Roll Your Own CDI

Are You Going to Roll Your Own CDI?

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If you build the basic cdi use higher watt resistors, I used 1w 18 ohm and 2w82 ohm. The 1/2 watt resistors have overheated on some.
 
Greg58 said:
If you build the basic cdi use higher watt resistors, I used 1w 18 ohm and 2w82 ohm. The 1/2 watt resistors have overheated on some.
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Cool will do, found some from the same supplier for the same price lol.

Everything else looks good otherwise then?

Think i'll give the basic one a go first before getting any more complicated hehe
 
Evertything else should work, on my first cdi the scr required too high of a voltage to fire the gate making the bike sluggish at low rpm. With a different scr it worked correctly.
 
cdi=more to to wrong.. parts burn out.. id hate to be 20 miles out on my motorized bike and it fail... go the normal route.. unless its a cdi designed for a honda bike like a regular motor cycle ..
 
Half Dead said:
I've read heaps in this thread and am pretty sure I have the Idea of what to do to make the basic one, just want to make sure all the parts I've located are right



Capacitor:
10Pcs DIP Metallized Polypropylene Film Capacitors 1uF

Diode:
25PCS 1N4007 1A 1000V Rectifier Diode DO-41 Tape
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Wow!
I was heart broken when I saw the prices of MPF capacitors, until I saw your links.
You are saving me a crap-ton of bux.

And the 1n4007's

(I put these 2 things on my ebay watch list so far.)

Going to look at the rest of what you found.

Thanks.

PS, I read the whole thread yesterday and today! Some of it twice!
 
One other question:
Can I mix 1W and 2W resistors? I can only find 2W 18ohm resistors at the quantity and price I want.
 
Toadmund said:
One other question:
Can I mix 1W and 2W resistors? I can only find 2W 18ohm resistors at the quantity and price I want.
Click to expand...

2W resistors will be fine as the W(watt) value only means how much power they can handle. The higher the W value the more power(heat) they can soak up. You can go up in watt value but never go down in the value. So if a circuit calls for a 100 ohm 1W resistor you can use a 100 ohm 2W or even 3W resistor in its place. But do know that the high the W value the more it will cost for the part many times.
 
dracothered said:
You also may want to check out the thread for the CDI (Modified CDI) down below in my signature. It is a copy and improved CDI that you can buy from a vendor online.
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I am quite interested in that, but first things first. I'll make the simple one for now. It'll be an improvement.

It's been awhile since I've done electronics projects, I'm a bit rusty.
But compared to 22 years ago, electronic parts are so much easier to find.
 
Greg58 said:
If you build the basic cdi use higher watt resistors, I used 1w 18 ohm and 2w82 ohm. The 1/2 watt resistors have overheated on some.
Click to expand...
Yes, during one half cycle, all the current is flowing through the resistors, so they should be rated at a higher wattage.
 
whipaway said:
I think that as RPMs go up, you would want to advance the timing, in other words, have the spark occur earlier.
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2 strokes are weird compared to 4 strokes.
Folks here who have experimented with adjustable ignitions on these HT engines have found that retarding the ignition as the RPM's go up proved better than advancing it.
I still gotta agree with you though, it makes no sense to me either.
 
Opinions on this, I assume it's just fine:
5P4M-SCR-400V-5A-NEC-THYRISTOR-
A lot of the buying leads on the SCR's that Rohmell posted from ebay are out of date and not available and/or at a good price.


Screw it, I just bought 5 for under 7 bux S&H included, they are rated -40C
 
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I've read through this post with some interest. I have to say there is much more going on with this seemingly simple system then meets the eye. You firstly need to go way back to basics and understand how the points magnetos work. You need an SCR not a triac for this to work, when you know how the magneto works and how the SCR functions you'll realise why.

We manufacture direct fit replacement CDi units for 70s machines, as well as a few of our own design (google rex's speed shop)

Going down the road you guys are isn't going to give you the system you want.
.bf.
 
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I am really no salesman, but I'm a developer.
Read here to understand how SCRs, Tyristor and Triac work. And read carefully.
http://de.scribd.com/doc/42776869/scr-traic-diac-Report
Then take your Osco and look which polarity reaches the capacitor and the gate. Then you know, which kind of device you have to choose.

I have developed my own programmable digital CDI in 2010. My wife has got one, about ten of my friends have got one and we all use it in our 30cc Saxonette. It is a magneto ignition without pickup and without battery, just like in our HT motors. I have build a lot of analog CDIs, which are very simple compared with the digital ones.

Professer Dave wrote somewhere in this thread, that he wanted to start developing a digital ignition. That was about May 2012. Doesn't matter, that he hasn't finished yet. All in all my lasted 18 months. And I'm proud of it.

Multipaul
 
Parts on ebay are dirt cheap, still waiting for my SCR's and tantalum capacitors though, then I can build this one:
boardlayoutwithretard.jpg

It's retarded.

Then I will consider the modified jag clone.
 
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