Re: Ballast Resistor Wire
Posted: Wed Sep 09, 2020 3:13 pm
Assuming he is talking about your 6 cylinder Corvair, his guidance...erco wrote: » Wed Sep 09, 2020 1:45 pm
Just received this email reply from Pertronix after asking which Flamethrower coil to use:
"You need to use the 3.0 ohms coil when not using a ballast resistor."
Your Pertronix Team,
Marvin Grebow Jr.
Technical Dept.
...matches their usage chart (below)...
I believe their engineering/design/application theory goes something like this:
The Pertronix instruction sheet consistently advises installers to bypass/remove the ballast resistor or resistor wire from the primary circuit. This is intended to feed the Pertronix Ignitor (I or II) electronic ignition (breakerless) control system with full battery voltage (nominal 12 VDC). This is the correct voltage that the electronic module was designed for and it is what the design engineers expected it to be powered by. The instruction sheet tells the installer to connect the red Ignitor power wire to the positive terminal on the ignition coil, which will be a decent source of 12 VDC battery voltage (after the ballast resistor has been bypassed) that is switched on and off by the vehicle ignition switch. At the same time, the ignition coil will have been upgraded to a high performance ignition coil like the Pertronix Flame-Thrower 40,000 Volt secondary output coil. THIS COIL IS DESIGNED TO OPERATE ON 12 VDC BATTERY VOLTAGE. However, Pertronix also recommends the use of the Flame-Thrower 3.0 ohm coil (at 12 V) on 4 or 6 cylinder engines, or the Flame-Thrower 1.5 ohm coil for 8 cylinder engines. The difference is the expected DUTY CYCLE (the cycle of operation of a machine or other device which operates intermittently rather than continuously). The 4 or 6 cylinder engines have only 4 or 6 distributor cam lobes, so the amount of time at any given engine RPM that the ignition circuit is ON (closed) and feeding power to the ignition coil is LONGER than the duty cycle in an 8 cylinder engine (which has more distributor cam lobes switching coil power on and off during each crankshaft revolution). The shorter duty cycle (coil charging time) in an 8 cylinder engine means the coil needs a higher current level to fully charge in the available duty cycle time. At 12 Volts, 1.5 ohms of primary resistance, instead of 3.0 ohms, means more electrical current flowing. This is right for a V-8, but would cause a 1.5 ohm coil to run hotter on a 4 or 6 cylinder engine. THAT IS WHY THEY SPECIFY 1.5 OHMS FOR A V-8, AND 3.0 OHMS FOR A 4 OR 6 CYLINDER ENGINE. At 12 VDC, the current flow is optimized for the coil duty cycle by selecting the correct primary circuit resistance of either 1.5 ohms (for V-8) or 3.0 ohms (for 4 or 6 cylinders). Capisce?
At 12 VDC, you can still use a 1.5 ohm coil with a Corvair 6-cylinder engine, but it should be in conjunction with an external 1.5 ohm ballast resistor or resistor wire. However, doing so would drop the feed voltage at the coil positive terminal to approximately 7 VDC, so connecting the Pertronix Ignitor inside the distributor to the coil positive terminal would under-power the Ignitor electronics — with only 7 VDC instead of 12 VDC. In such a case the Pertronix Ignitor red wire should be connected to the ignition primary circuit BEFORE the ballast resistor or resistor wire, which is where 12 VDC that is switched on and off by the ignition key is found.