Re: Re: Re: 12V Conversion

Posted by RAB on March 13, 2004 at 23:55:31 from (195.93.34.11):

In Reply to: Re: Re: 12V Conversion posted by RL on March 13, 2004 at 19:51:56:

RL,
A coil is a coil, but not all coils are the same. Confused?
The rate of current rise is important as the coil 'turns' oppose this increase. It's called inductance. The current through an inductor rises exponentially with time - faster at first, then more slowly
Supposed 'sports coils' have a lower resistance and inductance, allowing more current and therefore more spark energy, but points have to handle this and burn up faster than standard coils. They are only better at high revs.
A 12 coil is 12 volt unit or a lower voltage unit with a resistor in series to reduce the maximum current to a safe value. The resistance will limit the non-running current through the coil (if the points are closed when the engine stops).
A ballast resistor coil is a lower voltage coil (6 or 8 volt) with an external resistor in circuit at all times, except on cranking with starter motor. This allows more current to flow for a stronger spark energy at cranking voltage.
Points and condenser operate at 12 volts while closed and open, but have to cope with about 300 volts when the points are just opening due to the inductive voltage generated by the coil as the current in the coil is turned off (and the magnetic field collapses). No change for either voltage, generally. Old ones for 6 volt systems were probably better than those for newer 12 volt systems as they had to pass more current for equivalent spark energy!
One of the most important factors of the Ketteringham circuit is probably the dwell angle - the time the points are closed, allowing the current to build up in the coil, but for a 4 cylinder tractor running at 1500rpm it is less important than, say, an 8 pot motor running at 5500rpm as the theoretical spark enegy is proportional to the current flowing at the time the points are opened (provided no energy is lost back across the points as they open, etc etc.)
Things are a mite more complex than above, but I think I have given you enough to think about!
There are some super internet sites which explain the Ketteringham system better than me.
Regards,RAB
Regards, RAB

Follow Ups:

• Re: Re: Re: Re: 12V Conversion RL 07:16:08 03/14/04 (2)
  • Re: Re: Re: Re: Re: 12V Conversion john 14:58:00 03/14/04 (1)
    • Re: Re: Re: Re: Re: Re: 12V Conversion Larry from MD 15:20:12 03/14/04 (0)

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