igniter/inline resistor/coils question

The KZ1000E 1979 power to the coils goes through an inline resistor. The resistor is supposed to have ~1.5 ohms resistance and the coils are supposed to have ~1.5 ohms resistance. I don't understand electric as well as I should. Does this mean you could bypass the resistor and use 3 ohm coils? I spent part of yesterday testing the electrical bits I have on hand for my project bikes. I really could use someone who understands this stuff to explain the theory. I know some of you folks have done this or done that and it seemed to work... I am looking for the "theory" of the inline resistor in the path of the power to the coils. Thanks!

Lou is a lot better at explaining this stuff than I am, but I'll give it a shot until he gets here

To start off, I think the reason for the 1.5 ohm coils is to transfer more energy to the spark, and the reason for the resister is to limit the current flow through the coils to avoid overheating and burning them up.

Current flow equals heat, and the more current the more heat. Resistance in series is additive, thus 1.5 ohms plus 1.5 ohms = a 3 ohm load, so by removing the resister and replacing the coils with three ohm coils, the total load remains the same.

So there should be no problem involved in replacing the stock coils and resister with 3 ohm coils.

Just something to think about till Loudhvx arrives

Yes, you should be able to use two 3-ohm coils and eliminate the resistor.

Theory:
There is a difference between a resistor and a ballast-resistor.

A normal resistor is meant to have a constant resistance to reduce the current in an ignitor (or points). This reduces heat and stress in the ignitor, or points, and the coils (as Steell mentioned). However, it does cut down on available primary current for producing spark.

Incidently, I don't think a low resistance coil necessarily gives you more spark energy all the time (though it could), but it does charge faster and will thus give more energy at higher RPMs when the charging time is 1/10th that of idle.

A ballast resistor increases in resistance as it heats up. To understand its purpose you have to understand the nature of ignition coils. With ohms law, you can find the current in the coil's primary, but that assumes a steady state condition. The current doesn't jump up to its maximum level immediately. It takes time. At idle, a coil easily reaches its maximum current. At very high RPM, the current may only reach 1/2 of its maximum before spark occurs. This means at high RPM there is less spark energy available.

The stock Kawasaki ignition makes up for this a little bit by increasing the dwell angle at higher RPMs.

Another way to get more current at higher RPMs is to use a ballast resistor. At idle, the dwell time (not angle) is very long. This means the coils reach their maximum current and stay that way for a long time. The resistor heats up and its resistance increases. This reduces the current. As the RPMs increase, the coils will no longer reach their maximum current. This means the current in the ballast reduces thus its temperature reduces. This means its resistance goes down and the coils will get more current (or at least more than it would have if the ballast was a normal resistor).

In cars, at startup, the ballast is usually switched out of the circuit to get full spark energy at start. On bikes, the ballast is usually always in the circuit. It's not a big deal though because at a cold start, the ballast is cold and has low resistance.


And since we're on the subject, the Dyna S and Dyna III solve the problem by producing a very high, constant dwell angle. The problem is this really heats up the coils especially at idle. Luckily new coils seem to be able to handle this. But the true question is will they still be working in 30 years?

Post edited by: loudhvx, at: 2006/03/26 19:11

i've been trying to read up about the electical of these bike, and vehicles in general and keep hearing people talk about dwell time and dwell angle, if its not to long or complicated could you explaing this loudhvx? or maybe suggest a book or website that would explain it?

Thanks guys for the help... I didn't want to start buying new stuff till I was sure about what the effect would be. I have four ST coils (supposed to be 1.5 ohms) but all four vary between about 3 and 7 ohms primary resistance. Both of the inline resistors are about 3 ohms as well. I suspect it would be best to junk the coils and resistors and just buy some decent 3 ohm coils. I also have one bad ignitor but have a spare some where that I couldn't find yesterday. All the pickup coils test out OK...

First, dwell is a term used with Kettering style ignitions. Kettering is the guy who invented the flyback ignition. It is a type where the ignition coil has a primary side and a secondary side. The primary side is "charged" with current. It takes time for the current to increase so it takes time to "charge". When the current is abruptly stopped, the collapsing magnetic field in the primary side induces a very high voltage in the secondary side which causes the spark.

Since CDI (capacitive discharge ignition) and magneto ignitions work on a different principle, the term "dwell" is not often used in those applications.

Dwell, in terms of Kettering ignitions, is the period when the points are closed. This is when the primary side of the spark coil is being charged with current. If you have a transistorized version of Kettering ignitions, the dwell is the period when the transistor is allowing current in the primary side of the coil.

Dwell can be described many ways.

Dwell time is actual time during which the points are closed.

Dwell percentage (also called duty-cycle) is the percentage of time the points are closed versus the closed-time plus the open-time.

Dwell angle (in crankshaft degrees) describes the angle of crank rotation during which the points are closed.

Dwell angle (in camshaft degrees (also known as distributor degrees)) describes the angle of cam rotation during which the points are closed. (In old cars, the distributor rotates the same amount as the camshaft.)

Why so many ways?
Because coils need a certain amount of time to reach their full current, we are interested in actual dwell time to determine if the coils are charging long enough to produce sufficient spark.

Dwell percentage gives you an idea of how long the coil is charging versus how long it is sitting idle (during which time it is cooling off). This gives you an idea of how much heat stress it will be under.

Crankshaft dwell angle is used because on bikes like our KZ's, the ignition runs off the crankshaft (or a shaft running at the same rotational speed as the crankshaft). This lets us directly measure the angle during which the points are closed.

Camshaft or Distributor degrees is used on old cars because the points ran inside the distributor which turns the same speed as the camshaft. The cam always turns half the speed of the crank so cam speed and crank speed are always different by a factor of 2. This is important to know when using a dwell-angle meter. You have to be aware if it's measuring crank or cam angle.

Obviously it's just a matter of some math to convert from one dwell measurement to another (you also have to know the RPM in some cases to convert to time). Dwell time changes with RPM (on a typical points setup) whereas dwell angle or percentage does not.

Modern electronic-ignitions may try to increase the dwell angle as the RPMs increase to give more charging time at higher RPMs. The stock Kaw transistor-ignitions do this to some extent.