Voltage Selection and Application ```Name: Trevon Status: Other Grade: Other Location: OK Country: United States Date: May 2006 ``` Question: 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? Replies: 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. Vince Calder Trevon - 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. Larry Krengel Trevon, 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. Ryan Belscamper Click here to return to the Engineering Archives

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