Re: Does the coil in the primary coil of a transformer loses some current when

Hi Howard,

That's a good question.

The simple answer is yes. In an ideal transformer, meaning one that does not exhibit any losses, the current in the primary coil is exactly equal to the current in the secondary coil multiplied by the turns ratio of secondary to primary. Let's say that you have a transformer with 100 primary coil turns and 10 secondary coil turns. The turns ratio of secondary to primary is 0.1, so if the secondary coil draws 1 Ampere, the primary will draw only 0.1 Amperes. The voltage goes the other way, if 10 volts appears on the secondary, 100 volts must be applied on the primary.

Saying at another way, voltage on the secondary is multiplied by the turns ratio, whereas current is divided by the turns ratio. If the voltage goes up, the current goes down by exactly the same factor. This is important. It is essentially a by product of conservation of energy. In this case, power is conserved. Power is the product of voltage times current. Transformers are passive devices, so they cannot create power. They can only transform it from high voltage/low current to low voltage/high current, or vice-versa. The power appearing at the secondary must come from somewhere. If the secondary circuit uses power, it must come from the primary. If secondary current increases, so does the primary current.

Of course, we don't live in a perfect world, so real transformers are not 100% efficient. Real transformers lose power due to resistance of the coils, core saturation, eddy currents and other factors. Power transformers, like the ones used by power utilities are extremely efficient, possibly exceeding 95%. This means that only 5% of the power supplied to the primary is lost and not transferred to the secondary. The loss mostly results as heat. For this reason, large power transformers are often encased in circulating oil to keep them cool.

A number of experimenters have tried to cheat conservation of energy by hooking up transformers in a variety of circuits. They hoped to achieve "free energy", but this simply does not work. Transformers are passive, they can only give back what you give them, nothing more. You can learn more about transformers in any introductory electrical engineering text. You can also read about them in the Encyclopedia.

I hope that answers your question. If not, drop me a line at madhu@madhu.com.