It has been over 100 years since the first DC dynamo’s were built to power electric lights. Shortly after Edison’s direct current debut, Nicola Tesla and George Westinghouse gave the world AC powered motors. And the “War of the Currents” has been going on ever since. Although its been less visible of a ware in recent years.
Some of the crazy publicity stunts conducted during the “War of the Currents” are legendary. Edison made the claim that the only thing AC power was good for was electrocution of convicted criminals.
AC power won out, of course. DC power cannot overcome significant losses due to resistance drop over over distance. And in order for electricity to serve more people, its all about the delivery system.
So today, no one gives a second thought to the power that comes from our outlets. 120 volts alternating at 60 cycles a second. 220 volts 50 hertz in Europe and some parts of Asia. But its all AC.
Ironically, the DC motor is still around. We still make millions of DC motors, seemingly a contradiction. DC motors with brush commutation are everywhere. The series wound motor operates on AC as well as DC so its versatility guarantees its survival. Vacuum cleaners, sewing machines, many food grade mixers, woodworking tools, all use the good old brush motor.
Most battery powered toys, toothbrushes and many small power tools use the classic dc brush motor. Battery power makes dc the exclusive choice for motor technology. Batteries are, of course, dc. So anything portable has to have a power source, which is still a battery, regardless of the particular battery technology. In a car its the same. Starter motors, windshield wiper, power windows, all dc.
Over the last few decades AC motor control technology has made huge performance strides taking the place of DC motors in a lot of applications. The controls cost has dropped dramatically to the point that AC variable speed solutions have displaced most DC solutions.
But what’s the hidden assumption that keeps DC solutions alive? DC is very efficient.
So who really won?
Well maybe everyone. AC power transmission is unquestionably more efficient for delivering power. And AC motors are less expensive for air handling and constant speed operation. But DC motors are more efficient at the point of use. So we have both.
So the real lesson is that one solution doesn’t work for everything. Not really a surprise, I suppose, but very instructive. We need to keep in mind that when it comes to energy, there is usually not one solution to the problem.