Why a Resistor?
 

I know Henry Ford is right, plus he wouldn't have put it in there if it was not needed, but why is there a resistor in the 6 volt system, going to the coil and points? In a 12 volt there is a resistor that knocks it down to 8 volts or so, so the points don't burn out. We've got the same basic points, at 6 volts they should be OK if they are OK at 8, so why knock the voltage down to 4.5?

Re: Why a Resistor?
 

Good question Henry...I think it's actually to prolong life of the coil.

Re: Why a Resistor?
 

AI Response:



The resistor in the Ford 6-volt ignition system is used to drop the voltage to the coil, ensuring it operates at the correct voltage level of about 3 to 4 volts, which helps prevent overheating and extends the life of the ignition components. Without the resistor, the coil could receive too much voltage, leading to potential damage.
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Purpose of the Resistor in the 1934 Ford 6 Volt Ignition System

Voltage Regulation

• The resistor is used to drop the voltage supplied to the ignition coil.
• A typical 6-volt ignition coil operates best at around 3 to 4 volts.
• The resistor helps maintain this optimal voltage, preventing overheating and ensuring efficient operation.

Protection of Components

• The resistor protects the ignition points from excessive current.
• Without it, the points could burn out quickly due to high voltage, leading to ignition failure.

Starting Assistance

• When starting, the resistor allows a higher voltage to reach the coil temporarily.
• This provides a hotter spark for easier engine starting, which is crucial in older vehicles.

Re: Why a Resistor?
 

AI said:
"When starting, the resistor allows a higher voltage to reach the coil temporarily.
This provides a hotter spark for easier engine starting, which is crucial in older vehicles."

I don't get this statement. (I know this is AI generated, which often gets bum info when it searches the internet) Is there any truth to this as it applies to our cars?

Many later cars did work this way. A 12 volt to 8 volt ballast resistor was bypassed during cranking.

But on our cars, the resistor is always in the circuit. I have measured the voltage reduction as the resistor gets hot, is only a few tenths of a volt. So don't see how, on our cars, the resistor helps start-up. Am I missing something about how a resistor functions?

Re: Why a Resistor?
 

Jay, you are not missing anything. The resistor in our old Fords operates all the time.

Re: Why a Resistor?
 

I have witnessed the same thing, very little voltage reduction when resistor is hot. My car starts quite well, but I am inclined to bypass the resistor via the solenoid connection and diode route.

Re: Why a Resistor?
 

i'll have to put my multimeter on the connection to the coil both with ignition on and the engine not running and with it running, both cold and hot. just to see how my car is set up, as it may have been altered in some way.

i'm beginning to wonder if the massive misfiring that consistently occurs in my original '41 engine, when fully warmed up, is being caused by the original style coil on my "diver's helmet" distributor, possibly involving a ballast resistor. as in is it working? is it not working? has it been disabled maybe? IDK

or i might simply buy one of those "modern canister coil" conversion kits install a modern 6v coil and run a wire directly from the battery to the coil, in order to bypass any issues involving a ballast resistor, altogether. it would also eliminate the possibility that the wire to the coil is some sort of "resistor" wire too.

Re: Why a Resistor?
 

I was always told that, because the distributor was put in a difficult place to access, Henry instructed Mallory that the distributor needed to run for (x)? number of miles with out needing attention.


4.5 volts was decided on to prolong points life and to minimize the need to check the adjustment.


I was also told by the old guys of them reaching under the dash, holding a penny, and shorting the resistor for starts on cold mornings.


Geoff Kiwi

Re: Why a Resistor?
 

The resistor will not show a reduction until the points are closed. Full battery voltage with open points, then about a 2 volt reduction when closed. By design, maximum voltage of 4 is available, self regulating as the resistor gets hot. (A cold conductor is able to deliver higher voltage than a hot conductor.) It’s a beautiful design that works better in theory than in practice.

Re: Why a Resistor?
 

multiple answers lowering the voltage will make the coil last longer but that depends on coil design also the resistor design the factory coil resistor has 0 resistance when not in use and this increases as usage continuse so when you cold start your actualy feeding a 4 volt coil 6 volts but due to crank loads cold weather ageing battery etc its lucky to get 4 see where this is going full voltage on crank also when running your actualy supplying 8 volts to the resistor so that needs control theres a lot of engineering in that ignition system so leave it alone unless you want to rework the entire thing change 1 thing create 7 more problems

Re: Why a Resistor?
 

See, its more complicated than it looks.

Re: Why a Resistor?
 

The resistor in an early Ford does not have a fixed resistance. When cold (on start up) when current has not yet heated it up, the resistance is low, allowing more voltage to the coil as the starter's heavy current lowers the battery voltage at its terminals. As the current continues to flow through the resistor (called a thermistor; temperature variable resistor) continues, it gets hotter and its resistance increases. Hopefully the engine has started, the starter is disengaged, the battery voltage increases and the resistor is in its full resistance.

