Test bench for cdi

[Florek]

hello , i see thread about test bench cdi without motor, but i dont find any results there. its look simple. for the max simplicity of ignition lets think engine have 2 coil, one charge coil that charge capacitor inside of cdi, this charge coil provide about 300-500v ac depends on motor. second coil is trigger coil that produce small voltage about 5-10vac , so when trigger coil produce 5vac this voltage go to cdi and trigger scr that release voltage (300-500v) stored in capacitor to wire that go to hv coil that is connected to sparkplug. so i think that, if i have cdi, and dont have engine, to test cdi, i should apply voltage lets say even 50v to 2 wire going to cdi, one ground wire , and second wire that is normally conected to charge coil, this should charge capacitor to about 50v right? then next i provide small voltage to two wire simulating trigger coil, so one wire is ground, and one wire its that wire what go to trigger coil , and then send 5v so that cdi think that its time to give spark. before i apply 5v on trigger wire, i connect dmm one lead to ground, second lead to wire thats going from cdi to iginition coil , and in the moment that i send 5v to trigger wire, i should see on dmm aobut 50v on wire that going to ignition coil right?

 

[GA_Boater]

Theory and real world don't always coincide.

It's more than voltage, it's pulsing voltage that triggers a CDI. Why not install it and follow the trouble shooting procedures?

 

[F_R]

Florek, I'd say your idea is basically correct. I've also been knocking the idea around of constructing such a test device myself. Probably a few minor details to work out. To my way of thinking, the capacitor could be charged with simple 120VAC wall voltage. It is rectified within the power pack before being applied to the capacitor. A 5V pulse of the proper polarity should trigger it. At least that would be my first guess.

 

[Crosbyman]

FR,... capacitors only hold DC …... from the previously rectified 300-500 AC then discharge when triggered via SCR`s

https://www.elprocus.com/capacitor-discharge-ignition-cdi-system-working/

 

[Florek]

yes but problem is that i try with ac and dc and still cant release the volgate from capacitor

 

[GA_Boater]

yes but problem is that i try with ac and dc and still cant release the volgate from capacitor

This because you don't have the bench setup that a CDI maker uses to test new units.

You are trying to apply a voltage to charge a cap and the voltage needs to be a continuous cycle to maintain the charge. The rest of the circuitry the cap is connected to is bleeding off the charge.

 

[racerone]

You test the kill circuit first.-----If there is no spark on both leads you test the components under the flywheel.----No need to remove the flywheel for that.-----If those are good a new powerpack is installed.-----Both ignition coils do not fail at the same time.-----No fancy bench tests needed in my opinion.

 

[F_R]

FR,... capacitors only hold DC …... from the previously rectified 300-500 AC then discharge when triggered via SCR`s

Ain't that what I said?

 

[Florek]

but i want test without engine

 

[GA_Boater]

Are you still working on this?

https://forums.iboats.com/forum/eng...johnson-evinrude-outboards/10641743-cheap-cdi

 

[Florek]

Are you still working on this?

https://forums.iboats.com/forum/eng...johnson-evinrude-outboards/10641743-cheap-cdi

no, in my life i repair few cdi, thats why i want this test bench to be sure that cdi work, and i dont always have engine

 

[Crosbyman]

Ain't that what I said?

I think… you said could be charging the capacitor with AC BEFORE rectifying ….

then added

" It is rectified within the power pack before being applied to the capacitor"

you a right…

I guess it all works out in the end when you read it again ​

 

[gm280]

You have the concept down pretty well. You could use any AC voltage to charge the coil. I would avoid straight from the well receptacle though and try something a little safer to keep from any serious shocks while experimenting. Maybe a step down transformer to isolate direct higher voltage (and current) until you get it all working. The AC needs to be constant as well.

And you could also make a simple 555 timer circuit to provide the trigger pulse(s) as well. That way you would get both positive and negative edge trigger pulses to trigger the SCR to fire. Very simple setup and you would have your bench test setup.

Calculate the average RPM of the engine at idle and make your 555 timer circuit duplicate the correct pulse cycles for that speed per number of cylinders needed. Then you will get many triggered outputs to monitor.

An O'scope would be great to monitor the pulse outputs for any abnormalities.

I've built CDI circuits for vehicles back in the day. Nothing different with these CDI circuits in use today. Same concept and builds...

 

[Florek]

You have the concept down pretty well. You could use any AC voltage to charge the coil. I would avoid straight from the well receptacle though and try something a little safer to keep from any serious shocks while experimenting. Maybe a step down transformer to isolate direct higher voltage (and current) until you get it all working. The AC needs to be constant as well.

And you could also make a simple 555 timer circuit to provide the trigger pulse(s) as well. That way you would get both positive and negative edge trigger pulses to trigger the SCR to fire. Very simple setup and you would have your bench test setup.

Calculate the average RPM of the engine at idle and make your 555 timer circuit duplicate the correct pulse cycles for that speed per number of cylinders needed. Then you will get many triggered outputs to monitor.

An O'scope would be great to monitor the pulse outputs for any abnormalities.

I've built CDI circuits for vehicles back in the day. Nothing different with these CDI circuits in use today. Same concept and builds...

great, have any idea how schematic should look?

 

[gm280]

I could draw up a schematic if need be. But simple look up a typical 555 timer circuit and look for a pulse generator setup. Then change the resistors and capacitor with that circuit to give you the output frequency you are wanting. Pretty simple to do that. And that will be your trigger pulse. Then use a small 120 volt to 24 volt AC step down transformer for the charge setup for safety reasons. Nothing really fancy...