Homemade CDI

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Reply to
Rob / gompy.net
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Bookmarked! Quite interesting. Say, what voltages and how much energy do you get on the HV-side?

Nick

Reply to
Nick Müller

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

Reply to
Rob / gompy.net

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

Reply to
steamer

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

Wayne...

Reply to
Wayne Weedon

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

Reply to
steamer

Interesting numbers. :-))

600V are enough to ignite at what CR and what spark plug gap? And 90MJoule. Frightening!

Nick

Reply to
Nick Müller

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...

Reply to
Wayne Weedon

He meant milli Joule not Mega Joule !.

Greg

Reply to
Greg

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

Mark Rand RTFM

Reply to
Mark Rand

"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.

Reply to
Rob / gompy.net

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.

Reply to
Rob / gompy.net

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

Reply to
Duncan Munro

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

Reply to
Rob / gompy.net

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

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A half Farad at 600V would be the size of a truck!, to put the numbers into perspective 45MJ is about the energy stored in 16 car batteries. His capacitor only stores 0.045 Joules of energy, 45 milli Joules as I said.

Greg

Reply to
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

Reply to
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:

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AWEM

Reply to
Andrew Mawson
[1F caps]

And not to forget the low currents allowed!

Nick

Reply to
Nick Müller

--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..

Reply to
steamer

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...

Reply to
Wayne Weedon

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