Marks has already addressed some of this. But, I spent all that time typing, so....
TwoTired
I believe that the issue is with limiting the "high inrush currents" to the coil and damage to the breaker points (translation: burning up) and not wasting "23 Watts". As long as the magnetic field around the coil has built to its maximum value before the points open (di/dt) the ignition system will run much more efficiently by limiting the current in the primary winding.
Well, at the risk of interfering with Hondaman's business venture. There are a few things I'd like to point out. I've also done some circuit designs and CD ignition is the exact thing needed for bikes that have limited alternator output and require a higher spark voltage. I've had a CD operating on my 72 ford truck since about 1980 or so.
First Stated goal was to
preserve some battery juice and make a healthier charging system
Second Stated goal was to use lower ohm primary coils, such as
Dyna or Accel
or others like the gold wing.
I'd like to point out that you don't need a resistor for each coil. One in line with power to both will serve the same purpose, to limit current draw and make them closer to the stock 5 ohm loads that the charging system can more easily handle.
"Wasting 23 watts" speaks directly toward the first goal and is quite important to charging systems that only produce 40-50 watts at idle and 150 watts peak.
An inline resistor will reduce inrush and total current drawn by any coil it is deployed with, as well as the energy stored in he coil. The inline resistor will also reduce the voltage production capability of the low ohm coils. Which brings up the question of just why you have low ohm coils in the first place?
The coils develop voltage potential by means of a turns ratio. This is the number of turns of wire in it's primary winding relative to the number of wire turns in its secondary or output winding. The higher the differential, the higher the multiplication.
Low ohm coils have less windings in the primary in order to increase this ratio. You COULD also add more windings to the secondary to achieve this goal, however wire has resistance and more wire increases resistive losses. So, the trade off favors reducing the primary winding of the coil. Also, less wire is also cheaper to manufacture, as it uses less material in increases profits on a per unit basis.
For illustrative purposes, lets say a coil has a 1000 to 1 turns ratio. Putting 12 v into the primary gets you 12,000V out the secondary (Not really, there are other losses in a real physical design, but the principle stands.) Putting in 9V (as in during electric start) gets you only 9000V output.
The gold wing coils are low ohms for starting purposes where the starter motor drags down the system voltage, particularly when the engine, and oil are cold. High battery loads, lower the output voltage. The high turns ratio still produces good spark voltage during such times because of its turns ratio, but the high current draw increases coil heating and, yes, the point contacts, too? So, there is a ballast resistor that reduces the effective primary current draw, as well as the developed voltage potential of the coils during normal run operations. I don't believe the gold wing needs to conserve power from a weak charging system. The designers simply wanted it to start quickly and reliably.
If you want to mimic the Gold Wing system, get its ballast resistor (there is only one, wired in series with all the coils) and its ignition switch, from a Gold Wing and adapt it to your bike equipped with Dyna or Accell 3 ohm coils, or the GL coils.
However, it should be noted that such an arrangement is NOT a high energy ignition. If you got your low ohm coils to get a high spark voltage, inserting a resistor in series with it's primary will also reduce the voltage output capability of said coils.
In my opinion, to get both high energy and low power consumption from the alternator, CD ignition is the way to do it. What this does is boost the voltage going into the coil from 12v to 300-400 Volts. This massively increases the voltage output of any coil. And 5 ohm coils can then produce far more developed spark voltage than any Accell or Dyna coil operating at 12V, simply based on the turns ratio.
With such a system you get faster starts, and you can increase the spark gap for more efficient fuel combustion, and greater spark plug efficiency over an extended life of the spark plugs. Further, CD systems can use a points trigger with as little current drawn through them like the Hondaman ignition unit. So, points longevity is vastly improved. Wear issues are related to rubbing block, primarily.
The CD system in my truck is still using the same set of points it got when I installed the CD unit (1980-ish). I've replaced the spark plugs once. And the fuel economy increased 3 MPG. Which may not sound like much, but going from 12 MPG to 15 MPG is significant. The CD unit did blow its voltage converter transistor once. This renders the CD unit inoperative, of course. But, happily there is a switch to convert it back to conventional at the press of a button. The truck ran as before, though without the benefits. No reason an SOHC4 unit(s) couldn't be designed to have the same bypass switch.
What I want to know is, what happened to the coil per plug ignition system Hondaman teased us with many posts ago. What happened to that Mark? I thought that had enormous potential. (If you'll pardon the pun)
Cheers,
