Topic: Question about coil relay mod

[jessezm]

Hey folks, quick question:  For those of you that have modded their bikes to feed power to the coils directly from the battery via a relay, have any of you had problems blowing the 10 amp fuse that the mod calls for?  My bike has basically all new connectors and I've inspected all the original wiring and connections thoroughly.   The only odd things about my set up is that 1, I'm using one of those A123 Excel batteries (the small one, actually!), and 2, my Dyna ignition had a bad pickup and was only firing on one coil.  Oh, I'm using the 5 Ohm coils as well.  It blew the 10 amp fuse after running a few minutes.  Afterward, I bypassed the relay and it ran fine on the one functioning coil getting power through the handlebar switch as usual.

Do you think I should try it again with the new ignition?  And perhaps a 15 amp fuse?  Is there anything about the A123 Battery that might be overloading the circuit?  I realize that this mod is probably not really necessary, I just thought it would be a cool and easy way to get a little extra juice to the coils.  Of course, I have no real understanding of electrical theory (bracing for TwoTired's response!)

[TwoTired]

What type fuse did you select?  Fast blow, slow blow, quick blow, or standard?

Batteries don't push power.  It is the load that determines how much is pulled from the battery.

Have you checked the voltage at the coil's input?

5 ohm primary with 12V applied draws 2.4 A.
5 ohm primary with 15V applied draws 3 A.
The dyna-s leaves both coils on most of the time so you can add the currents of both coils. 

How much load are you putting on the coil secondaries?  Resistor plugs? resistance wire?, resistor plug caps?  Spark plug gap is___?
Energy draw from the coil output is replaced through the primary and the current provided it.

Coils have an impulse draw that can exceed steady state or average draw.  Combine that with a quick blow fuse and the repetitive current spikes can pop quick blow fuses.




...Is it also cool to be blowing fuses?

[jessezm]

Hah, thanks for the reply!  I used one of those blade fuses that glows when it pops--I'm not sure if it's a quick blow or not, but I will try it next with a normal 10 amp blade fuse.  The plugs are gapped correctly at .028".  The plugs are Denso X24ES-U, and the plug caps/wires are the kind that come with the Dyna-S ignition and coils (at least they came with mine).  I'm not sure if they are resistor caps or not--how can I tell?

Oh, in the meantime, it turns out that the ignition was fine, and it seems that it was one of my Dyna DC8-1 coils that was bad.  So now I'm waiting for Dynatek to test that and replace it.  It's strange, though--I got good primary and secondary Ohm readings on both coils.  Thought it might be a bad ground but there is continuity to ground on both coils.  The technician said it could be shorting out internally, so they are going to test it under load.  I hate how long this is dragging out!!!

[jessezm]

Oh, that is a non-resistor plug, by the way.