Transformers
Transformers...... things that go Hmmmmmmm..... Its amazing that a chunck of steel and a few thousand wraps of wire can make such a difference. And when you take that mess of wire and metal and caress it, whisper sweet things into its primary, and love it dearly, it will "put out". ;)
Transformers come in all sorts of sizes, types, and configurations. The most popular transformer for low to medium powered coils is the NST ( Neon Sign Transformer ). The other popular choice is the OBIT or MOT ( Oil Burner Ignition transformer and the Microwave Oven transformer). Voltage ranges for the NSTs can start as low as 6000 volts output and go as high as 15,000 volts out. The power output for NST's normally range from 30 milliamps to 60 milliamps, and in rare instances, if you are lucky, you can find the most coveted 120 milliamp unit.
The good thing about the NST's is that they are "current limited". The inside of the NST has been designed to allow only so much current to flow through the coils. You can basically just plug these puppies into the appropriate wall socket voltage and use them as is. The OBIT is also a current limited transformer.
By now you are going Hmmmmmmm... what about Non Current limited transformers??? Wellll ... these are transformers that can eat fuse boxes for breakfast. The MOT and the ever beloved "Pole Pig" ( distribution transformer , those big ones on the telephone poles) are of the non current limited variety. If you were to plug these into the wall socket, it would blow the fuse, pop the breaker, set fire to the walls, and in general be a bad situation. Okay... so what do we do to keep this from happening???? We limit the current going into the transformer by either going through a huge resistive element ( hot water heater core, electric stove coil, BIG resistors etc.) or else you can use something called an inductor.
An Inductor is basically an iron core with wire wraped around it. With enough wraps of thick enough wire, the current can be limited into the transformer. More on this topic later......
Resistive elements make for a smooth running coil BUT as you continually
add more resistance to allow more current to the transformer, the voltage
going to the transformer continues to drop. This is not good....
Inductive current limiting is a better choice because the voltage stays
pretty much the same as the initial input voltage. By adding more inductors
to the system, it increases the amount of current to the transformer. BUT...
this type of system causes something called "bucking", it causes a surging
of power into the transformer. This bucking can eventually cause problems
and cause the transformer to play dead..... forever. Soooo...
why not use a combo of both types of current limiting? You can, the
resistor smooths out the bucking, the inductors allow for a higher supply
voltage.
10 KVA Distribution Transformer
10 KVA "Pole Pig" in a shortened case with a homemade cap in the way ;)
"Pole Pig"