Dwell and Ballasts (Was multi Coils)

[John Dammeyer]

Hi Bruce,

You might look at the ballasted coils the same way as the P&H injectors.
A resistor in series with a lower voltage coil (8V) allows the current
to build up much faster than a 13.85V coil yet limits the total current.
This means at high RPMs the current has a chance to reach maximum before
the spark occurs.  The same technique is used in the LR type Stepper
motor drivers and the P&H injectors that use a resistor to limit maximum
current.

What some cars did in the 'olden' days was switch the battery voltage
directly to the coil (in effect shorting the ballast resistor), while
cranking. This would create a higher current and hence juicier spark at
cold engine temperatures or even just a normal spark while the battery
was pulled down when cranking.  Clever really.  Then as soon as the
ignition key was released and returned to the run position the coil
voltage was supplied through the ballast.

If you have a coil that is designed for a ballast and you run it
without,  it may burn out while idling and if the engine stops in a
position where you have the coil turned on it will get hot.  Dwell just
represents the amount of time that the coil current is flowing and I
believe that they test that with an RC network inside the meter.

If the coil current builds up faster then it will appear that there is a
different dwell, hence the difference between ballasted and unballasted.
But remember,  the dwell meter was originally used to set point gap
dynamically after an initial static setting with feeler gauges.  The US
cars had a screw setting so it could be adjusted while the engine was
running.  The foreign cars did not so more emphasis was placed on using
feeler gauges and checking with the dwell meter if you had one.

Regards,
John Dammeyer.


> Date: Mon, 26 Jun 2000 14:19:30 -0400
> From: "Bruce Plecan" <nacelp at bright.net>
> Subject: Re: Multi Coil Setups
>
> Years ago, it was taught at various service schools that the Ballasted
> Ignitions were fixed dwell, and those without were variable dwell.
>   Some  manufacturers (subaru) years ago used both on one model year,
and
> you used a dwell meter to tell em apart
> Grumpy
>
>
> >
> > Can anybody share the secondary functions (if any) of the ballast
> resistor?
> >
>
>


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