Ignition current handling capacity

[flyanimator]

Good Morning to everyone! I realize this has been attempted before but final resuslts have never been posted as far as I can tell.

Yes, this is another attempt to discover an automotive coil replacement for our bikes. I found a source for a good starting point that was used on a Kawasaki KZ1300. Since they can use the same aftermarket coils that we can, I figured there may be a possibility of adapting the same automotive coils that they use onto our machines.

Here is the site where I found it.

http://www.kz1300.com/techarticles/z1300-gm-coil-swap.html

Before I can successfully plan such a swap there are a few questions I need help answering. If any one can shed some light on these issues would be very greatful.

One of my questions is What is the current draw that a dyna S ignition systen can safely handle? Most auto coils have a much lower resistance than our coils which would increase the current draw across the ignition system. This can lead to overheating components and less money in our pockets.

I am tried the same coils as used in the kz site without any modificitation or current limiting device (resistor or other circuit) and the engine has fired up quickly and runs smoothly. I have not let it run for very long at all this way so as to prevent overheating of the ingnition components to the point of failure. As I have calculated, current draw through the system with 3ohm dyna or accel coils is 4 amps while current draw with the original 5ohm coils would be 2.4 amps. With the coils I am attempting to adapt with a resistance of .5ohms, current draw jumps to a whopping 24 amps. With the setup in its present state, it is clear to see that this current draw is high even if only b feeling how hot the inline fuse on the col relay mod gets. Thus, my question of how much current a dyna S can safely handle. Since the coil relay mod is in place, the current being drawn by the ignition system passes only through the Dyna S and the coils since the starter kill and ingition switch only operate the relay (which is rated for 30 amps and can safely handlethe increase current). If anyone has the technical specifications on the Dyna S, please let me know. This is the missing piece of the puzzle that i would need in order to formulate some type of circuit that can dissipate the extra current.

I realize that many may say that this is a waste of time, but I have some extra time on my hands. Being a finance student I also realize that reducing cost is very important. There is a high probability that this trial may result in savings for many of us GS owners, especially those of us who have not been blessed with unlimited resources or extremely supportive spouses. The coils being used can be sourced from a salvage yard for a few dollars or new from your local auto part store for about $30 per coil as opposed to $70 per coil for dynas or even more for accels. Beside the cost savings, wait time can be greatly reduced as well, instead of waiting a week for the UPS man to bring us our coils, we can just hop over to the closest O'reilys or Autozone and be done with it the same day. I'm sure we would all rather be riding than driving in a cage for a week or until our parts arrive.

Now that I have probably bored everyone with my essay like post, I'll stop myself and just wait for responses from everyone.

Thank you in advance for any insight you may have to offer.

[Steve]

Not sure what the ultimate current-handling capacity is, but they are designed to be used with most common systems that are about 3 ohms. If the new coils are only .5 ohms, just put a 2 or 2.5 ohm ballast resistor in there so the system still sees the same resistance and current.

By the way, I was fortunate in that neither of the Kaw 1300s that I had ever had ignition problems.

.

[flyanimator]

Thanks steve. I know that the system works well with 3 ohms however, adding a resistor in series will produce a voltage drop that will not allow the coils to function properly. If a 2.5 ohm resistor were used to increase resistanceto 3 ohms, then this would translate to a 10 volt drop across the resistor and only 2 volts feeding the coil. The 3 ohm system provides 4 amps to the coils, however the automotive coils i'm using are happy playing with the 24 amps being fed to them with the .5 ohm resistance. I'm not sure how the Dyna S feels handling them though. If the resistors were wired parallel to the coils then this would effectively control the current going through the coils but would also decrease the total resistance that the system sees thereby increasing current as well.

Perhaps I am mistaken as to how a resistor is typicaly wired into the system. Maybe someone on the forum can enlighten me on the matter.

From what I read on the KZ site, this swap was not done to fix an issue with the ignition or even to increase performance, only help with availability issues and to save some money on replacing the coils (they have 3 COILS!!!).

Anyone else know how much current the Dyna S can take?

[posplayr]

Anyone else know how much current the Dyna S can take?

(14.5-1.5)Volts / 3 ohms = 13/3 = 4.3 amps. That is where the Dyna is happy.

At that current it is dissipating about (4.3*1.5)=6.4 watts when closed.

If you use a 0.5 ohm coil then

(14.5-1.5) Volts / 0.5 ohms = 26 amps

At that current it is dissipating about (26*1.5)=39 watts which normally requires a heat sink on the order of a typical R/R. It will work for a while till it goes into thermal overload and fries.

If you have a 0.5 ohm coil that was used on a 12V system, it was made to produce spark to fire a typical AFR. It should work with what ever ballast resistor that was designed into the system.


BTW if you think the Dyna will get hot, the coils well really be getting hot as they are having to dissipate

26A*13V=340 watts a piece (when energized).


That would be a peak load of 50 amps when both coils are energised together. The R/R will also fry at that point but more than likely you will never get that much out.

Unless you can get into the 3 ohms region for total resistance you will have problems.