No subject

Thu May 30 05:48:45 GMT 2013

to destructive ends if simple precautions aren't met.  Electronic control
means that we can charge coils in very little time and yet maintain current
limits.  Coils can prematurely degrade quite gradually if they are overstressed.
The user may not notice the subtle changes in drivelability and power.  If 
possible, keep an eye on the coil temperature and any sounds it may be making 
(internal arcing).   DO NOT run the coils with the secondary side disconnected.
Recently, we had a customer bring in a Delco coil that had decided to split
apart, probably after testing without the plugs connected.  It was only a 
few hours old.  The dead coil had then cooked the ignition amp (and two 
spares).  Other failures have only shown up at high engine loads or after
running on the bench for a few hours. 

I use an adjustable charge time of 1.0 to 5.0 mS.  Various coils prefer more
or less charge time but as a rough guide I start from a small value and
increase until there is no noticeable change in idle speed stability.  The 
coils then require at least 1.0 mS to discharge, but this is only an issue
at high speeds on single coil distributor systems. 

One of the problems of high energy ignition conversions is crossfiring in
the distributor.  My 1974 build dizzy has a much smaller diameter than
current model electronic ignition triggered units and will fire the wrong
cylinders indescriminately if there is the slightest hint of moisture inside.

> ...... There's no 
> point in turning the coil on longer than it takes for this to happen, because no 
> additional energy will be stored.  

There is one small point to add here.  As the engine accelerates the, start
of coil charge time has to be brought forward from the time that would have 
been calculated on the previous firing.  This calculation can be
avoided if an extra amount of coil charge time is added above that which is
required for peak current during steady state operation.

In my application, I manage to solve this problem by starting the coil charge
time a minimum of 30 deg before firing if it has not already started charging.

> Ed Lansinger

I hope this spreads some light.


             Robert Dingli           r.dingli at

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA

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