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coil resistance


BFRieck
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Normally unballasted. The ballasted system was introduced in the 60's to improve starting. Idea is that if you use a coil for a lower voltage system it gives a bigger spark - and yippee the car starts better. Trouble is the coil overheats in normal running and dies.

So put a resistor in series and you're back somewhere near where you started. Short the resistor out as you operate the starter and you've got your lower voltage coil!

Wonderful - did it make any difference - well I was running cars without it during the 70's and they always started well even when living outside - even my Triumph Stag which had lost its one sometime before I got it.

Resistor may be visible or incorporated in loom. Switching is done by extra spade terminals on the starter solenoid.

Don't think early S3's had them - later ones may be different.

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Looks like I've smoked this out. According to an FFR manual, the "black box" contains ballasted resistors that step the voltage down from 24v to 10v. These components also suppress interference with the radios which FFR vehicles normally carried.

So, unless one is trying to maintain total FFR purity, there is no need for anything except the 24v to 10v converter. It is my understanding that a commonly available 24v to 12v converter should work - the primary side of the coil is somewhere between 3 and 4 ohms in resistance indicating a converter rating of less than 5 amps. There are commonly available 24v to 12v converters widely used in the golf cart industry which are durable, sealed, and waterproof units for less than $30 with a rating of either 5 amps or 10 amps (the 10 amp ones being a bit more costly). Either should work well.

I had also wondered whether the distributor "cared" what voltage it received (the idea being that I could just use a 24v coil and dispense with the converter. The answer is definitely yes - 24 volts would quickly burn up the points.

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