Re: [T3] CDI System

["Jim Adney" <jadney@vwtype3.org>]

On 19 Dec 2000, at 11:13, Fuhriman, Mark wrote:

> I have decided to try a capacitance discharge electronic ignition
> system on my '69 FI Fastback.  But I am having a hard time locating a
> local supplier. I found a company called Universal that offers
> something that might work: <http://www.wic.net/~univcorp/>  They have
> two CDI models: a "681" and a "581".  Both are described as "magnetic
> capacitive discharge ignition". Anyone know what the "magnetic" part
> is about?

I've been using CDI ignitions for over 30 years. The units I use were 
designed and sold by Delta and sold as kits by Heath for awhile. I 
think Universal is the offspring of Delta, but the items on their web 
page don't look like what I have. OTOH, there is no reason to believe 
that it should not change in 30+ years.

I've always liked the CDI concept. You have a system which still uses 
all your original parts and that can be bypassed with a switch if the 
CDI unit fails. With the CDI installed, the points last virtually 
forever and don't need adjusting as long as you keep the cam follower 
lubricated. The CDI uses a non-inductive trigger current thru the 
points to turn on an SCR at the proper moment. An inverter charges up 
a capacitor to 400V and this is discharged thru the SCR when the 
points open. The energy stored in the capacitor oscillates with the 
inductance of the coil for one full cycle and is then mostly restored 
to the capacitor where it is available for the next cylinder.

The CDI system will not give you any more power than a well tuned up 
standard ignition, which is exactly the same as what you will get 
with any other system. I did find, however, that the CDI would fire 
at times when the standard ignition would not. This at times made it 
easier to start the car.

-
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Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
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