Aribert :
The overheating problem is not caused by the red wire being connected to
12v, but rather by the amount of current drawn through the coil when the
unit connects the yellow wire to ground (through the output
transistor). Hence using a low resistance coil will increase the heat,
and using the low resistance ballast will increase it even further.
In a nutshell, there is a transistor inside the Crane that performs the
same function as the points originally did, ie connecting the yellow
wire to ground. However, unlike the points, that transistor always has
some voltage drop across it, and so generates heat proportional to that
voltage drop, times the current through the coil when the transistor is
'closed'. During normal operation, the transistor conducts roughly 1/2
of the time, but with the engine stopped it conducts all of the time, so
the power dissipation goes up. I suspect (don't know) that the Allison
used a germanium transistor that has a lower voltage drop and hence
generates less heat, while the Crane was redesigned with a 'modern'
silicon transistor with a higher voltage drop. The XR3000 works
differently, and is 'smart' enough to shut down when the engine isn't
turning.
I actually agree with George that connecting the red wire directly to
12v will not hurt anything, I just don't think it's likely to help,
either. But again, I would suggest you not use the 0.8 ohm ballast but
instead a 1.2-1.9 ohm ballast as the instructions suggest. Frankly, if
it were my car and I was contemplating burning up a $100 ignition, I
wouldn't use the MSD Blaster coil either. If money is a problem, a trip
to the local junkyard should turn up a coil from almost any Chrysler
product from 1960 through 1990 that will work fine, and if you can find
one before about 1972, a ceramic ballast resistor as well. Shouldn't be
over $10 for the pair.
Randall
aribert wrote:
>
> I was interested if there was any other possible voltage drop/drain that
> I
> had not thought of. In respect to running full voltage into the module,
> I
> have been told that it will overheat the transistor that does the
> switching. I know from expen$ive personal experience that if the
> ignition is left on for more that 5 minutes there is a good chance that
> the XR-700 module will be fried
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