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Ballast System coil replacement


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Had some issues driving the spitfire on a very hot day when she just stopped after showing symptoms of an electrical fault, ie under load loss of engine power and then dying, happened after I had driven some fifteen miles. Manage to get her going again after some twenty minutes after looking at fuel, no issues and fiddling with electrical connections reseating  them. Electronic ignition all ok.  The coil was extremely hot, and I mean hot, too hot to touch. Got to the TSSC meeting after another fifteen miles without incident but the coil was again to hot to touch. Same thing happened on the way home after fifteen miles or so she died with the same symptoms as before, got her going again and onto the drive. So I got a new  Accuspark Sport 1.5 ohm ballast coil as a start to try and resolve the problem thinking the coil may be an issue as others at the TSSC meeting had suggested. When I measure across the contacts it shows 2.2 ohms not 1.5 ohms. So does it go on the car and if so what is the effect of this coil being over the 1.5 ohms.  It has been suggested by he who shall rename nameless that these extra ohms may increase the spark hence the “sport” reference. All answers gratefully received.

Paul B

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If the coil is too hot to to touch, this is indicative of a coil with a low resistance.  If it is 1.5 ohms it must be connected to the ignition switch via the white/pink resistance wire so that it only receives 6 volts during normal running.  Has this wire been bypassed to obtain 12 volts for the electronic ignition?  If so, then you need a 3 ohm coil.  Alternatively, has the feed from the starter solenoid been misconnected so that it supplies 12 volts continuously rather than only when the starter motor is actuated?

As for the coil, the extra 0.7 ohms may just be due to the resistance of the test leads.  If it is 2.2 ohms it will pass less current and run cooler, and for the same inductance, provide less energy to the ignition system. But the extra resistance could be due to more turns on the primary giving a higher inductance and more energy but at the expense of a longer rise time.  After saying all that, I think that the replacement coil will work fine provided it is only being supplied with 6 volts via the resistance wire.

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just to add do make sure the coil polarity is right the coil neg- to dizzy/points    the pos+ to the white pink ignition  ballasted  feed 

having it back to front gives you what you describe stops and wait then restarts 

grahams idea of the link to the starter sol is on the 12v live side is well worth a check

Pete

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