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Post by buicknick on Dec 31, 2007 18:26:24 GMT -5
I just bought myself a rusty XT500, it has the CDI ignition like the SR500, so i thought I'd come here and ask some questions. It didn't start so I metered everything, and it checked out. I have it narrowed down to the CDI box. I don't feel like spending much money on this bike yet, so I dissected the CDI box. I got the circuit mostly figured out, but I am curious about how the system exactly works so i can "fill in the blanks."
When does it use the low speed pulser/charger vs the highspeed? is it only during cranking(or should i say kicking)?
Is there a advance curve, or does it just switch from the low speed to high speed circuits to advance the timing all at once? The circuit is pretty simple, and I don't really see much in it for applying an advance curve.
Thanks,
Nick
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Post by buicknick on Jan 2, 2008 17:09:47 GMT -5
I guess no one knows?  Anyone want to hook up a timing light to their bike and see how the advance comes on, with a curve or all at once, and at what RPM? Also does anyone have a bad CDI box they would like to give away? The disassembly of mine was rather crude (cutting the metal away, freezing it, and smashing it with a sledge hammer.) Although I was able to get almost 100% of the circuit (including resistor values ;D ) there are a few missing links that I would be able to figure out if i had another box the tear down. I'll pay shipping, or pick up if within Connecticut, USA. The circuit is rather simple, should be able to be built for $15 worth of parts. Hopefully I'll have a working schematic to share shortly! |
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Post by StewRoss on Jan 3, 2008 1:47:46 GMT -5
Hi, Sorry I can't assist on this one...I'm more 'in tune' with the mechanical stuff... SR  |
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Post by sjef on Jan 3, 2008 5:10:05 GMT -5
Hallo Nick, here is a drawing of the ignition system with all values to measure  good replacement cdi are sold by hyperpak australia adjustable cdi: asuotani and kedo info www.transmic.net/gbindex.htmthere is a thread on the german sr forum  and remember there are 3 different cdi depending on yeasr of make and sr400 or 500 hope this helps regards sjef |
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Post by buicknick on Jan 3, 2008 20:42:13 GMT -5
Sjef, thanks a ton! The last schematic you posted matched what i got from mine exactly, and filled in my missing stuff.
Thanks!!!
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Post by wotavidone on Jan 3, 2008 21:19:53 GMT -5
Looks very simple. The only questionI'd have would be what sort of thyristor to use.
Is NTC just an adjustable resistor? If so what is its function? Also what is value of condensor? Is it inside the CDI box?
I have measured mine with a timing light, and I reckon there is an advance curve. i.e. advance progressively rises from 2000 to about 4000 rpm if I remember correctly. But it intrigues me how it would manage it with this very simple circuit. Very interested to see if this NTC adjustment can be used to adjust the rate and extent of advance, some real possibilities for manageing engine knock, etc.
Mick
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Post by caferacercarl on Jan 5, 2008 2:10:35 GMT -5
They have three coils supplying the CDI, the low speed is only up to about 1,400rpm then the high speed plus the little horse shoe pickup in the middle of the stator is the advance coil. hope this helps, Carl, caferacer mc.
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Post by buicknick on Jan 5, 2008 17:32:05 GMT -5
An NTC is a thermistor, it changes resistance with temperature, I believe it is being used to adjust the circuit for temperature effecting the SCR. The condensor, or capacitor, is inside the CDI box. I don't know the value of it, but looking at other CDI schematics it seems most have around a .5uf rating. It needs to be big enough to hold some charge, but if it is too big it will not charge/discharge quick enough at higher rpms.
I am thinking that it achieves the timing from the sine wave that would be coming in from the pulser coils. I am guessing that the pulser's signal starts at say 26 deg tdc, and peaks at 12 deg. If this signal gets feed straight to the scr(thyristor) the timing will be at 26deg. But there are the resistors inline with it, bringing the amplitude of the sine wave down, and pulsing the scr later. As engine speed increases the amplitude of the sine wave increases, and will pulse the coil sooner and sooner as rpm goes up until 26 degs. I do not know if that's how it works, but it's my guess, I'll find out when I get this thing rigged up.
