How many volts in the 94 M104 Waste Spark system? - Page 2 - PeachParts Mercedes-Benz Forum

Chas H · #1 03-06-2010, 12:52 PM

Quote:

Originally Posted by Matt L

There is no condenser in the ignition circuit?

Any ignition circuit that I have ever touched in the past has had a condenser in parallel with the primary coil. The breakdown of the field causes a reverse EMF (i.e., voltage) which charges the capacitor. Then, true to form, the current reverses and the process repeats - a few times.

If you've ever seen an o-scope hooked to an ignition circuit, you would never again claim that the circuit was DC. It is an AC spark. The first half-wave is the strongest, yes, but it's still AC.

Condenser haven't been used since points went away. There may be small condensers in the igniter circuit, but you won't see any discrete condensers hanging about.
The current in a spark plug circuit does not reverse. Does the voltage on your oscilliscope ever drop below the zero line?

Matt L · #2 03-06-2010, 01:30 PM

Quote:

Originally Posted by Chas H

The current in a spark plug circuit does not reverse. Does the voltage on your oscilliscope ever drop below the zero line?

Fakes:

http://stixpix.com/t%2022.html

http://www.highperformancepontiac.com/tech/hppp_0612_pontiac_ignition_systems/photo_06.html

http://www.mainlineauto.com.au/support/downloads/ca9000/training/IgnitionSystems.pdf

I can't find any online images of an actual scope. But this is what they look like.

Matt L · #3 03-06-2010, 01:58 PM

The schematic that you posted matches no ignition system that I've seen. Certainly not a points system. You did agree that the points switched the negative lead. Take a coil and an ohm meter and you'll see that there is no internal connection to the ground. The secondary current needs a complete circuit to function, and the circuit is completed through the battery to the ground.

Chas H · #4 03-06-2010, 04:05 PM

Quote:

Originally Posted by Matt L

The schematic that you posted matches no ignition system that I've seen. Certainly not a points system. You did agree that the points switched the negative lead. Take a coil and an ohm meter and you'll see that there is no internal connection to the ground. The secondary current needs a complete circuit to function, and the circuit is completed through the battery to the ground.

Whoops, that schematic is indeed incorrect.

Here's one that is correct.

Matt L · #5 03-06-2010, 04:45 PM

That's almost right. It shows a box between the condenser and ground. If that's the ballast, it's in the wrong place. It's also my understanding that the common point is usually the + connection and not the points connection. This can be verified with an ohm meter.

When those points open, the ringing occurs between the primary and condenser (as in any LC circuit). That causes an alternating magnetic field in the core, thus the AC at the plug wire.