Transformers

Transformers/Ignition coils

Transformers step-up (increase), step-down (decrease), or pass-through (same level) AC voltage or pulsed DC voltage. A basic power rule applies to transformers; power-in equals power-out. The unit of measure for Power is the Watt. 1 Watt = 1 Volt x 1 Amp.

A transformer has three main components:

• An iron core - The iron core is wrapped with two separate coils of wire. The job of the iron core is to strengthen the magnetic fields of the transformer.
• Primary winding - The input side of the transformer. This coil of wire is tightly wrapped around the iron core of the transformer.
• Secondary winding - The output side of the transformer. This coil of wire is tightly wrapped around the primary winding of the transformer.

There are three basic types of transformers: 

• Step-up transformer - The primary coil winding has less windings of wire than the secondary coil does. A 1:2 step-up transformer has half as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 24 V AC will be induced into the secondary winding, however, the output amperage will be cut in half to 6 amps.

• Step-down Transformer. - The primary coil winding has more windings of wire than the secondary coil does. A 2:1 step-down transformer has twice as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 6 V AC will be induced into the secondary winding, however, the output amperage will be doubled to 24 amps.

• Pass-through transformer - In a 1:1 transformer, the primary coil winding has just as many windings of wire as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 12 V AC will be induced into the secondary winding, and the output amperage will be 12 amps. The advantage of a 1:1 transformer is that there is not a direct electrical connection between the two coils. If one side of the circuit gets short circuited, the other side will remain isolated.

Examples of transformer use on automobiles:

• Air-Bag Systems - Air-bag systems need a backup power supply to use in an accident in which total battery power loss is experienced. The air-bag computer typically has step-up transformers inside of it. These transformers are used to charge large capacitors inside the computer. The capacitors are charges to 24 volts or 36 volts depending upon system design. The capacitors will function like a backup battery when necessary.

• High Intensity Discharge (HID) Headlights - There are no conventional light bulbs on this type of system.  The HID system emits light which has a color that is closer to true sunlight than conventional light bulbs.The HID system is made up of a ballast transformer and an arc tube. The headlamp ballast receives the headlamp low beam supply voltage, which would normally be used to directly supply the low beam headlamp. The HID headlamp operation consist of 3 states:

• Startup or Strike State - When the headlamp switch is turn to the ON position the ballast may draw up to 20 amps to being the strike state. The ballast will provide multiple high voltage pulses to the arc tube in order to start the bulb. The voltage provided by the ballast during the startup state ranges from -600 volts to +600 volts.

• Run State - Once an arc is established, the ballast will provide a higher than steady state voltage to the arc tube in order to keep the bulb illuminated. This is called the run up state, on a cold bulb this state could last as long as 41 seconds. On a hot bulb the run up state may last as long as 15 seconds.

• Steady state - Steady state operation begins when the bulb reaches the 35 watt power level. The ballast provides the bulb with a minimum of 55 volts during steady state operation.

• Ignition coils - An ignition coil is an example of a step-up transformer, the primary coil input voltage is 12-15 V and the secondary output voltage is 20-60 kV. This means for every primary coil winding there are at least 2000 secondary windings. This also means that the output amperage will be at least 2000 times smaller than the input amperage. Secondary ignition voltage is high voltage, but amperage is low.

The following are commonly used ignition coils:

• Coil-per-plug ignition system. This system uses a short spark plug wire to connect the coil to the spark plug. The coil is typically mounted on the cam cover or valve cover. The coil has a built in ignition module to trigger the coil. The ignition module is controlled by a computer, this allows the spark timing to be adjusted per cylinder firing event.

• Coil-over-plug ignition system. With improved combustion chamber designs, the spark plug is centrally located in between the intake and exhaust valves.  Each spark plug has its own ignition coil; however, because of the centrally located spark plug, there is no spark plug wire. The spark plug boot is connected to the coil and the spark plug.   Having a coil per spark plug allows ignition timing and dwell adjustments to be made per cylinder firing event.  This design is in response to tighter emission regulations for NOx.