Any ideas what a ballast resistor does?

Home Forums Motorcycle help wanted Any ideas what a ballast resistor does?

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  • #8806

    Not urgent but a tech question I would like to know the answer to


    Yes. When starting a car, the wiring via the start switch allows you to give the coil a full 12V and then a ballast resistor cuts in to drop the voltage that the coil runs at. Not seen very often on bike circuits though!
    Hope that helps

    GSX Rat

    My understanding of the ballast resistor is as follows. A coil works at something like 9 volts(for arguments sake – it might not be exactly but bear with me) so the ballast resistor is used during normal running conditions to drop the voltage from the car/bike electrical system to the required voltage as imperial stated. However, during heavy load conditions on the battery such as cranking the engine over , pulling massive current the voltage across the battery drops so the coil is supplied straight from the battery (reduced voltage remember)so that it continues to function and provide a strong spark.

    GSX750 Ratfighter / GSX600F / Beamish250 / Honda70 Rat

    Blackboard paint – Covers a multitude of sins!


    GSX Hooly – exactly so – as found on 1100 Goldwings which run 6v coils with a ballast – 12v fat sparks for starting and reduced voltage for running.

    Matt Black and no other


    Ballast resistor – does it fight fat??!! – I’ll shut up now..

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