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Exploding coil


Les Henson
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I fitted a new dizzy and carb to S2A this morning - the guy had been advised by the AA that they were both shot, after they recovered him to Swindon from Sheffield.

Even after carefully setting the timing, checking fuel supply, tappet clearance, leads etc, no matter what I did the engine would run badly, backfire out of the carb AND the exhaust at the same time, cut out all of a sudden, and other what seems like timing-related problems.

A garage in Sheffield had fitted a new coil, and what I thought was a radio suppressor, so I assumed that was ok.

Anyway, I had the engine fast idling, and was fiddling with the dizzy timing, when the coil burst - spraying hot oil over my left arm, side of face and neck.

On closer inspection - the radio suppressor was actually a condensor, so there were two of then in line, including the one inside the new dizzy. Wiring was as follows:-

Ignition feed to minus on coil

Positive terminal on coil to distributor, with one condensor plumbed into the wire with a Bodgelok.

With it like this, the positive wire fron the coil was going through two condensors by the looks of it.

Guts of the coil, which was extremely hot:-

med_gallery_2_28_746913.jpg

Coil housing on the bulkhead - first condensor close by.

med_gallery_2_28_669083.jpg

I have to fit a new coil, and will remove the condensor on the bulkhead, but need to know if this was the likely cause of the coil bursting - don't want it to do it again :(

Les.

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Les,

The capacitor should not be there as it is no required, but it also did not cause the problem.

I strongly suspect that there was either a short circuit turn in the coil primary winding, or the coil was a 9 Volt, designed to have resistive ballast in circuit.

Either of the above will cause the coil to get excessively hot ……… then the oil expands ………….. and the coil pops out the end of the can………

This is a fairly unusual occurrence ……….but not unknown

Ian

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The extra suppressor (condenser) should be on the ignition live side of the coil, not the contacts (-ve) side.

Too much capacitance accross the contacts will mean that the primary current will fall too slowly when the contacts open, thus giving a poorer spark and causing the coil to overheat.

I would go along with Ian and make sure you use a proper 12v coil designed for an old-fashioned contact breaker type ignition system.

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The extra suppressor (condenser) should be on the ignition live side of the coil, not the contacts (-ve) side.

Too much capacitance accross the contacts will mean that the primary current will fall too slowly when the contacts open, thus giving a poorer spark and causing the coil to overheat.

Yes, I had considered that ............... .............. but the value of the capacitor is too low to be significant at the low frequency pulsing of 4 cylinder ignition.

Taking it one step further, the C + R (of the coil) would form a pulse shaper .......... but again the time constant will be of no significance.

Ian

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The scotchlock'd condensor is a quick roadside fix if the original condensor is faulty. Especially if the correct condensor is not available or a bit fiddly to fit.

(As you know condensors can be a bit hit/miss from a diagnosis point if the damn thing runs ok when you look at it!) :huh:

Coil wiring wrong way around, stupid! :blink:

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The scotchlock'd condensor is a quick roadside fix if the original condensor is faulty. Especially if the correct condensor is not available or a bit fiddly to fit.

(As you know condensors can be a bit hit/miss from a diagnosis point if the damn thing runs ok when you look at it!) :huh:

Coil wiring wrong way around, stupid! :blink:

I rember some coils being fitted with a retainig colar to keep the top from blowing off. It might have been on Escorts ( CVH Engine XR3). I can only rember one letting go after the ignition had been left on whilst beeing towed. We were always told to disconect iff had to tow with the ignition on. Certainly the condenser on the wrong side plus the wrong voltage is not good. (Ex AA Patrol 22years.)

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F’ Christ’s sake……………Condensers are used in plumbing and steam related systems …………………. f’king CAPACITORS are used in ignition systems ……………bloody morons :P …………………mutter…. mutter….. mutter…… :angry:

:D:D

Ian

Depends how old you are :blink: I remember when it was spelled condensOr !

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BBC is older than Noah, he predates the dawn of time by several millenia, people have hypothesised he is merely a legend but I know he is in fact a travelling Alien... your both right, old school condensor, capacitor more up to date, mere semantics... Ian weren't you fighting the evil empire on Tattoene when Condensor was being used as a name on Earth?

:huh:

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