Excitor coil signal conversion

Thread Starter

Vforce94

Joined Jan 11, 2023
21
Hello,

I am trying to custom fit electronic ignition to the motorcycle, the ignition that I'm trying to fit has only an excitor coil that gives AC signal of around 50V at peak for CDI timing when cranking the engine. The original ignition and CDI uses an inductive pickup for timing the spark.

My question is how can I convert excitor coil signal to inductive signal, i know that i should build a custom PCB with the required components but I need a little guidance with that if possible.

Best regards,
Armando
 

LowQCab

Joined Nov 6, 2012
2,650
Using any signal other than the "Inductive-Pickup" will NOT work.

The "Inductive-Pickup" sets the "Ignition-Timing-Advance", for the Engine, and
it MUST be used regardless of the type of Ignition-Module You would like to install.

It's almost impossible to create "better" performance than
the original factory installed Ignition-System.

You will not gain any Engine-Power by changing the Ignition-System.
.
.
.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
To explain things better, i have inverted rotor ignition from racing scooters that also has lighting output, therefore with lower rotor mass engine response is a lot quicker than with stock ignition. I am simply looking for a way to convert excitor coil pickup signal (ac waveform) to inductive signal in order to regain timing functionality with the original CDI.
 

MisterBill2

Joined Jan 23, 2018
13,804
If the "exciter coil" was also used to power the lighting then that is not the signal that fires the spark, but it probably does store the charge on the capacitor to fire the plug. and spark timing needs to advance with RPM and that gets complicated. And it sounds like you have removed the the original trigger mechanism for triggering the spark.
And I have no idea as to what "inverted rotor ignition" means.
Magnetic pickups are available in many sizes and a means to mount one in the correctly timed position should be easy. Using the charging coil to trigger the spark will make the spark timing depend on the electrical load.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
Hello to everyone, so inverted rotor is just a term for an ignition where the rotor is spinning inside of the stator instead of over the windings. Picture attached. mvt-dd_12-54477-01.jpeg
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
It has four wires, two for lighting and two for excitor coil, red-black is excitor iutput, green-yellow is ground.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
If the "exciter coil" was also used to power the lighting then that is not the signal that fires the spark, but it probably does store the charge on the capacitor to fire the plug. and spark timing needs to advance with RPM and that gets complicated. And it sounds like you have removed the the original trigger mechanism for triggering the spark.
And I have no idea as to what "inverted rotor ignition" means.
Magnetic pickups are available in many sizes and a means to mount one in the correctly timed position should be easy. Using the charging coil to trigger the spark will make the spark timing depend on the electrical load.
I took that into consideration but I am not sure where to mount the neodymium magnet on the rotor for the inductive pickup to be able to read the timing point without disbalancing the rotor.

I am also open to that idea which i like even more than signal conversion because then i could use the original inducitve pickup but I am not sure where to mount it. All ideas are welcome.
 

MisterBill2

Joined Jan 23, 2018
13,804
It does not seem like mounting a magnet on the rotor will leave the rotor balanced very well and at high RPM that will cause a problem, just as you stated.
So one option is to sense the peak point of the exciter pulse that charges the capacitor for the CD ignition system. Was the ignition trigger coil separate from the other coils?
It would seem to me that the "programmable racing CDI " may have some means to trigger off of the exciter winding charging pulse. Or is the new coils and rotor package product entirely separate from the new CDI package, and sold by a different company? I see that there is quite a bit of adjustability provided for the new fixed coil set. so I am guessing that there is a reason for that adjustment already.
Is there any information provided with the programmable racing CDI system that describes what sort of trigger pulse it should work best with? That would be a very good starting point. I am thinking that an optical pickup might be a better choice because then it would only require a visible mark on the rotor. And a photodiode or phototransistor can have a much faster response.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
It does not seem like mounting a magnet on the rotor will leave the rotor balanced very well and at high RPM that will cause a problem, just as you stated.
So one option is to sense the peak point of the exciter pulse that charges the capacitor for the CD ignition system. Was the ignition trigger coil separate from the other coils?
It would seem to me that the "programmable racing CDI " may have some means to trigger off of the exciter winding charging pulse. Or is the new coils and rotor package product entirely separate from the new CDI package, and sold by a different company? I see that there is quite a bit of adjustability provided for the new fixed coil set. so I am guessing that there is a reason for that adjustment already.
Is there any information provided with the programmable racing CDI system that describes what sort of trigger pulse it should work best with? That would be a very good starting point. I am thinking that an optical pickup might be a better choice because then it would only require a visible mark on the rotor. And a photodiode or phototransistor can have a much faster response.
The new ignition is MVT Digital Direct DD12. The stator has four wires coming from it, two are for lighting generator output(single phase) and the other two are exciter coil output and ground wire.

The reason for using this new ignition is that all other racing ignitions made for Aprilia RS 125 are without lighting, and I want the bike to stay road legal, because of that I need lighting output(55w-the highest power rating that i was able to find with inner rotor ignition).

