If I were to connect an ignition coil directly to a battery

[indr]

What would happen? Provided a spark plug is attached to the coil, too...

[CycleDoc59]

Each time you break the connection to the battery, the plug will fire.

I sometimes bench-test coils by connecting the coil to a battery and sparkplug.
Or better, to a spark-tester with a much wider gap of 10mm or more.

[Turkeycreek]

This is a good way to install a flame thrower. Just need a source of gas or propane, a metal tube and you are in business

[CycleDoc59]

Originally Posted by Turkeycreek

This is a good way to install a flame thrower. Just need a source of gas or propane, a metal tube and you are in business

Cars would sometimes get a spark plug installed in the side of the tail pipe, downstream
of a propane bottle connection. Don't tailgate.

[ragtoplvr]

For the flame thrower they used a model T coil that had points that vibrated all the time to drive the flame thrower plug.

Or you could use a normal 12 V relay with 2 sets of contacts, one set wired as a buzzer, the other drives the coil.
If you used it a lot, it would not last long but for a novelty it is perfect When gas was 20 cents a gallon this was fun.

Rod

[Storm Shadow]

a proper flame thrower, is run by gasoline, or petrol, force fed by compressed air into the petrol tank, to push it out. pump and ignition were two separate buttons too, so u could spray petrol 100 meters away, yes they do travel a bloody long way, not like movies, to run into a bunker, and then ignight it.

ive often thought about a efi fuel pump 12v battery, to make something, quight illegal...

[Two Speed]

Originally Posted by indr

What would happen? Provided a spark plug is attached to the coil, too...

Since you don't mention if you want to make things go boom as above, or jury rig an existing ignition system, if you hook it up and leave it powered,
1. The engine won't turn off when you turn the key off.
2. You'll burn the coil up if its "on" and not running.
3. Drain your battery if the engine isn't running.

[Benesesso]

One more little goodie. 6V car coils are meant to run at ~6.7 volts. 12V car coils are built to run at ~9-10 volts continuously. They'll take 12-13 volts intermittently.

[FixerDave]

Originally Posted by Storm Shadow

a proper flame thrower, is run by gasoline, or petrol, force fed by compressed air into the petrol tank, to push it out. pump and ignition were two separate buttons too, so u could spray petrol 100 meters away, yes they do travel a bloody long way, not like movies, to run into a bunker, and then ignight it.

ive often thought about a efi fuel pump 12v battery, to make something, quight illegal...

Off topic, but my understanding is that flame throwers are actually legal (used in agriculture or something or other). As a topic, it comes up in the anti/pro-gun rants. Sure, why ban X when flame-throwers are legal?

On topic again... a coil is just a transformer. They only work when the input is changing. 12v, just connected - not changing, will just heat the coil up, nothing at the output at all. You need to make and break the input to get spark on the output.

David...

[Storm Shadow]

Originally Posted by FixerDave

Off topic, but my understanding is that flame throwers are actually legal (used in agriculture or something or other). As a topic, it comes up in the anti/pro-gun rants. Sure, why ban X when flame-throwers are legal?

On topic again... a coil is just a transformer. They only work when the input is changing. 12v, just connected - not changing, will just heat the coil up, nothing at the output at all. You need to make and break the input to get spark on the output.

David...

ah different countries

[Wasser]

Originally Posted by Benesesso

One more little goodie. 6V car coils are meant to run at ~6.7 volts. 12V car coils are built to run at ~9-10 volts continuously. They'll take 12-13 volts intermittently.

That's why every owner of an old Chrysler product always carried a spare ballast resistor in the glove box or, a jumper wire to get to the parts store.

[Benesesso]

Originally Posted by Wasser

That's why every owner of an old Chrysler product always carried a spare ballast resistor in the glove box or, a jumper wire to get to the parts store.

+1. I was wondering how long it would take before someone jumped in on this. Let's wait and see if anyone can explain why they did it that way.

[Beezer]

when the starter engages, the battery voltage drops, so the coil is designed to run on the lower voltage (about 10V) to produce a hot spark. once the engine starts and the system resumes normal voltage, current to the coil is reduced by the ballast resistor. in start mode the coil is wired to the main buss through the key switch. in normal run mode the key switch puts the resistor is in series with the coil so the voltage will be reduced to the coil only

[Benesesso]

Nailed it.

[MotorradMike]

Originally Posted by Benesesso

One more little goodie. 6V car coils are meant to run at ~6.7 volts. 12V car coils are built to run at ~9-10 volts continuously. They'll take 12-13 volts intermittently.

So why are 6V coils meant to run at 6.7V?