Roll Your Own CDI

[Ratchetbirds]

Okay, got the bulb and resistor at Radio Shack and started testing all the new ones first. I bought a batch of 25 SCR's from e-bay and 2 new ones tested bad in the bag. My first unit I built worked great for 50 miles. All the other units I have built have bad scr's in them. I have been soldering since I was a lil kid and use heat sinks and all. So I am very glad to be able to test SCR's now. I still have a cdi testing board I made but never have been able to test a good unit on it. Starting a new unit after I finish this post.

 

[rohmell]

Wow, sorry to hear about your bad SCRs. A similar thing happened to me, some of my 82 ohm resistors for some reason measure 136 ohms!
Good thing I didn't build any CDIs with them, or else I would be scratching my head over it for a while.

 

[nightcruiser]

Maybe try ordering some new SCR's from Mouser.com rather than off Ebay? Mouser will have everything you need, and the parts will be good.

 

[rohmell]

I had forgotten that I bought a batch of 25 SCRs, and went to test them, 7 bad ones found.

Here's a quick and dirty SCR test:


Wet the tip of your finger and touch 'A' and 'G' at the same time to trigger SCR.
(The tab is connected to 'A' internally, and your finger is the resistor!))

 

[Ratchetbirds]

Oh man, that is down and dirty. I love stuff like that. Well my new CDI wouldn't fire so I decided to be a smarter repair man and start with some basics. First checked my magneto coil resistance. Zip, nada, nyet. So, out comes my last OEM coil and in goes my home rolled coil. Wish me luck.

 

[GearNut]

Good luck!

 

[nightcruiser]

Oh man, that is down and dirty. I love stuff like that. Well my new CDI wouldn't fire so I decided to be a smarter repair man and start with some basics. First checked my magneto coil resistance. Zip, nada, nyet. So, out comes my last OEM coil and in goes my home rolled coil. Wish me luck.

So you also blew your magneto when your home made CDI blew?

 

[Ratchetbirds]

Naw, there was water in the magneto case, alot. It was probably the mag that took out the CDI.

 

[nightcruiser]

Naw, there was water in the magneto case, alot. It was probably the mag that took out the CDI.

or the water took out them both! Water bad... lol
Did you get her running again now?
What SCR are you using again?

 

[Ratchetbirds]

Yes, true...water very bad. No luck yet. Tomorrow I will be taking off the Ign. coil. Thank goodness I have a spare. The SCR says GE on it but it doesn't look right. Probably some Chinese company named General Erectric. I had to work on the 3 phase motor of a vertical knee mill once and it was made in Taiwan by "The Great Big Electric Company", I kid you not.

 

[nightcruiser]

Yes, true...water very bad. No luck yet. Tomorrow I will be taking off the Ign. coil. Thank goodness I have a spare. The SCR says GE on it but it doesn't look right. Probably some Chinese company named General Erectric. I had to work on the 3 phase motor of a vertical knee mill once and it was made in Taiwan by "The Great Big Electric Company", I kid you not.

Does it have a part number?

 

[rohmell]

The lot of 25 that I got off of eBay are GE C106D1 SCRs.
Based on the general appearance and construction of mine, they look very 1970s-ish.

25 PCS GE C106D1 C106D 400V 4A SCR RECTIFIER DIODE BOX7 | eBay

EDIT:
Ha Ha, I was right saying these SCRs are from the 70s, the GE datasheets are 1971 and 1977:
http://www.datasheetarchive.com/C106D1-datasheet.html

 

[nightcruiser]

The lot of 25 that I got off of eBay are GE C106D1 SCRs.
Based on the general appearance and construction of mine, they look very 1970s-ish.

25 PCS GE C106D1 C106D 400V 4A SCR RECTIFIER DIODE BOX7 | eBay

EDIT:
Ha Ha, I was right saying these SCRs are from the 70s, the GE datasheets are 1971 and 1977:
C106D1 datasheet and application note, data sheet, circuit, pdf, cross reference, pinout | Datasheet Archive

Why not just get new SCR's from some place like Mouser.com? They have lots to choose from...

 

[Ratchetbirds]

For me, part of this build has been about saving money. I priced out other sources like Mouser and was depressed at the prices, minimums, and shipping rates. The ones I got from e-bay were a smokin hot deal. Bad on me for not testing them first. Now I know. If I had to do it all over again, I would do it the same. Sad thing is I am out of diodes and will be buying more....from e-bay. The SCR's Rohmell purchased are exactly the same as mine. On another thought the Chinese have a great idea in potting their CDI. It protects it from moisture as well as piracy..argh.

 

[nightcruiser]

For me, part of this build has been about saving money. I priced out other sources like Mouser and was depressed at the prices, minimums, and shipping rates. The ones I got from e-bay were a smokin hot deal. Bad on me for not testing them first. Now I know. If I had to do it all over again, I would do it the same. Sad thing is I am out of diodes and will be buying more....from e-bay. The SCR's Rohmell purchased are exactly the same as mine. On another thought the Chinese have a great idea in potting their CDI. It protects it from moisture as well as piracy..argh.

Honestly, Mouser ain't that bad on price or shipping, nevermind the cost of the bad ones you throw away and your time dealing with the bad parts... Another plus is they have so much to choose from, you can order your main parts in qty but also order 1 off of different parts to experiment with and ship it all in one small box for $5 bucks...

 

[rohmell]

I buy from Mouser, Digi-Key, Allied Electronics, etc., but sometimes the deals that can be found on eBay are hard to beat.
I look at it this way: 25 SCRs on eBay cost $8.95 delivered. That means initially, each SCR is 36 cents.
With 7 bad SCRs, the price each for the good ones is 50 cents each.
I don't think any of the big electronics distributors can beat that!

 

[nightcruiser]

I buy from Mouser, Digi-Key, Allied Electronics, etc., but sometimes the deals that can be found on eBay are hard to beat.
I look at it this way: 25 SCRs on eBay cost $8.95 delivered. That means initially, each SCR is 36 cents.
With 7 bad SCRs, the price each for the good ones is 50 cents each.
I don't think any of the big electronics distributors can beat that!

But 7 are bad right from the get go, how long will the others last? Wouldnt it be worth it to pay a few cents more and get reliable parts, instead of something that looks like some kind of knock off part that has a high failure rate?

 

[rohmell]

The 7 bad one were rejected because they had poor gate triggering and transient response, which is not a factor with the CDIs being built here due to the low resistances that are connected between the gate and ground, but I rejected them because they might be used in some non-CDI projects.
If all 25 of the SCRs were planned for CDI use, they all would have been OK.

 

[nightcruiser]

The 7 bad one were rejected because they had poor gate triggering and transient response, which is not a factor with the CDIs being built here due to the low resistances that are connected between the gate and ground, but I rejected them because they might be used in some non-CDI projects.
If all 25 of the SCRs were planned for CDI use, they all would have been OK.

But didnt the experimental CDI fail in short order?

 

[Ratchetbirds]

Not at all. My CDI failed due to moisture in it's box and in the magneto case...over a tablespoon's worth. The SCR in the original CDI did not fail, btw. I only built a new unit because that is how I roll. I had 2 bad SCR's in my lot of 25. I possibly burnt 2 when soldering them in the pc board, being excited, old, and blind. What I am trying to say is 6 different people, six different ways to do something. This is how I do it, basically the same as Rohmell. He is just an electronic whiz-bang guy. Knows is stuff, he do.


Just brought in my Ign. coil for testing and yepper, my secondary is gone, too. Primary is there. So the lesson here boys and girls is: Make sure all your electrical is water proof/tight before riding in heavy rain or snow. Check it often.
.
.
.
.