1969 J-3600 232 coil voltage question

[will e]

No doubt that it juices the coil while starting.

I was just 'mind thinking' why. My knowledge of electrical circuits is better than many but second semester at best!

If the solenoid has '12 full volts' so does the rest of the car during cranking (but we know this is not true). If there was 12volts while cranking there would be no point for its own cranking circuit.

The opening/closing of the circuit to the coil, triggered by points or ignition box, is 'slowest' during cranking. This would give the coil plenty of time (the longest) to build a charge compared to, say, 4000 RPM.

During cranking the 'normal' circuit to the coil has reduced voltage from cranking and an additional reduced voltage from the resistor wire, ballast or internal resistor. Does the combination of the two cause the voltage to be low enough that the coil cannot operate? Is it too low to create the magnetic field? It's just a curiosity I have.

[tgreese]

Dunno - didn't seem important when Jeep put the 232 in the Wagoneer and J-trucks. When did it appear? Did Ford do it first? Seems likely it's more an issue of whether the starter supports the bypass or not. According to the OP, the Prestolite starter may not support the bypass, but the Ford solenoid with the bypass terminal applies to Fords as far back as 1953. When the 350 was introduced, its Delco starter has the provision for the bypass, and Jeep included it.

The manufacturers had the resources to evaluate the bypass, but paper records from that testing almost certainly went in the dumpster many decades ago. Notable that Jeep went to the Prestolite BID in 1975, with no bypass. They even went so far as to use the Ford solenoid without the bypass terminal, presumably to save a few cents and avoid service issues (can't connect it wrong if there's no extra terminal). When Jeep went to the Duraspark, the bypass terminal on the solenoid came back, but instead of juicing the coil, it was used to signal starting to the module. The module responded by retarding the spark for easier starting. I suspect this indicates that the bypass was not really essential to effective coil performance.

Even with the resistor in there, the points/module opens and the coil windings float up to full voltage. The discharge cycle always goes from fully charged to ground potential, given sufficient dwell. It's a passive AC circuit - one could learn something by evaluating it as an R-L-C with a known cycle time. Sophomore physics, and certainly part of the undergrad EE curriculum.

[tgreese]

Here's an example of how to evaluate the effect of the resistor from my sophomore Physics book, "Physics, Part 2" Halliday & Resnick 3rd Ed. This is mostly for Will who points to his basic electrical knowledge from college (I presume).

HRp1 (600 x 248).jpg

HRp2 (600 x 812).jpg

I'd compare the peak voltage in the inductor with and without the addition of the external resistor. I expect you could lump the internal and external resistances together into the R term and that would be a valid model for the system performance. The main thing you need that you don't have here is the inductance of the coil, and the capacitance of the condensor. You could make a WAG that the coil is 1 H and the condensor is 0.1 uF and get a good idea of how the performance changes.

Intutively, changing the R changes the damping factor of the oscillations. With less R, you will see a longer discharge cycle with more oscillations, not a different frequency or amplitude.

Don't be put off by this guys - all this math is mostly to address Will's thoughts on the topic and not meant as an answer to the OP's original question - except for maybe the first paragraph of the preceding post.

[J20Hunter1]

This is why I like this site .You guys have a lot of knowledge on the FSJ"s .My main goal is to get tis truck running and drive for a while,then figure out which way to go with it.It is all original 1969 Custom cab 3600 w/ 232/auto one owner very little rust.Interior is great nothing on truck has been hacked.I have an 75 and 82 J20 for donor if I want to convert.It does need rear springs ,some are broke.

[tgreese]

Sorry to dwell on this (pun intended), but I must be honest and correct myself.

Thinking about this on the subway yesterday, I realized my above post with the equations is wrong in one important respect. The coil, ballast resistor and condensor do not make the L-R-C circuit I described above. Instead, the coil is in parallel with the condensor instead of in series. The coil circuit will not oscillate like an L-C or L-R-C circuit would. Instead, it's more like an L-R circuit, where the coil is a switched inductor with the resistance in series. Changing the resistor still changes the damping of the circuit, but no oscillations. See H&R 36-3. The ballast resistor limits current through the coil and makes the charge-discharge cycle slower. Slower discharge makes a weaker spark.

If you add a capacitor in series, you get a capacitive discharge (CD) ignition like MSD sells. I believe they also include a switching power supply that boosts the coil voltage, and the capacitor makes the whole system oscillate to make multiple sparks - its "hotter, longer spark." Not what the OP is asking about, however.