12 volt coil on a 6 volt engine

G

Gabalus

Senior Member
Hello,

My 6 volt coil failed and I just have a 12 volt coil to run tomorrow morning.
What do you think about that ? Does it work ? Very well ? Limits ?

Thank you
 
No extra ballest resistor needed. It will work but will have a lower output voltage to plugs, engine may not run as well, but if you have do not have a 6 volt coil it is worth trying.
 
billwill said:
You should a ballist resster in line to reduce voltage
Click to expand...

I think that's the other way around. Using a 6v coil on a 12v battery requires a resistor - a lot of 12v coils include a resistor (put there to prevent burning up the coil should the engine stop with the points "on.") but many don't.

I say just do it. Otherwise known as "nike-it." If it works - it works. If not you can't hurt much.

Joe K
 
Gabalus said:
Hello,

My 6 volt coil failed and I just have a 12 volt coil to run tomorrow morning.
What do you think about that ? Does it work ? Very well ? Limits ?

Thank you
Click to expand...

First, let me ask: What do you mean by "a 12 volt coil"?

Can you measure the resistance with an ohm meter across the the 2 coil posts?

Some "12 volt coils" read out at about 1.5 ohms and require an external ballast resistor to be able to use them on a 12 volt car. You can run a 1.5 ohm "12 volt coil" on a 6 volt car without a ballast resistor and it will run great.

Some "12 volt coils" read out at about 3 ohms and can really only be used on a 12 volt car. The spark out of this "12 volt coil" when used on a 6 volt car will be very weak. The car might start but you won't like how it runs with the weak spark.

If you have a NAPA near you, you can get an IC-12 coil for your 6 volt car that will be around 1.5 ohms.

Lots of confusion around coils and volts. I hope this helps.
 
Thank you ! It's clear now.
I don't have an ohm meter.
My 12 volt coil ( not damaged ) is propably 50 years old.
Perhaps, last chance : I'll try to call an old man who owns old cars.
 
I don't have an ohm meter.
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WHAT? How can someone NOT have a VOM? Especially when Harbor Freight is GIVING them away for free?

Yeah. I know. They're offshore sourced. And they're not that accurate. And they're not that well made.

But FREE is FREE. At least until the end of the month of April - or while supplies last.

See attachment below

Joe K
 

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Many [ but not all] internally ballasted coils will have markings as such on the outside.
Your 12v coil should work fine if not internally resisted.
Once you get ahold of a volt meter, regardless of 6 or 12 volt systems you only want 6-8 volts feeding the points.
 
Gabalus said:
Thank you ! It's clear now.
I don't have an ohm meter.
My 12 volt coil ( not damaged ) is propably 50 years old.
Perhaps, last chance : I'll try to call an old man who owns old cars.
Click to expand...

A 50 year old "12 volt coil" will have 1.5 ohms on the posts, I can almost guarantee it. They were all externally resisted in the 60's, one way or another. Internally resisted 3 ohm coils came later.

Just use it! It will cause no harm. It might just run poorly. You'll know soon enough.
 
Mike V. Florida said:
I agree with Jim. How many old cars (12v) had an external resistor.
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Most. Chrysler mainly with their famous external ballast resistor, Ford had it both ways as did GM using either a mounted resistor as Chrysler, a resistor wire or resistor coil. Some coils were noted as such but not all. Many folks then were not aware of the resistor wire.
 
Patrick L. said:
Most. Chrysler mainly with their famous external ballast resistor, Ford had it both ways as did GM using either a mounted resistor as Chrysler, a resistor wire or resistor coil. Some coils were noted as such but not all. Many folks then were not aware of the resistor wire.
Click to expand...

Like Jim said, go for it!
 
I've run any number of 12v coils on 6 volts. They always worked fine. A guy has to learn how to do things like that if you want to save yerself in a squeeze. 50+ years ago, we didn't have money for a new coil. We had to make do. Go for it!
 
Joe K said:
WHAT? How can someone NOT have a VOM? Especially when Harbor Freight is GIVING them away for free?

Yeah. I know. They're offshore sourced. And they're not that accurate. And they're not that well made.

But FREE is FREE. At least until the end of the month of April - or while supplies last.

See attachment below

Joe K
Click to expand...



Like Joe said... I would get a meter and measure it to know what you have... it should be between 1.2 and 1.5 ohms. If it is it should be fine.

I gave a voltmeter and troubleshooting seminar at the MARC Membership national. All the guys in our group picked up the free meters from Harbor Freight when they could, so everyone attending the seminar went home with a free meter from the seminar.
They are not the best, but will get the job done.

Again, get a meter and check it ( all wires off) and see what the ohm reading is.

Good luck!
Larry Shepard
 
My 75 MGB is a 12 volt car with a 6 volt coil. There is a resistor wire which is shorted out by an extra contact in the starter solenoid when you turn the key. This puts 12 volts to the coil to warm up the spark for starting. Many cars had similar setups hence the external resistors. Not many people know that.

Ian
 
According to my parts man, all coils are 6 volts. The ones marked 12 volts are internally ballasted to reduce the voltage to 6 and the ones without the internal ballast will be marked to use an external ballast resistor. Use the coil and you may never change it.
 
Joe K said:
WHAT? How can someone NOT have a VOM? Especially when Harbor Freight is GIVING them away for free?

Yeah. I know. They're offshore sourced. And they're not that accurate. And they're not that well made.

But FREE is FREE. At least until the end of the month of April - or while supplies last.

See attachment below

Joe K
Click to expand...

I have one and have no idea how to use it---been brand new for 10 years in the tool box
 
Until High Energy Ignition (HEI) came out in the late 1960s, 12-volt coils were usually 8-volt coils as were many of the 6-volt coils. If the 12-volt coil is pre-HEI, it should work with an input of 6 volts.

Early 12-volt ignition systems used an 8-volt coil. When the ignition switch was turned to the START position, 12 volts went to coil to provide a higher voltage spark. When the switch went into the RUN position, a resistor or resistance wire dropped the coil voltage to 8 volts.
 
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