Voltage Conversion for Scientific Dummies

Transformer coils 120V to 12 V

In case you haven't noticed it by now, we here at the Antisocial Network are mighty peeved by all the freelancers who know nothing about a topic and yet run out and write about it anyway. One of the more irritating types of content written by these bozos is answering the wrong question, probably because the freelancer had no idea that there was a different interpretation. One such internet post, which we found at eHow.com (no surprise there) came from a guy named Kurt Schanaman, We found Kurt trying to explain "How to Convert 120V to 12V" at HomeSteady.com.

Schanaman's opening salvo in his alleged how-to? This:

"Household current in North America is distributed through the power system as 120 volts AC (alternating current). AC voltage is distributed for the purpose of operating larger appliances, such as ovens, refrigerators, stoves, heaters and television sets. Some appliances require this 120 volt AC power to be converted to 12 volts DC (Direct Current)."

While that's more or less correct, there's a big ol' problem in Kurt's intro; which is that no one asked how to convert 120V AC to 12V DC. In other words, some high-school physics student (or perhaps a trade-school student) was asking about voltage conversions for class. If Schanaman had ever taken a class in physics or electrical work, he might have been familiar with the a step-down transformer. Heck, he even mentioned "step-down" in his warnings section: "Conversion from 120 volts to 12 volts is a 'step-down' process that requires a power supply for conversion," Duh. The problem with Kurt's answer is pretty simple: what he tells people to do to convert between 120- and 12-volt current is

"[Buy] a power supply capable of supplying 12 volts..."

Dumbass: that's not what the OQ wanted. What the OQ wanted was the rules for designing a step-down transformer. What Schanaman should have written was instructions along the line of

1. Make a transformer with two sets of loops, one at right angles to the other.
2. The 120-volt input current will run through the outer set of loops. 
3. The 12-volt output current will run through the inner set of loops.
4. The number of turns on the two coils are given by the relationship Vo/Vi = No/Ni, where Vo = input voltage, Vi = input voltage, No = number of turns on the output coil, Vi - number of turns on the input coil

Based on that formula, the number of turns on the output coil should be 1/10th of the number of turns on the input coil.
That's what Schanaman should have said, but he didn't. Instead, his "how-to" consisted of telling his readers to go buy a power converter. If there is still anyone wondering why we've named Kurt the Dumbass of the Day, speak now or forever hold your peace.

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