Don recently sent me several coils to test on a rebuilt A4 I have in my garage. The test was to measure voltage at the coil + terminal and current through the coil primary at various engine RPM. I first measured the resistance of each coil and then measured the voltage and current at 0, 700, 1500 and 2000 RPM. The 0 RPM measurement is with the ignition switch on and the engine off. I have the Pertronix Ignitor installed. I tested 4 coils total, three that Don sent me and one that I had purchased about ten years ago, an Ametek coil with part number CAS-4012-1. The results are attached in a PDF. The voltage was measured at the coil positive terminal and the current meter was connected between the coil negative terminal and the black wire to the EI module.
Some observations from the tests:
1) The current is highest when the engine is off and the ignition switch is on (0 RPM). In this situation, the current through the coil primary can be calculated by dividing the coil + voltage by the coil internal resistance, I=V/R
2) The current decreased in the primary circuit when the engine was started and continued to decrease as RPM increased. This is due to the expanding and collapsing magnetic field generated in the coil as the EI/distributor switches the current on and off. The faster the current is switched on and off, the more the magnetic field opposes the current flow.
Some observations from the tests:
1) The current is highest when the engine is off and the ignition switch is on (0 RPM). In this situation, the current through the coil primary can be calculated by dividing the coil + voltage by the coil internal resistance, I=V/R
2) The current decreased in the primary circuit when the engine was started and continued to decrease as RPM increased. This is due to the expanding and collapsing magnetic field generated in the coil as the EI/distributor switches the current on and off. The faster the current is switched on and off, the more the magnetic field opposes the current flow.
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