Ignition Question

[lastcowboy32]

oscilloscopes don't lie...

but, without the resistor, the voltage at the top of the coil would remain at 12V for the entire time, and the current through the coil would be higher.

so... sure a 6V coil won't suffer dielectric breakdown or arcing from 12V being on it... the voltage doesn't kill the coil.

but, without the inline resistor to limit the current, the current, due to 12V being across the coil, will kill a 6V coil... over time. It won't happen after just one cycle.

There was a time when ford engines (my Ford 3000) purposely used a 6V coil in a 12V system... as I'm sure you know.

They were a convoluted mishmash of wiring and ratings... and special "resistor wire" instead of a discrete resistor that you could see.

All so that, when you engaged the starter, the 6V coil would momentarily get full 12V battery voltage for a few cycles for a nice hot spark to supposedly get better starting performance.

Worked great, for many years... until the tractors became 30 or 40 years old, and people had to fix the ignition, and auto parts stores stopped stocking "resistor wire"... and the aftermarket coils had vague markings like... "6V Coil, do not use in 12V system"... without adding the subtext of

"Unless it's a 12V system that uses a 6V coil with resistor wire and a starter bypass of said resistor wire, in order to possibly slightly improve cold start performance to the detriment of long term servicability."

 

[lastcowboy32]

Ford wasn't the only perpetrator of that either.

My brother had a John Deere 1520, 3cyl gas... vintage around 1970.

The wire to the coil burned out. He re-wired it, put a new coil in, using the JD part number (which called out a 6V coil, but not marked as such)

He didn't recognize that the wire he replaced was "resistor wire"...with higher resistance than plain old wire...

So, he ended up running his 6V coil in a 12V system for many years... and they would last for a while. After replacing a few coils, he somehow caught wind of the resistor wire thing... and he fixed his problem (I can't remember if he wired in a discrete resistor or found a 12V coil)

 

[JMOR]

(quoted from post at 12:17:42 06/19/23)
Ford wasn't the only perpetrator of that either.

My brother had a John Deere 1520, 3cyl gas... vintage around 1970.

The wire to the coil burned out. He re-wired it, put a new coil in, using the JD part number (which called out a 6V coil, but not marked as such)

He didn't recognize that the wire he replaced was "resistor wire"...with higher resistance than plain old wire...

So, he ended up running his 6V coil in a 12V system for many years... and they would last for a while. After replacing a few coils, he somehow caught wind of the resistor wire thing... and he fixed his problem (I can't remember if he wired in a discrete resistor or found a 12V coil)

hat arrangement was standard on many automobiles and trucks before solid state ignition systems. I have done the same thing on an 8N, but with a diode instead of a starter solenoid terminal or relay.

 

[Dave G9N]

Darn it. You made me realize that I've been looking at ballast resistors for over half a century without ever once asking what the difference is between a load resistor and a Ballast Resistor (link) or why the ballast resistor looked like a heating coil. Not that I knew that a resistor could be called a load resistor. The link says that a ballast resistor is a variable resistor that increases resistance as it heats up. So you get a little more voltage until the ballast resistor warms up and it reduces the heat load on the coil as it heats up.

All resistors (everything that conducts electricity is a resistor) generate heat equal to the resistance times the voltage, which is mathematically same as resistance times current squared. Voltage also equals current times resistance. When you double the voltage to the coil, the current doubles too, so you get 4 times as much heat. So, yeah, a 6V coil can get a bit warm on 12V.

I also found a decent description of The care and feeding of points (another link)which provides a lot of detail in addition to what has been said here.

 

[lastcowboy32]

(quoted from post at 12:35:54 06/19/23) Darn it. You made me realize that I've been looking at ballast resistors for over half a century without ever once asking what the difference is between a load resistor and a Ballast Resistor (link) or why the ballast resistor looked like a heating coil. Not that I knew that a resistor could be called a load resistor. The link says that a ballast resistor is a variable resistor that increases resistance as it heats up. So you get a little more voltage until the ballast resistor warms up and it reduces the heat load on the coil as it heats up.

All resistors (everything that conducts electricity is a resistor) generate heat equal to the resistance times the voltage, which is mathematically same as resistance times current squared. Voltage also equals current times resistance. When you double the voltage to the coil, the current doubles too, so you get 4 times as much heat. So, yeah, a 6V coil can get a bit warm on 12V.

I also found a decent description of The care and feeding of points (another link)which provides a lot of detail in addition to what has been said here.

I'm safe, until people start talking about "tension" and "reluctance"... when they start using those terms... I realize that they have that old school electronics knowledge that they erased from the textbooks by the time I went to college for my EE.

I have to start taking notes and get out my "old school electronics jargon dictionary"... otherwise, I'm lost.

Long and short of it is...

For the original poster.
He can use a 12V coil with his 12V system...

or a 6V coil with a "ballast" resistor that may theoretically give him a little boost of spark for cold startups, because it's low resistance cold and higher resistance warm...

or a 6V coil with a regular resistor with resistance about equal to the ballast resistor's "hot" resistance, which will protect his coil, but won't give him the little cold start boost.

On my 3000, the resistor wire was long gone. I disconnected the starter bypass and used a 12V coil... for longevity reasons.

I figured that you don't need the spark boost for cold startups, if you keep your engine properly tuned.

 

[lastcowboy32]

PS... I recently wanted to do the points and condenser on my 2N.

Amazon had a whole distributor... housing, cap, and all of the internal parts with properly gapped points (I checked when it came)... for something like 35bucks.

