Coils

[flatjack9]

Can a 12v coil be run on a 6v system? I read many conflicting opinions.

[koates]

Hi there, If the 12 volt coil is marked on the bottom "use with resistor" or on its side label or on its box marked similar then it can be used on a 6 volt system with no resistor required. These coils are actually designed to operate on 6 to 8 volts. There are various types of 12 volt coils and you would need to test the primary winding with an ohm meter to determine what you have if it is not marked. Regards, Kevin.

[flatjack9]

What value would you be looking for?

[Paul Bennett]

Can a truly 12v coil be run on 6v using a 6v to 12v converter?

[koates]

flatjack, A 12 volt "use with resistor" coil will read approx. 1.2 to 1.8 ohms across its primary winding, depending on manufacturer. Remember this coil is designed to operate on 6 to 8 volts through an external resistor. Likewise a marked straight 6 volt coil will have similar ohms reading across its primary winding, ie approx. 1.5 ohms. A straight "marked" 12 volt coil will have a primary winding reading of approx. 3.5 ohms. Regards, Kevin.

[koates]

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Originally Posted by Paul Bennett

Can a truly 12v coil be run on 6v using a 6v to 12v converter?

Paul, I don't know why you would really ask this question, but I don't know why someone would do that when the correct voltage coil is available to buy. A step up converter uses power to achieve the step up so the ignition current draw would be excessive, and distributer points life reduced. NOT PRACTIBLE AT ALL. Regards, Kevin.

[Brian]

How about the opposite; can a 6 volt coil be run on twelve volts?

[flatheadmurre]

Originally Posted by koates

Paul, I don't know why you would really ask this question, but I don't know why someone would do that when the correct voltage coil is available to buy. A step up converter uses power to achieve the step up so the ignition current draw would be excessive, and distributer points life reduced. NOT PRACTIBLE AT ALL. Regards, Kevin.

The current through the coil and points would still be set by the coil resitance and nothing else so points life will be as designed.
But the stepup will draw twice the current plus internal losses from the battery...and a stepup delivering in the 5A range cost more then a correct coil.

[flatheadmurre]

Originally Posted by Brian

How about the opposite; can a 6 volt coil be run on twelve volts?

Just add a resistor to keep the current down to around 4A and it will work fine....The coil might work fine taking a higher current through it depending on if it has the cooling capacity or not...the points will burn out fast if you start pushing high current through them.

[Paul Bennett]

Originally Posted by koates

Paul, I don't know why you would really ask this question, but I don't know why someone would do that when the correct voltage coil is available to buy. A step up converter uses power to achieve the step up so the ignition current draw would be excessive, and distributer points life reduced. NOT PRACTIBLE AT ALL. Regards, Kevin.

KOATES: I risk hijaak to ask because I keep getting people wanting me to convert the car to 12v to get a good strong 12v system spark for the engine such as with late model Pertronix. Yes, a 12v converter would draw more battery power but the distributor and coil would not know whether the 12v power came from a 6v>12v converter or directly from a 12v battery.

[Brian]

How about the opposite; can a 6 volt coil be run on twelve volts?

For years I ran my 35 on original 6 volt system, using a generic black bodied coil with a goldie colored top, no brand name. Subsequently, converted to 12 volts and still using exact same coil! No resistors anywhere in the circuit.My 8N tractor runs the same type coil, again, another conversion to 12 volt, again with no resistor! I've had many people tell me that this can't be done; that it'll burn up the 6 volt coil. I don't know why this hasn't yet happened after, what, about twenty five years.

[koates]

Brian, without knowing the specifications of your coils, ie primary winding resistance its hard to say what you have. A good test would be the current draw of each coil, engine stopped, points in distributer closed and ignition ON. Could also test current draw with engine running. A nice figure would be around 3 amps. Engine running test will show a lower current draw. More than 4 amps would be getting too high and points life would be reduced and would indicate that the coil was not suitable for 12 volt operation. Or it may need a resistor in line. Regards, Kevin.

