idiots guide to dc and ac
09-18-2006, 09:15 AM
#2
DC flows in one direction at all times - from negative to positive. AC alternates its direction regularly many times per second (called "frequency"). In North America the household AC current frequency is 60Hz (Hertz or cycles per second).
Some devices don't care which direction the current is flowing. For example, a light bulb contains a simple filament that heats up when current flows. It doesn't matter which way the current is flowing so the light bulb can run directly from AC current. Many electronic devices require current flowing always in one direction (DC). So they have those power "bricks" that convert the AC wall current into direct current. Larger electronic devices have the power conversion built in (computers, home stereos, etc.). The device that converts from AC to DC is called a rectifier.
We use AC for power distribution mainly for cost reasons. Power loss through transmission lines due to resistance increases with higher current. So providing more and more power to neighborhoods would require much larger (and more expensive) cables to handle more current. However, increasing voltage reduces the current needed for the same amount of power. AC can be easily changed to different voltage levels using a device called a transformer that does it with minimal loss of energy. That way the power companies can step up the voltage to hundreds of thousands of volts for long distance transmission then step it down to about 22,000 volts in neighborhoods and again to 240 volts where it comes into your house. Using the very high voltage means that a much smaller amount of current is needed so the wire can be smaller (and cheaper).
Your car produces alternating current when running (that's why it's called an alternator) but it has a rectifier built in that converts the output to direct current to be stored in the battery and to power the car's electrical components. Again, this is due to cost - DC is generally easier to work with and the transmission distance of several feet is not the problem that cross-country transmission is.
Some devices don't care which direction the current is flowing. For example, a light bulb contains a simple filament that heats up when current flows. It doesn't matter which way the current is flowing so the light bulb can run directly from AC current. Many electronic devices require current flowing always in one direction (DC). So they have those power "bricks" that convert the AC wall current into direct current. Larger electronic devices have the power conversion built in (computers, home stereos, etc.). The device that converts from AC to DC is called a rectifier.
We use AC for power distribution mainly for cost reasons. Power loss through transmission lines due to resistance increases with higher current. So providing more and more power to neighborhoods would require much larger (and more expensive) cables to handle more current. However, increasing voltage reduces the current needed for the same amount of power. AC can be easily changed to different voltage levels using a device called a transformer that does it with minimal loss of energy. That way the power companies can step up the voltage to hundreds of thousands of volts for long distance transmission then step it down to about 22,000 volts in neighborhoods and again to 240 volts where it comes into your house. Using the very high voltage means that a much smaller amount of current is needed so the wire can be smaller (and cheaper).
Your car produces alternating current when running (that's why it's called an alternator) but it has a rectifier built in that converts the output to direct current to be stored in the battery and to power the car's electrical components. Again, this is due to cost - DC is generally easier to work with and the transmission distance of several feet is not the problem that cross-country transmission is.
09-19-2006, 02:58 AM
#3
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Originally Posted by WhiteBird00
DC flows in one direction at all times - from negative to positive. AC alternates its direction regularly many times per second (called "frequency"). In North America the household AC current frequency is 60Hz (Hertz or cycles per second).
Some devices don't care which direction the current is flowing. For example, a light bulb contains a simple filament that heats up when current flows. It doesn't matter which way the current is flowing so the light bulb can run directly from AC current. Many electronic devices require current flowing always in one direction (DC). So they have those power "bricks" that convert the AC wall current into direct current. Larger electronic devices have the power conversion built in (computers, home stereos, etc.). The device that converts from AC to DC is called a rectifier.
We use AC for power distribution mainly for cost reasons. Power loss through transmission lines due to resistance increases with higher current. So providing more and more power to neighborhoods would require much larger (and more expensive) cables to handle more current. However, increasing voltage reduces the current needed for the same amount of power. AC can be easily changed to different voltage levels using a device called a transformer that does it with minimal loss of energy. That way the power companies can step up the voltage to hundreds of thousands of volts for long distance transmission then step it down to about 22,000 volts in neighborhoods and again to 240 volts where it comes into your house. Using the very high voltage means that a much smaller amount of current is needed so the wire can be smaller (and cheaper).
Your car produces alternating current when running (that's why it's called an alternator) but it has a rectifier built in that converts the output to direct current to be stored in the battery and to power the car's electrical components. Again, this is due to cost - DC is generally easier to work with and the transmission distance of several feet is not the problem that cross-country transmission is.
Some devices don't care which direction the current is flowing. For example, a light bulb contains a simple filament that heats up when current flows. It doesn't matter which way the current is flowing so the light bulb can run directly from AC current. Many electronic devices require current flowing always in one direction (DC). So they have those power "bricks" that convert the AC wall current into direct current. Larger electronic devices have the power conversion built in (computers, home stereos, etc.). The device that converts from AC to DC is called a rectifier.
We use AC for power distribution mainly for cost reasons. Power loss through transmission lines due to resistance increases with higher current. So providing more and more power to neighborhoods would require much larger (and more expensive) cables to handle more current. However, increasing voltage reduces the current needed for the same amount of power. AC can be easily changed to different voltage levels using a device called a transformer that does it with minimal loss of energy. That way the power companies can step up the voltage to hundreds of thousands of volts for long distance transmission then step it down to about 22,000 volts in neighborhoods and again to 240 volts where it comes into your house. Using the very high voltage means that a much smaller amount of current is needed so the wire can be smaller (and cheaper).
Your car produces alternating current when running (that's why it's called an alternator) but it has a rectifier built in that converts the output to direct current to be stored in the battery and to power the car's electrical components. Again, this is due to cost - DC is generally easier to work with and the transmission distance of several feet is not the problem that cross-country transmission is.
Except there's no such thing as "AC current" or "DC current" ..... sorry...had too 
