120 volts, I could not use this wire because it will overheat.
However, if we raised the voltage to 240, we would only need 1/2 the amperage to move the same amount of total power.
This is important as the change in voltage allows us to move very large amounts of power without having to use excessively large diameter wires. Also, when we want power at a low enough voltage to be safe to use, we can lower the voltage.
All because of the transformer.
Well, what if we coiled 2 separate coils around that core?
One that carried the original current from a power source and one that was connected to a load.
Now, if I powered up the circuit, then shut it off, when the field collapsed, power would be induced into that second coil of wire. Well, I guess that would be interesting also, but again, who cares? Well, let's start fooling with these windings.
Let's take that original coil that we ran power thru. We will call that the primary coil. Let's coil the wire around the core 100 times. Then let's take the other coil, we will call it the secondary coil. Let's coil this one 10 times around. If I powered up the primary coil with 120 volts, and I checked the voltage coming out of the secondary what do you think you would get?
It would get 12 volts. One tenth of the voltage.
If I energized the secondary with 120 volts, I would get 1200 volts in the primary.
So why? Each wire has become a magnet. If there are 10 coils in the primary, there are 10 magnets. Each wire(magnet) has its own magnetic field. When they collapse, they collapse 10 fields.
If the secondary has 100 coils, those 10 fields cross 100 secondary coils. This induces 10 times the voltage.
So what wonderful result do we have? We were able to easily change the voltage.
This part is called a transformer.
So, again who cares? Why do we want to change the voltage?
Remember volts times amps?
If we want to move a specific amount of watts, we need to know the voltage and the amps required by the circuit.
Example: let's say the circuit requires 20 amps at 120 volts.
When we look up the wire ampacity in the NEC, we see that #12 wire will handle this load.
But if the load is 35 amps at 120 volts, I could not use this wire because it will overheat.
However, if we raised the voltage to 240, we would only need 1/2 the amperage to move the same amount of total power.
This is important as the change in voltage allows us to move very large amounts of power without having to use excessively large diameter wires. Also, when we want power at a low enough voltage to be safe to use, we can lower the voltage.
All because of the transformer.
We gone to a fairly long explanation about the use of the transformer. However, the transformer does not work with DC.
So, we use alternating current (AC).
Recall the collapsing magnetic field. It generates power in any wire it crosses. But in DC, it only collapses when the power is shut off. You would get just a momentary pulse when the power is shut off.
Alternating current rises, drops to zero then reverses polarity and rises again. The cycle completes 60 times a second in the US. Each time the voltage drops to zero, the magnetic field collapses. With this continuing rising and collapsing of fields, we get a pulse of power inducted in the secondary of the transformer. That is the reason for alternating current.
So, we use alternating current (AC).
Recall the collapsing magnetic field. It generates power in any wire it crosses. But in DC, it only collapses when the power is shut off. You would get just a momentary pulse when the power is shut off.
Alternating current rises, drops to zero then reverses polarity and rises again. The cycle completes 60 times a second in the US. Each time the voltage drops to zero, the magnetic field collapses. With this continuing rising and collapsing of fields, we get a pulse of power inducted in the secondary of the transformer. That is the reason for alternating current.