Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 03-20-2015, 02:49 AM   #1
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 5,528
Default Ignition coil with resistor

I had an ignition coil fail on me recently and the only one I could find to replace it at short notice was supposed to have a resistor used with it. Fortunately, someone there knew how to connect it, Is it just connected in series with the coil? What is the point of it anyway? Is the coil actually made for a lower voltage and the resistor is left out of the circuit while the battery is cranking the motor and therefore only able to deliver a lower voltage but drops the voltage to the coil during normal running?
I've converted to 12 volts.
__________________
Yesterday is History.
Tomorrow is a mystery.
Enjoy Today.
Synchro909 is offline   Reply With Quote
Old 03-20-2015, 03:01 AM   #2
Mike V. Florida
Senior Member
 
Mike V. Florida's Avatar
 
Join Date: May 2010
Location: South Florida
Posts: 14,052
Send a message via AIM to Mike V. Florida
Default Re: Ignition coil with resistor

If you have converted to 12 volts you need to coil and resistor combination. Either in the coil or external to it.

For those that are 6 volts, you need a coil designed for an external resistor.

There were ign systems that were designed to add and remove resistance during starting and running, but not the A.

http://en.wikipedia.org/wiki/Ignition_coil
__________________
What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II
Mike V. Florida is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 03-20-2015, 06:32 AM   #3
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 5,528
Default Re: Ignition coil with resistor

Quote:
Originally Posted by Mike V. Florida View Post
If you have converted to 12 volts you need to coil and resistor combination. Either in the coil or external to it.

For those that are 6 volts, you need a coil designed for an external resistor.

There were ign systems that were designed to add and remove resistance during starting and running, but not the A.

http://en.wikipedia.org/wiki/Ignition_coil
Mike, Thanks for the reply.
I'm aware the A didn't have a resistor. The coil I have is clearly marked 12 Volts, yet it has a resistor. It is therefore clearly intended to run on less than 12 volts. It is not a 6 volt coil in a 12 volt system with a resistor to drop the voltage at the coil to 6 volts.
__________________
Yesterday is History.
Tomorrow is a mystery.
Enjoy Today.

Last edited by Synchro909; 03-20-2015 at 06:38 AM.
Synchro909 is offline   Reply With Quote
Old 03-20-2015, 06:49 AM   #4
Bob Bidonde
Senior Member
 
Bob Bidonde's Avatar
 
Join Date: May 2010
Location: Long Island, NY
Posts: 2,102
Default Re: Ignition coil with resistor

When 12-volt ignition systems first came out about 1955, car makers continued to use the 6 to 8-volt coils they had with the 6-volt ignition systems, so a resistor was used to reduce the voltage. A three position ignition switch was used so when starting the car, the resistor was bypassed and the coil got 12 volts. When the key went into the run position, the resistor went back into the circuit so the coil ran with 6 to 8 volts. Some coils had the resistor built-in, and others had an external resistor.

High energy ignitions (HEI) systems resulted in another change, and coils in this type of system are truly 12-volt coils.
__________________
Bob Bidonde
Bob Bidonde is offline   Reply With Quote
Old 03-20-2015, 07:06 AM   #5
Mike V. Florida
Senior Member
 
Mike V. Florida's Avatar
 
Join Date: May 2010
Location: South Florida
Posts: 14,052
Send a message via AIM to Mike V. Florida
Default Re: Ignition coil with resistor

With a coil that uses an external resistor you should see 1.2 to 1.4 ohms across the primary.
Coils with an internal resistor (for 12volt systems) should read about twice of that above, 3 ohms.

Coil test
__________________
What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II
Mike V. Florida is offline   Reply With Quote
Old 03-20-2015, 07:12 AM   #6
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,061
Default Re: Ignition coil with resistor

Sponsored Links (Register now to hide all advertisements)
A coil with an internal resistor is to reduce the voltage to the points. Points do not like 12 volts.
Patrick L. is offline   Reply With Quote
Old 03-20-2015, 08:06 AM   #7
Joe K
Senior Member
 
Joe K's Avatar
 
Join Date: Jul 2010
Location: Cow Hampshire
Posts: 3,613
Default Re: Ignition coil with resistor

Quote:
A coil with an internal resistor is to reduce the voltage to the points. Points do not like 12 volts.
Kettering (developer/refiner of the coil/points ignition) found that 4 amps is about the practical limit for current in a points type ignition. Thus resistance to limit current through the coil.

Discussion of the difference in resistance of a 6v and 12v coil at http://www.yesterdaystractors.com/cg...rtips&th=26558 - and the use of resistors to achieve a correct current.

Joe K
__________________
Shudda kept the horse.
Joe K is offline   Reply With Quote
Old 03-20-2015, 09:23 AM   #8
Bruce Lancaster
Senior Member
 
Join Date: May 2010
Location: Madison, NJ
Posts: 5,230
Default Re: Ignition coil with resistor

And...there are quite a few different values of resistance in the resistor, so when buying a coil match up the resistor at same time by the catalog rec or from OEM usage. And, of course, find out if it even uses one or has its resistance internally! Reistor application is not generic.
And there were also 6 V coils that used a resistor too, including early V8 Fords and some others. Don't buy a coil and a resistor separately without reference to what the coil requires.
Bruce Lancaster is offline   Reply With Quote
Old 03-20-2015, 09:33 AM   #9
Tom Wesenberg
Senior Member
 
Tom Wesenberg's Avatar
 
Join Date: May 2010
Location: Mpls, MN
Posts: 27,480
Default Re: Ignition coil with resistor

Did your other coil fail because it was oil filled and mounted upside down?
Tom Wesenberg is offline   Reply With Quote
Old 03-20-2015, 10:55 AM   #10
marc hildebrant
Senior Member
 
marc hildebrant's Avatar
 
Join Date: May 2010
Location: Cape Cod
Posts: 1,128
Default Re: Ignition coil with resistor

Quote:
Originally Posted by Patrick L. View Post
A coil with an internal resistor is to reduce the voltage to the points. Points do not like 12 volts.
You meant to say current as the voltage isn't a problem for the points.

