Discussing CDI charateristics - Page 2 - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #11 of 56 Old 01-05-2019, 06:50 PM Thread Starter
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@chrider

Martin,

That does seem to be a reasonable explanation. A bit odd in presentation; perhaps the associated word chart didn't make it into the manual.

Now, your comment on RC networks interests me. This CDI system has a conventional pick-up (crank position sensor) coil. The reluctor bar on the rotor is in two pieces. The leading edge of the first piece corresponds to 10*BTDC and the second corresponds to 40*BTDC. Those points correspond to the "Fire" and "Full Advance" markings on the rotor. The duration of each piece is 10* with a 10* gap between them.

Given that, can you describe how an RC network would work to cause the advance? I'm a bit befuddled. I understand RC for charging/discharging, but not using it to create an advance curve.

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post #12 of 56 Old 01-05-2019, 11:01 PM Thread Starter
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Martin,

One suggestion that was offered (as conjecture by a person whose opinion I trust on such matters) is that the pick-up coil's signal becomes stronger as rpm increases. As that signal increases in strength, it reaches the thyristor threshold earlier thus causing an advance in timing.

That does offer an explanation as to why the Gen 2 reluctor bar is so long so perhaps that is how the TCBI on the Gen 2 works. For the older KLR600 CDI, though, I wonder. The KLR600 rotor is too neatly perfect for it to be a progressing threshold sort of thing. The KLR600 has an initial timing of 10*BTDC and a full advance at 40*BTDC, so a total of 30* of advance. The reluctor bars start at 40*BTDC and have a span of 30*BTDC. It is as if edge detection of the reluctor has to perfect and the advance happens by some other means.

I'm trying to imagine an analog circuit that could, based upon frequency, delay triggering the capacitor by up to 30*. With no advance circuitry, the spark would occur at 40*BTDC. The advance is all-in by 3000rpm, so what must happen is that the circuit retards that spark to ~10*BTDC at idle and the advance curve occurs because the circuit is sensing rpm and reducing the retard until it is gone at 3000rpm.

What could it sense and how could that retard the spark? At 1200 rpm there are 20 revolutions per second, or one revolution every .050 seconds, or 50 ms. To retard the leading edge signal by 30 degrees would be to delay it for about 4 ms. How do you do that?

Tom [email protected]

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post #13 of 56 Old 01-06-2019, 07:35 PM
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Tom,
I am an electrical engineer, but I've not given CDI circuits any thought before, and while I could come up with some electronic mechanisms, not sure they would be practical. Usually when I start with something I don't know anything about, I look through the internet for ideas. There may be very simple design ideas for this particular problem, but I have no idea. I've spent only a few minutes looking into this, so this might all be FOS (Full of Shit), but here are a few observations:

Glancing at your chart and accounting for the +/- 2 deg angular tolerance, there seems to be about a +/- 10% tolerance in the RPM axis. That would be a reasonable tolerance for an analog circuit that uses a capacitor based circuit to establish some time/rpm reference. I don't think using the crank signal amplitude for that would provide this kind of accuracy over the life of the system, and changes in pickup coil performance would directly affect the spark advance, something I'd be concerned about.

The first few home-brew circuits I found all used PIC microcontrollers to figure out the advance based on RPM. I have not yet figured out how typical analog circuits are done for this application.

I also noticed that the pickup signals have a negative pulse associated with the leading edge of the reluctor, and a positive pulse with the trailing edge, or vice versa. Your oscilloscope shot shows that too. One circuit I looked at used the leading edge negative pulse as input into the (microcontroller based) timing circuit, and the trailing edge positive pulse to trigger a spark at 0deg TDC to facilitate starting. I don't know whether all ignition systems retard for starting, but in Lycoming engines I played with, accidentally firing at 10deg before TDC during cranking typically cracked the starter mount. I think the circuit should fire at TDC or later until RPM information has been established.

I can't invest any time into this right now, but my next step would be to translate the angle vs. rpm curve you got into a time advance vs. rpm curve. That, combined with the location of the reluctor edges available would define what the circuit is supposed to do, and which parts of the curve can be directly derived from the reluctor edges.

Martin
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post #14 of 56 Old 01-06-2019, 10:00 PM Thread Starter
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Martin,

I cannot say for sure that the CDI is purely analog; I was just looking at a patent that was granted in 1975 to a couple of Japanese fellas that seemed to be mostly digital. The 555 was around then and their design has flip-flops and gates, so why not the Denso hardware 10 years later?

The Kawasaki schematics are no help, they simply have an AMWO* I-O box labeled "Ignition Timing Control Circuit".

What I am going to do is worry less about how it does it and concentrate on what it does. That was what I was originally after; the circuitry is a squirrel that ran by.

It may take me another week or so to get around to figuring out the Gen 1 advance curve. After that, it may be another week before I can get the KLR600 ignition installed.

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Tom [email protected]

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post #15 of 56 Old 01-07-2019, 01:03 PM Thread Starter
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I pulled all the CDI posts out of the "What did you do to your KLR today" thread and put them in their own thread; this topic didn't belong there.
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post #16 of 56 Old 01-09-2019, 12:58 AM
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This is really neat, I actually took an old CDI apart once, I think I still have it lying around, although I believe it was a Chinese knockoff. It was mostly digital, the only analog on the board seemed to be for power conditioning and output boosting. It actually had an MCU that I figured probably didnt have write protection on it, and originally I thought about trying to dump the FW in order to create my own somewhat tune-able CDI box. Although I never got that far unfortunately, since another chinese knockoff CDI was only $30 or something and OEM one was like over $130.
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post #17 of 56 Old 01-16-2019, 04:26 PM Thread Starter
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It's raining cats and dogs. The hills are sliding down the burn areas. News is boring. No car chases in LA today.

What to do, what to do?

I know! Weird Science from the Shop of Horrors!

I'm still looking at data to see if I can develop a curve, but this was too much fun not to share.

Tom [email protected]

“Some days I feel like playing it smooth. Some days I feel like playing it like a waffle iron.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

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post #18 of 56 Old 01-16-2019, 04:42 PM Thread Starter
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This is a bit better.
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Tom [email protected]

“Some days I feel like playing it smooth. Some days I feel like playing it like a waffle iron.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
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post #19 of 56 Old 01-16-2019, 04:55 PM Thread Starter
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Still better. The ignition was dumping noise onto the trigger line so I changed the scope trigger to the ignition line so the trace wouldn't jump.
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Tom [email protected]

“Some days I feel like playing it smooth. Some days I feel like playing it like a waffle iron.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
Noli Timere Messorem
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post #20 of 56 Old 01-16-2019, 05:09 PM
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Tom, can you break it down for me, what we're seeing here?

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