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Post by davedunsboro on Jan 6, 2008 7:57:55 GMT -5
This is a very interesting thread ! The black box unplugged & exposed We obviously have some very clever lads amongst us to nut this one ! I'd say your on the right track & with the info you have it must be possible to build one of these . Its really a case of how far you want to go or is it easier to just buy the generic one & retro it as once its been hit with a hammer could you trust it or do you build the whole thing( I'm OK I've got a spare in the box) so by the time I need one I hope you've got the answer cheers Dave.
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Post by buicknick on Jan 6, 2008 14:48:53 GMT -5
Building it with all new parts. I actually built the prototype, but the thyristor i used wasn't the right one, it was all i had laying around. I work in electronic manufacturing so I'm gonna order the right one Monday. It did charge up the cap, but it wound not discharge it.
For today I'm gonna rig up two transistors together to make a thyristor. They are small transistors, so i am expecting them to blow up quickly, but it should let me know if the circuit will work.
I'll post later with the results.
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Post by wotavidone on Jan 7, 2008 0:06:51 GMT -5
Nick, you are the man!!!
If you seriously can reproduce the CDI for $15 or $20 worth of parts, and a bit of patience with a soldering iron, you are simply worth your weght in cockyshit.
And mate, that is a lot of cockyshit.
One thing we probably forget somewhat is that no matter how much we all love SR's, not every forum member has an unlimited budget. So, its really good to see some serious DIY help for potentially expensive problem.
Keep slaving away, mate, and post it all when you are done.
Mick
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Post by caferacercarl on Jan 7, 2008 1:16:26 GMT -5
Ask the guy's at small coil rewinds in Geelong,they have a wealth of knowledge and will gladly chat to you and tell you all the values/specs that you might need, for free!! and even give you the voltage outputs at differen RPM from the stator windings that deal with the spark. carl.
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Post by wotavidone on Jan 7, 2008 17:35:27 GMT -5
It's the internals of the CDI that impress me. I have never seen the circuit diagram for a real motorcycle one before, only electronics magazine projects and kits, and motorcycle manuals just show a blank box. I am amazed at how simple it is.
I have to say though, its an d**n good point about the voltage outputs at different revs.
It reminds me of a thing that happened to me years ago, when in a previous life I rented out Public Address systems for sporting events and the like.
When a speaker stopped working after a hard day at full bore, it was usually just the voice coil burnt out, and a quick change of coil was all that was needed.
However, occaisonally the coil would test OK, but the speaker would hardly issue a whisper.
I finally woke up what the drama was: overheated magnets lose their strength. There was no cure for this, various mobs could source Toa voice coils, but no one could deliver the magnets.
It is something to consider when troubleshooting ignition problems - when the coils test OK for resistance, but don't put out anywhere near enough voltage, the battery doesn't charge and you are thinking about getting your stator rewound, ask your self how hot your magnets have got. If you can't pick up your biggest spanner with the magnets in the flywheel, maybe they've lost their guts?
MIck
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Post by buicknick on Jan 25, 2008 18:01:34 GMT -5
Been busy with other things, but i finally got the correct SCR, and I have spark!!! unfortunately the carb is not on the bike, so i couldn't actually start it. I'll rebuild the carb tomarow, and hopefully have it running sunday. Once I get it running I'll post the part numbers i used.
On a side note, I looked at the odometer, I bought the bike without even checking the mileage... this 1980 xt500 only has 2500 miles on it!!!!! just wish it looked like it, lol.
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Post by andy on Jan 26, 2008 2:46:47 GMT -5
Nick,your research into this often discussed area is brilliant,no bullshit.12 months ago i replaced my c.d.i with one from hyperpak[new zealand] it works fine and told me there wasnt much up with the old one! occasionally when funds permit i go on a new for old binge! if with your skills you can develope a proggrammable/adjustable advance curve c.d.i i reckon you've struck gold.well done.
Andy [lil 'ol england]
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Anyone want to hook up a timing light to their bike and see how the advance comes on, with a curve or all at once, and at what RPM?
