question about CDI and regular ignition

[Larry Koutz]

John
This letter you wrote was very informative.

I would like to know what Voltage/ current it takes to "fire" a waste spark
ignition. And maybe a little more on how they work and are triggered.

Thanks!

Larry Koutz

-----Original Message-----
From: John Dammeyer <johnd at autoartisans.com>
To: diy_efi at diy-efi.org <diy_efi at diy-efi.org>
Date: Wednesday, July 11, 2001 10:06 PM
Subject: RE: question about CDI and regular ignition


>There are essentially 3 different types of coils out there.
>
>1. 8V volt coil used on older cars with a series ballast resistor which
>was switched out during cranking.  This meant that during cold weather
>or a flat battery there would still be sufficient spark.  Once the
>starter switch is released the ballast resistor is put back in the
>circuit and the coil runs on 13.8V.
>
>These coils worked really well with the older transistor ignition (A
>power transistor was switched by the points and this lowered the current
>and therefore arcing and subsequent point damage.)
>
>These coils also worked well with the CD ignitions of the time.  Delta
>made one and Radio Shack remarked it as an Archer Kit in the early 70's.
>It ran a ~15KHz oscillator generating about 300V which charged up a cap.
>An SCR triggered by the points dumped the 300V from the cap into the
>coil.  Hence Capcitive Discharge Ignition.  It had a button on the side
>which switched out the CDI an dran on the conventional points.  You
>could hear the whine of the unit so you knew when it worked.
>
>2. Standard 12V coil without ballast driven by a CD ignition similer to
>the one above.  Note that SAAB (now GM) has a patent on a paraticular
>method of creating the 300V to dump into the capacitor.  They even go as
>far as to charge the cap during the part of the engine cycle when the
>start motor has the least amount of load.  Real cool.
>
>3. Low resistance coils.  These are the latest now that semiconductor
>technology has improved.  These coils (like the FORD quad or hex) have
>an extrememly low resistance and would draw more than 100 Amps before
>they resembled toast.  The driver circuit limits the current to a
>defined value (10A I think) just before the coil needs to fire the spark
>plug.  The secondary of the these coils are connected not as an
>autotransformer like standard coils but each end of the winding goes to
>a spark plug.  The current goes from the center electrode of one plug to
>the outer electrode and the cylinder head.  It then jumps from the outer
>electrode to the center electrode of the other plug and back into the
>coil.
>
>Called waste spark,  it is said to clean the sparkplug during the
>exhaust stroke.  Yeah right... What it does is save a transitor for each
>pair of cylinders and that is good thing.
>
>Hope that helps.
>
>
>Cheers,
>
>
>John Dammeyer
>
>
>> -----Original Message-----
>> From: owner-diy_efi at diy-efi.org
>> [mailto:owner-diy_efi at diy-efi.org] On Behalf Of Jack
>> Sent: Wednesday, July 11, 2001 1:12 PM
>> To: diy_efi at diy-efi.org
>> Subject: question about CDI and regular ignition
>>
>>
>> Hi,
>>
>> Got a question about regular ignition and CDI ignition. What
>> is the main difference between a regular coil and a CDI coil?
>> From a ohm meter, the CDI coil seems to have a lot less
>> resistence (hence higher current/voltage??)
>>
>> Also, the driving signals seems to be a lot different. What
>> type of signal
>> (voltage/current) is required to drive CDI coil?
>>
>> Really appriciate if anyone can give me some insight in this subject.
>>
>> Thanks,
>>
>> Jack
>>
>>
>>
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>>
>
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