Simply put, a transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors i.e. coils—that's plural. Because of that magic word... "coils" this post relates to my series on induction here. I'll try not to repeat myself too much. Try to think of this as a sequel. We use transformers to step up or step down the voltage in a circuit, or to convert AC power to DC power. (like wall warts) This is more important than you think. Everything in the world runs on AC power, and that requires DC to AC conversions.) In 1802, Humphry Davy invented the first light bulb and it began an international human obsession with lighting up everything.The transformer was destined for ubiquity.
Most sources agree that the first transformer was an induction coil, invented by Rev. Nicholas Callan in 1836. His was not even the first induction coil with two coils. But he was probably the first experimenter to figure out that the relationship between the primary and secondary winding and the number of turns of wire. (That's directly proportional by the way. The more turns the secondary winding has than the primary coil, the more EMF it produces. But Callan wasn't using his coil as a transformer. He was using it to increase the voltage output from a battery. It was a critical step, but not exactly a modern transformer. It might have been even more important in a way that Callan suggested in an 1857 that joining together the secondary circuits of a number of coils might be able to power an arc light. That got some peoples attention, possibly even Mr. Bláthy.
The first big name in transformers is Ottó Titusz Bláthy. The term "transformer" itself is generally credited to Ottó Bláthy. He was an electrical engineer in Hungary who started his significant work around 1880. He was employed at the Ganz Works in Budapest. they built ships, submarines, cars, planes and even power plants so Bláthy had access to a big shop. He worked with Miksa Déri and Károly Zipernowsky in developing the ZBD model alternating-current transformer in 1885. This was a toroidal-type transformer for use in their incandescent AC powered lighting.
They were overcoming the short comings of DC: heat loss, distance limitations, etc.They developed an array of improvements to make a primitive transformer work better. Zipernowsky had developed the shunts and Déri largely performed the testing. But our man Otto here designed it's iron core. He was their youngest engineer, just 22 years old. The end result was a set of 75 transformers that stepped down 1.35 kV to power over a thousand light bulbs. They had started the project with a Gaulard-Gibbs transformer. More on that tomorrow...