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midnite2336

Ignition coil gets hot

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I have a 1948 Chrysler which has been changed to 12 volt, with ignition on and car not running after 5 to 8 minutes the coil gets very hot. Is the coil bad or what?

 

Thanks. 

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Most any coil will get hot after that time, particularly if the distributor points are closed, not a good practice to be doing this. ?

 

In short, you have the battery current flowing through the coil direct to earth and the coil will heat up just like the old bar type electric radiators. 

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This should be in the technical section.

You did not state if you have a dropping resistor hooked up to the coil for the rum position,.

You may have a shorted coil, many of the new coils from overseas have come come pre-shorted.

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1 hour ago, 28 Chrysler said:

This should be in the technical section.

You did not state if you have a dropping resistor hooked up to the coil for the rum position,.

You may have a shorted coil, many of the new coils from overseas have come come pre-shorted.

 

Nevertheless if the points are closed it will get hot.

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8 hours ago, hchris said:

 

Nevertheless if the points are closed it will get hot.

Yes!  The coil can draw 4 to 5 amps when the points are closed and the engine is not running.  Kinda like grabbing a 25W light bulb when the power is on.

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Normal for this to happen.

But don't leave the key on like that.

If you need the key on to do other work unhook the coil.

 

But doesn't that 12 volt conversion screw up the shifting?

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Depending on who did the conversion (for whatever reason) they may not know (probably didn't) that 12 volt coils need either a voltage dropping resistor, as mentioned above, a resistance wire (VERY unlikely) or a coil with an internal resistor.

You didn't say how long you've owned this car.

If it's something you recently got and you find it winds up eating the points like potato chips I will guarantee the coil is running full voltage all the time.

Leaving the ignition switch on when the points are closed is a no-no.

It not only heats up the coil but the points get pretty hot too.

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Many aftermarket replacement coils advertise "internal resistor".

Not sure if using these along with a resistor built into the circuit would be overkill.

 

Input ?

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Your 1948 Chrysler when it was set up for six volts drew 5 amps of current when the points were closed and the engine not running from what I find in a tune up guide book.  If you double the voltage to 12V the current will double to 10 amps which is not good for the coil or the points.  You need to add resistor in the stock coil circuit to limit the current back to the desired 5 amps assuming the 6v coil is still being used. That resistor would be about 1.5 to 2 ohms to get in the amps in the right ballpark.

Edited by TerryB (see edit history)

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13 hours ago, autoluke said:

Many aftermarket replacement coils advertise "internal resistor".

Not sure if using these along with a resistor built into the circuit would be overkill.

 

Input ?

 

One or the other......not both.

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