The Ford Barn

newshirt · 06-23-2013, 01:53 PM

Can any permanent damage occur if the battery is allowed to completely discharge through the ignition coil?

For me, this has happened accidently because I turn off the gas valve and allow the engine to use up all the fuel in the carb before putting it away for the night. I have, on occasion, walked away to attend other things and forgotten to remove the key from the ignition. Of course, the car runs fine after recharging the battery.

Last year, a "perfectly good" coil shorted and caused my points block to melt down. I believe two such battery drains had occurred that year, months before the meltdown. My new rule is to never leave the car without pulling the ignition key first. But I'm wondering if the internal insulation in that coil had been compromised by draining the battery through it. (Heat, no break in duty cycle.)

Are these just unfounded fears?

BRENT in 10-uh-C · 06-23-2013, 02:50 PM

Generally it does not hurt the coil. Like you have experienced, all that happens is the points become hot and sometimes will only need to be filed clean again. You weren't so lucky it seems last year!

See if you can find someone with an old coil tester to do a test. Mine actually heats the coil first and then I can test the coil's output.

Tom Wesenberg · 06-23-2013, 05:05 PM

My friend lost a coil after the key was left on for only 30 minutes. 4 amps of current running through the coil, when at rest with the points closed, does produce a lot of heat. 4 amps x 6 volts = 24 watts of heat. I've also read about a coil catching on fire from being left on.

I shut my gas off first, but only wait a few seconds before I push the spark up and turn the key off.

jmeckel · 06-23-2013, 07:17 PM

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Most modern day coils are not completely full of oil and not made to be mounted inverted (they will last longer mounted term up, just not the right way for a coil in an A). They like to over heat and fail. So that being said, leaving the key on with the points closed is very hard on these coils.
Best to not leave the ing. switch on, with the motor off for very long.

06-23-2013, 01:53 PM	#1
newshirt Senior Member Join Date: Jan 2011 Location: Colorado Springs Posts: 868	Battery discharged through ignition coil Can any permanent damage occur if the battery is allowed to completely discharge through the ignition coil? For me, this has happened accidently because I turn off the gas valve and allow the engine to use up all the fuel in the carb before putting it away for the night. I have, on occasion, walked away to attend other things and forgotten to remove the key from the ignition. Of course, the car runs fine after recharging the battery. Last year, a "perfectly good" coil shorted and caused my points block to melt down. I believe two such battery drains had occurred that year, months before the meltdown. My new rule is to never leave the car without pulling the ignition key first. But I'm wondering if the internal insulation in that coil had been compromised by draining the battery through it. (Heat, no break in duty cycle.) Are these just unfounded fears? __________________ Ray White

06-23-2013, 02:50 PM	#2
BRENT in 10-uh-C Senior Member Join Date: May 2010 Location: Eastern Tennessee Posts: 11,509	Re: Battery discharged through ignition coil Generally it does not hurt the coil. Like you have experienced, all that happens is the points become hot and sometimes will only need to be filed clean again. You weren't so lucky it seems last year! See if you can find someone with an old coil tester to do a test. Mine actually heats the coil first and then I can test the coil's output. __________________ . BRENT in 10-uh-C . www.model-a-ford.com ...(...Finally Updated!! ) .

06-23-2013, 05:05 PM	#3
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Battery discharged through ignition coil My friend lost a coil after the key was left on for only 30 minutes. 4 amps of current running through the coil, when at rest with the points closed, does produce a lot of heat. 4 amps x 6 volts = 24 watts of heat. I've also read about a coil catching on fire from being left on. I shut my gas off first, but only wait a few seconds before I push the spark up and turn the key off.

06-23-2013, 07:17 PM	#4
jmeckel Senior Member Join Date: Sep 2011 Location: Luck WI Posts: 550	Re: Battery discharged through ignition coil Sponsored Links (Register now to hide all advertisements) Most modern day coils are not completely full of oil and not made to be mounted inverted (they will last longer mounted term up, just not the right way for a coil in an A). They like to over heat and fail. So that being said, leaving the key on with the points closed is very hard on these coils. Best to not leave the ing. switch on, with the motor off for very long. __________________ Jon "If you choose to not decide, you still have made a choice!" RUSH Don't tell me what you know..... Tell me what you have done.