Ignition modules

"I am confused as to how do these things work as they only appear to have two wires? "

You and me too!  I am told that the module senses the build up of charge in the ignition primary and as if by magic acts like the points at the critical moment and collapses the magnetic field in the primary inducing a high voltage charge in the secondary.windings which is discharged across the plug gap. Some of the modules claim to include speed related variable timing in their circuitry  - another mystery. Perhaps there is a forum contributor who is into electronics and can offer a better explanation.

All I can add is that they do work and are reliable. That said, the main thing that they have to offer over a points system that is in good condition and properly set up, is reliability against points corrosion and cam follower wear when the machine is subject to periods of disuse and damp storage conditions.

We used them in our workshop when servicing machines that were then going to stand for for two or three months in conditions over which we had no control to avoid that late Spring phone call "you serviced my mower but it wont start"!

The Meco unit is available from Central Spares who are mainly a trade distributor  - or through any mower firm that trades with them. The Nova unit is available from an ebay trader who deals mainly in Kohler parts -  www.guypartsandservice.co.uk . 

In addition to the two above, there used to be some Australian made Atom modules but I've not seen them being advertised for a several years.

Electronic ignition modules designed to replace contact points in magneto systems essentially use a transistor as a solid state switch to interrupt the coil's primary circuit winding when the primary voltage reaches its positive peak, thereby doing what the points used to do but in a far more reliable and maintenance-free way.

Interruption of the primary circuit current flow causes the associated magnetic field to collapse which in turn induces (high) voltage in the coil's secondary winding that creates the spark at the plug.

Only two wires are required because it's just a switch in the primary circuit as the contact points are. The difference is that the electronic module makes use of the AC voltage that is induced in the primary circuit to power the transistor circuitry, whereas the points just act as a "dumb" switch operated by the cam on the crankshaft.

As for Atom, its inventors the Notaras brothers have a long list of patents to their names, the ignition module being just one:

1972: Atom Electronic Ignition System

Winner of ABC TV’s “Inventors” for 1976, this patented [patent expired in 2005] product was used extensively as a replacement for points and condensers fitted to small single cylinder engines with magneto ignition. It was used as original equipment on Atom’s own chainsaw production as well as to US, German and Indian manufacturers. Also, as a retrofit part to replace points and condensers. Many millions sold and much copied by overseas manufacturers.

• Winner ABC TV Inventor of the Year Award
• Australian Design Award No. 207
• New Implement Award – Orange Field Day 1977

http://pickersyard.weebly.com/atom-universal-electronic-ignition-module…

Thanks for this. Most interesting. So the timing is simply set by the peak voltage in the primary of the coil.  Brilliant.

Al