ROLL YOUR OWN CDI 2 : is it feesable?

[Wevil Kenevil]

After dissecting a few stock cdi's and a catnip stand alone CDI and spark coil and finding they had sub par components... I had enough of that game!

When I read AI all of the components that were on the bread board it actually told me that I was wrong about the BT 151 chip because the chip that was on there was way underrated and AI said it would probably blow up in just a very short amount of time. Which it did... It also suggested upgrading the diodes for component protection.


Specifically the bt151 chip ( high to mid range voltage) which should have been used, I found in place a 2p4m a low voltage unit.

I bought all the capacitors resistors diodes ect. In groups of 25 for @ 7 bucks a piece except the bt 151 chips. I paid 10 for 10 of them. For about a $40 total. Which you can do cheaper buying just one of each for about 18$.

And though roughly the same price as you would find for one online this one will last you so much longer AI said that it should last the life of the bike

The breadboard, Which I made from copper shielding tape and old breadboard. I just cut the shapes of the connection points out of the copper tape and then use the adhesive on them to stick them to the breadboard. And then drilled my holes for my components.and soldered them on. To avoid short circuit sand all of the old Trace leads off.

As for the housing, I am using a small water tight electrical project box I already had. 2 bucks on line.

And it's worth noting that you should upgrade the diodes for extra blow back protection.

 

[Greg58]

Good luck, I built a couple back when rohmell did the first thread. I used a large pill bottle for my components and a MC coil from Amazon, one ran great at high end but lagged at low end, once I got one to work I lost interest and move on to something else. Mine looked like Frankenstein built it.

 

[Wevil Kenevil]

Good luck, I built a couple back when rohmell did the first thread. I used a large pill bottle for my components and a MC coil from Amazon, one ran great at high end but lagged at low end, once I got one to work I lost interest and move on to something else. Mine looked like Frankenstein built it.

Luckily I have some small project boxes left over from when I was building gps vehicle trackers...they are more than what I said in my o,p, they are like 6 bucks now... but if it works roll with it!

 

[Wevil Kenevil]

Something I discovered. The BT 151 chip comes in a few different sizes and when building or rebuilding a CDI it's important to get the correct one. Though a 500r is good and will work there are better choices.... This will explain it better...

BT151 variants are different models of the BT151 silicon-controlled rectifier (SCR), a type of thyristor used for power switching. These variants mainly differ by their voltage rating and physical package, which are indicated by the suffixes at the end of the part number.
Common BT151 variants

• BT151-500R: A standard BT151 with a 500V repetitive peak off-state voltage and a 12A RMS on-state current.
• BT151-650R: A variant with a higher 650V off-state voltage.
• BT151-800R: A variant with an 800V off-state voltage.
• BT151-1000RT: A high-voltage variant with a 1000V blocking voltage.

Packaging variants

• BT151 (no suffix): Comes in the standard TO-220 package, which is a common through-hole component package.
• *** BT151X: Comes in a TO-220F package, which is an insulated version of the TO-220 for better thermal management. (*** this is the one I suggest since heat seems to be the number one killer of cdi's)
• BT151S: Comes in a TO-252 (DPAK) package, a surface-mount package used for space-constrained applications.

Functional characteristics
Beyond the core BT151 model, variants can be designed to have different functional characteristics for specialized applications:

• Gate trigger current: Some variants may be designated for low or high gate trigger currents (IGT), depending on the required sensitivity of the switching.
• On-state current: While the standard BT151 has a 12A RMS current, other BT151-series components exist with different current ratings.
• Holding current: The amount of current needed to keep the SCR in its "on" or conducting state can vary between variants.

So as you can see a 500r is sufficient for the job there are better choices to make your CDI more durable. So if you have a CDI unit that has not been potted you will be able to replace the BT 151 chip with something of a greater value to give it more durability.

Long story short the bt-151x 800r 12a Rms To 220F chip is the way to go, as it will not affect the way the bike performs. The timing and spark strength and duration are controlled by the resistors and capacitors proceeding the bt151 chip..