The coil always gets warm when running, but it gets hot if the ignition is
left on without it running and the points, for example, are closed, and this
is bad for the coil and points. If the points are open there will be no
current flowing in the coil and it will stay cool. A standard 12v coil is
about 3 ohms primary resistance, that represents about 4 amps, or 48 watts
if powered continuously. With the engine running the points are opening and
closing with a duty cycle of about 2/3rds i.e effectively about 32 watts
which is why a running engine has a cooler coil. However sport coils can be
lower resistance than this, hence higher current and wattage, and hotter to
the touch. A Lucas Sport I have has a primary resistance of 2.4 ohms. 6v
coils used on rubber bumper cars with a loom ballast resistance in series
are by comparison about 1.5 ohms primary resistance, and if used without the
ballast resistance i.e., in a chrome bumper car results in double the
current and wattage, and even when running this can damage the coil and
points. The above conditions apply when simple electronic triggers like the
two factory systems and Pertronix etc. are used but can be very different if
other full electronic ignition systems are used. Check your coil primary
resistance for peace of mind.
PaulH.
----- Original Message -----
From: "Thomas Pokrefke" <pokrefke1@comcast.net>
To: <mgs@autox.team.net>
Sent: Tuesday, April 13, 2004 2:32 AM
Subject: Ignition Question
> My MGB has a 12 volt Accel sport coil. The (+) side is hooked up to a
keyed
> 12 volts and the (-) side is hooked up to the black wire from the
> distributor (aftermarket electronic ignition module).
>
> The coil gets very warm, almost hot, to the touch. This happens if the
key
> is "on" regardless of the engine running or not. Is this normal?
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