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-   -   Discussing CDI charateristics (https://www.klrforum.com/1987-2007-wrenching-mods/70233-discussing-cdi-charateristics.html)

Tom Schmitz 01-03-2019 06:50 PM

Discussing CDI charateristics
 
EDIT: I moved some posts from the "2019 What did you do to your KLR today" thread because this topic was basically a high-jack to that thread.



I put an oscilloscope on the pickup coil and the ignition coil, looking at the waveforms. Does that count?

I painted the KLR600 engine covers silver, too.

samuel 01-03-2019 07:01 PM

What were the waveforms like?

Tom Schmitz 01-04-2019 01:53 AM

This trace is from the pick-up coil. The distance from the negative spike to the positive spike represents the length of the reluctor bar. I can't remember how long it is or what the central angle is. I think I have that info over in the Gen 2 >Gen 2 ignition thread.
https://farm5.staticflickr.com/4837/...0f8a883f_o.png

This trace is from the coil. It is the tach signal.
https://farm8.staticflickr.com/7842/...a97f917f_o.png

I had to make a couple of cables that would bring the signal out to where I could latch onto it with the oscilloscope. Today I just played around to see if I could get the signal and what it looked like. What I plan on doing is connecting a two-channel scope up and getting these traces displaying well.

The pick-up coil trace should lead the coil trace by some milliseconds that will represent 10° of initial timing advance. As I increase rpm I should be able to see the ignition timing advance and plot theGen 1 ignition advance curve. I'll do the same with the KLR600, though I will be using a KLR250 CDI unit there.

samuel 01-04-2019 12:22 PM

Quote:

Originally Posted by Tom Schmitz (Post 676983)
I think I have that info over in the Gen 2 >Gen 2 ignition thread.

I don't know what a reluctor bar is… can you point me to that thread?

Quote:

Originally Posted by Tom Schmitz (Post 676983)
…getting these traces displaying well.

It looks badass. Having oscilloscopes in a motorcycle dashboard (not to imply this is what you're doing) would be Ultima Farkle!

Quote:

Originally Posted by Tom Schmitz (Post 676983)
The pick-up coil trace should lead the coil trace by some milliseconds that will represent 10° of initial timing advance. As I increase rpm I should be able to see the ignition timing advance and plot theGen 1 ignition advance curve. I'll do the same with the KLR600, though I will be using a KLR250 CDI unit there.

Are you planning on tweaking the ignition, or is this more of an exploratory research thing?

Tom Schmitz 01-04-2019 06:42 PM

A reluctor is a piece of metal that passes by a coil that has a magnetic bar at its center. When the reluctor passes by the coil it first creates a pulse in the coil. As the reluctor leaves, it creates a pulse opposite in polarity from the first pulse. These pulses are used to tell some other component to do something. In the case of the CDI (simplistically), it is telling the capacitor to fire. Thus, the reluctor and the pick-up coil establish the ignition timing.

In motyorcycle terms a reluctor bar is a raised strip of metal that is on the outside of the rotor. The pick-up coil sits in the generator housing in very close proximity to the reluctor bar as it passes by.

Quote:

Originally Posted by samuel (Post 677011)
I don't know what a reluctor bar is… can you point me to that thread?

In this thread I alluded to the reluctor bar issue https://www.klrforum.com/2008-klr650...n-gen-2-a.html. To elaborate on the comment in the first post, the two ignition systems are triggered somewhat differently and the reluctor bar is longer on a Gen 2. There has been an ill-advised practice in some quarters to simply grind off the extra bit of the Gen 2 reluctor bar when using it in a Gen 1. The reason for using a Gen 2 rotor in a Gen 1 bike is that it is claimed that the Gen 2 rotor will deliver an extra amp of current in the Gen 1 generator. This claim has never been substantiated nor has there ever been an explanation of how this was measured nor has it been explained what the mechanism is. I have never seen any Gauss meter figures and subsequent math to support the idea. I am not saying it isn't the case, but the details seem needlessly shrouded in mystery.

I say "ill-advised practice" because Denso went to great pains to balance the rotor and the amount of material being ground off exceeds the amount of material removed for balancing. Thus the grinding is putting the rotor quite out of balance. There has never been any addressing of the balancing issue with this mod, either.

