Roll Your Own CDI

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Are You Going to Roll Your Own CDI?


  • Total voters
    123

DuctTapedGoat

Active Member
Dec 20, 2010
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Nampa Idaho
Quickie parts list for the CDI:

Diodes: 1000 PIV 3A
Resistors: 18 and 82 Ohm 1/2W
Capacitor: 2uf 600V Film/Foil Polypropylene
SCR: 1000V 3A

Due to the wide variety of ignition coils that can be used it is better to overrate the components to be safe, although for the most part, you can use just about any parts that you may have lying around.

The component values are not set in stone; for example, I used 400 PIV 1A diodes in my prototypes with no problems.
I used an SCR that is just too big for the purpose (600V 63A, inverter grade), but that is what I had lying around, so I threw it in.

An old TV with a CRT should provide all of the parts except maybe for the SCR, although some TVs used an SCR in the power supply circuit. Heck, you might even be able to use the flyback transformer as your ignition coil! (I'm gonna try it!)
So, I've got an old flyback transformer from an RPTV - I agree, we gotta try it out. I'm still hunting locally for a pot that can handle high voltage and/or an SCR. Smallest I have that's high tolerance is 1500V 8A, and I dunno about that one.
 

Greg58

Well-Known Member
May 1, 2011
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Dang I knew I should have stayed away from this thread, I just might have enough fork lift parts in my tool box at work to try this. My wife allready says I spend too much time in my shop
 

rohmell

Active Member
Jun 2, 2010
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Dang I knew I should have stayed away from this thread, I just might have enough fork lift parts in my tool box at work to try this. My wife allready says I spend too much time in my shop
What kind of voltage rating on those forklift SCRs? They might have a too low voltage rating
 

Greg58

Well-Known Member
May 1, 2011
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I don't remember the voltage ratings on the recs, that one thing I'll have to check Tuesday. I have the caps and most of the other thing here at home. It just got me thinking of what I had and what it would take to make a better cdi. I have a rt180 yamaha coil that is still good, it may work for this.
 
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Greg58

Well-Known Member
May 1, 2011
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Voltage is going to be a factor, the only parts I have found that may work are rated 480v a/c. R/M were you talking about a/c or d/c rating.
 

flybytaco

Metal Molding Madman
Oct 17, 2009
1,170
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seekonk MASS
can you use a stock cdi and rework it? rohmell how much you looking to get shoot me a pm I have the perfect coil for that cdi.
 

rohmell

Active Member
Jun 2, 2010
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can you use a stock cdi and rework it? rohmell how much you looking to get shoot me a pm I have the perfect coil for that cdi.
If you can get the potting compound out of the stock CDI, it can be reworked.
Try MEK or DMSO to see if the potting material can be removed.
 

GearNut

Active Member
Aug 19, 2009
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Would one just soak the CDI box in the solvent for a day or two to soften it?
Can the solvent damage any of the components, IE penetrate inside them or damage the coating on the resistors, capacitors, coil and whatnot rendering them unreadable?

The only think I have dug out potting from was a dead Harley Davidson voltage regulator.
They used black RTV silicone. I was not successful in saving the circuit components as the silicone was murder to pick and scrape out.
 
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rohmell

Active Member
Jun 2, 2010
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Those solvents can wreak havoc with most components. Even if the resistors and capacitors' markings are gone, they can still be measured with test equipment.

We know the basic schematics of these devices, so it is not a problem to recreate a CDI circuit that would work, but it would be interesting to know what specific components and values are used in the Chinese Kit CDI.
 

LS614

Active Member
Dec 22, 2009
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CT and MA
it's pretty hard to find scr's for cheap. Where did you get those scrs with the threaded shafts rohmell? those look like they would dissipate heat a little better :)
 

rohmell

Active Member
Jun 2, 2010
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it's pretty hard to find scr's for cheap. Where did you get those scrs with the threaded shafts rohmell? those look like they would dissipate heat a little better :)
I once worked for a semiconductor manufacturer, and those SCRs were test units and samples.

These SCRs are cheap, and you get 25 pcs, they are the same as those used by other CDIs that have been mentioned in this forum:

http://cgi.ebay.com/25-PCS-GE-C106D...949?pt=LH_DefaultDomain_0&hash=item5d2ebc397d
 
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rohmell

Active Member
Jun 2, 2010
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Actually, you don't need such a heavy-duty industrial-strength SCR.
400, 600, 800 volts is fine, I scoped my CDI at around 318-320 volts peak.

Other CDI circuits floating around all seem to be using a 400V 4A SCR, so you don't need some huge SCR rated at 50, 40, 20A, or whatever.