Easiest tune up I ever did.

I bought the distributor and a new (6V) coil... it cost 80 bucks with shipping. I unbolted the old... bolted on the new... done.

Now... If I want, I could order points, condenser, rotor, cap and such... and rebuild my old distributor and throw it on a shelf, so my next tuneup is easy and quick also.

 

[lastcowboy32]

PPS... A spark tester (looks like a spark plug with an adjustable gap) is handy to have with these old tractors.

Without one, people just start tearing their ignition apart and replacing stuff.

Also handy for diagnosing coil failures, because coils, when they DO fail... often work fine when they are cold and then short out once they warm up. If you have a spark tester handy, you can plug one in when the tractor is hot and diagnose the fact that your spark went south... a lot faster than trying to remove a spark plug.

 

[HFJ]

(quoted from post at 17:21:05 06/19/23)
PPS... A spark tester (looks like a spark plug with an adjustable gap) is handy to have with these old tractors.

mine doesn't look like a spark plug - but i'd go so far as to say "handy" is an understatement

my 2N tool box holds the PTO cover, a spare shear bolt for my mower, and my spark tester, set to a quarter inch gap. i don't even bother to carry tools for the shear bolt. i've only snapped it once, and i'm never more than about 150 yards from tools if i do snap it again. the first time, it was about a 50 yard walk. for the time being, i still enjoy walking.

 

[HFJ]

PS: i am a Bruce (Va) acolyte. [i:6904345b4d]"Don't have an adjustable gap spark tester? GET ONE!"[/i:6904345b4d]

:mrgreen:

 

[WILLIAM4536]

THANKS HFJ

 

[JMOR]

(quoted from post at 16:50:04 06/19/23) THANKS HFJ

o not take everything in this thread and carve it in stone as there are multiple mis-understandings & statements. among Several different posters.

 

[HFJ]

(quoted from post at 18:18:10 06/19/23)

(quoted from post at 16:50:04 06/19/23) THANKS HFJ

o not take everything in this thread and carve it in stone as there are multiple mis-understandings & statements. among Several different posters.

william's post was a reply to my statement about firing order. was it inaccurate? if so, what is the correct order?

 

[JMOR]

(quoted from post at 18:55:39 06/19/23)

(quoted from post at 18:18:10 06/19/23)

(quoted from post at 16:50:04 06/19/23) THANKS HFJ

o not take everything in this thread and carve it in stone as there are multiple mis-understandings & statements. among Several different posters.

william's post was a reply to my statement about firing order. was it inaccurate? if so, what is the correct order?

didn't say anything about firing order, in response to all the above posts, I did say "Do not take everything in this thread and carve it in stone as there are multiple mis-understandings & statements. among Several different posters.". Read, or would just prefer to argue?

 

[HFJ]

ok :roll:

 

[Btzj02]

[/quote]

True that. What ever keeps the old Ford running is the important part!

 

[lastcowboy32]

(quoted from post at 04:21:58 06/20/23)

o not take everything in this thread and carve it in stone as there are multiple mis-understandings & statements. among Several different posters.[/quote]

Amen.

I had a whole thing typed out here with the differential equations that govern how the coil primary, coil secondary, condenser, points and spark gap work...

But, suffice to say, somebody at Ford, and other companies solved them 80 years ago and selected parts that make a spark that makes the engine go.

There is no confusion at all, if everybody kept their machines original, bought parts to original specifications and followed the original shop manuals.

But... part availability changes

And... most tractors of that vintage acquire some mixing and matching... 12V conversions... these pertronix ignition thingies... and anything else that the internet wants to sell you.

And... part of the fun of owning something as simple as an N tractor is messing it up; so you can learn how to fix it... and get that safe feeling that you have at least one tractor on the farm that you can take care of without requiring an Indy pit crew, technicians and engineers

 

[TRS]

I think you may have just solved an issue I'm having. I have the EI, 12v, can type coil setup that i just added. I left the ballast reistor in place. When engine gets hot it starts acting up, cutting off, losing power. This is prob due to the resistor becoming more effective as heat builds and it's inhibiting the spark?? I just need to ditch the resistor and junction everything together to send 12v direct to the coil??

 

[JMOR]

Do you have it wired such that current to the EI module is passing thru resistor? That would be incorrect. Only coil current thru resistor? IF your coil has high enough resistance in primary (~3 Ohms) to be considered a true 12v coil, then skip the resistor.

 

[buickal]

(quoted from post at 13:48:30 06/22/23) Do you have it wired such that current to the EI module is passing thru resistor? That would be incorrect. Only coil current thru resistor? IF your coil has high enough resistance in primary (~3 Ohms) to be considered a true 12v coil, then skip the resistor.

No. According to my research I need to wire the igniter to the key on 12v power lead that goes into the resistor so it could get the 12v power it needs. The coil however gets its power after current runs through the resistor. My goal is to get rid of the resistor when I get rid of all points with my thinking being that if I get a 12v coil, I wouldn t need the resistor anymore because the 12v key on power could run strait to the coil and not through the resistor.

This post was edited by buickal on 06/22/2023 at 02:53 pm.

 

[TRS]

(quoted from post at 13:48:30 06/22/23) Do you have it wired such that current to the EI module is passing thru resistor? That would be incorrect. Only coil current thru resistor? IF your coil has high enough resistance in primary (~3 Ohms) to be considered a true 12v coil, then skip the resistor.

Thanks jmor. Accidentally hijacked the thread. Taking out resistor and fitting get up!!