Roll Your Own CDI

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Are You Going to Roll Your Own CDI?

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Professer_Dave

New Member
May 25, 2012
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Greg58 said:
Sounds like you guys have this thing figured out, I have been following this thread with interest but have never built anything on this scale. If and when I start one I may have to lean on you guys a lot! Greg.
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Greg58,

I'm not sure 'we' have it 100% figured out, but that doesn't matter. I can say the current design posted here sure has the stock Chinese CDI beat. I agree with ivan H; build one and it'll put a smile on your face! Plenty of folks here seem willing to help if you are not of the electrical persuasion and have questions ... Just do it.

Best,
Dave
 
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ivan H

Member
Oct 8, 2011
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Very well said Perfesa Dave. For the partisipants of the 2 threads involved in this project, congrats, well done. I'm sure that like I, most have never seen 1 of these cdi's except 4 the pics etc shown in these threads. I would like 2 thank Rohmell 4 all he has done 4 us all. Rohmell, u have fielded every question thrown at u, & there have been a few. U r a schollar & gentellman & this would not have come 2 fruition without u. We r endebted 2 u. We dont need an exaact copy of anything, just a working part that is available 2 us all free of charge in the interest of furthering the hobb . If all aspects of these Chinagirls is treated like this has been by members of this forum it can only benefit us all. Qell done guys. Cheers
 
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ivan H

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Oct 8, 2011
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Sorry 4 the typo's in that last post,,,, blame the bar staff (I'm t the pub & have been all arvo) 4 serving me so many drinks. Cheers
 
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nightcruiser

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Mar 25, 2011
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I started following this thread at the beginning but haven't kept up with it lately, now I see it is 45 pages long! WOW!
I am assuming you guys have come up with a final version of the schematic for the home made CDI? If so, can you please direct me to it, I am thinking about building one up this summer just for fun...
I had purchased a coil last summer that I thought might work, but I was disappointed to see the way it was constructed wouldn't allow me to pull off the wire and boot from the unit. (the wire rotates at the coil, messing with this setup seems the only thing I could do is break it!) It has a rather large plastic plug boot, unfortunately my bike frame is extremely small and I cant get this boot on the plug when the motor is mounted, so I cant use this coil. Does anyone know of a coil that works with this CDI that I can remove the wire from and install a regular automotive wire with a rubber boot? The space is so tight on my bike that a flexible rubber boot is the only thing that is going to work for me...
 
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ivan H

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Oct 8, 2011
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Go to page 43, this thread & scroll thru a little way, there's a copy of the origonal hand drawn (slighty worse 4 ware when I did it) schematic that I snail mailed 2 Headtrauma 2 get posted after I had run the cdi for some months, & also the Rohmell redrawn 2 b more legible schematic, & also pics posted of both sides of the board posted by Drewd, plus a layout showing slightly different resistor values in a couple of places, so u can use iether 1. Cheers
 
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nightcruiser

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Mar 25, 2011
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ivan H said:
Go to page 43, this thread & scroll thru a little way, there's a copy of the origonal hand drawn (slighty worse 4 ware when I did it) schematic that I snail mailed 2 Headtrauma 2 get posted after I had run the cdi for some months, & also the Rohmell redrawn 2 b more legible schematic, & also pics posted of both sides of the board posted by Drewd, plus a layout showing slightly different resistor values in a couple of places, so u can use iether 1. Cheers
Click to expand...
I wasn't sure if that was the circuit that came from this thread or something different, thanks for clearing that up...
Has everyone found a 400V 4A SCR to be sufficient? It seems going a bit beefier on the SCR wouldn't be a big deal, a C106DG is only 70 cents. I've been looking through mouser trying to find a good SCR to use, any advice on what to look for in a SCR would be appreciated.
Also, I am wondering how much current is expected to flow through these jumpers? I was thinking of perhaps using a bank of dip switches instead of jumpers on my CDI if the current requirements aren't too high...
Thanks to everyone who put their time and energy into this project, and anyone who takes the time to answer my questions... you guys rock!
 
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ivan H

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Oct 8, 2011
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With the coil lead/boot, my coil is same, non removeable lead & rather than use the crappy Chinese bakelite boot I soldered an eye 2 the lead,, removed plug nipple & put eye on & replaced nipple, & ran like 4 at least a month til I got 2 th bike wrecker's & got a better, still same design as th Chinese boot, but without the bad connection to lead & spark leak. I even ran it in light rain, no prob. Cheers
 
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ivan H

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Oct 8, 2011
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with a different scr, if the gate threshold characteristics r the same it'll b same as, otherwise it'll alter the timing. With the current question, Rohmell or Perfessa Dave would b more qualified than me 2 answer, as I've never done any testing of the cdi other than in situ on the road, but 1/2 watt metal film resistor r more than capable so far, & I've done a lotta miles on, if thats any indication. Cheers
 
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Professer_Dave

New Member
May 25, 2012
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Milwaukee, Wisconsin
Both jumper currents have to be low due to the resistance in series with them and low voltages (like milliamps ... certainly not more than a few 10s of milliamps); so dip switches should be fine.