We must have talked about it in another thread as well because I have these two images showing the difference in the central angle of the bar. Danged if I know what thread it was.

https://farm1.staticflickr.com/17/31...dec79e53_z.jpg
https://farm1.staticflickr.com/306/3...058d4038_z.jpg


It looks badass. Having oscilloscopes in a motorcycle dashboard (not to imply this is what you're doing) would be Ultima Farkle!

An oscilloscope is simply a voltmeter that is really fast and lets you see the shape of the voltage. A voltmeter gives you the average of a waveform. And no, it wouldn't be in the dash. These shots were downloaded from my pocket oscilloscope. I find it very handy when electromagnetics is involved.

Are you planning on tweaking the ignition, or is this more of an exploratory research thing?

It is exploratory research. I simply want to know. There is this chart in the KLR600 manual that I have never understood. I have looked at it many times and recently, as a part of 'let's be stoopid and get rid of the electric start so we can make the KLR into a rad lightweight trail bike' I found I needed to convert to an '84 KLR600 ignition. That had me looking at the chart again, and for a long time, because the advance curve is different (the 600 has 10 more degrees of advance than the Gen 1 650). Since I couldn't fathom what it meant I decided to go look for myself. This one is for a KLR250, but the KLR600 is similarly constructed.
https://farm5.staticflickr.com/4827/...4d2c8bd8_z.jpg

How do you read that chart? There are two lines that each appear to represent an advance curve. One starts with 8*BTDC, the other with 12*BTDC. That I get. But what is the advance at 2700RPM? If you read it the way I was taught to read a chart in the 5th grade, there are two x,y-intercepts associated with 2700RPM, thus the advance is 23* BTDC and 35* BTDC. And that ain't possible.


samuel 01-04-2019 11:56 PM

Quote:

Originally Posted by Tom Schmitz (Post 677017)
There are two lines that each appear to represent an advance curve. One starts with 8*BTDC, the other with 12*BTDC. That I get.

I'm afraid I don't get it though… the two lines, what do they represent? I would think that there would be just one advance value, either 8° or 12°, so I don't get there being two lines in the first place (i.e. at idle).

It seems that the two x,y-intercepts scenario is present throughout the range, right? At 1K, it's 12° and 8°; at 2K it's 10 and 22; and at 27K it's 23 and 35. When you say that's not possible, do you mean "having two values for the advance isn't possible," or are the values outside the range you'd expect?

Perhaps the chart is made to accommodate two scenarios: One where the timing is set to 8° at idle, and another where it's set to 12. Then, each of the two curves represents a result starting from one of these values. However, if it were a matter of a simple setting, I would expect the "break" (the point on the X-axis where the curve starts its ascent) to appear at the same RPM for both curves (currently it's at ca. 1600 and 1900). However, I know exactly zilch about how the timing advance occurs on the KLR (or how the ignition system works on this machine at all actually… I'll have to read up on this).

This manual… is it made to cover more than one bike? Two bikes with different ignition systems/timing curves perhaps?

Tom Schmitz 01-05-2019 07:28 AM

Quote:

Originally Posted by samuel (Post 677045)
I'm afraid I don't get it though… the two lines, what do they represent? I would think that there would be just one advance value, either 8° or 12°, so I don't get there being two lines in the first place (i.e. at idle).

Exactly that, there should be only one curve.

It seems that the two x,y-intercepts scenario is present throughout the range, right? At 1K, it's 12° and 8°; at 2K it's 10 and 22; and at 27K it's 23 and 35. When you say that's not possible, do you mean "having two values for the advance isn't possible," or are the values outside the range you'd expect?

Right, the advance can't be two values. The values are within the range one would expect, but advance at a certain rpm can only be one value. At least, with this ignition system. A more sophisticated system could have different advance values that were dependant on more than rpm, such as throttle position, mass airflow, knock sensing, relative humidity, elevation, let your imagination run wild. That requires digital processing of inputs; the CDI is purely analog.

Perhaps the chart is made to accommodate two scenarios: One where the timing is set to 8° at idle, and another where it's set to 12. Then, each of the two curves represents a result starting from one of these values. However, if it were a matter of a simple setting, I would expect the "break" (the point on the X-axis where the curve starts its ascent) to appear at the same RPM for both curves (currently it's at ca. 1600 and 1900). However, I know exactly zilch about how the timing advance occurs on the KLR (or how the ignition system works on this machine at all actually… I'll have to read up on this).

