Bosch CDI

[Rana1]

Hello everyone.

I've heard and read few times that cdi's transfo works at 3KHz. Today using an oscilloscope I found it does over 4KHz at 14v input and only at ~3KHz at 4-9v of input.
Is that ok?

Thanks for your help

[T77911S]

yes

[Rana1]

Than you

[wwest]

Originally Posted by Rana1

Hello everyone.

I've heard and read few times that cdi's transfo works at 3KHz. Today using an oscilloscope I found it does over 4KHz at 14v input and only at ~3KHz at 4-9v of input.
Is that ok?

Thanks for your help

If I remember correctly the frequency, INSTANTANEOUS frequency, is a function of the load level on the inverter, the closer the CAPACITOR is to reaching a full charge the higher the inverter frequency will become. What you "hear" with the engine stopped, is the frequency that results from the CAPACITOR being fully charged.

What is most important is that the DC-DC inverter be able to charge THE capacitor to at least 300 volts in the <3 milliseconds between plug firings at 7200 RPM.

[ischmitz]

I typically see around 3.6kHz at rest and yes the frequency shifts slightly with varying supply voltage but not to above 4kHz. And once the box is loaded up (running at 6k RPM) the inital run-in is at a slightly higher frequency.

If the box is damaged (shorted SCR or coil connected and shorted capacitor) the frequency changes to something above 4kHz because the DC/DC converter now works against a dead short. Once you reduce the supply voltage it comes back to the 3.5 kHz. You might have a damaged box if that is the case with yours.

Ingo