If I were to connect an ignition coil directly to a battery

[muddywater]

Originally Posted by MotorradMike

So why are 6V coils meant to run at 6.7V?

From my experience, to make them difficult to start.

[Benesesso]

Originally Posted by MotorradMike

So why are 6V coils meant to run at 6.7V?

Because that's ~ the normal 6V car voltage when the generator/voltage regulator is in "charge" of things.

[ttpete]

Ford put the ballast resistor in the wiring harness, and got the 12 volt starter boost at the starter relay.

[Wasser]

Originally Posted by ttpete

Ford put the ballast resistor in the wiring harness, and got the 12 volt starter boost at the starter relay.

Yup and GM had the resistor in the starter solenoid. Terminal "R" to be exact.

[GreaseMonkey]

Geez there are a bunch of err, "mature" gentlemen on this forum!

...Because of course you'd diagnose the ballast resistor by the symptom that the car would start and it would immediately die when you released the key. IIRC it would be a $6-$9 repair including the part.

[dan-c]

I drove a wrecker 3 years for AAA. Only ballast resistor I ever replaced was on a Chrysler product. Luckily as was mentioned they were usually behind the glovebox.

[ttpete]

Originally Posted by Wasser

Yup and GM had the resistor in the starter solenoid. Terminal "R" to be exact.

Actually, the solenoid just shot the full 12 volts to the coil when it engaged the starter. The resistor was elsewhere. Ford did the same thing with the starter relay on the fender panel because they used a Bendix Folo-Thru starter drive that didn't need a solenoid to engage.

[GreaseMonkey]

Originally Posted by dan-c

I drove a wrecker 3 years for AAA. Only ballast resistor I ever replaced was on a Chrysler product. Luckily as was mentioned they were usually behind the glovebox.

The one behind the glovebox is the A/C Resistor Block. The Ballast resistor is in the engine compartment on the firewall either in the center or towards the passenger side usually.

[Benesesso]

Can you find my resistor? This was my old '52 Ford with a '55 Buick 322 V8. Car was 6V, engine 12V. Anyone remember center-tapping a battery?

Check out the thick Chrysler radiator!

[Wasser]

Originally Posted by ttpete

Actually, the solenoid just shot the full 12 volts to the coil when it engaged the starter. The resistor was elsewhere.

You are correct, and I was wrong on the "R" terminal.

The "R" terminal on the solenoid is for Resistor by-pass.

The resistor that GM used on point ignition systems was, the unique resistance wire they used from the ignition switch to the coil.

Benesesso could probably explain the use of different alloys used in making wire that would create resistance and not get so hot as to turn into a toaster oven and melt the loom.

I'm trying to remember back 40 some odd years ago and, nichrome comes to mind as the type of wire GM used.

[Benesesso]

Originally Posted by Wasser

Benesesso could probably explain the use of different alloys used in making wire that would create resistance and not get so hot as to turn into a toaster oven and melt the loom.

I'm trying to remember back 40 some odd years ago and, nichrome comes to mind as the type of wire GM used.

Good question--I don't know. Nichrome would work, but would be way out of its element. You don't want a red hot heating element inside an insulated wire. I know the white ceramic "dropping resistors" got good and warm, but the resistance wire didn't get red hot.

[FixerDave]

Originally Posted by Wasser

... I'm trying to remember back 40 some odd years ago and, nichrome comes to mind as the type of wire GM used.

Yeah... my father called it nichrome... right after I bypassed the wiring harness on the Buick hit-to-pass race car I set up... had to pull as much as I could of that wire out of the harness and wire it back in. Never did understand why it had to be there until I read this thread. Makes sense now... thank you.

As for the heating bit... power out is volts * amps... a couple of volts drop on the minor current a coil would draw isn't going to amount to much power and thus heat.

David...

[Beezer]

been a while since I fooled with a balast resistor, but ya, nicrome wire in ceramic is the way I remember it. so.... 2-3 amps of coil current and a 2 volt drop across the resistor is 4-6 watts. not all that much heat.

yes, I had a couple trucks with a dual post battery... we even had a company up here that made them. we also used to tap a screw into the cell connector between 3rd & 4th cells to run the gauges. pretty much everything else was easy enough to convert. I even had a positive ground GMC truck once

[ttpete]

Originally Posted by Beezer

been a while since I fooled with a balast resistor, but ya, nicrome wire in ceramic is the way I remember it. so.... 2-3 amps of coil current and a 2 volt drop across the resistor is 4-6 watts. not all that much heat.

yes, I had a couple trucks with a dual post battery... we even had a company up here that made them. we also used to tap a screw into the cell connector between 3rd & 4th cells to run the gauges. pretty much everything else was easy enough to convert. I even had a positive ground GMC truck once

Back in the day when the first OHV V-8s came out, they were all 6 volt. The old hemi Chryslers especially had cranking problems. We fixed a lot of them with what was sold as an ABCO Automatic Battery. It was a 12 volt battery that was split into two 6 volt halves, and had a couple of relays mounted on the terminals. You ran a wire to the starter relay to activate the battery relays when the starter was engaged, they connected the two 6 volt sections in series, and the engine cranked on 12 volts. When the key was released, the sections were re-connected in parallel, and the car ran and charged the battery on 6 volts.

BTW, 6 volt Fords were positive ground.

[kenny61]

You can get a coil with a built in ressitor. that what i did when i had to redo something once never had a problem

Information about Ignition Coils - Certain ignition coils require an external ballast resistor (off any 1955-57 General Motors vehicle) or a full-length resistance ignition wire (off any 1958-74 GM vehicle) to prevent from putting too much voltage through the primary circuit and ignition points, which could burn them up. A ballast resistor or resistance wire is basically a voltage reducer that reduces 12 volts down to anywhere between 6-9 volts, depending on the load. (The ballast resistor shown here is the same used on the 1955-57 GM vehicles.) But if a coil reads "12 VOLTS" on its casing, then it has a built-in resistor. A resistor may not be needed with many new coils because most of them nowadays have a built-in resistor. And using a resistor doesn't effect the voltage output of a coil. It only prevents from burning it up, and it saves wear on the ignition points. The reason manufacturers don't install a resistor inside some high-performance coils is because these coils draw more amps from the battery. This causes the resistor to operate at a higher temperature, which could overheat and damage the windings within the coil. If you prefer to use a high-performance coil, when you purchase one, be sure to ask the salesperson if it has a built-in resistor or if it requires an external one. This is important for the life of the coil.