Voltage Selection and Application
Country: United States
Date: May 2006
I am not a student but am learning about
electricity. I am trying to figure out why we use 110 volts for
ousehold application vice 12 volts, 3 volts, and so on. Why can
I use 18 volts in my laptop but not for the microwave?
There are many detailed "reasons", but the one that is most
fundamental is the need to deliver enough power to the device.
Power = Energy per unit Time. And Energy is the Voltage times the
Current. Household appliances just require too much energy to
operate at low voltage. Laptops, flashlights, etc. require very
little energy to operate. So they can be powered by batteries.
Higher voltage is chosen for situations where greater amounts of
power are transmitted. Power is volts times amps. If you wanted to
transfer a large amount of power with low voltage, it would require
larger amperage. The size of the conductor required to carry
electrical current increases with the numbers of amps transferred,
but is not affected significantly by the voltage. Higher voltage
requires a smaller conductor for any given situation.
If you have seen the size of the cable used to power the starter on
your car... it is quite large. It runs on 12 volts, but requires
significant power... therefore it demands a large number of amps and
a large power cable.
High tension power transmission wires carry a large amount of power
by increasing the voltage to the range of 33,000 volts and keeping
the number of amps and therefore the size of the conductor down.
In the case of your computer, little power is required, therefore
even at a lower voltage (perhaps 3 to 9 volts), smaller, lightweight
conductors can be used.
The 110 (which is likely 117) volts used in your house is a compromise.
While I am not certain of the original cause for widespread use of
110 volts in household wiring, (I could speculate early lightbulbs
were the probable factors), I do know that for modern electronics
the need for voltage is much lower. Most of your home electronics
actually work off of either 5 or 15 volts, and include internal
powersupplies to produce this from the 110 volts supplied by an
outlet. Televisions and (CRT) computer moniters are a notable
exception, as thier design actually requires much higher voltages,
which are again produced by an internal powersupply. Microwaves fit
into this later catergory of devices which require rather high
voltages to work properly.
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Update: June 2012