Tuesday, October 19, 2010

DC vs AC Power

DC power, or Direct Current power was the first power to fully electrify a city (Brockton, Massachusetts). Thomas Edison designed it that way, and invested heavily in DC power plant technology. He ran into some problems, however.

Edison wanted to keep the voltage low(100V), to keep people safe. The loss of voltage at these low levels due to the transmission wire's resistance was significant. (Vload=Vsource-IRwire) He sought out some solutions, but they had problems as well. He could reduce the wire resistance by increasing the wire's cross section, but that would really impact the cost of the wires. He could have a large amount of wires transmitting to high demand areas, but again, the cost would soar. In electricity distribution, money is what matters, and Edison was a businessman.

The solution to Edison's problems came from Nikola Tesla,a Croatian scientist Edison brought the the United States to help him. Tesla suggested using AC power, or Alternating Current power. He suggested this because of an invention known as a transformer only works in AC power, and it could jack up the voltage across the wires reducing lost voltage. Then when it got to the load, it could be stepped back down to safe levels by another transformer. It solved all the problems and was cheaper than DC's solutions to the voltage problem.

An example of an AC signal

Edison hated the idea of AC because he had so much invested in DC. He argued that the high voltage transmission lines were far too dangerous, and went to great lengths to get the public on his side (even publicly electrocuting animals, such as elephants). Eventually he was converted, and the AC we use today proliferated.

A lot of our devices we use today run off DC sources (a nintendo DS, for example, gets charged off DC. the plug has a AC/DC converter to change the outlet to DC and a lower voltage. I've even designed an AC/DC converter in a lab before, so it's not that complicated.


  1. Did you know you can run DC current into water without messing up the circuit, but with AC, once it comes into contact you blow the breaker.

  2. Tesla brought so many things to this world :D
    lucky for us he left Croatia, because here he wouldn't succeeded with any of his ideas :D :D

  3. so when do we use each one?? they still do the same thing

  4. I learn something every time I visit your blog.