Super C 12v coil w/resistor

[theog9n]

Hello
We have a super c that We just put all new wire harnesses on. In that process we came across a external resistor that wasn't in the wiring diagram. So we purchased a new 12v coil with an internal resistor. Since that was put on the coil seems to get really warm/hot with just the switch on. What could be causing that?

Thank you
Matt

 

[Jim.ME]

(quoted from post at 22:13:52 05/22/22) Hello
We have a super c that We just put all new wire harnesses on. In that process we came across a external resistor that wasn't in the wiring diagram. So we purchased a new 12v coil with an internal resistor. Since that was put on the coil seems to get really warm/hot with just the switch on. What could be causing that?

Thank you
Matt
<img src=https://www.yesterdaystractors.com/cvphotos/cvphoto126354.jpg>

<img src=https://www.yesterdaystractors.com/cvphotos/cvphoto126355.jpg>

The wires inside the coil are sized and wound in a manner that provides the right resistance for 12 volt use; there is no resistor as such inside it. Engine running or stopped, if the points are closed there is current passing through the coil, and points, when the key is on. Flowing current makes heat. There is more resistance in a true 12 volt coil than a 6 volt using an external resistor (some of the heat in a 12 volt system using a 6 volt coil and external resistor is in the external resistor so the coil should be cooler). More resistance equals more heat.

 

[Janicholson]

The coil operates about 1/2 the time. (points closed) and is off 1/2 the time (points open) when leaving the key on (not running) it is onn all the time, and will over heat. Short, minute long, on not running is OK, more is destructive. Jim

 

[John T]

A 12 volt tractor can use EITHER:

1) A 6 Volt coil PLUS an external series voltage dropping (12 down to 6) ballast resistor ORRRRR

2) A full true 12 volt rated coil (no external ballast required)

FYI A full true 12 volt coil has a LV primary winding resistance of around 3 + or - Ohms

A 6 volt coils has a LV primary resistance of around 1.5 + or - Ohms

A typical old farm tractor ignition coil (even if some call internal ballasted) DOES NOT HAVE A DISCRETE STAND ALONE RESISTOR TUCKED AWAY INSIDE THE CAN. The necessary 3 or so ohms of resistance comes solely from the resistance of the LV primary windings NOT from wire PLUS some internal resistor.

With ignition on if the tractor isnt running THE COIL WILL GET FAIRLY HOT but not near as hot when running when the points are opening and closing

Make sure the coil has around 3 or so ohms of LV Primary resistance (12 volt coil) if it ONLY has around 1.5 (6 volt coil) it will overheat badly on a 12 volt tractor

John T

 

[BarnyardEngineering]

Don't leave the switch on when the tractor is not running.

Why? Because the coil will get HOT because it just keeps charging and can't discharge to create a spark. Exactly what you are experiencing.

This is a case of, "Doctor it hurts when I do this." "So don't do that."

This post was edited by BarnyardEngineering on 05/23/2022 at 06:15 am.

 

[BarnyardEngineering]

there is no resistor as such inside it

The label seems to refute that. Clearly says "internally resisted."

But what is a resistor in many cases, but a coil of wire?

 

[John T]

Good morning Sir, you state But what is a resistor in many cases, but a coil of wire?

You are CORRECT I FWIW agree EXACTLY (may it be said great minds think alike ?? lol) they make in many
cases WIRE WOUND RESISTORS in addition to carbon or other material resistors. As we both know the
resistance in an old farm tractor ignition coil is derived primarily from the total resistance of all
those coils/windings of wire NOT wire PLUS an internal stand alone resistor ...... There are resistors
(wire wound or carbon) and there are inductors, and sort of step up type of transformers they create,
which are used to make an ignition coil.

Of course, as I'm sure you know, an ignition coil is primarily AN INDUCTOR AND TYPE OF TRANSFORMER its
the inductance and mutual inductance across the LV Primary and HV Secondary INDUCTORS (IE coils of wire)
that allow for the increased voltage from 12 plus to several thousand volts (when the points open and the
magnetic field collapses) necessary to arc jump current across the spark plug gap. A couple resistors
alone tucked inside the can wouldn't allow sufficient mutual inductance and transformer action to raise 12
plus volts to several thousand, that takes inductors/step up transformers ..

PS as Ive posted before (see picture) THEY DID INDEED MAKE COILS THAT CONTAINED A TYOE OF INTERNAL
RESISTOR TUCKED AWAY IN THE BOTTOM OF THE CAN (internally ballasted) but Ive NEVER EVER seen one used on
old farm tractors, have you or anyone here ??????????

PS2 Hey Im sure you know all this (not posted for your benefit) but hopefully we can help others...

Fun and a pleasure to sparky chat with you, I enjoy your comments. You have a nice day and G _ _ bless you
and yours


John T

 

[JMOR]

(quoted from post at 09:14:13 05/23/22) Don't leave the switch on when the tractor is not running.

