Alan_Thomas
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| posted on 5/8/06 at 07:36 PM |
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Coil getting very hot
I am running a crossflow using a std ignition off a 12v coil. (no ballast resistor)
Doing some work on the car and had ignition on for about 5 mins and I could not toch the coil it was that hot. Is this normal? Even the wiring to the
coil was hot suggesting massive current draw. any idea anyone how much current a coil should draw with ignition on but engine off?
Any other ideas?
- Alan 
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rusty nuts
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| posted on 5/8/06 at 07:41 PM |
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Have found coils on many cars with contact breaker ignition get very hot when ignition is left on . Can't tell if you have a problem though.
Would suggest taking car for a test run and checking coil after .
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David Jenkins
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| posted on 5/8/06 at 07:56 PM |
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If you have the ignition on when the points are closed then the coil will get very hot - to the point where it boils or blows a winding!
They were never intended to operate like that, which is why you should always turn the ignition off when the engine isn't running.
One of the blessings of electronic ignition...
David
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2Fast
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| posted on 5/8/06 at 07:56 PM |
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I would suggest you don't leave the ignition on for extended periods with contact breaker ignition unless the engine is running, i've done
it in the past and killed the coil.
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mackei23b
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| posted on 5/8/06 at 08:39 PM |
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I ran a crossflow without a balast resistor and got a huge misfire, on looking at the top of the coil there was arcing as the insulation had broken
down!!
Would recommend using a balast resistor if it is normaly required unless specified otherwise.
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nitram38
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| posted on 5/8/06 at 09:01 PM |
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It is also possible that you have used a coil that was designed for use with a ballast resistor.
These are designed to run at a lower voltage, hence the resistor to drop the voltage across the coil.
The system is wired so that on holding the ignition key in the start position, 12v is applied briefly across the coil (bypassing the resistor) which
gives a stronger spark to help starting.
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Alan_Thomas
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| posted on 5/8/06 at 09:28 PM |
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Checked with a meter - 4.6Amps = 55W a lot of heat to go somewhere when the engine is running this power is disappated by the secondary which produces
the spark. So the answer is, as suggested, don't leave the ignition on without the engine running.
It is a coil designed to run without a ballast resistor so this must be the 'norm'
I have most of the parts to go EDIS and wasted spark so looks like a job for the winter - Alan
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Monkeybasher
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| posted on 6/8/06 at 12:12 AM |
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I remember reading about this problem on the megasquirt forum, but cant remember any of it.
Hope this helps
sorry
steve
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907
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| posted on 6/8/06 at 06:18 AM |
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quote:
Originally posted by David Jenkins
If you have the ignition on when the points are closed then the coil will get very hot - to the point where it boils or blows a winding!
They were never intended to operate like that, which is why you should always turn the ignition off when the engine isn't running.
One of the blessings of electronic ignition...
David
Hi,
David is spot on.
Many years ago I borrowed my brother in laws car and burnt the coil out by leaving the ignition on.
Nothing like having to fork out hard cash to make you remember something.
If you need to work on your electrics with your ignition on just disconnect the wire from the coil that goes to the dizzy.
This has the same effect as the the points being open.
Points after all are only an earth switch.
hth
Paul G
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02GF74
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| posted on 6/8/06 at 07:27 AM |
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doing the sums, the power dissipated is about 40 W (this iswhne running IIRC), - can you hold a 40 W lamp nulb in your hand 
I suggest you wrap a piece of bread around the coil so when you finish working, you can have some nice toast with your cuppa!
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britishtrident
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| posted on 6/8/06 at 10:01 AM |
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Quite normal for a standard 12v coil to get hot in these conditions, however do check it is the corret coil for the job
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David Jenkins
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| posted on 6/8/06 at 11:46 AM |
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The difference when the engine is running is that the coil only works to a 50% duty cycle - points closed for a while, magnetic field builds up, then
the points open, the field collapses and a big spark is generated.
Therefore the coil only gets heated half as much, and gets a chance to cool before the next connection.
David
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