Motorcycle CDI

[Aaron Murakami]

I'm asked quite often about putting the plasma ignition on a motorcycle, but I'm always wondering about the CDI's that are so popular on bikes... can they be modified to produce the plasma like a car CDI?

This site was sent to me that shows an example of a bike cdi diagram: http://mastercircuits.blogspot.com.a...08/dc-cdi.html



The CDI module you see in those images or similar seem to be put on race bikes with no battery - my question is how is the cap charged with just a magnet on a flywheel that pass the coil 2 times per full cycle? It's normally wasted spark so it sparks on the compression and exhaust cycles.

Does anyone know the setup for a bike CDI with no battery?

[maxc]

I'm asked quite often about putting the plasma ignition on a motorcycle, but I'm always wondering about the CDI's that are so popular on bikes... can they be modified to produce the plasma like a car CDI?

This site was sent to me that shows an example of a bike cdi diagram: http://mastercircuits.blogspot.com.a...08/dc-cdi.html



The CDI module you see in those images or similar seem to be put on race bikes with no battery - my question is how is the cap charged with just a magnet on a flywheel that pass the coil 2 times per full cycle? It's normally wasted spark so it sparks on the compression and exhaust cycles.

Does anyone know the setup for a bike CDI with no battery?

Maybe some schematic is missing and the engine starts on inductive? Here a good thread on 1/3 of energy gos back too battery. http://speedtalk.com/forum/viewtopic.php?f=1&t=42274

[Willem Coetzee]

I know on dragsters my friends use magnetos, and many places on the internet says that motorbikes are powered by magnetos. That would then be the same principal than small generators and so on. But on our little Ryobi genie, it sounds like it spins at a very low rpm at start up, so I'm not so sure that the magnet spinning at that speed can produce enough umph, but maybe it does -very good question.

It all comes down to that the faster the magneto spins, the more voltage the CDI primary gets, they say. Good for when the engine is already going, cause their is no load on the poor battery, if a battery is present.

But because the magneto induces a (+) and (-) pulse into the pickup coil, one will have to make a plan with that pulse of the two that has the wrong polarity for the primary coil...

Maybe have two parallel 1000A6 diodes inline to the primary coil, so that the wrong polarity pulse do not go to primar coil, but reflected off the diodes and captured by another cap, and that cap discharged though a bridge... so the primary gets sort of two pulses of only the one correct polarity (hopefully) - then a HV diode from secondary to primary (+) will make sense, IF the HV secondary output is (+).

On a single cylinder motor cycle engine I can envision a double solution for the waste spark:

A reed or hall switch on the exhaust valve can actuate maybe a fuel injector type solenoid (so it can withstand up to the high rev band) that PRE-switches a little isolator block into a gap in the HV spark plug wire, thereby not allowing the HV to go to the spark plug...

But on the same axle or what ever of the solenoid is also two little conduit blocks on both sides of the isolator, so when it blocks the HV to spark plug, at the same time the one conduit block closes a circuit that steps down the HV to charge say a 400-500 cap, which cap is connected in parallel onto the spark plug and does not discharge without the normal firing HV.

Remember this "hv switch" PRE-SELECTS by jumping to its new position BEFORE the HV secondary is discharged so it ALREADY stands IN one of its desired positions at HV discharge, so there is no normal "switching" electric corrosion on the blocks like in a motor or generator or what ever.

So when the exhust valve closes, the solenoid is actuated back to its "HV spark" position, again, PRE-SELECTED, so that when the HV is discharged, it this time discharges to the spark plug, and its booster cap also discharges.

Therefore, if the HV diode is put in position a la Murakami Ignition Method, there might be a small "RE event" that grows a bit bigger as the engine revs up and the magneto generates more voltage for primary CDI discharge, and then the booster cap ads the Lorentz Force to blow up the plasma into a cloud and shoot it into the combustion chamber.

This is what I was working out for my car - I never mentioned it in the plasma ignition thread because I've never came to build it, since the it has 4 cylinders and it would mean I had to have 4 times more components...

So I don't know if cost wise it is viable for everybody that has an engine that has 2 or more cylinders - I sure can't afford it know, because here in South Africa, secondhand parts are gold, and are sold at just under the price of new parts - sick.

Any case, guys with more SSR knowledge might have a cheaper way of such switching of the HV, but I could not find any indication on the HV ssr's exist, or if one can connect them in series to achieve HV switch capability - so I also did not further chase that avenue, cause it also might eventually become cost inefficient with driving circuitry and more stuff that can blow and burn or whatever.

I do see in some patents that series strings of SCR's are suggested as a HV switch unit, maybe driven in paralell with one able drive circuit - so one could maybe actuate such a drive circuit to switch such a SCR switch for each cyclinder's spark plug - I got no clue what it would cost me here in South Africa to acquire enough SCR's and a proper drive circuit, plus hall sensors and components for each exhaust valve.

Another issues in a multi-cylinder engine, whether motor bike or car, with reed or hall sensors in the camshaft space, is (1) space itself might not be enough or improper geometry, and (2) you will have to take your wires through the cam casing metal.

Where I halted with the whole idea of eliminating the waste spark, is when I looked rather just having one hall sensor on the cam belt pulley itself for each spark plug's HV switch, positioned in relation to each cylinder's exhaust valve, whish much cooler and way more doable, but had no better or cheaper HV-switch solution.

Long story short 0 I'm sure that a motorbike engine might be way more friendly toward a plasma ignition setup due its already existing CDI - a few finer details just needs to be taken care of.