Understanding V-Twin Electrical System

Discussion in 'Electrical' started by Brewmaster77, Aug 12, 2011.

  1. Brewmaster77

    Brewmaster77 New Member

    Does anyone know of any great online sources for fully understanding the electrical system in a V-Twin engine? Just looking to educate myself on the electrical flow throughout my bike. Also, does a standard dual-fire ignition coil on a v-twin receive A/C power or pulsating D/C? Thanks in advance folks.
  2. Hoople

    Hoople Account Removed

    Probably more than you care to know but,,,

    The primary side of the coil receives a DC pulse or "shot" in order to generate the secondary high voltage. The coil is a step up transformer having a primary winding (battery & ECM side) and a secondary winding (spark plug side).

    Transformer action (voltage step up) can only take place when AC or pulsating DC is applied to the primary. Since we are not looking for a continuous spark across the gap of our spark plug, just one shot or pulse of DC is needed to create the secondary spark.

    On the late model bikes, the primary winding of the coil is "sinked" to produce the spark. All that means is one side of the primary is always hooked to 12V (the system relay provides that). The other side of this primary winding now needs Ground to produce current flow. The ECM provides this "ground shot" to the winding whenever a spark is needed. Since the late model bikes are single fire & each cylinder has it's own spark advance map, the coil is actually 2 separate coils in 1 package. The ECM provides a ground shot for "each" coil.

    The interesting part of the whole process is that the spark across the spark plug is created when the ECM releases or removes the wire from ground not when it applies the wire to ground. You would think the Hi voltage was produced when you drove current through the primary but it is the opposite. The High voltage is produced in the secondary when the ECM removes the wire from ground.

    Hope this helps..
  3. FerrousBueller

    FerrousBueller Junior Member

  4. Brewmaster77

    Brewmaster77 New Member

    Thanks a lot Hoople. This was exactly the in depth answer I was looking for. Just one follow on question. So am I understanding correctly that the battery provides the voltage to the primary winding to be stepped up (Both early dual-fire ignition coils and later single-fire ignition coils) ,while the ECM controls the timing via switching between open/closed positions? You mention late model bikes having the 12V Batt hooked directly to the primary windings of the single-fire ignition coils. How does this differ from earlier models?