• Capacitive discharge ignition circuits

    From bob prohaska@21:1/5 to All on Sat Sep 25 04:03:41 2021
    Does anybody know of links to well-informed descriptions
    of how AC capacitive discharge ignition circuits work?

    The case at hand is a 1986 Suzuki DT4 outboard motor. It's a
    2-stroke 1-cylinder 4 HP engine, probably not much different
    in ignition requirements from any other small engine. It uses
    two bar-style pickup coils, one to charge the cap and one 180
    degrees away to fire the plug. The CDI box is distinct from
    the pickup coils, all are distinct from the ignition coil.
    Parts are no longer available. There's a photo at http://www.zefox.net/~bp/dt4/PXL_20210923_005603433.jpg

    The initial diagnosis was an open ignition coil, but a
    replacement produced one spark and nothing more. Maybe
    the new ignition coil killed the CDI unit, or maybe we're
    barking up the wrong tree entirely.

    With a better idea how it worked in general, there might be
    a chance at identifying some other engine with compatible
    parts, or, in the best case, of identifying and fixing the
    trouble. At this point it appears the two coils in the photo
    are functional.

    Thanks for reading, and any ideas!

    bob prohaska

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  • From Phil Allison@21:1/5 to bob prohaska on Fri Sep 24 22:17:22 2021
    bob prohaska wrote:
    ================
    Does anybody know of links to well-informed descriptions
    of how AC capacitive discharge ignition circuits work?

    The case at hand is a 1986 Suzuki DT4 outboard motor. It's a
    2-stroke 1-cylinder 4 HP engine, probably not much different
    in ignition requirements from any other small engine. It uses
    two bar-style pickup coils, one to charge the cap and one 180
    degrees away to fire the plug. The CDI box is distinct from
    the pickup coils, all are distinct from the ignition coil.
    Parts are no longer available. There's a photo at http://www.zefox.net/~bp/dt4/PXL_20210923_005603433.jpg

    The initial diagnosis was an open ignition coil, but a
    replacement produced one spark and nothing more. Maybe
    the new ignition coil killed the CDI unit, or maybe we're
    barking up the wrong tree entirely.

    With a better idea how it worked in general, there might be
    a chance at identifying some other engine with compatible
    parts, or, in the best case, of identifying and fixing the
    trouble. At this point it appears the two coils in the photo
    are functional.


    ** I used to work on CDIs back in the 70s for a kit retailer.

    Those ones use a pair of 2N3055s in a self oscillating inverter to produce 300VDC.
    Then an SCR to fire a charged 1uF poly cap into the vehicle's coil.
    The usual points controlled SCR firing - so a bit different to a 2 stroke OB.

    However, the commonest failure was the 1uF cap.
    It had to be a special, high pulse current type to survive at all.

    Oil filled, metal can ones were good - if you can find any.
    Otherwise a " polypropylene " fluoro PF correction cap would be OK too.



    ...... Phil

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  • From Mike S@21:1/5 to bob prohaska on Sat Sep 25 02:01:10 2021
    On 9/24/2021 9:03 PM, bob prohaska wrote:
    Does anybody know of links to well-informed descriptions
    of how AC capacitive discharge ignition circuits work?

    The case at hand is a 1986 Suzuki DT4 outboard motor. It's a
    2-stroke 1-cylinder 4 HP engine, probably not much different
    in ignition requirements from any other small engine. It uses
    two bar-style pickup coils, one to charge the cap and one 180
    degrees away to fire the plug. The CDI box is distinct from
    the pickup coils, all are distinct from the ignition coil.
    Parts are no longer available. There's a photo at http://www.zefox.net/~bp/dt4/PXL_20210923_005603433.jpg

    The initial diagnosis was an open ignition coil, but a
    replacement produced one spark and nothing more. Maybe
    the new ignition coil killed the CDI unit, or maybe we're
    barking up the wrong tree entirely.

    With a better idea how it worked in general, there might be
    a chance at identifying some other engine with compatible
    parts, or, in the best case, of identifying and fixing the
    trouble. At this point it appears the two coils in the photo
    are functional.

    Thanks for reading, and any ideas!

    bob prohaska


    Part numbers https://www.megazip.net/zapchasti-dlya-lodochnyh-motorov/suzuki/dt4-2462/dt4-8058/dt4-vg-767164/electrical-13320932

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  • From Wond@21:1/5 to bob prohaska on Sat Sep 25 15:20:16 2021
    On Sat, 25 Sep 2021 04:03:41 +0000, bob prohaska wrote:

    Does anybody know of links to well-informed descriptions of how AC
    capacitive discharge ignition circuits work?

    The case at hand is a 1986 Suzuki DT4 outboard motor. It's a 2-stroke 1-cylinder 4 HP engine, probably not much different in ignition
    requirements from any other small engine. It uses two bar-style pickup
    coils, one to charge the cap and one 180 degrees away to fire the plug.
    The CDI box is distinct from the pickup coils, all are distinct from the ignition coil. Parts are no longer available. There's a photo at http://www.zefox.net/~bp/dt4/PXL_20210923_005603433.jpg

    The initial diagnosis was an open ignition coil, but a replacement
    produced one spark and nothing more. Maybe the new ignition coil killed
    the CDI unit, or maybe we're barking up the wrong tree entirely.

    With a better idea how it worked in general, there might be a chance at identifying some other engine with compatible parts, or, in the best
    case, of identifying and fixing the trouble. At this point it appears
    the two coils in the photo are functional.

    Thanks for reading, and any ideas!

    bob prohaska

    ISTR there's one in the venerable GE semiconductor manual

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