Interesting Jim. ‘Mechanical’ failure of internal comments due to thermal expansion isn’t something I’d thought of to be honest. Just for ref, and without getting into specific temps etc, my coil reference is an example I hold up just to try and demonstrate how electronic components have changed over the years, coils used to be oil filled and have to hang in the breeze, and they’d still fail! Nowadays they’re tiny, and buried deep in the hottest part of the engine.
Anyway, back to the heat topic: what kind of electrical related things can influence the heat inside the EI unit? Can different coils create more or less heat? Differences in wiring, or wiring issues, switches, etc? HT leads, plug caps, plugs used?
So, what I’m wondering is why do some units fail and some don’t. Moreover, why do some
people suffer multiple failures and others zero?
Surely something is causing different internal conditions ??
There are two common failures in an electronic ignition like the Tri-spark.
One is failure of the actual junction in the transistor due to over current or voltage which heats the junction to the point of cascade failure. This is usually due to the wrong coil or over voltage from the charging system. This type of failure is abrupt and the unit is dead and will not operate again once it has cooled.
The type of failure I have seen more often with the Tri-spark [and other shake and bake ignitions] is the failure where it stops operating when it is hot -like after a shutdown and hot soak. This is a failure due to mechanical stress of the heating and cooling cycles. And yes the wrong coil or voltage may make the cycles more severe and cause this failure sooner, but basically due to expansion and contraction of the circuit board and components some connection opens up. It may be a connection inside the component itself or one of the hundreds of connections between the components of the circuit. This type of failure often works again after a cool down period.
So how do you prevent it?
You mount the heat producing components on a good heat sink away from the engine. If the
heat sink has good heat absorption and dissipating abilities the temp change of the component will be slow and the swing will be less. Then you will have a unit that will survive for a long time -as long as the current and voltages are correct.
Ignition coils that are mounted on the plug do not usually contain electronic components -beyond a coil of wire and several connections. And failure is very common. I replaced hundreds of them when I ran Jim's Auto.
An ignition like the Altair does have a single electronic component mounted in the points cavity. It is a Hall sensor [a transistor that changes state when exposed to a magnetic field] They do not generate any substantial heat on their own and with only a few connections are relatively free of heat induced failures.
The plug gap and coil wire resistance can also influence the life of the ignition driver. The higher the voltage goes before the plug fires, the higher will be the kickback voltage. The kickback voltage is the high voltage induced in the primary winding of the coil after the plug fires. That is why disconnecting a plug wire will often damage an ignition unit. The kickback voltage goes extremely high -possibly higher than the voltage rating of the drive transistor. The higher the resistance of the plug wire and plug and the higher the cylinder pressure, the higher will be the kickback voltage.
By the way, damage from high kickback voltage may not produce an immediate failure, but the damage may cause a failure on down the road.
So between units of the same build, why does one Tri-spark fail early and the next does not
-I don't know, luck of the draw maybe. [just like my luck at the casino -always bad]
Or maybe it's one or a combination of the things I mentioned above. Jim
