Removing the starting relay !!!

[ydderf911]

Hello all,

Is it possible to remove the starting relay and the resistor ballast like in this schematic:


If not, does anybody know where i can buy the resistor ballast and the starting relay ?
Thks and rgds,
Freddy

[edmayo]

It all comes down to which ignition coil is being used, OEM coils needed the resistor, most modern aftermarket coils do not. I believe the resistance across the primary should be about 3 ohms. John Cramer did an excellent posting on this, try searching 'ignition coils'

[304065]

Freddy,

It depends whether you are still using points, and the conditions under which your car is operated.

Points carry a maximum of about four amps before they burn up even regardless of the condenser (the condenser is there for two reasons: to tune the frequency of the coil primary breakdown and to prevent a second spark plug between the points).

The Ballast resistor relay logic, which you have so cruelly eliminated from my original diagram above , provides that during normal operation, the resistor is in-line with the coil primary. A Bosch coil is about 2,1 ohms, and the resistor is 0,9 ohms, for 3,0 total, which with a nominally +12V circuit will give. . . drumroll please. . . four amps.

To operate the starter solenoid one turns the ignition key, which puts +12V on the yellow wire to the starter solenoid, energizing it, making the high-amp connection between starter motor and battery, and moving the pinion into position. In an SWB car the yellow wire also is connected to pin 86 of the resistor relay, which causes the relay wiper to move, connecting pin 30 (power from battery) with pin 87, which sends battery power to the resistor box.

Inside the resistor box there is a ceramic tube with a coil of wire wrapped around it. This creates 0,9 ohms resistance. One end of the tube has two terminals on it, the other has one. In normal operation, one end of this, the one with a single terminal, is connected to the "wye" connector from the ignition switch (which splits power with the fuel pump). The other end has a terminal that goes to the coil, and a terminal that goes to 87 on the relay.

When the relay coil is energized, instead of the coil receiving a reduced voltage due to the resistor (around 9V) it instead receives full battery voltage. But here's the rub! Full battery voltage, when the starter is cranking, is around 9-10V! This is why I ask what conditions you plan to operate in-- if you need good cold-start performance it might be a good idea to keep this system.

So if you plan to eliminate the relay and resistor, AND you are still using points, you need a coil with an internal resistance, like the Bosch blue coil, which will give you around 3 ohms primary resistance. This is basically like having the resistor connected all the time. In cold temperatures when the battery voltage drops WAY down when the engine is cranking and the engine oil is like peanut butter, you will suffer decreased ignition energy. This might not be a problem if you are on the Riviera in summertime, etc!

Now, if you had some sort of electronic ignition, like a Pertronix Igniter, or some kind of hall-effect driver to replace the points that would trigger a Bosch ignition module (like a BIM 124, for example) then you could have a situation where you were able to switch about seven or eight amps to the coil! This would allow you to use a coil with much lower primary resistance (12v/8a= 1,5 ohms primary resistance, just like that in the Pertronix Flamethrower coil!)

The advantage of more coil current is faster charging, for greater ignition energy at high RPM when it's needed most. The disadvantage is higher heat. Of course Porsche mounted the coil on an aluminum plate in all years, they knew what they were doing!

Hope this helps, let me know if you have questions.

p.s. Ed knows I am telling the truth he saw me take apart a perfectly good working ignition system, replace it with Kettering, drive to the golf course and back and then reverse the whole process! I have a simpler solution in the works in my Mad Scientist Laboratory. . .

[gsjohnson]

You're too much John...Great stuff!

[ydderf911]

Hi Jhon,

Thanks a lot for your support on my problem.

Yes I have a Bosch blue coil, and my car is supposed to be used only during "warm" temperature because i don't have any "intenal heating" system (I removed everything). So normally, i would not start the engin below 10°C !!!

Sorry for my "not enough technical" english, but in this case i'm understanding from what you wrote me that i can simply remove the Relay and the resistor. I can only do the wiring like in the schematic below.

And If really needed i'll put a CDI BHKZ like you proposed.

Thks for sharing your knowledge.
Rgds
Freddy

[304065]

Freddy, yes. Wire from terminal to coil positive, wire from coil negative to points. With a Bosch 027 "Blue" coil you will be fine until about 5,000 RPM.

Good luck and have fun!