TOPIC: NHT ignitions

Found a nice article that I will have to investigate for using HEI modules with low ohms/inductance coils for short dwell, high energy spark. They are much more energy efficient which is a bonus. Might compete with the $400 systems for under $100. The lucas AB14 is one that is to be improved for short money such as on jag XJ 12's.

HERE IS THE LINK

AB14+ tech upgrade?

When NHT started, 1949, there were post war early K2F magnetos, eventually K2FC versions, and in the end again K2Fmagneto's too. Well here in north america in the land of commando the pre commando are largely 2nd class it seems except for "the few the proud the marines"...oh sorry jumped off track there. The pre commando are full of LUCAS magnetos. I own 4 NHT slimline(and 3 BSA A-10), so I am familiar.
20+ years in electronics and physics and full of curiosity, I am fully aware of these little "stink bombs" LOL.
I have researched and rebuilt several for my norton and BSA A-10 Twins.
I would imagine I am talking in to an echo chamber and am on my own...HELLO...hello...silence?
Any Question or comments before the funeral?

You're not necessarily talking to an echo chamber. I find these posts interesting and informative, but have little experience with electrical systems. I usually have to research things further in order to try to better understand the posts, and often don't feel that I can contribute to the threads in any meaningful manner.

FWIW, my bike currently has a Tri-Spark ignition installed.

Eric

Good question came in a email
Hi Dave,

I have a question about 12V single coil (dual output) to be used in combination with electronic ignition (such as Pazon/Boyer) for Norton Commando. I have been using single coils with 3 ohm resistance for a long time but last year I had reported a couple of failures (then measured 2.8 and 2.9 ohm) resulting in misfiring especially when the engine gets hot. Replacement of coil cured the problem.

What I read about coil resistance is that the lower 3 ohm coil will give best spark (high peak current) but can overheat your ignition and the higher 4 ohm coil (lower peak current) runs cooler but give a weaker (starting) spark. So I tend to go for the 4 ohm coil in future!? What do you recommend?

Your opining is much appreciated.

Thanks TC

The semiconductor ignitions are mainly restricted by "average current" not really by surge current that may be controlled by "coil resistance" but actually is "inductance". Inductance can moderate surge current.
Most folks don't understand the difference between resistance, which describes steady state current flow without time as a consideration. Inductance is a for measuring an inductors current and is AC in nature as DI/DT of (I) current over (T) time.

Most transistor peak current rating is over double the average current rating. Average current is it's normal running limit. The RITA could run 10 amps surge but only desired 5 amps continuous.
For example I repaired a RITA that ran a 1 ohm coil for almost 15 years. (12-14v) divided by 1ohm = 12-14 amps. A rita is 98% duty cycle(time) so it was running 11.76-13.72 amps. The unit was using over 100wats of power. An old boyer at 75% duty cycle would probably die much quicker as the plastic and potting would retain the heat and the RITA transistor would shed heat to the aluminum housing heat sink.
To add to the physics problem is that most newer transistors are of a smaller size and are not as thermally resistant to these abusive heat/temperature conditions.
HEAT IS THE KILLER
Heat at the semiconductor junction will eventually destroy it's doped silicon layers. At first not working very well and finally unable to control the electricity as it death spirals from self heating.and if enough current is able to burn it open, otherwise it stays nonfunctional electrically shorted forever.
No switching on/off causes no sparks

Using coils with higher resistance(inductance) will certainly help the ignition maintain a healthy average current level and reduce the heat/temperature condition.
Intelligent ignition mounting to enhance cooling is also highly desirable.