This is actually a possible drawback of my design with the series resistors. Jumper A passes a little higher current than the conventional parallel resistor design. Still likely OK for most switches though ...

I used the below STMicro SCR I got from Digikey (600V, 8A, $1.40) with great success. The data sheet even calls out CDIs as one of the applications for this part! Nothing on my board gets even slightly warm after the 10 mile ride from work.

http://www.digikey.com/scripts/DkSe...ng=en&keywords=497-2551-5-ND&x=6&y=15&cur=USD

Regards,
Dave
 
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Professer_Dave

New Member
May 25, 2012
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Milwaukee, Wisconsin
ivan H said:
Go to page 43, this thread & scroll thru a little way, there's a copy of the origonal hand drawn (slighty worse 4 ware when I did it) schematic that I snail mailed 2 Headtrauma 2 get posted after I had run the cdi for some months, & also the Rohmell redrawn 2 b more legible schematic, & also pics posted of both sides of the board posted by Drewd, plus a layout showing slightly different resistor values in a couple of places, so u can use iether 1. Cheers
Click to expand...
FYI, the redrawn schematic on page 43 is missing a connection dot at the junction of the SCR kathode wire and the horizontal wire that is crossing it. This is electrically all one node and should be connected. Just don't want anyone to get caught up by that ...

Dave

P.S. My other post said it was awaiting moderator approval? Just in case it doesn't show up later, I believe the jumper currents are low (10s of mA at most) and a dip switch should be fine. As for the SCR, I used a 600V, 8A device from STMicro (Digikey part number 497-2551-5-ND, $1.40). Nothing on my board gets even the slightest bit warm on a 10 mile ride ...
 

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ivan H

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Oct 8, 2011
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Good catch on that Dave, I hadnt noticed as I hadnt looked closely at. Hopefully we can have the schematics edited, & maybe some1 could post a redrawn schematic in the "modified CDI & CR80 coil" thread so people dont have 2 rely on my shaky 1. Yeah, my cdi doesnt get hot at all, & I've done some long rides. I dont have the scr heatsunk either, just a touch of acid free silicone between it & the board 2 damp vibration. Cheers
 
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ivan H

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Oct 8, 2011
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australia
Sounds good Dave. Could u adapt it 2 accommodate both single AC fed CDI's & the much more commonly used types that r triggered by another low voltage input from a seperate coil? HI Drewd, I was just looking at the pic of the back of ur Jag board, (thanx 4 posting), it might b an idea 2 redo a couple of those soldered joints. They should b shiny silver, dull grey 1's could possibly b dry joints. Cheers
 
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Professer_Dave

New Member
May 25, 2012
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Milwaukee, Wisconsin
ivan H said:
Sounds good Dave. Could u adapt it 2 accommodate both single AC fed CDI's & the much more commonly used types that r triggered by another low voltage input from a seperate coil?
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ivan H,

The design I linked to in my earlier post uses the additional coil ... so that job appears to be complete already. My goal is to make a drop in replacement for the analog CDI in the 66cc/80cc Chinese engines. Although it might make this task easier, I don't want to add any additional trigger coils or modify anything else mechanically. I'm afraid if I do that, very few people would go through the trouble to use it. I plan to get angular position information from the zero cross of the AC signal (just like the analog version does now) or possibly get it from the peak of the ac signal (if I need an earlier mark in the rotation to allow adequate processing time) using a simple differentiation circuit followed by a zero cross detector.

If anyone has any ideas, or has tried this in the past, I would like to hear about it and learn from your experience.

Thanks,
Dave
 
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ivan H

Member
Oct 8, 2011
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australia
Hi Dave, I did glance at, but between nokai phone screen & my eyes, uno. I gotta have on largest font just 2 read type. Need glasses & a magnifier 2 do soldering & the like. I hope it all goes well 4 u. Cheers
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
There r several other CDI's that Rohmell has posted in this thread that have been successfully used, including a couple that u can experiment with retard curves & when the retard kicks in, & even 1 that will charge a battery whilst running, which is handy feature. Chears
 
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nightcruiser

New Member
Mar 25, 2011
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USA
ivan H said:
There r several other CDI's that Rohmell has posted in this thread that have been successfully used, including a couple that u can experiment with retard curves & when the retard kicks in, & even 1 that will charge a battery whilst running, which is handy feature. Chears
Click to expand...
Do you have any idea in which page these other designs are posted? With 46 pages in the thread its kinda hard to find... I am putting together a mouser order of parts for my CDI experiment and would like to get enough parts to try a few different designs. I'm also ordering some parts for an experimental LED lighting system as well, researching torch LED's is taking a bit more time than I had expected, so I still have time to add in more CDI parts...
 
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ivan H

Member
Oct 8, 2011
622
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australia
No mate, I dont, sorry, & I'm using a phone 2 go online which makes it a little harder. I did have them saved but lost the phone. I know they're a ways back. If I find them I'll let u know. B good 2 c how u go with the light. Cheers
 
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