The old ignition has separate two-wire inductive pickup that sends pulses to the racing CDI as the magnet triggers the pickup coil. The racing CDI is made originally for Aprilia RS so it is exactly the same as the original CDI, except for the programmable ignition curve.

New rotor has some timing marks but since the signal has to be AC pulse with relatively low aplitude, cca 2V to 5V working range, I'm not sure what should I use.

The first idea was to CNC machine a disc that I can screw to the rotor and mount a magnet on it with counter ballance for the magnet but that would be really hard to balance and again it would add mass that I'm trying to lose.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
P.S. The new ignition also comes with its own CDI that is not suitable for my project because it is not programmable nor does it have power valve output because it was made for two stroke scooters.
 

MisterBill2

Joined Jan 23, 2018
13,804
One bit of good news about the pickup installation is that there is another magnetic pickup scheme that does not require a moving magnet. That could allow a much simpler rotating portion for the inductive pickup system. That is the variable reluctance pickup arrangement, which has the magnet inside the coil, and the moving portion simply has a gap in the magnetic material. That can be as simple as a flat disk with one half magnetic steel and the other half non-magnetic stainless alloy, and the trigger pulse generated as the transition passes the pickup. No signal conditioning required because the signal is similar. Many makers of regular magnetic pickups also sell variable reluctance pickups as well. That can solve the balance problem and not add much mass either.
 

shortbus

Joined Sep 30, 2009
9,762
No, I want to convert the excitor coil output to the inductive signal output so i could use the programmable racing CDI that i have, it also operates exhaust valve. That is a 2 Stroke motorcycle.
You seem to be counteracting your self here. You say you want to use a "programmable racing CDI" and from reading about your inverted ignition that is exactly what they say it has. But from myold mind, after working on motorcycles most of my life, it seems the the ignition advance needs to be tied to RPM not a program.
https://www.rrd-preparation.com/en/...-21-lighting-for-mecaboite-minarelli-am6.html

The second question is where is there an exhaust valve on a 2 cycle engine. That's another new one on me. Other than a piston port I never knew of a 2cyle bike engine with an exhaust valve.
EDIT - I forgot about 2cycle, 71 series Detroit Diesels!
 
Last edited:

MisterBill2

Joined Jan 23, 2018
13,804
OK, the simple way to convert the peak of the exciter voltage into an inductive pulse is a diode in series with a capacitor feeding a small transformer. As the exciter voltage rises the capacitor will charge through the diode, passing current through the transformer primary in one direction. A soon as the peak passes and the voltage starts to fall, the diode will be reverse biased and the current will cease, creating an inductive pulse in the transformer secondary, connected to the CDI system. So that gives the simulated pickup pulse with no active circuit required, and total isolation from the rest of the system, so no ground loop issues.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
You seem to be counteracting your self here. You say you want to use a "programmable racing CDI" and from reading about your inverted ignition that is exactly what they say it has. But from myold mind, after working on motorcycles most of my life, it seems the the ignition advance needs to be tied to RPM not a program.
https://www.rrd-preparation.com/en/...-21-lighting-for-mecaboite-minarelli-am6.html

The second question is where is there an exhaust valve on a 2 cycle engine. That's another new one on me. Other than a piston port I never knew of a 2cyle bike engine with an exhaust valve.
EDIT - I forgot about 2cycle, 71 series Detroit Diesels!
That ignition is made for scooters and it uses different type of signal to advance timing and because of that they are not directly compatible so thats why I'm making this adaption. The exhaust valve is also called power valve and it is used to reduce exaust outlet size to reduce hesitation at low rpm.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
OK, the simple way to convert the peak of the exciter voltage into an inductive pulse is a diode in series with a capacitor feeding a small transformer. As the exciter voltage rises the capacitor will charge through the diode, passing current through the transformer primary in one direction. A soon as the peak passes and the voltage starts to fall, the diode will be reverse biased and the current will cease, creating an inductive pulse in the transformer secondary, connected to the CDI system. So that gives the simulated pickup pulse with no active circuit required, and total isolation from the rest of the system, so no ground loop issues.
Thank you for your reply, I am good with automation systems and repairing simpler electronic systems but I am not good with designing one, is there any chance that you could make a circuit drawing, I can give you all the info that you need about the input/output values.
 

shortbus

Joined Sep 30, 2009
9,762
That ignition is made for scooters and it uses different type of signal to advance timing and because of that they are not directly compatible so thats why I'm making this adaption.
So why not get a Hall sensor as your pick up? Get one made for acting with a single polarity (Ithink they most commonly use magnetic south, but may be wrong) This would allow you to use the existing magnets in the flywheel to get a DC pulse to the ignition rather than the AC pulse that it normally makes. They are normally AC because the magnets in the flywheel has both N and S poles, and that generates the AC output.
 
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