modified cdi and cr 80 coil

Ok, sorry I've been away for a while, recently got flooded out to the max from a cyclone that went thru. Right, the SCR has a black side with writting on & the other side is (glassivated) metal. Looking at it with the black side with writting on it facing you, the lead out connections (left to right) are K, A, G. The tantalum capacitors are polarised. Look at them thru a magnifying glass & u will see a + close to 1 leg. The + must go to earth, as the timing network operates under a negative voltage, making earth positive in respect to the negative voltage. I'll have to go back & look at the schematic to see which jumper ur asking about, (I use a slightly modified variant of the CDI). I'll check & get back 2. Cheers
 
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Ok, so Jumper 2 is in the timing network & is affecting how steep the retard curve (at higher rpm) is. It is on a 0.47uf tanalum cap. You will see that there are actually two of these 0.47uf caps in the network. For more adjustability, they can both be put on a jumper to earth if u like. Now to your question. Start without the jumper, or jumpers if u put them on both caps removed. When u have found the setting with the "A" jumpers (on the 120 & 220 ohm resistors) that give the best Low RPM performance, u can then see wot setting of these "B" jumpers in the timing network give the best Hi RPM performance. U do this by experimentation. Test for "A" jumper setting @ Lo RPM with the motor under load, like up a hill u have chosen so u can compare performance. Test for "B" jumper setting on a flat straight road where u can wind it out. Wot ever setting, with either A or B jumpers gives the best performance is right for your application. When testing for A & B jumper settings, start with none so u get like a base line for comparison, then add a jumper & do another run, & so on & so on. Cheers
 
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Thanks Ivan.
I am about to solder everything and I noticed something on the circuit diagram that Draco has made.
It's on the right side of the diagram, the one 4.7uF 35v and two 0.47uF 35v. Their (+) legs are shown to go to ground.
Ground is (-).
Is this intentionally to have the (+) legs go to (-) ground?

Sorry to question your diagram, Draco. I just want to make sure before I secure all the solder.
 
misel said:
Thanks Ivan.
I am about to solder everything and I noticed something on the circuit diagram that Draco has made.
It's on the right side of the diagram, the one 4.7uF 35v and two 0.47uF 35v. Their (+) legs are shown to go to ground.
Ground is (-).
Is this intentionally to have the (+) legs go to (-) ground?

Sorry to question your diagram, Draco. I just want to make sure before I secure all the solder.
Click to expand...

Yes that is correct the way it is drawn up as it is the same on the original rough diagram by Ivan.
 
Re: Waterproofing a mag?

Hi, yes, that is correct, the + on all 3 tantalum caps goes to ground, which is actually "0 volts". The AC voltage from the magneto is first rectified to DC in the CDI by the diodes. The + half of the AC is used to charge the polypropylene charge caps. The - half is sent to the R/C network formed by the tantalums & the 760 ohm resistor. Notice this is connected to the SCR's gate. When this - voltage reaches a certain potential (a couple of volts "negative", the SCR is triggered into conducting. Anyway, because earth is at "0 volts potential", the negative voltage the timing network run's on is negative with respect to "0 volts". So 0 volts is positive in respect to the negative voltage, (& the + voltage is even more + with respect to it, a couple hundred volts more, at least), therefore the 3 tantalum caps + legs go to earth. If they ar place in a circuit operating on + voltage, the other unmarked leg would go to earth. I specified tantalum caps as they are very stable in timing networks,,, alas, they're polarized. Again, all 3 tantalum caps must be oriented with the positive marked leg going to earth. Cheers
 
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Hi I've been reading this thread and the "Roll your own cdi thread" for a few months now and have finally got round to making my own. I've carefully followe the Circuit diagram provided by Dracothered(Many Thanks), i have tested the cdi on my bike and played around with the jumper settings and it will only run the bike for 30seconds to 1 Minute before dying, i have checked all the resistors, diodes and cap, all seem fine and in the correct place and polarity. however i noticed my SCR is C106d 4a 400v which in the diagram says 8a 600v. i was wondering if anyone would know whether this could be the cause of my problem?
 
Sounds like it's overheating and shutting down. I think when it gets real hot the resistance goes way up and nothing can get through. Replace the part with one with the right values and I'd bet the problem is solved :)
 
Hi thanks for the input i actually put the stock cdi on and went for a ride just then and it died after 1 minute aswell, I then realised i had put on a new fuel tank cap the same time as i put the cdi on and my issue was simply that the fuel tank wasnt breathing properly how embarrassing hahaha
 
[email protected] said:
Hi thanks for the input i actually put the stock cdi on and went for a ride just then and it died after 1 minute aswell, I then realised i had put on a new fuel tank cap the same time as i put the cdi on and my issue was simply that the fuel tank wasnt breathing properly how embarrassing hahaha
Click to expand...

That's why it is advised to only do one mod at a time or you could cause your self to chase a ghost and make you want to pull your hair out. Glad you found you problem fairly quickly. :D
 
Hi, I think the 400V SCR will be ok, I use the 600V so they have a decent safety margin in regard to voltage. They're only cheap so maybe use the 1 u have while getting a 600V 1, & swap it out when u get. Same with charge caps, the higher AC voltage rating u can get, the better. 250VAC will do without failing, I use because I can get them off the shelf locally & have had no problem, but 400VAC would be better 4 the same reason. Glad u found the problem & it wasnt the CDI u built. Is it running smoother, reving higher? Just a quick tip if u have the unit set on the more advanced variation (27 ohm pulldown resistor & 100 ohm series resistor in circuit), make sure its not running too advanced. Listen for a metalic rattling sound on firing which would indicate this. The center electrode of ur plug is also an indicator. It should have an even coating of oxide completely covering the side of the center electrode. If the very end 1/2mm or so shows a band of bare metal u r running too advanced & the heat generated by this is burning the oxide off. Cheers
 
Just about any single lead coil would work. I think even a car raceing coil would work, too, as long as it has the same wireing. Of course, then again, who needs a coil as big as one of these engines...

zpt
 
Hi, thats exactly wot u want. The CR80 coil gives a really hot spark, better than most of them. The lead from the free end of the charge caps in the CDI goes to the spade terminal on the coil. The earth lead from the CDI goes to the core of the coil with a large eye connector. Cheers
 
Just put mine together tonight, tested it, no spark. Are the charge caps ( i rhink thats what they are....2 biggest things on the board) directional? I'll be re checking all the connections and orientations in the morning.
Also, if jumpers 4 And 5 are left totally open, will you get any spark? I'll be jumping them to jag settings but would just like to narrow down what my problem is.
Thanks for the help in advance!
 
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Glad u found the problem easily. Yes the SCR (silicon controlled rectifier) has a cathode (K), gate (G) & anode (A), & must be oriented correctly, as must all diodes & the 3 tanalum timing caps (the + marked legs go to earth). The large charge caps & all resistors are not polarized & can go in either way. Cheers
 
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