[koates]

Originally Posted by Paul Bennett

KOATES: I risk hijaak to ask because I keep getting people wanting me to convert the car to 12v to get a good strong 12v system spark for the engine such as with late model Pertronix. Yes, a 12v converter would draw more battery power but the distributor and coil would not know whether the 12v power came from a 6v>12v converter or directly from a 12v battery.

Paul, now I understand why you would want to do this. The step up converter would have to be able to supply something like 5 amps to power the coil for the Pertronix. That means the current draw out of the battery by the converter could be something like 8 or 10 amps maybe. I don't know how well this would work really. You could try it and see what happens. The worst you could do is blow up the Pertronix unit or the converter or both but then you have plenty of dollars don't you ? Converters of this size (current rating) require nice heavy supply cables and a good steady 6 volts plus supply into them otherwise they tend to drop out of operation. I have had this happen to several I have used to power 12 volt radios, tapes etc. When I turned the headlights on and the engine was at idle which lowered the voltage in the system on a 6 volt car then the converter dropped out (ceased working) and the radio stopped working. In your case the engine would stop (no ignition). Anyway please try it and I will wait for your report back. Regards, Kevin.

[rotorwrench]

The only problem we have these days is the fact that there are very few well made automotive condensers any more. If a person can get a good quality condenser, the OEM system works very well with good reliability. I would venture to say that it would likely be as reliable as the Pertronix systems since they are so sensitive to voltage spikes that that they tend to burn the module out at the drop of a hat. They have to have the right components for reliability and an inverter can also cause reliability problems if it's a poor quality unit. Way too complicated for me. I like simple and reliable.

[tubman]

Quality condensers? I still have these available. Modern "severe duty" film capacitor in a classic "Trash Can" styled housing that mounts on the outside of the distributor housing. Lots of developmental time determining the proper components. I already have a bunch in the field, including my '51 Ford, '67 Corvette, and the Chrysler hemi in my dirt car. $40 plus shipping.

[G.M.]

Originally Posted by rotorwrench

The only problem we have these days is the fact that there are very few well made automotive condensers any more. If a person can get a good quality condenser, the OEM system works very well with good reliability. I would venture to say that it would likely be as reliable as the Pertronix systems since they are so sensitive to voltage spikes that that they tend to burn the module out at the drop of a hat. They have to have the right components for reliability and an inverter can also cause reliability problems if it's a poor quality unit. Way too complicated for me. I like simple and reliable.

I agree with you on the simplicity and reliability of the original stock Ford
system. This has been made more reliable by the introduction of the Ford
coils from 32 to 48 being rewound and insulated with modern high temp
materials by Skip Haney in Florida. He has rebuilt well over 20,000 Ford
coils and removed the heat break down problems. In over 20 years NO
ONE that has his coil ever paid for repairs to a coil he rebuilt. Using a
stock coil and ignition makes finding a problem very easy to find and
repair. Look at all the past posts on abortions to the ignition system,
they go on and on trying to fix the problem. My advice, stay stock. G.M.

[42guy]

I have been using one of Skips rebuilt coils and crab dist. maybe 12 years. Still going strong.

[Brendan]

i know if you run a 6 volt Ford coil on 12 volts it will blow its top off

[G.M.]

Originally Posted by Brendan

i know if you run a 6 volt Ford coil on 12 volts it will blow its top off

You can run a 6 volt coil on 12 volts but you need right resistor.
The problem is when the polarity is reversed the coil windings
are not correctly wired. If the 6 volt coil is run on 12 with the 6 volt
resistor the coil will get hot and melt the tar in the coil and leak. Let
get hot enough it will split the top of the coil. On a normal 6 volt
system if the ignition switch is left on and the engine is not running
there is a 50/50 chance to melt the coil. The 50% come in as to
whether the points are open or closed. If closed the windings become
a big resistor and depending how strong the battery is will melt the
coil or with a weak battery it will run down. Points open there is no
connection of the windings to ground. The real danger is with the
ignition switch on and a battery charger running. This could lead
to the coil catching on fire. The only way a Ford 6 volt coil with the
original Ford resistor will melt is with the ignition switch left on and
the engine not running. G.M.

