No spark all 4

[TopCatGr58]

Hey CZ and Steve,

I wish I understood a 1/10th of what you both are saying, but that will be for another life! From what you're saying Steve, that the low voltage performance characteristics that CZ is finding with the TCI in his test rig regrettably do not duplicate the real world on bike in use application.

And so I think I will continue to believe in the anecdotal evidence that has been collected over the years that when the battery/system/harness voltage gets near or below the 10.5 threshold "something" happens that prevents the ignition "system" from functioning properly and results in a total loss of spark at the plugs despite the fact that the engine can still crank. I don't believe our diagnostic procedures to determine the causal affect for this symptom will change anyways.

T.C.

[crazy steve]

Being an 'electrical' guy as opposed to 'electronics', this is really straining my expertise! While the theory is the same for both, the practical application is two very different things...

TC, what you're seeing is that CZ demonstrated that the TCI will operate at fairly low voltages. The TCI is nothing more than a high-speed 'switch' for turning the coils on/off. Think of it as a solenoid; instead of operating a starter, it's running the coils. But the same issues can exist; while the 'solenoid' can be working, if there's issues in the 'starter' side of the circuit (burned contacts, poor connections, bad starter) it won't. If you reduce voltage to the coil enough, the high voltage generated won't give you a good enough spark to fire the plug.

CZ, what you're asking really should be explained by an engineer who's familar with the components. There's a lot of factors involved; the design of the coil windings, core size/shape/material, no doubt more. But the 'short' answer is you have both induced EMF and CEMF (counter electromotive force) at work in the primary and secondary windings that push/pull at each other, changing the voltage you see impressed on the primary winding. Add in the capacitance of the spark plug, and all three 'impedance' factors are at work. If you could figure out a way to connect the coil secondary to a purely resistive load, you could eliminate the capacitive reactance but I'm not sure how you would go about that...

[CaptonZap]

Please ignore the pervious post, I goofed


Yep, you're right Steve,
There is definitely a counter EMF in there, and the next step is to get on a 2 channel scope and see what the time relationship between the transistor and the coil primary voltages looks like.
And TC, you are absolutely correct, where the rubber meets the road, nothing has changed insofar as battery condition goes. As far as the TCI working goes, my test rig gives true results, since the voltage spikes we have been discussing are just through the final transistor "switch" that Steve talked about, and have no bearing on the internal workings of the TCI electronics, as long as the supply voltage to it is kept above 5-6 volts. Keep your voltage up.

Good Super Bowl.

CZ