Hall Sensors & Magnets

For older engines, the switch, or "points" is usually triggered by the cam shaft.  A cam lobe will cause the "points" to momentarily close, which energizes the coil.  When the points open, current to the coil stops, causing a collapse of the primary magnetic field in the coil, which then causes a high voltage surge in the coil secondary, which then makes the spark in the spark plug.

See Animated Engines for a demonstration of a "points" system.

Like all things mechanical, "points" can get dirty, require adjustments, wear out, and thus will eventually cause ignition problems.  "Hall Effect" devices and transistorized ignition modules resolve these issues.  A "Hall Effect" device is basically a low amperage transistor usually mounted very close to the cam gear.  Attached to the cam gear, and at the proper location, is a small magnet.  When the magnet passes by the Hall sensor, a small electrical charge is sent to the ignition module, which amplifies this current several times before sending the appropriate current to the coil.  When the magnet exceeds the sensing range of the Hall transistor, current stops in the Hall, which stops current to the ignition module, which stops current to the coil, again, causing a high voltage surge in the coil secondary to fire the spark plug.  Simple, eh? 

The Hall Sensor and a magnet can be used instead of mechanical contacts (breaker points) with our ignition modules and most other electronic ignition units. 

Need more general information?  Read more here.

Micro Switch and Capacitor (while supplies last)

For builders who wish to go the less technical and more traditional route, we have a limited supply of 5 amp micro-switches and capacitors. These may be used in place of the Hall Sensor/Magnet or points.  The switches were found in a parts surplus box, and may be new, or slightly used.  There is no documentation, so you'll need to figure out how to install and wire them on your own.  Should be simple enough to deduce with an ohm meter.

A capacitor should be installed in parallel with the switch.  See bottom diagram in CoilPrimer.pdf