Excellent intuition, but the ignition system is not adjustable. That is, you cannot set the initial advance point. It is nominally set at 10*BTDC. What I might be able to buy is that the chart is intended to say that the advance curve will fall somewhere between these two limits and that it is simply poor chartsmanship that makes it so hard for me to understand. It is a pretty crude analog system, but why they would publish anything other than the nominal is odd. Or, I'm overthinking things again...

This manual… is it made to cover more than one bike? Two bikes with different ignition systems/timing curves perhaps?

No, it was just the one bike. The ignition system was changed with the '87 KLR and, to my knowledge, even though the advance curve was changed there was never any chart to accompany the change. Perhaps the committee in charge of ignition system changes looked at the chart and couldn't figure it out either, so decided not to publish a new one ;^)

........

Voyager 01-05-2019 08:53 AM

Quote:

Originally Posted by samuel (Post 677045)
I'm afraid I don't get it though… the two lines, what do they represent? I would think that there would be just one advance value, either 8° or 12°, so I don't get there being two lines in the first place (i.e. at idle).

It seems that the two x,y-intercepts scenario is present throughout the range, right? At 1K, it's 12° and 8°; at 2K it's 10 and 22; and at 27K it's 23 and 35. When you say that's not possible, do you mean "having two values for the advance isn't possible," or are the values outside the range you'd expect?

Perhaps the chart is made to accommodate two scenarios: One where the timing is set to 8° at idle, and another where it's set to 12. Then, each of the two curves represents a result starting from one of these values. However, if it were a matter of a simple setting, I would expect the "break" (the point on the X-axis where the curve starts its ascent) to appear at the same RPM for both curves (currently it's at ca. 1600 and 1900). However, I know exactly zilch about how the timing advance occurs on the KLR (or how the ignition system works on this machine at all actually… I'll have to read up on this).

This manual… is it made to cover more than one bike? Two bikes with different ignition systems/timing curves perhaps?

Well, I am new to the KLR and have not yet delved into the ignition system, but I will offer a guess based on other engines I have worked on in the past. However, i am NOT saying this is how the KLR works.

Many older engines with carburetors and no ECU, used a combination of mechanical timing advance and vacuum timing advance. The two curves “might” be showing the advance at each RPM if only mechanical advance is active (generally when at WOT when the vacuum falls to near ambient) and at partial or closed throttle when the vacuum is highest. The combination of vacuum and mechanical advance means that the advance curve is now a family of curves based on how much vacuum is present. If this chart had shading or cross hatching between the curves, I would be more confident in my guess, but since it just has the two separate curves, I am less confident. And if someone familiar with the KLR chimes in and says that no vacuum is provided to the advance system on the KLR, then my guess goes out the window.:smile2:

Tom Schmitz 01-05-2019 09:16 AM

The KLR ignition (well, the CDI at least, the Gen 2 igniter is a different animal) has neither mechanical nor vacuum advance. The initial timing is fixed at a nominal 10*BTDC by virtue of the placement of the reluctor bar on the rotor.

The timing advance occurs in the CDI unit through some sort of electrickery which I don't yet understand. It may have something to do with proximity, velocity, triggering speeds, thyristors, resistors, or all of the foregoing. But it is definitely electrickery.

chrider 01-05-2019 02:13 PM

Quote:

Originally Posted by Tom Schmitz (Post 677061)
The KLR ignition (well, the CDI at least, the Gen 2 igniter is a different animal) has neither mechanical nor vacuum advance. The initial timing is fixed at a nominal 10*BTDC by virtue of the placement of the reluctor bar on the rotor.

The timing advance occurs in the CDI unit through some sort of electrickery which I don't yet understand. It may have something to do with proximity, velocity, triggering speeds, thyristors, resistors, or all of the foregoing. But it is definitely electrickery.

Tom,

My guess would be that the chart is meant for checking the performance of the CDI and that the two curves represent the acceptable limits, with the measured performance expected to be somewhere between the two curves. A +/- 2 degree tolerance from nominal seen here for the y-axis is what I am used to from aircraft engines, and some additional variation in the rpm axis would be expected since this CDI is likely an analog circuit using RC networks for timing elements.

Martin


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