As others have said, the use of a 6 volt coil running on 12 volts during the start of the engine helps to deliver a "hotter" spark during the startup of the engine.

Marc
marc hildebrant is offline   Reply With Quote
Old 03-20-2015, 11:11 AM   #11
Willie Krash
Senior Member
 
Willie Krash's Avatar
 
Join Date: Jan 2012
Location: Phoenix, Oregon
Posts: 661
Default Re: Ignition coil with resistor

Just to add to the conversation the starter was tied in front of the resistor and powered the coil during the cranking cycle. If you're cranking the engine and the battery breaks down to 9.5-10V you get better firing voltages to the plugs while cranking. Every volt counts toward upping KV firing voltage
Chev used this early on in a "foot feed" starter. The switch used a resistor bypass.
You may notice starter solenoids are marked S and R
__________________
Mike Stitt
"A business that make nothing but money is a poor business."
-Henry Ford
Willie Krash is offline   Reply With Quote
Old 03-20-2015, 12:02 PM   #12
dansluck
Senior Member
 
Join Date: Dec 2014
Location: Nevada
Posts: 117
Send a message via AIM to dansluck Send a message via Yahoo to dansluck
Default Re: Ignition coil with resistor

Tom I live in rural Nevada and when you break down it is a long way to get parts. I always install a coil with primary facing up. Learned that as a kid. Good Day to ya. Dan
dansluck is offline   Reply With Quote
Old 03-20-2015, 02:09 PM   #13
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,061
Default Re: Ignition coil with resistor

I'm just trying to keep this simple. I'm smart enough to understand about current. Most folks like simple, especially me.
That said, points do not like anything over 6-8 volts.
Run 12 volts thru a set of points without a resistor/reducer stuck somewhere in front of them and see how long they last. Been through it.
Patrick L. is offline   Reply With Quote
Old 03-20-2015, 02:23 PM   #14
marc hildebrant
Senior Member
 
marc hildebrant's Avatar
 
Join Date: May 2010
Location: Cape Cod
Posts: 1,128
Default Re: Ignition coil with resistor

Patrick L,

Just trying to help. The 12 volts isn't the problem with the points...rather the increased current via ohms law is what damages the points.

If you know this, then I'm just trying to keep the story accurate for those that are reading this thread and may not understand why 12 volts is a problem ?

After all, many cars were built that ran 12 volts and points.

Marc
marc hildebrant is offline   Reply With Quote
Old 03-20-2015, 02:33 PM   #15
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,061
Default Re: Ignition coil with resistor

Quote:
Originally Posted by marc hildebrant View Post
Patrick L,

Just trying to help. The 12 volts isn't the problem with the points...rather the increased current via ohms law is what damages the points.

If you know this, then I'm just trying to keep the story accurate for those that are reading this thread and may not understand why 12 volts is a problem ?

After all, many cars were built that ran 12 volts and points.

Marc





Which one[s] ran 12 volts through the points ?
Patrick L. is offline   Reply With Quote
Old 03-20-2015, 04:07 PM   #16
marc hildebrant
Senior Member
 
marc hildebrant's Avatar
 
Join Date: May 2010
Location: Cape Cod
Posts: 1,128
Default Re: Ignition coil with resistor

Patrick L.

My 66 Olds Cutlass used 12 volts and points....

Not sure though why the question as many cars had 12 volts and coil\points.

Marc
marc hildebrant is offline   Reply With Quote
Old 03-20-2015, 04:16 PM   #17
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,061
Default Re: Ignition coil with resistor

Quote:
Originally Posted by marc hildebrant View Post
Patrick L.

My 66 Olds Cutlass used 12 volts and points....

Not sure though why the question as many cars had 12 volts and coil\points.

Marc




That didn't answer my question. Pretty much all cars in the 50s/60s were 12 volt and used points. But, none ran 12 volts through the points for more than a couple seconds, most didn't allow 12 volts through them at all.
Patrick L. is offline   Reply With Quote
Old 03-20-2015, 04:41 PM   #18
marc hildebrant
Senior Member
 
marc hildebrant's Avatar
 
Join Date: May 2010
Location: Cape Cod
Posts: 1,128
Default Re: Ignition coil with resistor

Patrick L.

Very confused...thought that we were talking about breaker points ?

Signing off.

Marc
marc hildebrant is offline   Reply With Quote
Old 03-20-2015, 04:48 PM   #19
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,061
Default Re: Ignition coil with resistor

Quote:
Originally Posted by marc hildebrant View Post
Patrick L.

Very confused...thought that we were talking about breaker points ?

Signing off.

Marc




We are. 12 volt systems run no more than 8 volts through the ignition breaker points.
Patrick L. is offline   Reply With Quote
Old 03-20-2015, 05:32 PM   #20
Afordman31
Senior Member
 
Afordman31's Avatar
 
Join Date: May 2010
Location: Michigan
Posts: 530
Default Re: Ignition coil with resistor

Snyder’s installation instructions:
 
A-12000 COIL

This coil is imprinted that it is 12-volts, use with
external resistor. If you are running 6-volts, the coil is good for 6-volts as it is, ignore the 12-volt writing on the side. If you are running a 12-volt system, you will have to add an external ballast resistor to the
coil. This coil is only 12-volt if it is used with an external ballast resistor.


Afordman31


Attached Images
File Type: jpg coil.JPG (33.7 KB, 25 views)
Afordman31 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 03:33 PM.