Opinions Please - True Or False
Discussion
Is the below correct or incorrect - I will not reply to any posts but will read through the replies with great interest -
1) The capacitor plays a very important part in the points and coil ignition system
2) When the contact points open the capacitor allows the several amps of current flowing in the coil to drop to zero in a rapid but controlled manner
3) This change in current induces a peak of 100 to 200 volts on the coil primary which is stepped up to 7 to 14 kilovolts at the secondary – enough to cause a spark at the plugs under operating conditions from idle to full power
4) The capacitor value is a compromise. If it’s too small more arcing takes place at the points reducing their life. If it’s too large the current changes too slowly and the peak voltage is reduced
5)The ideal value of the capacitor is in the range 0.2 to 0.4 microfarads but is not unduly critical
6) Lucas originally chose 0.4 microfarads for the Austin 7, but later replacements may be 0.2 microfarads
7) With no capacitor fitted not only does severe arcing take place at the points but more importantly even with new points the primary and secondary voltages are severely reduced
8) With no capacitor fitted tests showed no more than 7 kilovolts even with the coil output open circuit
SUMMARY
With no capacitor fitted the result is that the engine may start with difficulty and idle but when the plugs demand greater firing voltage as the throttle is opened and cylinder pressure increases a bad misfire will ensue. Continued operation allows the points to burn up and go high resistance, causing a further reduction in output voltage and a worsening misfire
1) The capacitor plays a very important part in the points and coil ignition system
2) When the contact points open the capacitor allows the several amps of current flowing in the coil to drop to zero in a rapid but controlled manner
3) This change in current induces a peak of 100 to 200 volts on the coil primary which is stepped up to 7 to 14 kilovolts at the secondary – enough to cause a spark at the plugs under operating conditions from idle to full power
4) The capacitor value is a compromise. If it’s too small more arcing takes place at the points reducing their life. If it’s too large the current changes too slowly and the peak voltage is reduced
5)The ideal value of the capacitor is in the range 0.2 to 0.4 microfarads but is not unduly critical
6) Lucas originally chose 0.4 microfarads for the Austin 7, but later replacements may be 0.2 microfarads
7) With no capacitor fitted not only does severe arcing take place at the points but more importantly even with new points the primary and secondary voltages are severely reduced
8) With no capacitor fitted tests showed no more than 7 kilovolts even with the coil output open circuit
SUMMARY
With no capacitor fitted the result is that the engine may start with difficulty and idle but when the plugs demand greater firing voltage as the throttle is opened and cylinder pressure increases a bad misfire will ensue. Continued operation allows the points to burn up and go high resistance, causing a further reduction in output voltage and a worsening misfire
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