if car batteries are dc sources then how do they work with the ignition coil?

Question

well all know that inductor transformers don't work with dc currents and the battery is a dc power source and the ignition coil is an inductor transformer (just to start the engin it has to step up the voltage) so how does it convert the current from dc to ac to be compatiable with the ignition coil

Answer 1

An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system which transforms a storage battery's 12 volts to the thousands of volts needed to spark the spark plugs.

This specific form of the autotransformer, together with the contact breaker, converts low voltage from a battery into the high voltage required by spark plugs in an internal combustion engine.

source http://en.wikipedia.org/wiki/Ignition_coil

If you connect a battery to a transformer through a switch, and were to open the switch, the transformer tries to keep the current flowing, and generates a large momentary voltage.

That's what the ignition coil does, it connects the battery to the spark plug through a transformer, and contact breaker, the car system opens and closes the contacts to create the high voltage spark required by the spark plug.

Answer 2

Actually the background which drives the ignition coil is a collapsing magnetic field within the coil.
So the trick is to have some current running through it (in the primary coil), and switch it off with an interruptor of some sort.
The magnetic field collapses and builds up a high voltage impulse in the secondary coil, which is connected to the spark-plugs.

It does not matter much wether this current for the magnetic field's buildup came from DC or AC. but in case it was AC it would have a limited time to build up before the voltage changes its polarity, which is ... the idea behind AC.

So in this case DC ist first choice, cause for having a proper timing in the engine its necessary to have the interruptor decide when its time to let the field collapse.
Using AC lets say 50Hz would mean it would collapse 100 times a second .. this is useless for a strong field to build up.

The only device in a car using AC is the generator, cause generators usually produce AC which is then converted into DC with a regulator.

the coil itself has two magnetically combined spools. The primary with just a few windings is designed for having a high current running through it. the secondary has alot more windings, thus creating a low current, but a high voltage.
its definedly not designed to operate as a transformer in common sense, its designed to give a pulse on the secondary coil after an intentional field-collapse in its core.

Answer 3

A transformer works with AC current only. AC current makes the magnetic field in the primary coil expand and collapse. The secondary coil picks it up and produces AC current at a different voltage/current ratio, depending on the copper wire windings. When you induce direct current from a battery. All it does is create a flow through the primary coil with a steady magnetic field. The steady magnetic field does not create any current in the secondary coil. Hope this helps. Kind of difficult to explain without pictures.

Answer 4

Each ignition coil has two windings, primary and secondary. The battery is connected to the primary winding thru an ignition control module (can be part of the ECM). The ignition control module turns the power from the battery ON and OFF. When the switch is closed or ON, the current from the battery flows thru the primary winding resulting in a large magnetic field. When the module switches OFF, the primary current stops flowing, the magnetic field collapses and induces high voltage (low amperage) into the secondary windings. This high voltage jumps the gap(s) in the spark plug creating the spark.

Answer 5

You do not need AC to generate large voltages in a coil,
inductance is analogous to electrical momentum. A
coil resists any change in current because of its tendency
to build up or tear down a magnetic field.

To prove this all you need to do it to attach a battery and
current limiting resistor in series to set up a current
in the coil and then separate the wires and interrupt it
... you will get an arc because of the huge electrical
inducation that you generate by trying to change the
current flow.

- You can hurt or kill yourself here ... so do not do
it unless you know what you are doing. -

The magnetic field collapses and tends
to keep the current flowing, but there is no circuit so
the voltage gets extremely high, and can arc like
lightning between wires or across a switch - or across
a spark plug gap.

Answer 6

actually it is not necessary ac current. The coil is part of a switched LC (inductor capacitor) circuit, by switching this circuit, the dc voltage is boosted, so from a 12V source it is possible to have 1000's V to ignite a spark. The same components: inductor, capacitor, switch; in a different configuration serve as a step-down dc source (the one inside your computer is basically it, but uses transistors as switches). Both types of configurations are called conmuted sources, and they do the equivalent work of ac tranformers in dc circuits.

Answer 7

The induced voltage in a conductor is proportional to how fast the magnetic field around it changes.
AC causes a relatively slow undulating change.
Interrupted DC drops to zero almost instantly. (This is called a very fast skew rate.)
Energy stored in the magnetic field induces the high-voltage in the secondary coil as the magnetic field collapses.
I think the condenser (capacitor) is only there to absorb the charge from the counter-EMF (Electro Motive Force or counter-voltage) induced in the primary circuit. Otherwise this counter-EMF would cause arcing across the points and they would burn out quickly. (The points are the two contacts of the switch which controls the primary circuit.) (Points have been replaced by solid state switches in most modern cars.)
btw generators generate DC, alternators produce AC.

Answer 8

A ruhmkorff coil is used where its idea is based on a coil wrapped with 1000s turns of a wire (works as an induction coil) which is responsible for inducing a spark of high voltage this coil is connected to simple automatic system (depends on magnetism of the coil to a slide which make the coil's circuit close and open) also a capacitor is used hope u got it

Answer 9

The alternator generates AC current, hence the name. DC current comes from using diodes.

Answer 10

there is a AC/DC converter somewhere in there, just like there is one in any battery-powered device with an electric motor (toy cars, cell phones with vibrators, CD players, etc.)