Ignition Coil Q & A

Author: Tri-Spark   Date Posted:27 April 2011 

Q: Brett in Australia asks “I’m installing one of your Classic Twin ignitions on my 850 Commando and I’d like to use a single coil with twin outputs. It has 4 ohm primary resistance. Do I wire it as per the diagram in the instructions but without the black link wire between the coils?”
A: The minimum coil resistance recommended with the Classic Twin is 3 ohms so your 4 ohm coil would be fine to use. As you said the wiring is the same as in the instructions but you eliminate the link wire shown between the 2 coils when using a single coil.

Q: Alan in California asks “is the voltage regulator is required when fitting our Classic Twin ignition system on a 650 Triumph.”
A: The regulator is a recommended upgrade to the charging system but is not required to get the new ignition system operational.

Q: Peter in the UK asks “I’d like to order a Tri-Spark kit for my Rocket 3. What coils do you recommend to go with it?”
A: We recommend our Tri-Spark 12 volt Power coils with the triple kit. They have the same dimensions as the Lucas coils that came with the Rocket 3 but with higher spec materials we get twice the spark duration over the Lucas coils.

Are all coils pretty much the same – no way!

A long spark duration is desirable for easy starting especially on cold engines where the fuel mixture is the most varied. High spark intensity minimises the chance of misfiring, reduced plug fouling and can make the most of high compression and highly tuned engines.

These coils would also be compatible with the original points ignition in the triples except the T160 which would require 6 volt coils with its original points setup utilising a ballast resistor.

Click here for further information about our coils.

Q: Stuart asks “I see on your web site you recommend 6 volt coils with your twin ignition (Classic Twin) but my bike has a 12 volt battery. Why is this?”
A: First up, the Classic Twin is a 12 volt ignition system designed to work with a 12 volt electrical system. The reason for the 6 volt coils is they are wired together in a series circuit and as such they present a 12 volt load to the ignition module. It’s simply 6 + 6 = 12. In series circuit the 2 loads add together to equal 12 volts. This is commonly done with other similar ignition systems.
If 12 volt coils were used instead, they would make a 24 volt load and would be under powered by the 12 volt electrical system resulting in a weak spark.

Coils Compared 4 volt 6 volt 12 volt
Lucas ( 17M4) 4 volt 1.0 Ohms primary resistance
Lucas (17M6) 6 volt 1.8 Ohms primary resistance
Lucas (17M12) 12 volt 3.6 Ohm primary resistance

Tri-Spark 4 volt 1.0 Ohms primary resistance
Tri-Spark 6 volt 1.9 Ohms primary resistance
Tri-Spark 12 volt 3.5 Ohm primary resistance

Comments (1)

I get it!

By: on 15 July 2023
Finally grasp the concept of the need for two six volt coils.... Thanks

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