Dwell and Ballasts (Was multi Coils)

[Ade + Lamb Chop]

On 27 Jun 2000, at 8:36, John Dammeyer wrote:

> 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.

Never looked at it this way before.... thanx
 
> 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.

Minis did it for years.... I changed mine to a metro dizzy with 
electronic points (a big fat transistor?) which gives a dwell of 
almost 0degs (might be almost 90 cannot remember which way 
round it is).. This means that the "points" are closed almost all the 
time. This means the coil has a lot longer to charge up.
 
> 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.

On Lucas dizzies you loosen the screw and lever the points 
open/closed a little and tighten the screw. I use to use a dwell 
meter far more accurate than measuring the gap with a dwell meter.

Back to Efi

Ade

ICQ. 75653589
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