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Electronic ignition conversion and ballasting


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While I've got the carbs off my '79 Elite for a spruce up, I though I would try out fitting an Accuspark electronic ignition kit. It's very cheap, and seems to get good reviews on the whole.

One issue is that they say it works best without a ballast coil/resistor. I'm a complete novice on all this, but I understand that the standard 79 Elite 502 would have a ballast resistor - I've not hunted it out yet.

Now the Accuspark people explain how I can keep the resistor/coil OK , but suggest moving to an unballasted system gives best results.

The question I have is doubtless uninformed, but here goes: Is it sensible to replace the ballasted coil with a standard 12v 3ohm version, fit the electronic ignition and scrap the resistor. Or is the ballasting still needed, given the starter motor etc?



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You only need the ballast resistor on that type of coil due to the ignition system originally fitted being sensitive to voltage drop, so go for a new coil (non-ballast type) and wire in as per accu-spark. I've not done it on a Lotus but have just done it to the Elf with similar dissy.

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A ballast resistor is provided to step 12v down to 6v, as your car has a 6v coil! A 6v coil is used because the starter circuit bypasses the ballast resistor and feeds 12v to the coil under cranking conditions. (thats what the 'spare' wire on the starter motor feeds). This is to provide a much 'fatter' spark for starting (but would damage the coil if used continuously). To answer your question, yes you can bin-off the ballast resister and replace the old coil with a 12v version.


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ballast resistors are used to raise the resistance of the coil to reduce the current draw through the points/switching medium . most coil/ballast combinations are around 3 ohms. The cranking bypass to the coil allows the coil to draw a higher current, hence producing a larger spark when the starter motor is running. It's important to use the correct resistance of coil with either points or electronic ignition other wise you'll burn out your module/points. For a lumenition you need a 3 ohm set up. If you use Ohms law (volts=resistancexcurrent) where the resistance is ohms, current amps you'll see that at 13.8v (battery voltage) a 3 ohm coil will draw 4.6 amps, where as a 1.5 ohm coil will draw 9.2amps. modern coils are around 0.8ohms so draw 17.25 amps! modern engines run huge plug gaps, so need a far more energetic spark with peak KV of over 40000 volts!

i hope this helps



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  • 1 month later...

I might add, that the resistor is not a electronic component, like you might know from radios, etc. It is a wire in the harness. It has a pink cloth casing, you can find it in the wiring harness in the right footwell. For some reason it can not be found in the wiring diagram in the official workshop manual. Ask me how I know, I searched for 2 days why there was no power to the coil, until I found the wire, broken off the connector in the harness... :veryangry:

Our car is a 1974 federal Elite.

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  • 3 months later...
  • 6 years later...

@Herc I have a similar issue with my Esprit S1. Though fitted with a Luminition Magnatronic "pointless" system. Note: not the one with the separate Luminition box.

The new loom has a ballast wire, and have the corresponding ignition coil (measuring 1.4 ohms). What was your solution in the end?

Edited by Fridge
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