Ignition Coil ?

[wwholden]

Working on a college project. Anyone know the voltage level at the negative side of a ignition coil for a car?

 

[Paulie B]

Technical question that I don't pretend to know.
If I was to guess I would think the same as the positive or nothing.
Good question sir.

 

[wwholden]

Yeah Im looking for the voltage to the primary coil. The secondary coil should be around 12KVs since it drives the spark plugs. Im not sure if the primary coil is just 12v or if its is stepped up before it enters. I read somewhere that its around 100Vs but dont know how.

 

[Blaaster]

Current flowing in the coil produces a magnetic field in the core and in the air surrounding the core. The current must flow long enough to store enough energy in the field for the spark. Once the current has built up to its full level, the contact breaker opens. Since it has a capacitor connected across it, the primary winding and the capacitor form a tuned circuit, and as the stored energy oscillates between the inductor formed by the coil and the capacitor, the changing magnetic field in the core of the coil induces a much larger voltage in the secondary of the coil. More modern electronic ignition systems operate on exactly the same principle, but some rely on charging the capacitor to around 400 volts rather than charging the inductance of the coil. The timing of the opening of the contacts (or switching of the transistor) must be matched to the position of the piston in the cylinder.

Above screed found in Wiki.

In older vehicles they used a ballast resistor to lower the voltage to the coil which was switched in after the motor was started.

I believe it was to assist starting, allowing the full battery potential to the coil to produce a better spark when cranking, when the battery was under load.

 

[wwholden]

I understand how it works. I just need to know the voltage level on the negative side of the primary coil. Like if I were to hook a oscilloscope to it.