Lets look at a few things to set up how this works:
We can make a magnet by wrapping an insulated (varnish covered copper wire) around a bar of iron, and applying DC (direct current) to the wire, the bar of iron becomes magnetized.
We can generate a current pulse, in a coil of copper wire by moving a magnet across a coil of wire, the magnet being moved past the coil of wire induces current in the coil of wire, (if we just sit the magnet next to the coil of wire nothing happens), the movement of the magnet and the collapsing magnetic field is what generates the current in the coil of wire.
These are the basic principles of motors, generators, and transformers...
Now lets look at a simple generator, using a magnet and a coil of wire, we fix a bar magnet on a spindle were we can turn the magnet past the coil of wire, the magnet has a north and south pole, we will measure the polarity of the coil of wire we are generating current into with our magnet, when we spin the magnet and the north end of the magnet passes the coil we generate a positive current into the coil of wire (as the magnet moves the voltage climbs form zero and peaks when the north end of the magnet is closest to the wire, and falls back towards zero volts as the north end of the magnet moves further away from the coil of wire, this creates the positive half of an AC (alternating current) sine wave, then as the magnet turns the south pole of the magnet passes the coil of wire the current polarity of the coil is negative as the magnet moves by so as the magnet spins the output of the coil generates an AC sine wave, if the magnet turns a complete revolution 60 times in one second the output of the coil is 60 Hz, the coil peaked positive then peaked negative (one sine wave 60 times in that second.
Now lets look at a transformer two coils of wire in close proximity to each other, one the primary coil, and the other the secondary coil (some iron to help with magnetic properties), a transformer will not work on DC, we can power the primary coil with a battery and it will make a magnet out of the primary coil, but just like our magnet sitting by the coil of wire in the above example we induce no current in the secondary coil of wire. Remember we had to swing the magnet past the coil of wire to generate current in the coil of wire, now if we hook a battery to the primary coil of our transformer and switched the polarity of the coils wire on that battery back and forth, we would generate a magnet in the primary coil switching polarity of this magnet as we switched wires of the coil on the battery, if we could switch these wires on the battery 60 times in one second we would be making our primary coil a magnet switching from north to south just like we did with the spinning magnet in the example above, and the magnetism from the primary coil inducing an alternating current in the transformers secondary coil.
Normally the transformer is not fed with Direct current from a battery it is fed with alternating current.
We can step up, or step down voltage with a transformer, what's in is what's out, actually that is (watts in = watts out), the number of turns of wire in each of the transformers coils or windings determines voltage, the size of the wires of these coils in our transformers determine the current the coils can handle.
Lets look to winding our transformer to step up the voltage, for every one turn of wire in our primary coil we will wind ten turns of wire in our secondary coil.
So if we put 12 AC volts into the primary winding or coil we will induce 120 AC volts into the secondary coil, (because of the turns ration of our coils).
Watts in = watts out
If we have a one amp primary current, at 12 volts
(Using ohms law)
12volts X 1 amp = 12 watts (primary)
So watts out will also =12 watts on the secondary coil.
We already know because of the turn ration we have 120 volts so the secondary so we can figure the secondary amperage using ohms law.
12 watts / 120 volts = 0.1 amps (or 100 milliamps)
Notice when we step up voltage in the transformer we drop the amperage, but the wattage of both coils is the same.
Now lets use this same transformer and wire it the opposite as a step down transformer with the 10 turn winding as the primary coil, and the one turn winding as the secondary coil, this time we will supply the primary coil with 120 volts AC, to get 12 volts AC out the secondary, again we will use a one amp primary current,
120 V X 1A = 120 Watts (primary)
So secondary is also 120 watts at 12 volts
So the secondary amperage is
120W / 12V = 10 amps (secondary current)
Notice stepping down the voltage we have a higher current.
Now I said a transformer will not work on DC, we seen above sitting a magnet next to a coil did not induce current in the coil, or hooking a battery to the transformers primary did not induce current in the secondary, so a transformer will not work on DC.
But we can trick the transformer, with a DC current.
If we power a coil of wire with a battery we build a magnetic field from the coil of wire if we remove the battery this magnetic field collapses, to a secondary winding in a transformer this magnetic field of a building and collapsing of a magnetic field can appear to the secondary coil as a changing magnetic field (or a magnet swinging by it) it will induce a current in the secondary winding, if we keep doing this fast enough, but unless we change the polarity of our battery we do not change the magnet so the polarity of the magnet of the primary coil will be the same each pulse, so unless we change polarity of the battery we would not get an AC sine wave from the secondary of our transformer, it would be a series of DC pulses of current all either positive or negative depending on our battery polarity or primary magnetism (all north pulses).
Coil (high voltage transformer) works to make the spark for the spark plugs, the coils primary is fed 12 volts DC from the battery while the ignition points are closed, this builds a magnetic field in the primary winding of the transformer (at this point nothing is being transformed to the secondary winding) but when the ignition points open the primary coil in the cars high voltage transformer (car coil) induces a voltage in the secondary of the transformer (this many turn winding steps up the 12 volts to thousands of volts at a very low current) this high voltage fed to the spark plug jumps the gap across the spark plug to ground and fires the gas air mix in the combustion chamber driving the piston down turning your engine.
The primary coil which built a magnetic field when it collapses can generate a fast spike voltage that can go back across the opening set of points before the gap gets fully back open this can create an arc current across the points burning them as they open, to suck up this high voltage spike (to protect our points and make them last longer we use a snubber, in this case a capacitor (condenser) we wire this condenser across the set op points in our distributor to suck up this 400 volt spike to keep it from burning our ignition points (without this capacitor or condenser our points may only last a few days of driving.
Well I would like to go on and describe diodes and capacitors so we could get into a discussion of building a power supply for our silver cells but that will have to wait for another day.