After the war, the manufacturers simplified the concept. They added an additional terminal to the starter solenoid which supplied battery voltage only during starting. This wire bypassed the (fixed) ignition resistor only during startup. This resistor was initially housed in a ceramic block on the firewall. Later it was replaced by a resistor in the wiring during the points era.

Fords always started easier in cold (sub Zero) weather in the 50s than Chryslers because they always went with running voltage. At least that is my and my buddies gas jockeys' experience back then.

Re: Why a Resistor?
 

Common on 12v GM cars was an ignition switch that would bypass the external resistor while the engine was cranking to ensure the coil was getting max voltage and when the switch went from "start" to "run" the voltage then went through the resistor.

Re: Why a Resistor?
 

I've done some research based from written material on hand, namely Ford shop and service manuals, and think/hope the results will answer some of the questions on this post about coils.

Ford V8 6V systems used ignition resisters inline to coils up to '48. I don't have any resistance values from '32-'38, just schematics. 1939-'48 coil primary resistance measured .47-.51 ohms, and although I could not find the inline resistance value, pretty sure it would be around .5 ohms, for a total about 1 ohm, based on......


6V Fords '49 through '54 used coils with primary resistance of 1.05-1.15 ohms with NO inline resistance. I don't have info on '55s but would think they're the same.


In '56, Ford switched to 12V, with inline coil resistance of 1.3-1.4 ohms and coil primary of 1.4-1.5 ohms, giving a total of about 3 ohms.


1957 was the first year for an ignition resister bypass built into the new style starter solenoid, where the 1.3-4 ohm inline resister is bypassed to to the coil while starting, but allowing the same 3 ohm total coil primary resistance when running.


I don't know the specifics on why 6V system coil primaries were just over 1 ohm and 12V point system coil primaries run/ran around 3 ohms.


Bob

Re: Why a Resistor?
 

Just to confuse things coils do not have resistance they have impedance. I will leave it to someone else to explain that if they wish.
Any way the conclusion I come to is that the exceptions to Ohm's law complicate the numbers quoted, making them approaching benchmark at best.

Re: Why a Resistor?
 

Merriam Webster

impedance: The apparent opposition in an electrical circuit to the flow of an alternating current that is analogous to the actual electrical resistance to a direct current and that is the ratio of effective electromotive force to the effective current.

Say what?

Re: Why a Resistor?
 

ha! yes, a little difficult to decipher isn't it? :)

direct current...alternating current...effective current...effective electromotive force...electrical resistance...electrical circuit and finally apparent opposition! lotsa similar nouns and adjectives there. quite the definition and all in one sentence too! :)

which is, IMO, why those monumental forum arguments between two individuals, that are willing to go to the ends of the earth to prove they are right, always end up in a definition of terms using a dictionary (but only after a prolonged bout of quarreling over which dictionary and edition), and then....peter out like the last grains of sand through the fingers as the opponents finally realize that, in the end, there is nothing left to argue.

Re: Why a Resistor?
 

When Mallory was helping Ford's engineers design their V8 systems, Henry's insistence on using the distributor mounted coils required coil designs that were outside the normal ignition coil specs for the time. The Model A & B coil equired no resistor. The first V8 coils used a cylinder type coil but Ford needed more room down front for clearance. The divers helmet type coils and the later 21A types all required a bit more control of the available amperage in the power line to them in order to lessen heat build up. The little coils only needed 4 amps or so to do a good reliable job so Ford used a 0.8 OHM ballast to control the current draw. Yes, it also dropped the voltage but that's just the way OHM's law works. The current is what caused the heat build up so the resistor brought the heat level to reliable specs for those types of small coils.

Re: Why a Resistor?
 

Even though it is DC current through the coil, it is of an alternating nature, therefore impedance IS a factor. However, it seems that my thought is deviation from the original question. Sorry!

Re: Why a Resistor?
 

The breaker points provided a pulsating half wave DC power to the inductor coil that simulates alternating current. The condenser provides a prolonged collapse of the magnetic field and traps the back flow of voltage as it collapses. The high tension voltage to the plug is pretty high and the back flow is a lot less but still high enough to damage the points with no capacitor in the circuit.

Re: Why a Resistor?
 

Thank you. Finaly an explanation that makes sense to me. Using a little coil required use of an external resistor. It's that simple!

Re: Why a Resistor?
 

And mine too! I had to pull my "50 Chrysler with my Model A doodlebug out to the road, then coast the MOPAR down the hill I lived on to get it started. The A started with snow on top of the engine!

Re: Why a Resistor?
 

never mind