[BUBBAS IGNITION]

Guys this is a difficult discussion to follow and many of the replies are correct . However we need to stop and qualify a couple things.

What coil are we discussing ???? The early ford six volt coil or a later can type coil?
The early Ford Helment coil drives down the road at approx 3.4 volts after the resistor , this was changed when the coil went remote on the 1946 to 48 and then again in 1949 to 1953. Each system is a stand alone issue and each primary coil circuit is a different discussion.
Then add the fact that we use aftermarket coils from many suppliers with no regard to the actual factory design and the problem gets worse. I just was trying to help a friend with a ignition issue and finally after a year or so of problems he brought the coil and distributor into the shop for me to look at. The coil was green and said John Deere on it!! Testing showed very low resistance, i asked where he got that coil and he said off my neighbors lawn tractor!!!!
Maybe we need to start another thread and qualify the type of coil being discussed and forget the convertor issue ??

[G.M.]

Originally Posted by BUBBAS IGNITION

Guys this is a difficult discussion to follow and many of the replies are correct . However we need to stop and qualify a couple things.

What coil are we discussing ???? The early ford six volt coil or a later can type coil?
The early Ford Helment coil drives down the road at approx 3.4 volts after the resistor , this was changed when the coil went remote on the 1946 to 48 and then again in 1949 to 1953. Each system is a stand alone issue and each primary coil circuit is a different discussion.
Then add the fact that we use aftermarket coils from many suppliers with no regard to the actual factory design and the problem gets worse. I just was trying to help a friend with a ignition issue and finally after a year or so of problems he brought the coil and distributor into the shop for me to look at. The coil was green and said John Deere on it!! Testing showed very low resistance, i asked where he got that coil and he said off my neighbors lawn tractor!!!!
Maybe we need to start another thread and qualify the type of coil being discussed and forget the convertor issue ??

The 46 to 48 Ford coils operates at the same 3.5 to 4 volts as the 32 to 48
coils. After 48 Ford went to the round coil. G.M.

[BUBBAS IGNITION]

Originally Posted by G.M.

The 46 to 48 Ford coils operates at the same 3.5 to 4 volts as the 32 to 48
coils. After 48 Ford went to the round coil. G.M.

Thats just barely more than two D cell flashlight batterys. I always wondered if a flathead would run on two D cells ???????

You meant to say 1942 to 1948 didnt you...?

[G.M.]

Originally Posted by BUBBAS IGNITION

Thats just barely more than two D cell flashlight batterys. I always wondered if a flathead would run on two D cells ???????

You meant to say 1942 to 1948 didnt you...?

If the batteries supply 2.5 to 3 amps I don't see why they
wouldn't run the ignition on a 32 to 48 Ford. But I doubt
they would carry 3 amps. G.M.
I was thinking, 3 D batteries with no resistor??

[VeryTangled]

Attachment 334237

Originally Posted by G.M.

The only way a Ford 6 volt coil with the original Ford resistor will melt is with the ignition switch left on and
the engine not running. G.M.

G.M., you said almost exactly the same thing in post #15 of this 2011 thread...
https://www.fordbarn.com/forum/showthread.php?p=268584

But I found out another way. I have a car with a battery cutout. I roll-started the car which was pointed downhill. I had the cutout off, which I didn't notice since I didn't use the starter. Within ten miles I'd done this to the coil.

[G.M.]

Originally Posted by VeryTangled

Attachment 334237

G.M., you said almost exactly the same thing in post #15 of this 2011 thread...
https://www.fordbarn.com/forum/showthread.php?p=268584

But I found out another way. I have a car with a battery cutout. I roll-started the car which was pointed downhill. I had the cutout off, which I didn't notice since I didn't use the starter. Within ten miles I'd done this to the coil.

At least I'm somewhat consistent even at 85. G.M.