CDI Charging and Triggering

Discussion in 'The Garage' started by Zahnarzt, Aug 21, 2019.

  1. Zahnarzt

    Zahnarzt Crashes Much

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    All modern circa 1980 and newer bikes, quads, snowmobiles etc use a CDI to supply the momentary electrical current / voltage to the coil subsequently firing the plug.

    Where and how does the mystical "Black Box" get the timing and power to do its work?

    First: There are two power sources that charge the capacitors that will eventually discharge into the coil.
    1.The older of the two is an AC voltage provided by a coil located (usually) on an arm of the stator complex inside the engine

    2. A newer source is a 12V DC voltage provided by the battery. (There is circuitry inside the CDI that changes this into the high voltage needed to fire the coil.

    Next, there is a trigger coil (Sometimes a Hall effect sensor) that sends a "triggering Voltage" to the CDI to tell it to release the stored energy in the capacitor.

    OK... So what? In the decades I have been working on bikes and quads, the above mentioned system has always been a guessing game to diagnose. Most service manuals give resistance specs for the charging and triggering coils, BUT I, as well as others have replaced these parts that were out of spec only to have no resolution to the issue... WTH.
    For the last few years I have been testing the resistance of ALL the source and trigger coils of machines that come into the garage for any type of repair - usually carb cleaning.
    I would say, about 25% have out of spec values but were running just fine.

    My request (for the curiousness of it) and to help others, is for those that feel comfortable measuring these values on their own bikes and post it up so I can distill it into actual data.
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  2. Zahnarzt

    Zahnarzt Crashes Much

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    Another piece of information I use in diagnosis is the output voltage of these coils.

    I purchased a Direct Voltage Adapter (it measures peak AC voltage and converts it to a stable DC voltage that can be read on a standard Multi-Meter)
    I use a Electronic Specialties 640DVA purchased from Amazon for around $35
    I know this is not as precise as an oscilloscope but it gets me in the ball park.

    If you have access to a DVA that would be good information as well.
    If you work on any CDI equipped machines they will save you the investment cost the first time you use it.

    An example:

    1993 Yamaha Warrior/ Specified Resistance Charge Coil (270-330ohm), Measured 317ohms. DVA output 134V. Specified resistance trigger coil (171-209ohms), measured 217ohms, DVA output 3.8V

    Quad runs great

    2003 Yamaha Warrior/ No charging coil (DC CDI) Specified resistance trigger coil (459-561ohms), measured 432ohms, DVA output 5.5V

    Quad does not run - no spark. Coil test good... do I risk replacing the stator or the CDI?

    I assumed (with my limited knowledge that 5.5V was enough to trigger the CDI and ordered one.
    Plugged it in and it fired up first bump.

    I have an excel spreadsheet i am dumping all this data into.
    Any input is appreciated.

    Z
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  3. tntmo

    tntmo Oops, I did it again.

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    Interesting concept, I was just reading all kinds of data while trouleshooting my Vulcan Nomad trying to ensure that my ECU was ok. For that bike, there's no readings on the ECU, just the wires leading to it.
    #3
  4. KirkN

    KirkN Long timer Super Supporter

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    Just saw this thread, by searching CDI, as I'm struggling with the CDI in my 1983 PE175 (thread in 2 smokers / Old's cool).

    Trigger coil spec: 200~260 ohm. Actual: 235 ohm
    Charge coil spec: Trigger coil + 20~30 ohm (they're wired in series!). Actual: 265 ohm

    Trigger coil output: ~78 VAC (meter set to 250VAC scale).
    Charge coil output: ~85 VAC (ditto)

    Stock CDI measures 'bad' according to Suzuki manual's test table (continuity/no continuity between various CDI wires). Picked up a cheap generic $6 6-pin Chinese CDI and hooked it up with jumpers (trigger, charge, ground, output to ignition coil). My bike now gets spark, but only at high rpms (turning motor over with drill via the countershaft sprocket nut). Low rpms and the spark goes away.

    Had a generic Chinese 5-pin CDI onhand as well and gave IT a try - same exact results as with the 6-pin.
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  5. Zahnarzt

    Zahnarzt Crashes Much

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    I ordered a new CDI as the trigger voltage seemed within range.

    I was testing with a DVA which in theory measures the actual output barring having an oscilloscope. Digital multi meters have a speed at which they can pick-up and measure AC voltage point. Most are not fast enough to read the correct frequency.

    If you have some time and a few bucks i would recommend purchasing a DVA from Amazon and testing again, although the charge coil seems suspect for sure.

    If you do, pleas post up the values you get.
    #5
  6. KirkN

    KirkN Long timer Super Supporter

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    Interesting. My little meter seems to at least be responsive, although I cannot comment on it's accuracy. That is, at low rpms, the meter reads a lower voltage. As I speed the rpms up, the voltage being read increases until it seems to "max out" at the values I posted.

    Why do you think my charge coil seems suspect?
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  7. Zahnarzt

    Zahnarzt Crashes Much

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    Charging coils, in everything I've worked on, have been much higher voltage than triggering coils.
    Sometimes by a factor of 10. The capacitor takes a large hit to get fully charged, the trigger is just a low voltage gate.
    Let me see if i can find a service manual and wiring diagram. Manufactures in that era were trying a lot f new stuff and there is no real consistency in CDI boxes.
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  8. KirkN

    KirkN Long timer Super Supporter

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    Ahh, that does make sense, and does accord with what I'm getting. At higher rpms / higher voltage, I get spark!
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  9. Zahnarzt

    Zahnarzt Crashes Much

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    Ok, I called Scott @ CDI box.com and he said the specs you are giving are ok.
    He does build a box for the 83/84 PE 175/250/400 for 165$
    And... surprisingly he would take it back if it wasn't the problem. you pay shipping.
    https://cdibox.com/links-info/

    You may want to give him a call and reverify all the info. see what he can do for you.

    ( I have no affiliation with his site) he was just very helpful.
    #9
  10. Beezer

    Beezer Long timer Supporter

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    the manuals for older bikes often have the numbers for testing the CDI that were taken with an analog meter....

    a meter reads ohms by sending out a voltage and "seeing" how much it drops. it is calibrated to give an accurate ohms reading based on that drop.

    digital meters use much lower voltages to read resistance than the old analog type. both types read the same on straight resistance like a coil, but quite different on any circuit that has a solid state device in it like a diode or transistor. the reason is these devices have a constant voltage drop when forward biased... lets say about .7 VDC. if the old style meter's source is 9v , and is connected to a diode, .7 of that source drops across the diode. now if you put a meter that uses 3v on that same diode, it still drops .7, giving a totally different ohm reading. actually, the voltages vary with the scale selected, but it still holds true. be wary using manuals from the 80s, maybe even the early 90s when analog meters still ruled
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  11. KirkN

    KirkN Long timer Super Supporter

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    Interesting.

    However, my '84 PE175's manual gives resistance values only for the coils. For the CDI testing, it only gives continuity, or infinity as an expected result, not any specific resistance value. So, results should still be valid.

    And it's funny you mention that, because I did dig out my old analog meter, only to find that not only was it's 9-V battery dead, of course, but the battery connector had all but rotted away as well. Sigh. Not even sure where to FIND a 9-volt connector to put back in there anymore, short of salvaging some other device... :lol3
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  12. Beezer

    Beezer Long timer Supporter

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    actually... a 9v end is common as dirt. I have a local electronics store that has them in a bag on a hook. try evilbay
    #12