Re: Farmall B coil

Posted by Sam#3 on July 27, 2007 at 20:51:07 from (12.214.113.46):

In Reply to: Re: Farmall B coil posted by Dave H (MI) on July 27, 2007 at 18:26:55:

First, the term coil is a misnomer. It's a transformer which it made up of two coils the primary and the secondary. Inside the can the primary is connected to the two small terminals and the secondary is connected to the - or neg(.)itive terminal and the large socket at the end of the can. The primary consists of a few turns of wire and the secondary is made of many turns of wire and in this application is considered a step-up transformer.
The primary circuit consists of the breaker points (with the plate connected to ground), the primary winding, probably a switch, and a source or electromotive force (measured in volts.). The secondary circuit consists of the 'points, secondary winding, the distributor cap, the rotor, cap, and spark plug(s).
The operation goes like this: As the distributor rotates the points are opened and closed, When the points close the primary circuit is completed and current flows through the primary winding forming what is known as an electromagnetic charge. When the point open the charge decays and by an action called 'mutual inductance' an electrical current begins to flow in the secondary winding. By the step-up action of the 'coil' this creates a very large voltage in the secondary circuit (The blue spark.). That�s pretty much it in a nutshell.
The testing techniques given by others are just simulating the rotation of the distributor.
Electrical fundamental: In an open DC circuit the voltage measured at any point in the circuit will equal the open circuit voltage of the source.
If the points are open battery will be measured anywhere in the circuit. Rotate the engine a bit to close the points and you can see the voltage drops across the circuit.
Good luck and visit your local library for a "Basic Electronics" textbook.

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