Re: Condener Keeps burning up?
The conventional (Kettering) spark ignition system in automotive applications uses a coil which performs the dual functions of energy storage and voltage step up. It is typically about a 100:1 turns ratio. DC power is applied, producing a current of about 5 Amps through the 8 mH primary inductance, storing about 100 mJoule of energy. When the current is interrupted the points opening, (The points are a set of contacts mechanically driven by a multilobed cam synchronized to the engine), the voltage rises (L di/dt) to around 300-400 volts, which is stepped up to around 30-40 kV (open circuit) in the secondary. <br />The di/dt is limited to around 50 amps/millisecond by a capacitor (called a condensor, for historical reasons) across the set of points. If this capacitor isn't there, the rapid voltage rise as the points open causes an arc across the points, which absorbs some of the energy, and more important greatly reduces the di/dt, reducing the output voltage. (The points contacts also typically melt). Typical capacitances are around a microfarad ( i.e. it stores about the same amount of energy as the coil inductance does).<br />In typical use the coil is connected in series with a ballast resistor of a few ohms to reduce the voltage, which in turn reduces the current through the coil so it doesn't burn up. The ballast resistor isn't used during cranking (when the battery voltage is usually reduced to around 6-8 volts). A typical DC coil resistance would be around an ohm, and at 12 Volts, the DC current would be 12Amps, dissipating more than a 100 watts.<br />Source: Delco Remy......GM<br /><br />The condensor/capacitor does one and only one thing in an electrical circuit, it stores energy [electricity], this energy is released by electrical components, or a mechanical device [points]. Points are nothing more than a mechanical "switch" to release energy to the spark plugs. Regardless of its use, if the input voltage and amperage for which it was designed is exceeded it will fail. It cannot, will not, never will control electrical spikes in a circuit, [static]. A ballast resistor is not used on a boat for two reasons, they get hot, and with an extreme failure the potting material breaks away and there is a red hot wire, and possibly a spark, therefore the resistant wire is used in the circuit. People get overly concerned about voltage....amperage is what will kill you.<br />When the voltage regulator failed not only did the voltage go up to 16.7 volts the amperage also went up, the condensor failed in the circuit.
