Is your CDI AC or DC?

Is your black box an AC or a DC-CDI?
Here are a few tips:

  1. If the bike has no battery then it’s an AC-CDI
  2. What is the size of the CDI? ACCDI are smaller than DCCDI.
    Length=6cm then it’s an ACCDI, around 9cm it’s a DC-CDI.
    This method is not 100% reliable, some brands use big boxes for ACCDI
  3. Age of your bike? Old bikes are mostly AC whereas news one are more DC…
  4. Search in your Service Manual Technical Specifications for AC-CDI or DC-CDI mention.
  5. Look at the Wiring Diagram if the CDI is connected to the +12v line or only to the stator:
  6. AC-CDI is connected to pickup AND stator but NOT connected to +12v

    DC-CDI is connected to pickup only AND connected to +12v.
    Below the Red wire goes to the battery throughout the main sw:

  7. What is the reference or serial number printed on the CDI? Google it
  8. Google your bike with ACCDI and DCCDI key words
  9. The only reliable way is to measure the voltage between GROUND and the POWER source input of the CDI while the engine is running.
  10. Ie: On a GY6 CDI measure between GND pin 4 and Power pin 6
    If 12 to 15volts DC then it’s a DC-CDI
    If 50 to 100volts AC then it’s an AC-CDI
  11. While the engine is running, disconnect the battery and the regulator,
    The engine stall because it has no more +12v then it’s a DC-CDI
    The engine still run because it’s powered by the spinning rotor then it’s an AC-CDI

  12. If the cdi is dead and the engine not running, remove the sparkplug, rotate the engine with a drill attached to the nut on the clutch or rotor side and make the measurements above.

If the bike has a 12v battery, a DC-CDI can replace an AC-CDI but on the contrary an AC-CDI cannot replace a DC-CDI !

5 thoughts on “Is your CDI AC or DC?”

  1. Bonjour,
    Tombé sur votre site aprés de nombreuses recherches je suis ravi, car vos composants simples et accessibles devraient m’aider à passer mon r1100r bmw ( capteurs hall) avec des carburateurs bing 40mm.Encore en phase de reflexion je me laisserais tenter si vous pouvez m’apporter vos conseils en cas de doutes, notemment sur la compatibilité de ma bobine et de mon capteur avec votre boitier.Un grand merci en tous cas pour avois mis vos connaissances / compétences au profit de notre passion.
    Bien cordialement

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