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====== VSCDI3 ======

I want to introduce how a CDI can be developed. The following CDI was developed in 2016. But it's just a BETA-Version and has never reached a final status. So please read and enjoy. It is not recommended for recreation.

Its project name was VSCDI3.

{{ :1006-1-cdi-smallpcb-top.jpg?600 |}}

{{ :1007-1-cdi-smallpcb-bot.jpg?600 |}}

===== motivation =====

The VSCDI3 was created to work with Vape A70-3 and A70-5. It should have an easy structure with not to much components. The adjustment timing should be soft to work with nearly every engine with a moderate rev level.

===== circuit diagram =====

The basic design is close to the [[st_reference|ST reference]] design, but with an added negative wave handling and a modified signal shaping.

{{ ::1101-vscdi3-kicad.png?600 |}}

==== Negative wave handling ====

The branch with R1, R2 and D4 is limiting the negative waves. A first Version had R1 = 10 k (and R2 empty), but this created to much heat dissipation and the SCR get out.

The following values were obtained after measurement: 
  * U_Peak = 800 V
  * I_Peak = 0,08 A

A current of 0,08 A does not sounds much. But the Heat power loss is be calculated with:

  P = I² x R = (0,08 A)² x 10 000 Ω = 64 W

And 64 W are a huge heat load! So next time do the math and the measurement first. After a few more test R1 and R2 was dimensioned to 560 W each.

==== Signal shaping ====

Again a branch with D6 and R3 is handling the negative signal waves.

The positive signal waves are shaped with "the rest" between H5/white and the SCR gate.
With vary C1 and C2 the signal timing can be customized.

==== Capazitor ====

A standard size of the Capazitor C3 is 1 uF. But to get more energy at low revs it was contemplated to use 1,5 uF. By the way this are just thoretical approaches, no driving test have been made.

==== SMD elements ====

This elements were used for the SMD version with the pictures above.

^Element^Value^Comment^
|R1|560|3 W|
|R2|560|2 W|
|R3|330|-|
|R4|4,7 k|-|
|R5|100|-|
|D1...6|SL1M|-|
|Q1|STM TS820|-|
|C1|4,7 uF|Elko|
|C2|10 uF|Elko|
|C3|1 / 1,5 uF|-|
|C4|10 nF|-|

Note: The SCR ON CR708AG does not work with this scheme.

For a THT version the should be used UF4007 for the diodes and a TIC106M for the SCR