Sorry Randal, but power is used to drive the ICs in the unit as well as
supply voltage to the base of the transistor that turns on the coil. The
ICs, if they're anything like those in the Piranha ignition system,
require a minimum of 5 volts to operate. And although it may not make
any difference in the majority of cases where the connection is made, in
the case of a coil and resistor that are not matched, there could be a
problem supplying adequate voltage.
In this case, the coil measures 1.1 ohm and the resistor measures 1.7
ohms so:
( 12 volts/2.8 ohms)*1.1 ohms = 4.714 volts across the coil when the
ignition is on, not accounting for the voltage drop of the switching
transistor.
By the way, I designed my first electronic ignition more than 25 years
ago.
Randall wrote:
>
> Right. They've only been making these things for 20 years, and their
> manual still has such an obvious mistake in it.
>
> I'd like to suggest that, in the case of the Crane XR700, it actually
> makes no difference at all. It works similar to points, in that it
> fires the coil by shorting the yellow wire to ground to build a magnetic
> field, then interrupting it to cause a spark. The power from the red
> wire is only used to power the LED in the pickup, and the amplifier for
> the signal from the LED. 3 volts is probably enough, so whether it's 6
> volts or 12 volts just doesn't matter.
>
> Of course, for my XR3000, it does make a difference, which is why the
> diagram shows the ballast resistor shorted out ...
>
> Randall
>
--
George Richardson
Senior Electronics Engineer
Kinetics Thermal Systems Inc.
Wyvern - '57 Triumph TR3, TS15559LT -
http://www.merlingroupinc.com/tr3.htm
Griffin - '71 Triumph Stag - Daily Driver - when running!
Pikachu - '75 Triumph TR6 - undergoing repair
Kitty - '83 Jaguar XJ6 Vanden Plas - Waiting for engine overhaul
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