Why? Because the coil will get HOT because it just keeps charging and can't discharge to create a spark. Exactly what you are experiencing.

This is a case of, "Doctor it hurts when I do this." "So don't do that."

This post was edited by BarnyardEngineering on 05/23/2022 at 06:15 am.

Because the coil will get HOT because it just keeps charging and can't discharge to create a spark." Given that idea/theory, when one does finally turn off the key all that built up 'charging' should produce an "atomic" sized spark!! Stand clear!

 

[Jim.ME]

(quoted from post at 09:17:10 05/23/22)

there is no resistor as such inside it

The label seems to refute that. Clearly says "internally resisted."

But what is a resistor in many cases, but a coil of wire?

As I said, there is "no resistor as such inside it", as shown in the drawing of an old coil John T posted. The new coil is internally resisted by the way it is built, not by having a separate resistor inside tied in with the windings to provide the needed resistance value.

 

[John T]

As I said, there is no resistor as such inside it, as shown in the drawing of an old coil John T posted.

AMEN that's correct. I've (past used tractor dealer and farmer) NEVER EVER seen or heard of an old tractor
farm coil that contained a stand alone resistor hidden away inside the can. The ONLY reason I posted that
picture is for those who were not aware there were indeed a few old car coils that had an internal type of
resistor. I recall seeing some (old cars never tractors) that had a distinct ring at the bottom where the
resistor was located.

John T

 

[John T]

AMEN I AGREE you are correct yayyyyyyyy lol

An ignition coil is an inductor with coils of wire and soft iron and once current begins to flow and
stabilizes (an inductor opposes current charge as you know) and iffffffffffff the dwell time of current
flow (when points are closed) is sufficient, the magnetic field and core becomes saturated to a point and
no longer increases. IE it no longer continues to charge up similar to how a capacitor charges. A
capacitor stores energy in its electric field while an indictor stores it in the magnetic field, but you
already knew that

Best wishes, take care, its always nice sparky chatting with you

John T

 

[JMOR]

(quoted from post at 09:54:54 05/23/22) Good morning Sir, you state But what is a resistor in many cases, but a coil of wire?

You are CORRECT I FWIW agree EXACTLY (may it be said great minds think alike ?? lol) they make in many
cases WIRE WOUND RESISTORS in addition to carbon or other material resistors. As we both know the
resistance in an old farm tractor ignition coil is derived primarily from the total resistance of all
those coils/windings of wire NOT wire PLUS an internal stand alone resistor ...... There are resistors
(wire wound or carbon) and there are inductors, and sort of step up type of transformers they create,
which are used to make an ignition coil.

Of course, as I'm sure you know, an ignition coil is primarily AN INDUCTOR AND TYPE OF TRANSFORMER its
the inductance and mutual inductance across the LV Primary and HV Secondary INDUCTORS (IE coils of wire)
that allow for the increased voltage from 12 plus to several thousand volts (when the points open and the
magnetic field collapses) necessary to arc jump current across the spark plug gap. A couple resistors
alone tucked inside the can wouldn't allow sufficient mutual inductance and transformer action to raise 12
plus volts to several thousand, that takes inductors/step up transformers ..

PS as Ive posted before (see picture) THEY DID INDEED MAKE COILS THAT CONTAINED A TYOE OF INTERNAL
RESISTOR TUCKED AWAY IN THE BOTTOM OF THE CAN (internally ballasted) but Ive NEVER EVER seen one used on
old farm tractors, have you or anyone here ??????????

PS2 Hey Im sure you know all this (not posted for your benefit) but hopefully we can help others...

Fun and a pleasure to sparky chat with you, I enjoy your comments. You have a nice day and G _ _ bless you
and yours


John T
<img src=https://www.yesterdaystractors.com/cvphotos/cvphoto126393.jpg>

ohn, et al....
to be really specific, even those rare so called "resistor inside the coil" units actually didn't have the physical resistor "inside the coil", but rather under a cap attached to the bottom of the coil.

(53 to 55 Chrysler Imperial)

Additional note to posters original question: Typical dwell in points type distributor is around 33 degrees, meaning points closed and supplying voltage & current to the coil for 33/90 th of the time or 37% of the time in a 4 cylinder engine. However , when you stall engine & key on , points closed that 37% becomes 100%. At 12.5 volts and a 3.25 Ohm coil , 100% =48 Watts of heating power, whereas when running, 18 Watts of heat, so.....there you have the hotter coil when stalled & key left on.

 

[theog9n]

Hello everyone
Thanks for all the information! It sounds like everything is
working correctly the coil just got got because the tractor wasn't
running and it wasn't running because we had no spark. We ordered
points, condenser and new distributor cap. Hopefully once those
are replaced and set she will fire right up.

Thanks again!

 

[theog9n]

Hello everyone
Thanks for all the information! It sounds like everything is working correctly the coil just got got because the tractor wasn't running and it wasn't running because we had no spark. We ordered points, condenser and new distributor cap. Hopefully once those are replaced and set she will fire right up.
Thanks again!