Ignition coil questions...

[Bitsyncmaster]

This is how crappy DeLorean ignition is: if you don't bypass one of the resistors, you can't even start the damn car. Who dreamed this stuff up -- it's stranger than fiction.
Bill Robertson
#5939

That is not true. And everyone can test it just by pulling the blue/yellow wire off the resistor and try to start that way. Now if you have a weak battery then you may only start with the bypass.

[DCUK Martin]

This is how crappy DeLorean ignition is: if you don't bypass one of the resistors, you can't even start the damn car. Who dreamed this stuff up -- it's stranger than fiction.

You really haven't got a clue, have you Bill?

The resistors are there to limit current to the coil. This is Ohm's law in action. The most basic principle of electrics which you obviously still haven't grasped.

When cranking, the battery is being loaded quite hard on other stuff, so terminal voltage and its ability to supply current to the ignition system is reduced. Hence the laughably simply system to short out one of the resistors and provide the coil with extra current from the available voltage. It's only really necessary on a cold damp morning.

[content22207]

You really haven't got a clue, have you Bill?

The resistors are there to limit current to the coil. This is Ohm's law in action. The most basic principle of electrics which you obviously still haven't grasped.

Current = Voltage / Resistance. If you increase resistance, current will be reduced -- it's a mathematical certainty.

The stock resistor grid produces 1 ohm of resistance: 13.5 / 1 = 13.5.
My rewired resistor grid produces .25 ohm of resistance: 13.5 / .25 = 54.

We're talking about high performance coils here, not crappy Bosch coils (apparently the OP's Bosch coil physically disintegrated -- sounds pretty crappy to me). Pertronix coils are designed to operate with no resistance on the line in.

Any owner who upgrades his or her ignition coil, as the OP did in the first post of this thread, but leaves the stock resistor grid intact is significantly limiting potential benefits of making the change in the first place. Of course you should follow manufacturer's recommended wiring. If Accel wants one resistor on the input (I'm hypothesizing here -- I don't know for sure they do), rewire the resistor grid using one loose end and the common terminal. The only reason I'm running any resistance is because I don't know if the Bosch ECU is voltage sensitive at all. My 1969 Lincoln engine (Pertronix ignition ECU) operates at full charging voltage.

Resistors reduce voltage, and ultimately current, by converting electrical energy into heat. Once that happens, the energy is gone -- it will never come back (into the original electrical circuit -- heat from the resistors will heat up the air around them, burn anything that touches them, etc).

Bill Robertson
#5939

[Bitsyncmaster]

Bill, your correct that the current = voltage divided by the resistance. But to compute the current through the coil, you need to account for all the resistance.

The standard setup of one ohm resistor (two 0.5 ohm) and the standard coil resistance of about one ohm, plus the wire resistance. Lets just say the wire has no resistance.

So the current would be 13.5 volts divided by two ohms. So the circuit has 6.75 amps.

So your setup with 0.25 ohms (with the coil resistance at 1 ohm) would result 10.8 amps.

Now if you start changing coils with different resistance you can get into trouble not accounting for the resistance. If your coil has two ohms then you should not run any resistance but then when you start the car on a cold morning with a low charged battery you may not have enough current to provide enough spark.

All the coils I have seen recommend running from 6 to 10 amps. If your run higher currents your coil will overheat and loose efficiency.

[DCUK Martin]

Thanks Dave, you've saved me that effort! Bill, you need to read up on "potential divider resistor networks". See if you can wrap your brain around the wheatstone bridge circuit for example

In addition, I repeat for your benefit that you can't simply treat a coil as having a "resistance of 1 ohm" (or whatever) because it's an inductor and its very fucntion relies on transient behaviour.

Dave, maybe you can enlighten us as to the effect of higher currents on the ignition amp? I know they aren't prone to going pop, but I also know I couldn't get my turbo engine to run with anything other than a stock coil. I'm convinced there's some component matching going on there - that the amp is optimised for a certain current and for the coil's specific inductance ?

[content22207]

All the coils I have seen recommend running from 6 to 10 amps. If your run higher currents your coil will overheat and loose efficiency.

Not Pertronix coils:
PertronixCoilInstructions.jpg

Bill Robertson
#5939

[DCUK Martin]

Bill, clearly your ability to mis-read instructions so they say what you want them to extends beyond this forum.

If the vehicle in which the Flamethrower 2 coil is installed has a ballast resistor or resistance wire, and is equipped with the ignitor 2 or a capacitive discharge system... the ballast resistor may be removed.
....
If the vehicle is equipped with a ballast resistor... and is NOT equipped with one of the systems mentioned above, the ballast resistor should NOT be removed.

Is there something about this message I am misunderstanding?

Edit: I note with interest the very first sentence on that document. Care to argue that too?

[content22207]

Is there something about this message I am misunderstanding?

Nope:

... The only reason I'm running any resistance is because I don't know if the Bosch ECU is voltage sensitive at all....

Edit: I note with interest the very first sentence on that document. Care to argue that too?

Happy to: "In stock applications, with not one but *TWO* ballast resistors cutting coil input voltage to a ridiculously low 6-8 volts (really better suited for breaker point ignition than breakerless ignition), the manufacturer's recommended spark plug and spark plug gap will work best."

Can I hear an "Amen," brother Steve?

Poor Martin has been predicting the demise of my ignition ever since it was first upgraded, sometime in 2003. Since then it has traveled from New York to New Orleans, and as far west as Kentucky. Curiously, the only dead Bosch ECU I've ever seen came off a car with stock ignition.

Motor on, boys.

Bill Robertson
#5939

[Bitsyncmaster]

Dave, maybe you can enlighten us as to the effect of higher currents on the ignition amp? I know they aren't prone to going pop, but I also know I couldn't get my turbo engine to run with anything other than a stock coil. I'm convinced there's some component matching going on there - that the amp is optimised for a certain current and for the coil's specific inductance ?

I think the stock ignition ECU could probably handle more current then our 6 amps. It's only the output driver, PC board and connector that would set the limit. The ECU driver is connected to the coil with 18 AWG wire so that is why you are seeing 1.5 to 2 volts on the coil -. The output transistor drops about one volt and the wire the rest.

DC resistance is important. It sets the current when the "points" remain closed. That current is what drives the coil into saturation (magnetic). Then when the current is removed the collapsing magnetic field produces the spark voltage. So the inductance does affect how fast the field changes and hence the output voltage.

[DCUK Martin]

Happy to: "In stock applications, with not one but *TWO* ballast resistors cutting coil input voltage to a ridiculously low 6-8 volts (really better suited for breaker point ignition than breakerless ignition),

What's the resistance of "a ballast resistor" then, Bill? Could it not be that the DeLorean actually has "one" resistor made of two halves?

I have never "predicted the failure of your ignition system" I've simply recommended other people not copy you because your reasoning for changing the stock system is rooted in your own ignorance.