In a message dated 97-09-10 07:47:26 EDT, suhring@lancnews.infi.net (scott
suhring) writes:
> I am planning on upgrading my standard Lucas coil to the Lucas
> sports coil (as well as tuning the distributor, etc.). Please help
> me understand the difference between a balast and a non-balast coil.
> Also, how are these wired differently when going from a balast coil
> to a non-balast coil.
Scott:
Basically, A ballasted coil is designed to produce full spark output with
approximately 9 volts on the input (+ terminal). A non ballast coil is
designed to produce the same spark output, but with the full 12 volts on the
input.
With a non-ballast coil, the input to the coil is the same, 12 volts, whether
the engine is running, or being cranked by the starter motor. With a ballast
coil, the starter relay by-passes the ballast resister when the starter motor
is spinning the engine, and applies the full 12 volts to the coil. Since the
coil is designed to provide full spark with 9 volts, the application of the
full 12 volts produces a much hotter spark, which is an aid in starting.
After the engine starts, and the starter motor is off, the coil voltage is
dropped to 9 volts, and the coil output is the same as for a non-ballast
coil. The reason the ballast type coil is not run at the full 12 volts, for a
hotter spark, is to prevent damage to both the coil and the points.
With a non-ballast coil, power is applied to the coil directly from the
ignition switch, via a white wire. Power to the ballast coil comes from the
the ignition switch to the resistance wire, and then to the coil. When the
starter relay operates, power is applied from the battery, via a brown wire,
to the starter relay, and through the starter relay via a white/yellow wire
to the coil. This shorts out the resistor wire, by placing 12 volts on both
ends of the wire. With the same voltage on both ends, no current flows, so no
heat is generated. The current flow is shunted around the resistor wire. This
bypassing of the resistor wire places the full 12 volts on the coil.
As for the modifications required to switch from a ballast coil to a
non-ballast coil, it couldn't be simpler - just run a wire from the most
convenient white wire you can find (probably at the fuse box), directly to
the + terminal of the coil (of course, all the rules of good wiring practice
shouild be used). No need to remove the resistance wire, because it will now
be constantly bypassed, just as it was before when cranking.
Now here's the good news for you - your '70 TR6 does not have a ballast
resister, they were used only from '74 and later. As I understand it, the
modifications made to these cars to meet the environmental concerns made them
hard to start, so the ballast type coil was used to get the extra hot spark
during starting, since starting places the most stringent demands on the
ignition system.
For a more detailed explaination of igntion systems in general, see:
http://www.vtr.org/maintain/ignition.html
Hope this clears it up a little for you. If anything is still not clear, let
me know, and I will try to clear it up for you.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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