Yesterday we learned that a transformer is really simple: two coils of wire in close proximity to each other.  The power you put in one end is transfered magnetically to the other end with great efficiency and isolation because the wires never really touch each other.  The key to a transformer working is that it must have AC and will not work with DC.

In your high-end audio system you have one of these transformers connecting the power in the wall with every piece of equipment’s internal power supply and that chain is critical to the way your system sounds and performs.  We’re on the trail of learning how it works so that we can then move on to understand the importance of power.

In our story Thomas Edison could not use a transformer in his system – something he desperately needed to do – because his voltage didn’t move back and fourth.  Our friend Nikola Tesla had already figured this out and was waiting to implement these transformers in his system but need to invent a couple of key elements first.  But I digress from the story because we first need to understand why we’re even talking about transformers and AC in the first place.

Remember the problem Edison had?  His lights were at different brightness levels depending on how long the wire connecting them was and how many lights were sharing the wire.  To fix this he would need to send more electricity than all the lights combined needed down a central wire and then figure out how to tap into this higher voltage for each house that wanted a light.  His DC power scheme would not allow this to happen – because the lights would then get way too much electricity and blow up.  There was no way to selectively reduce the DC to the proper level for each home.

But now imagine instead of DC power traveling at high voltage down a central wire we use, instead, AC voltage.  Remembering that AC voltage is the same as DC voltage, only the plus and minus are alternating back and fourth 60 times a second, we can now connect a transformer to the main wire and have that transformer work – something that could not happen with DC.

So let’s now picture a main power cable running down the a busy street in New York.  Along the street there are 100 homes we wish to provide the same amount of power to.  In Edison’s DC system, every home that connected a light bulb caused the main power wire to drop in voltage and if all 100 turned their lights on at the same time, the lights all got dimmer and dimmer by 100.  But if we replace the DC voltage with AC and make the AC voltage 100 times higher than any home needs we solve the problem IF we can get 100th of the power to each home.

Our transformers now come into play.  Each of the 100 homes is outfitted with a transformer that magnetically couples the home to the main line and power comes into the home.  How do we get only 100th of the power?  Simple!  Remember that a transformer is two coils of wire?  The ratio of the two coils (the number of turns that make up the coil) determines the voltage.  So if the input coil has 1000 turns and the output coil has 1000 turns, then whatever you put into the transformer you get out 1:1.  But if the input has 1000 turns and the output coil has but only 10 turns, the voltage comes out 100 times less than what you put in.  By simply changing what we refer to as the turns ratio between the input coil and the output coil we can get more or less voltage at will.

Bingo.  With the AC system and transformers transforming the power from high to low, you can connect as many homes as you wish and all homes get the same level of brightness for their lights.  Problem solved.

So where does Tesla come in?  Well before Tesla we couldn’t do two things with AC power very well – generate it and use it to make a motor.

Tomorrow, Tesla puts it all together.

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