TOPIC:

Could I put any other brand coils into my KZ1000? Assuming the coils were 3 ohm primaries like the stock ones?

Bob

dyna,accel......

are aftermarket coils really any better than goodfactory units? better cold starting, less sputtering on the top end?

cary wrote:

are aftermarket coils really any better than goodfactory units? better cold starting, less sputtering on the top end?

Not sure they are better, but are slightly different. The Accel coils have a longer time to saturation than the stock electronic ignition coils, but they probably have a higher voltage capability. If your motor is in good condition and tuned properly, and your electrical is good, you won't notice much difference, if any.

Either way, new Accel or Dyna coils are less likely to leave you stranded than 25-year old coils.

Well, assuming a person didn't select 25 year old coils, I don't know any reason why it would not work. They'd be harder to mount for sure.

As for saturation, I think that's just advertising hype. I mean, you're talking mili-seconds here. They all saturate pretty much the same. Paint an accel coil black and when installed, the average driver is not going to be able to tell any differance. IMO.

Bob

Bob_79KZ wrote:

Well, assuming a person didn't select 25 year old coils, I don't know any reason why it would not work. They'd be harder to mount for sure.

As for saturation, I think that's just advertising hype. I mean, you're talking mili-seconds here. They all saturate pretty much the same. Paint an accel coil black and when installed, the average driver is not going to be able to tell any differance. IMO.

Bob

Unfortunately marketers love to throw around tech speak to sell stuff.

Advertising hype or not, it is still a measurable or calculable factor. It determines when your coil has reached the limit of not being able to produce any more energy. Beyond that, any more dwell creates nothing but heat in the coil and points (or ignitor). The stock coil reaches 90% electrical saturation in about 5 msec. The Accel coil reaches 90% electrical saturation in just over 11 msec. That's over twice as long.

At 10,000 RPM, the coil only gets 2 msec to work with (assuming a stock electronic ignition). The Accel coil is slower than the Kaw coil but still delivers adequate spark. I'd rather have brand new stock coils, but I use the Accels because they are newer.

So, what you are saying is, saturation is reached by dwell time and NOT the brand of coil you are using. Because it is a fact that there are no electronic circuits inside of an accel (or any brand) coil that tells it when it's 'saturated'.

It's the bikes own ignition system that ultimately determines how saturated the coils will become, not the coils. Coils are 'stupid'. They don't know when they are saturated. That's why too much dwell burns up coils.

In my opinion....

Bob

Bob_79KZ wrote:

So, what you are saying is, saturation is reached by dwell time and NOT the brand of coil you are using. Because it is a fact that there are no electronic circuits inside of an accel (or any brand) coil that tells it when it's 'saturated'.

It's the bikes own ignition system that ultimately determines how saturated the coils will become, not the coils. Coils are 'stupid'. They don't know when they are saturated. That's why too much dwell burns up coils.

In my opinion....

Bob

I'm just talking pure inductor-current saturation. It is an inherent quality of the coil itself. A coil of given inductance and resistance requires X amount of time to become 90% saturated with it's terminal-current. The terminal-current is the limit of applied-voltage divided by the DC resistance of the coil. I say 90% because that is commonly used to measure the time constant, since a coil theoretically never becomes 100% current-saturated.




The bike's ignition determines the dwell, and can limit the percentage of coil saturation at higher RPMs, but at idle, pretty much all coils get saturated. It is the high RPM operation we care about. At 10000 RPM, the stock KZ electronic-ignition dwell is about 120 degrees. As I said, that is 2 msec.

Regardless of the ignition system voltage, the Accel coil needs about 10 msec to reach 90%. The stock coil needs about 5 or 6 msec to reach 90%. (In physic-speak, the LR time constant is independent of voltage.)

