CDI Ignition - Help please!!!

Discussion in 'General Electronics Chat' started by Alex_atm, Jun 30, 2013.

  1. Alex_atm

    Thread Starter New Member

    Jun 30, 2013
    5
    1
    Hi guys,

    Greatly appreciate any help or insights you can offer (I am NOT very knowledgeable about ignition systems or electronics generally).

    I have a jet boat with a custom designed and built 2 stroke engine - so no manuals for this sucker.

    It has a simple 6 pin AC CDI ignition system much like this diagram but with 2 coils and 2 wires to the pickup (the second wire goes to the pin that is shown as empty in the diagram).

    http://www.chinesescooterreference.com/manual_images/wiring_stator_cdi_coil.jpg

    I have been having trouble with the ignition system and thought it was the CDI unit, I have now swapped out the CDI unit and tested again tonight (this has been going on for about 6mts now).

    So... what is happening on the test is:

    No spark at all when turning the engine over, when I stop turning the engine over I am sometimes getting a single spark as the engine stops. It dosen't matter which coil I use the result is the same.

    Any thoughts or ideas? I am really stumped but thinking that perhaps it is the pickup that is not working so not telling the CDI to fire, the spark at the end could be the CDI discharging once it no longer has current flowing into it.

    Thanks in advance and sorry if I have posted this in the wrong section!

    Alex.
    Sydney.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    What does the pick up consist of, a magnetic sensor or is it a set of points? Can you simulate the pick up sensor by pulsing the input ?


    What make/ model of CDI is it?
     
  3. Alex_atm

    Thread Starter New Member

    Jun 30, 2013
    5
    1
    The CDI is custom built - so no make or model sorry.

    The pick up is a magnetic sensor.

    I was thinking of simulating the input and seeing if there is a spark, how would I do this? Just with a 1.5v battery? (I don't want to toast the CDI).

    Thanks Dave.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Get a voltmeter on the sensor output, and move a magnet over it , see what pulse signal voltage is coming from it, it may be a 5V or 12V pulse.

    Do you have the circuit of the CDI?
     
  5. Alex_atm

    Thread Starter New Member

    Jun 30, 2013
    5
    1
    No CDI diagram unfortunately.

    I will try moving a magnet and measuring the pulse (I think I need a volt meter with a peak voltage setting as my cheap one cant measure a pulse that quick - any recommendations on a volt meter that wont cost me the earth?)

    I had previously measured 0.5v coming off the trigger when turning over the engine.

    I have been told that if the trigger is touching the timing striker plate (instead of the 2-3mm gap) it could be causing this problem. Does that sound plausible?

    Thanks again
    Alex.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    Yep , i think it should give a signal of at least 1 volt or so.

    You could simply pulse the sensor wire.

    post a photo of the sensor.
     
    Alex_atm likes this.
  7. Alex_atm

    Thread Starter New Member

    Jun 30, 2013
    5
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    How would I pulse the sensor wire?

    This is the trigger:[​IMG]
     
  8. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Hi,

    I'm actually surprised this thread hasn't been closed already. The terms of service clearly state no automotive modifications of any kind are allowed, due to safety and liability issues. While a jet boat isn't a regular automobile, I'm sure it falls under the same category.

    Good luck.
    Matt
     
  9. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    I notice you are in Australia. Here is an article from Silicon Chip May 2008 on a CDI kit sold by Jaycar for around $20. Ive built several of them. Your sensor looks very mutch like a triger coil type. It should give a pulse when a magnet is flicked past it. The red wire from the stator in your circuit would be the HV winding for the CDI. The restof the Silicon chip article gives a prety good description of how a CDI ign works.
     
    Alex_atm likes this.
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,777
    932
    The level of corrosion present on the one contact pictured, leads me to believe your problem may not be with the circuit parts, but with its connections instead. It doesn't take much corrosion to make a connection to resistive to function at voltages less than 12V
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    782
    How is the capacitor charged in your CDI?

    Some types have a transistor inverter while others have a 350-400V winding on the alternator.

    The first type can get a bit flaky under cranking load if the battery is old, the second type needs a good swing to get it going.
     
    Chris Edge likes this.
  12. debe

    Well-Known Member

    Sep 21, 2010
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    184
    Hi Ian, If you look at the circuit reference in his first post, it has a HV winding on the stator to charge the capacitor.
     
  13. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    CDI is a very specific type of ignition: capacative discharge. Most electronic ignitions are not CDI, they just have a FET device switching the coil neg lead to ground (replaces the points job) with solid state circuitry to convert the hall effect sensor signal to switch the transistor on and off.. Unless you can generate a schematic for this thing, you really have no hope of fixing it since you don't know what it is or how it is wired. Maybe it is CDI?
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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  15. leinahtan

    New Member

    Jun 13, 2007
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    cdi pulse input sometimes do have a polarity to fire the spark plug...

    by using an oscilloscope on the pick up coil you'll get the polarity..

    this is a positive to negative pulse polarity
    [​IMG]

    and this one is negative to positive one...
    [​IMG]


    the first pulse is the pulse that will be send and conditioned by the cdi to get it going...

    http://mastercircuits.blogspot.com/2013/05/programmable-dc-cdi-test.html

    this tester can test all type of cdi whether it be an AC or DC type..
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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  17. leinahtan

    New Member

    Jun 13, 2007
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    not on the ignition coil but in the pulser coil...this is the coil that send the right signal to the cdi for the correct timing of the spark..

    ignition coil just step up the voltage coming out from the cdi...

    I've done this many times.....not all cdi will work on any motorcycle..the magnet which is attached to the flywheel do have polarity....
     
  18. creakndale

    Active Member

    Mar 13, 2009
    68
    7
    I didn't see a ballast resistor in your drawing but if there is one, check to make sure it's not faulty.

    We had a 1976 Dodge Aspen station wagon with CDI ignition that suffered the exact same symptom as you are describing. It would crank over and over with not a hint of it starting. As the key was rotated back it would fire one time which seemed very bizarre. In this case the ballast resistor was located on the firewall and the theory was either vibration or occasionally being slashed with puddle water caused it to crack. It was a bad design so we kept a spare ballast resistor in the glove box.

    creakndale
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Its a little bit of a mystery what purpose a ballast resistor would serve on a CDI ignition.

    A CDI charges a capacitor to about 300 - 400V and dumps it into the coil primary, it would seem a bit odd going to all that trouble to get as much energy as possible into the coil - only to dissipate a large chunk of it in a resistor!
     
  20. Alex_atm

    Thread Starter New Member

    Jun 30, 2013
    5
    1
    Hi guys,

    Thought you may appreciate an update. I pulled the engine apart and had a play over the weekend.

    The trigger sensor was not properly positioned, it was too far away from the trigger magnet. In addition the kill switch circuit was earthing when turning the engine over (go figure?).

    Long story short - I now have a good strong spark! Thanks for all your help.

    Now to figure out what is up with my fuel system but that is a project for next weekend and a different forum! :)

    Thanks again for all the help and advice.
     
    debe likes this.
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