Igniter CDI Questions

[Escort Paul]

I read a lot of EFI forums
Alot of people including myself wonder about the role these play.
So I will dummy up and ask some questions,
hopefully someone can come back with some easily understood answers .

First why do you need them? non efi engines dont use them normally its just 12volt - coil - points- ground.
Whats the igniters role?
Do all igniters convert 12volt DC to AC voltage? lately Im reading how XXX brand igniters run at 850 to 1200 hertz
Do all ECU/EMS's require igniters and why? I thought the Bosch BIP373 Coil Driver transistor were all you needed for trigering.
if I have COP's /wasted spark /(add your own flavor here) Do I need them?

explain the difference between CDI and igniters

more to come but that will do for now

regards Paul

[jharvey]

Here's a link that does a good job explaining much of what you asked above.

http://www.jetav8r.com/Vision/Ignition/CDI.html

Basically CDI allows more control over the spark, as the energy storage is the cap, and the coil is more like the transformer.

[Escort Paul]

great little read that site.
Still doesn't answer the question of why or if I need igniters and yes it does explain what they do perfectly.

regards Paul

[Fred]

The ignitor or bp373 or whatever is just a power transistor of sorts. It is controlled by the low power ecu output and does the heavy lifting. It directly replaces the points in the old school setup. In a modern setup you want many coils, and you need an ignitor for each.

With points or an ignitor you get a long normal spark with moderate intensity. CDI uses tricks to create a shorter hotter spark, and often more than one spark per ignition event.

The trick is just a transformer that has the DC pulsed into it and creates a high voltage AC that is rectified back to a high voltage DC and stored in a capacitor. The capacitor is where the current is supplied from.

For traditional ign you use the coil for a flyback effect, with CDI you use it for a transformer effect. CDI can damage coils with weak insulation in the primary windings due to the high voltages applied.

CDI isn't necessary for most cases and can be worse than the long spark esp if the mixture isn't very homgeneous. CDI is also very noisy electrically so I'm not a fan of it unless required.

Does that help?

Fred.

[Escort Paul]

cheers Fred and Jharvey that does actually help.

I found reading MAGNECOR's site a very good read for information on the evils of CDI

[longracing]

I would not agree on CDI being evil, it was simply designed to suit high reving multiple-cylinder engines using a single coil and distributor. The cross-firing/shorting problems came from the much higher voltage being able to break done the insulation on weak leads & coil insulation.

These days the short coil-charge time is overcome by using multiple coils, each coil has enough dwell time. And with computer control the coil is powered for the minimum required time.

An ignitor is required to control the current and high generated voltages at the coil. This used to be done by Kettering points but is now controlled by the ECU. The ECU produces a low current 0-5Volt control signal while the coil requires several amps and will generate a few hundred volts of back emf on the primary side. The ignitor provides is the "worker" and isolates the ECU from voltages that would cause damage to the semi-conductors.

[Fred]

Evil or not, it *is* electrically noisy by its very nature and this can/does create problems for sensitive devices like MS units.

[Escort Paul]

I had a post in here its gone missing ...hmm strange.
Was just a TY to Longracing on explaining the igniters so well.
I say they're EVIL as on a high hp engine more power to ya, but I recently drove with a little brother of a friend,
the standard heavily worked shit box ...you know full exhaust 5foot muffler and so called chip of ebay for that magical 100hp more
and a CDI ignition that made my ears bleed through his subwoofer and exhaust.

regards Paul

[Fred]

I had a post in here its gone missing ...hmm strange.

I certainly didn't touch it! I think the chances of it going missing once up are pretty slim really. That would involve a database failure at godaddy, which while possible isn't likely. Are you sure you didn't hit "preview" instead of post and then close it?

[jharvey]

Are you sure you didn't hit "preview" instead of post and then close it?

Funny you mention that. I've done that several times.

On longer posts where I'm getting concerned I might crash and loose the post, I've added an edit line at the top, then posted. That way I get the saved copy, then when I'm done with the final edit, I remove the edit note, and do the final post.