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On Sun, 2002-06-30 at 21:42, Jim Adney wrote: > On 30 Jun 2002, at 23:42, Dave Hall wrote: > > > Could it be something to do with back emf being in the opposite direction to the > > applied emf? > > I think it's just a myth. The capacitance is there to prevent the voltage at the > points from rising faster than the points open, so that a spark has no chance > to jump across. While it is true that the coil and capacitor form a resonant > circuit, the actual resonant frequency doesn't really matter, and the direction > that the current flows is the same, at least immediately after the points open, > regardless of the frequency. > Ahhhhh, pardon, but this is not a myth. The condenser/capacitor is there for exactly suppressing the reverse EMF. We have to fight this problem all the time in industrial controls. When the electro magnetic field in the coil collapses, there is not only an energy spike generated in the secondary of the coil, but it is also generated in the primary winding. Therefore, we need a condenser to suppress this spike. -- Russ Wolfe '66 FB MT (It drove) '71 FB AT '65 Bug (not running) russw@classicvw.org http://www.classicvw.org ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/