Homemade CDI

Bookmarked! Quite interesting. Say, what voltages and how much energy do you get on the HV-side?

Nick

~600 Volt (0.5*C*(U*U)= 0.5*0.5*(600*600)=90 MJoule

--I give up; what's a CDI? I assume the "I" is for ignition..

Capacitor Discharge Ignition. Probably he most used technique these days.

Wayne...

--Aha. Using a cap doesn't fix the rate? By this I mean it still works at various throttle settings? Neat trick.

Interesting numbers. :-))

Nick

Not sure what you mean. CDI's basically work by charging a cap during the dwell period, and discharging through an SCR into the coil.

Been used since at least the early 70's. Of course most of the newer ones are controlled via a micro to give mapping etc.

Wayne...

He meant milli Joule not Mega Joule !.

Greg

No, he's got a half Farad 600V capacitor built into it. Wahay!

Mark Rand RTFM

"Mark Rand" schreef in bericht news: snipped-for-privacy@4ax.com...

Thats correct. (0.5*0.5(600*600)=90,000 Joule = 90 MegaJoule You need for a good spark only 45 MJoule, so if the Voltage is less grom the HV-coil it isn't a problem.

On some CDI's there is a connection with the gas-channel of the receiver, But linking the gas-channel to your CDI needs extra knowledge from your engine and ignition.

Do you have details on T1 (Bobine), the one that feeds the spark plug?

You can use any bobine from small bikes. If the engine have a coil into the flywheel, the bobine will be work for you.

No, he's got a half MICROFARAD capacitor, well actually 0.47uF to be precise, here's the link to his circuit:

Greg

Just to make the point, I've got an 85 microfarad 600V capacitor in my rotary converter that's about 3" in diameter and 8" long, half a Farad is nearly six thousand of those in parallel!.

Greg

I well remember my physics teacher saying that you'll probably never see a Farad capacitor due to the size etc, but now they are very common as memory back ups on pc's, with a volume of far less than a cubic inch, though admittedly only rated at 6v DC or so. Presumably due to improvements in dielectrics and the ability to make them very thin.

Here is an example:

And not to forget the low currents allowed!

Nick

--Well the followup questions: are these only used to start engines, or to keep them running? If the latter, how fast can the cap charge? What I meant was: what is the fastest it can be charged? Seems to me this would limit the number of cycles and thus limit the rpm of the engine..

I've actually seen CDI's claiming to be good for 30,000rpm+ The have been used on MotoX and roadrace bike for many years, and a lot of those are good for 20K+

Wayne...