Vincenti, Ross wrote:
> Andrew Mace wrote
> Subject: Re: balist resistor (why)
> > Chances are, unless the previous owner changed the coil to a non-ballasted
> > coil you will need a ballast resister....
> Yes, and no. Yes, assuming it is the OEM or OEM-type replacement coil,
> you need a ballast resistor. No, you probably don't need to add one. IMS,
> this vintage of Spitfire (U.S. version anyway) had the ballast resistor
> "built in" to the wiring harness; there is no external ballast resistor
> that one could point to and say 'there it is'. At least that's what I
> recall from a 1973 Spitfire that used to hang around awhile back! ;-)
> Morning, all.
> All this talk of ballast resistors has got me wondering about my Mk I Spit.
> I plan on checking my Bentley/Haynes/Autopress manuals back at home tonight
> for "the truth", but I am curious as to whether anyone has the answer at
> their fingertips.
> (1) My Mk I has the original Lucas 12 volt coil (which BTW polished up
> awfully damn nice if I don't say so) and I was unaware/unable to
> locate/completely braindead about the use of a ballast resistor. Just how
> much more quickly will the points burn out without the resistor? I don't
> recall ever dealing with this issue on any of my old American Iron vehicles
> and certainly didn't consider it when rebuilding the Spit. Inquirying minds
> want to know . . . . . . . . (2) What if I wanted to replace the Lucas coil
> with an aftermarket coil (gasp! - a non-original part - he's a Godless
> heathen), or maybe even an electronic ignition such as the Allison or Crane
> unit? If the sole purpose of the resistor is to reduce the voltage during
> "normal" running and is bypassed during starting, and the elec. ignition
> systems reduce the voltage across the points to millivolts (as opposed to a
> full 6 volts), then it sounds as though you would not need the resistor with
> an elec. ignition system. Thanks.
I'll try to take another swing at this topic. The ballast resister wire
is there to drop the voltage to about 7-10 v. while the car is in normal
run mode. It's supposed to be used with a 6 v. coil. During starting, the
ballast resister wire (which in a Spitfire is bundled in the harness and
is coded pink/white)is bypassed to provide a full 12 v. to the coil.
This momentary over-voltage provides a little more spark to get the
engine started a little more easily. If you run a 6 v. coil on the full
12 v., all the time, it will over heat and fail prematurely--not
instantly. If you replace the stock coil with a Lucas Sport or a Bosch
Blue the ballast wire can be bypassed. Those latter, internall ballasted
coils are designed to operate at the full 12 v. all the time.
As far as I know, the coil really has no bearing on points wear. That's
the purpose of the condenser (capacitor). Electronic ignitions are simply
high speed switching units, designed to replace the function of points;
i.e. they will replace points on all ballasted circuits, whether the
ballast is external, in the form of harness wire or ceramic block, or
internal to the coil, like the Sport of Bosch Blue.
Hope that helps,