RonKZ650 wrote:
One of these days I'm going to do some more current tests comparing the current draw ect, between the points and Dyna setups.
That would be great. Your previous tests were very interesting. Real data is probably always better than conjecture.
RonKZ650 wrote:
I just can't believe the Dyna draws any more current or could make the coils get hot.
It doesn't draw more
instantaneous current. It draws more
average current. It's very important to know which you are measuring when you take your data.
RonKZ650 wrote:
Doesn't the Dyna basically do the same thing as points?
Yes, but with one critical difference....
RonKZ650 wrote:
The points open, the electrical field colapses, inducing your 30kv spark into the secondary, then nothing happens until the points are closed again, then reopened to repeat. With the Dyna the same thing is done electrically every engine revolution, instead of mechanically using the points.
Yes.....
RonKZ650 wrote:
Once the electrical field colapses doesn't the coil just sit there idle waiting for the next signal to fire whether it be points or Dyna?
No. This is where the difference exists. With points, once the spark occurrs, the points wait about 180 degrees of crank rotation before re-applying the primary current. During this time the points cool down and the coils cool down.
The Dyna does not wait. It re-applies primary current almost immediately... something like 20 degrees or so after spark (I forget the actual number).
RonKZ650 wrote:
Even with points, depending on where your engine is turned in rotation the points are either closed or open, and either position in sitting, I can't imagine the coils heating, same with Dyna.
When the points are closed, the primary current is heating the coils. With the Dyna, it's as if the points are closed almost all of the time. With points it's about 50% of the time.
It's referred to as a duty cycle. The points have about a 50% duty cycle. The Dyna is more like 90% duty cycle. At first, it doesn't seem like much difference, 40%, but consider the "on" time versus the "off" time. 50/50 = 1. 90/10 = 9. The coils get very little time to cool so their heat build-up increases significantly, in the long run, with the Dyna.
But, all of this should not worry you. There are other factors that hedge the bets. When the bike is actually moving, there is much more air cooling the coils. Also, if you've ever stopped the bike and left the ignition on, chances are, at least one coil was "on" the whole time. It did not blow up, so the coils do seem to be able to stand the abuse of 100% duty cycle. Modern coils seem to be able to take more abuse than their ancestors.
There is one other factor that really makes a difference. Coils take a certain amount of time before the primary current will reach it's maximum value. At higher RPMs, the primary doesn't reach it's maximum value. This means the primary current doesn't actually reach it's maximum and therefore the heat dissipation will be less in the coil at higher RPMs. That is the purpose of a true ballast resistor. At low RPMs, the ballast heats up and reduces the primary current to prevent the coils from overheating. At a sustained high-RPM, the ballast cools down and allows more primary current to the coils to produce a bigger spark. The coils won't really get much hotter, because at high RPMs, the coils themselves will prevent the current from reaching its maximum. (On cars the ballast is switched out during start-up to get max current to the coil during starting.)
So why is the Kaw electronic ignition better? First, it does not allow the coils to turn "on" when the crank is not turning. Also, it's duty cycle is less than 50% so the coils get ample time to cool, therefore they use hotter coils. The kaw actually uses a variable duty-cycle setup. It's inherent in a reluctor-type pickup. At lower rpms, the duty cycle is lower. The dwell at idle can be below 100 degrees of crank rotation. At higher RPMs the dwell is around 120 degrees of crank rotation. 20 degrees doesn't seem like a lot, but it's the "on" time versus "off" time that makes a difference.
Incidently, "dwell" can mean several things so it must be taken in context. Dwell is when the points are closed, but it can be described as duty-cycle, or crank angle, or cam-angle (in cars), or actual time.
Post edited by: loudhvx, at: 2006/01/10 13:40
