BFRieck Posted February 21, 2013 Share Posted February 21, 2013 Anyone out there know the primary resistance for a 2.25 petrol Series III ignition coil? Bruce Quote Link to comment Share on other sites More sharing options...
secondjeremy Posted February 21, 2013 Share Posted February 21, 2013 1.6 ohms unballasted and 1.2 ohms ballasted? I think these were the figures I obtained when I was assured that a new coil was suitable for Land Rovers but suspected it was ballasted - so compared it with a few others. Quote Link to comment Share on other sites More sharing options...
BFRieck Posted February 21, 2013 Author Share Posted February 21, 2013 Thanks, do you remember whether a replacement should be ballasted or not? Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted February 21, 2013 Share Posted February 21, 2013 Depends if you have a ballast Quote Link to comment Share on other sites More sharing options...
secondjeremy Posted February 22, 2013 Share Posted February 22, 2013 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. Quote Link to comment Share on other sites More sharing options...
BFRieck Posted February 26, 2013 Author Share Posted February 26, 2013 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. Quote Link to comment Share on other sites More sharing options...
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