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Section : Ignition and Distributers
Posted By : Des Whelehan, 18-Sep-2003,
02:14pm
Hi, can anyone help, I have the problem of the Coil overheating on my Mk 3 Spitfire like others, but this was changed last year, and is now doing the same
again, any ideas !
Des
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Posted By : Josh Bowler, 18-Sep-2003,
02:42pm
Hello,
Sounds like you're using a coil that needs a ballast resistor on an unballasted system maybe. A ballast resistor needs to be fitted in series to the +
feed of the coil.
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Posted By : Roger Smith, 18-Sep-2003,
03:23pm
Hi
I agree, it does seem you have a six volt coil working on a 12 volt supply, so doubling the current and causing the coil to over-heat. Fitting a
ballast resistor will drop the voltage across it to the correct level, but this might cause you starting problems.
During starting, the ballast resistor is short-circuited, causing the voltage across the coil to rise to a (nominal) 12V all the time the starter
motor is activated giving a stronger spark.
Looking at the MK3 wiring diagram they don't appear to use a ballast resistor like Mk1V's. Perhaps a better bet is to fit another new coil?
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Posted By : Des Whelehan,
18-Sep-2003, 04:00pm
Hello, it is a 12 Volt coil that is fitted !
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Posted By : Roger Smith,
19-Sep-2003, 08:29am
Hi
Assuming your new coil is not faulty, then because it is a 12V system, and the battery acts as a voltage stabiliser, it is theoretically
not possible to overheat the coil by providing excessive voltage across it (famous last words!).
Have you checked the distributor bearings? If the dwell angle is out, causing the points to remain in contact longer than they should, then
this could cause the coil to overheat since the current will be flowing longer than it should. Whilst the points gap might be fine when the
engine is not running, it might be quite different at 3000 revs.
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Posted By : Des Whelehan,
19-Sep-2003, 11:39am
Hello
Thanks for the advice, but I have an Aldon Electronic Ignition fitted, which appears to be working ok.
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Posted By : Josh Bowler,
19-Sep-2003, 03:06pm
i reckon your using coil thats meant to be ballasted in an unballasted sytem, the coil wont say that its 6 volts or anything, but
it may say if it needs to be ballasted or not, either that or the coil is pooped
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Posted By : Roger
Smith, 20-Sep-2003, 09:41am
Hello again, Des
Well, that's my theory well stuffed - I was quite proud of it too!
One LAST thought. Did you buy the coil and Aldon System as a matched pair? I found the following comment on the Aldonauto
website:
"This new more powerful 'Ignitor II' shares all the same features as the original Ignitor with added extras. It takes the
electronic ignition module one stage further, by adding a powerful microcontroller, which controls the dwell period, for the best
possible spark over the entire rev range. It is highly recommended that the new Flame Thrower II super low resistant coil is used
in conjuction with the Ignitor II"
"Super low resistance" suggests higher current and so more power dissipation. However, with varying current, as with alternating
current, build-up of current flow is also dependant on Induction. With a low resistance/high induction coil the current build-up
for each spark cycle would be much slower - probably not reaching max. current while the engine is running (particularly if the
dwell angle is being controlled) and this would result in lower power dissipation. Just might be worth a try...
Regards
Roger
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Posted By : Des
Whelehan, 22-Sep-2003, 08:34am
Hi Roger
The Aldon is the original type, not the ignitor II, as far as I know, and I have a standard coil fitted, so may be I need the
high performance coil you mention.
Thanks to everyone for your help, I had never used this message board before and have found it really helpfull, thanks
again.
Regards Des