Core magnetic-flux saturation is a different factor completely. That is not necessarily measurable easily. There is a limit to how much flux an iron core can support. After it is saturated with flux, the coil can store no additional energy. I haven't studied the flux saturation of ignition coils, yet. I surmise I could measure it by applying increasing amounts of current to the coil before firing a spark and then measure the spark duration (on an o-scope). I would measure the current of the spark through a non-inductive resistor. ...just thinking out loud.

In the end, I believe that Dyna and Accel designed their 3-ohm coils as a good compromise to be used with points or electronic ignition. They work well for both.

Post edited by: loudhvx, at: 2006/09/28 04:12

I always knew we had some smart fellas around here..but wow.

I have no idea what the explanation is but on 750 turbos if you run grey Dyna coils you can use ordinary cheap ES plugs (£2 ea.) instead of the expensive EV/EIXs (£10 ea.) without fouling. The stock coils just foul the cheap plugs.

Loudhvx: Wow...that was a text-book answer...that applies to any coil with a metal core. Basic stuff.

But, its got to be better to have a coil reach 90% saturation in 5ms (takes lower dwell time)than to have a coil that takes 11ms.

As you point out, at higher rpms you need to get the job done quicker. Slower coils (accel), take 11ms to saturate. I don't think that a good thing as Martha would say.

But, this is getting far to serious. I was merely saying that if a fella wanted to install a set of honda, or suzuki coils in his Kawasaki and they were 3 ohm, they would probably work. But, I sure don't recommend it except in an emergency.

Thanks for the math lesson.

Happy Trails and travel safe,
Bob

Bob_79KZ wrote:

Loudhvx: Wow...that was a text-book answer...that applies to any coil with a metal core. Basic stuff.

But, its got to be better to have a coil reach 90% saturation in 5ms (takes lower dwell time)than to have a coil that takes 11ms.

As you point out, at higher rpms you need to get the job done quicker. Slower coils (accel), take 11ms to saturate. I don't think that a good thing as Martha would say.

But, this is getting far to serious. I was merely saying that if a fella wanted to install a set of honda, or suzuki coils in his Kawasaki and they were 3 ohm, they would probably work. But, I sure don't recommend it except in an emergency.

Thanks for the math lesson.

Happy Trails and travel safe,
Bob

Yes, I realize the math is getting a bit serious, but it's all stuff I had to do while designing ignitions. Unfortunately, the math says it all in the fewest words.

The math is for any inductor metal-core or not. But we can't assume a low time to saturation is necessarily good. My point is, a straight piece of wire, a foot long, is also an inductor and it saturates almost instantly, but it holds almost no energy in terms of an inductor.

There are tradeoffs between current-saturation times and energy-storage. In order to be "faster" and hold the same energy, the coil has to get physically bigger.

So there are three or four factors, roughly, that must be traded between. Size, speed, and energy-storage, with the fourth being final output-voltage (as two-strokes and turbos need a little more voltage to cut through the oil or denser air). You have to tradeoff between the three factors (assuming normally aspirated, 4-stroke motors). Assuming motorcycle coils are all the same size, you can tradeoff between energy storage and charge time.

If you go to car coils, you can charge very fast and store more energy, but it's tough to fit 2 or 4 car coils under the tank. In addition, the car coils are not needed and can burn up your points or ignitior if applied incorrectly. Motorcycles have much more dwell angle than a v-8 car.


Most 3 to 4 ohm coils are usually meant for about 180 degrees of crank dwell. Usually 2 to 3 ohm coils are for electronic ignitions with about 100 to 180 degrees of dwell. Some Honda electronic ignitions use 1 to 1.5 ohm coils, but they have very low dwell angles at idle.

The dwell-angle jumps up as the RPMs go up on motorcycle electronic ignitions using reluctors. However, when the dwell angle increases with RPMs the dwell TIME may still decrease because the RPMs can increase at a 10 to 1 ratio, but the dwell angle only increases at a 1.5 or 2.5 to 1 ratio.

Post edited by: loudhvx, at: 2006/10/01 22:09