Tack Ruben, it was very helpful.

How do I calculate rise time basing on capacitor ESR, coil resistance, and
some other parameter?

It's just a RLC system in the end, or does it hide some snare?

PS: great idea to parallel e.g. 10 0.1uF 600V caps instead of using one big
1uf 600V.. good for ESR but also for space. Also, easier to adjust capacity
to find the optimal one.

Hejd=E5!
Mario


At 08.16 2010.01.20, you wrote:
>> =

>> My dears,
>> I have a 2 stroke race engine and I'd like to make a CDI (Capacitive
>> Discharge Ignition) unit for it. As it is a 300cc 2 stroke enduro bike
>> mostly driven at low RPM in rocks, etc.. what I really need thus is a
>> fast voltage rise time to fire fouled plugs.
>> While I've been googling (literally) for days now, and searched the
>> PICList archives from 2004 on, I haven't found a simple answer to my
>> question:
>> =

>> What is the best type of capacitor to get a FAST rise time? I guess one
>> with low ESR.. yes, but how low? In the order of 0.005 to 0.02 Ohm?
>> =

>> What is the best type of transistor to trigger it (FAST rise time again)?
>> A SCR seems such a primitive device to me, I'd prefer something like a
>> MOSFET or a IGBP. Any pro's and con's of each valid solution?
>> =

>> Thanks a lot, it's always delighting to read you.. I only wish I could
>> contribute more often with something useful.
>> =

>> Mario
>> =

>
>I have made a couople of CDI type systems. Not used for ignition though bu=
t to =

>generate high voltage/field for corona discharging of electrostatic charge=
s =

>(ionizer).
>
>The capacitor type I have used are metalized paper (Evox/Rifa PME271M) whi=
ch =

>are chareged to around 450V through an IGBT transistor (high side switch) =
and =

>an inductor and then discharged through the high voltage coil with an SCR.=
 I =

>have also used a pulse capacitor with polypropylene as dielectric (Evox/Ri=
fa =

>PHE426) with very good results. This is used for lower voltages though =

>(charged =

>to around 40V with a P type MOSFET and then discharged with an N type MOSF=
ET).
>
>The way I have done it, the charging does not have to be fast and it =

>is charged =

>via the inductor for two reasons: 1. The final voltage over the capacitor =

>becomes roughly twice the power supply voltage and 2. The charging is slow=
ed =

>down so I can more easily control the charge time and thereby also control=
 the =

>output power.
>
>To lower the esr when discharging you could use several capacitors in =

>parallell.
>
>/Ruben
>
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
>Ruben J=F6nsson
>AB Liros Electronic
>Box 9124, 200 39 Malm=F6, Sweden
>TEL INT +46 40142078
>FAX INT +46 40947388
>ruben@pp.sbbs.se
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
>
>-- =

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