Chinese Kit CDI Reverse Engineering

[rohmell]

The purpose of this thread is to reverse engineer and duplicate the Chinese kit-supplied CDI module.
So far, we have determined:

 

[rohmell]

If anyone has a defective CDI, it would be great if you could try to open it up (I know, it's hard) and see if you can find any resistor values.

 

[Dirt Road Cowboy]

Well, I tried to chip my old one open, and it didn't come out pretty.

There is only one resistor, and I haven't been able to decipher any color code. That black stuff coats everything in there, and it cracked when I tried to chip the black stuff (epoxy?) off, so I couldn't get a reading with my ohm meter.

I will have to look closely with a bright light and magnifying glass to see if I can find any colors left.

This is what is on the PCB though:

1 resistor
1 capacitor
1 scr
4 diodes

Sorry, that really isn't much help.

 

[rohmell]

Does the PCB look like this?

 

[Dirt Road Cowboy]

Yes, that's the one.

 

[rohmell]

On your PCB, the first component looks to be a glass diode?

 

[Dirt Road Cowboy]

I think the first component is a black diode. The diode across the bottom of mine is a glass diode.

Black diode then resistor then black diode then another black diode then scr and the bottom diode is like the first one in the picture.
I believe the capacitor went to the scr and then to the coil, but I'm not positive since it broke off when I was trying to get it apart.

Sorry, I'm a bit rusty on my electronics. I haven't really done much electronic work in over 20 years.

 

[Wm Holden]

They dont use tubes anymore....

Just tryin to help!

 

[diceman2004]

this might be of interest
Make Your Own CDI

 

[rohmell]

They dont use tubes anymore....

Just tryin to help!

Microwave ovens still use a tube, a magnetron tube.

 

[rohmell]

I think the first component is a black diode. The diode across the bottom of mine is a glass diode.

Black diode then resistor then black diode then another black diode then scr and the bottom diode is like the first one in the picture.
I believe the capacitor went to the scr and then to the coil, but I'm not positive since it broke off when I was trying to get it apart.

Sorry, I'm a bit rusty on my electronics. I haven't really done much electronic work in over 20 years.

That's probably why yours didn't work, or didn't work for long (HA HA).
In this application, it seems that the black diodes are used for rectification and blocking, and the glass diode is a zener to limit the voltage being applied to the gate of the SCR.

 

[rohmell]

 

[rohmell]

We know that the black diodes are the standard 1N400x series, and that the SCR is a standard off the shelf device, like a C106.

The next challenge is to figure out the value of the resistor and the zener diode.

The typical SCR used in this type of application usually has a peak gate voltage of 5 V, so the zener is going to have a value less than that.

Zener voltages start at 1.8 and go up from there.

Time to break out the cakeboard and do some prototyping.

 

[nightcruiser]

On your PCB, the first component looks to be a glass diode?

Glass diodes are generally zener diodes....

Edit.... guess I was a bit late with that info.....

Nice to see someone doing this and posting results, I have wanted to disect a CDI for a while now but I dont have a dead one...

 

[mmmmudd]

Am I seeing the beginning of an analog cdi with adjustable timing, materializing before my very eyes?

 

[nightcruiser]

We know that the black diodes are the standard 1N400x series, and that the SCR is a standard off the shelf device, like a C106.

The next challenge is to figure out the value of the resistor and the zener diode.

The typical SCR used in this type of application usually has a peak gate voltage of 5 V, so the zener is going to have a value less than that.

Zener voltages start at 1.8 and go up from there.

Time to break out the cakeboard and do some prototyping.

What about that transformer? Would have to figure some specs on it and source a part to replace it as well....
As for the resistor and zener values, aren't there a few schematic diagrams floating around that have these details included? It seems this dissection has confirmed the fairly simple circuit which has been floating around for the CDI.....

 

[nightcruiser]

In the top picture, is that not the coil/transformer connected directly to the center terminal of the SCR? On the back side pic you have penciled in a CAPACITOR in this location? Your diagram shows a capacitor between the center of the SCR and the coil? Maybe I am confused, but this all doesn't seem to jibe....

 

[rohmell]

What you are seeing are the ribbed metallic film insides of a capacitor, part of its orange-red outer covering can be seen still stuck to the resistor in the photo.

 

[nightcruiser]

What you are seeing are the ribbed metallic film insides of a capacitor, part of its orange-red outer covering can be seen still stuck to the resistor in the photo.

Cool, thanks for the explanation, cause it was sure lookin' like a coil....
So what about that coil/transformer, what are the specs on it? Is there a picture of it?

 

[rohmell]

So far, no ignition coil has been recovered from the depths of its epoxy-filled grave we call the CDI module, so we don't know any specifics about it, except for its secondary coil resistance.