Exploding Coil

[mobylette]

We set off last Friday for our hols on the Isle of Wight. About 10 miles from the ferry while cruising at around 60 mph, there was a loud thump and an immediate loss of power. I coasted to a halt and opened the bonnet to find the coil had spat out its innards. (See picture)

I fitted a replacement coil new from Intermotor, and the engine fired up immediately. We carried on a further 10 miles with everything normal, and just entered the ferry terminal when the car started to lose power and died.

Suspecting the electronic ignition module had been fried by the earlier problem, I removed it and replaced with the points that I had taken with me for such an eventuality. The car started but popped and banged like no ones business. I suspected the condenser, as did the RAC man who turned up, but did not have a spare. By now the shops were shut, so it was a low loader home, and an early start the next day in another vehicle.

I am now back home. I bought 2 condensers from the "distributor doctor", fitted one and no difference. Changed the "new" coil for a spare and car is fine. Checked impedance of "new" coil, reads 0.8 ohms

So two coils dead. Could the electronic ignition have caused the problem before it failed completely? Could it be old HT leads with too much resistance or plugs with too larger gaps?.

I will be fitting new plugs and leads, and staying with points for the time being.[frame][/frame]

[Ufudu]

Interesting.

Any idea what caused the coil to pop? Did it overheat? The windings don't look fried, so something produced the necessary pressure to get it to pop.

It is possible that the first coil damaged the ignition module. Or the ignition module may have been on its way out anyway & popped the coil because it was not switching cleanly. In other words the semiconductors in the module were not switching fully on or off, so you still get a weak spark but resulting in a constant average current resulting in the coil overheating.

Installing the second coil had the same effect and that coil was damaged too. Then the module eventually died....

What type/brand was the module?

Erwin

[bmcecosse]

The coil you have now is WRONG - the Impedance must be 3.2/3.5 ohms. What you have is a coil designed for use with a 'ballast' ignition system and it is designed to run on 6 to 9 volts. It too WILL explode if you run it on 14 volts. Take it off immediately! The coil that has exploded looks to be a 'new' coil and I suspect it too had the stupidly low impedance. Maybe you can still measure that? You need to find a 'good old' coil - with the correct impedance. I can't comment on the possibility of the Ignition module having been damaged - I would get the car running nicely and reliably on points - and worry later about electronics......

[mobylette]

Perhaps I was not clear. The second coil to fail, the "new" one, now reads 0.8 ohms. The one that exploded has been in the car for the 10 years and the many miles that I have had the car, both with and without electronic ignition.

[bmcecosse]

Well - check it if you can. Yes - 0.8 ohm coils WILL overheat horribly, and while running will pass far higher current than intended through the points/electronic ignition. And check that the coil you are using NOW is indeed 3.2/3.5 ohms.

[mike.perry]

Sounds familiar, I had an exploded coil on my Traveller, standard ignition. I had just left the M4 and managed to stop on a reasonably wide road. Despite having my hazards on and back doors open cars were still queuing right behind me so that they could not pass. Eventually a friendly Land Rover stopped and towed me home.[frame][/frame]

[dalebrignall]

bog standard coil is all you need dont go for a fancy one

[bmcecosse]

So -both these coils appear to be the 'new Lucas' coils.......caveat emptor! If you have one on your engine, change it or at least carry a 'known good' spare.

[mobylette]

Thanks all for your replies. In reply to Irwin, I can't remember the make of the ignition unit, but it was supplied by ESM I think, and is of the sort described recently which is not really "electronic" but a contact breaker in a vacuum operated by magnets. See attached pics.

My question was, what could cause both coils to fail. I am pretty certain that this ignition unit was to blame by being partially closed circuit and therefore overheating both coils before it itself failed completely. When tested now (before I cut it open) it is permanently open circuit. The magnet makes no difference.

Martin[frame][/frame]

[dalebrignall]

the insulation on those wires looks suspect

[Ufudu]

Martin,

I don't know this type, it does not look like one from Luminition that EMS sells.

Electronic ignition usually uses optical sensors or Hall-effect devices to pick up the rotor position . I have not come across ones that use reed switches.

Either the optical or Hall-effect sensors are coupled to something like a tyristor that is triggered to conduct the high current. These can fail, usual open or short circuit depending on the failure mode. It can happen that they fail closed circuit, then the resulting heat and current leads to another part of the circuit failing open circuit, with the coil getting damaged along the way.

As others has said it is critical that you use the right resistance coil for the ignition module, that your generator is set correctly to limit the charging voltage to not damage the module (some are specced at 14.8V max) and that the module is secured to the distribute base tightly, using silicone conductive paste to improve the heat conduction away from the module.

Erwin

[kennatt]

whilst many love electronic ignition and good for them,there was and still is, nothing wrong with the mechanical points system as originally fitted.It takes very little maintenance and is just about bomb proof,and it is servicable,not a fit and throw away when it goes wrong,original system for me every time but everyone to their own as they say

[bmcecosse]

My views exactly.... However my TR7 came to me with electronic and it seems to work well (famous last words...) so I have a foot in each camp!

[katy]

A google search of LU142A (shown on the round piece in Mobylette's picture) tells us that it's a Pertronics piece.

http://www.amazon.ca/PerTronix-LU-142A- ... B00199BO0Q

[Ufudu]

Interesting. This is a Hall-effect device, that claims to have considerable protection to prevent damage as well as increasing the energy discharge into the coil. So it is not "just a switch". One caveat on one web site is that it "cannot be used with solid core ignition wires". As always the claim if that it works best with one of the manufacturer's coils.

From http://www.americanmotorfactors.com/con ... _Dist.html

Features
Operating Voltage: 8-V to 16-V DC
Temperature Range: -50 to 300F
RPM Range: 0 to 15,000 RPM
Can be used with most point-type coils, optimal performance achieved when used with our Flame-Thrower® 40,000 volt coil.
Works great in stock point-type distributors as a trigger for multi-spark CD ignitions, eliminating the need for expensive aftermarket distributors.
No complicated wiring makes installation easy.
A solid-state electronic ignition system. "Never change points again!"

The Ignitor II has many of the same great feature that the Ignitor has, but its smarter. Ignitor II units sense the coil current level and use a powerful micro controller to adjust the dwell. Variable dwell helps to maintain peak energy throughout the entire RPM range.
Features
Ignitor II systems develop up to 4 times more energy between 3000 and 5000 RPM than standard ignition systems. High RPM performance is improved when used with the Flame-Thrower II super low resistance (0.6 ohms) 45,000 volt coil.
Adaptive dwell maintains peak energy throughout the entire RPM range, reducing misfires while improving engine performance.
Develops on average 4 times more available energy between 3000 and 5000 RPM, and 2 times more available plug voltage.
Peak current level is reached just prior to spark for maximum energy without the heat build-up, increasing coil and module life.
Adjusts spark timing at higher RPMs to compensate for the inherent electronic delay.
Senses start up and develops more energy for quicker, easier starting. Built in reverse polarity and over current protection shuts down the system, preventing component damage.

[mobylette]

Thank you for your research. I don't think I will ever get to the bottom of this. First coil had been fitted for 14 years, was stamped "made in England" so I don't think this is the Asian made Lucas, and had been running with the electronic ignition for around 5 years. Second coil also stamped "made in England", lasted 10 miles . I don't know what the ignition module should read when disconnected, but it was open circuit across the two wires when we eventually expired.

All is now fine with points refitted and yet another coil.

I think it best to draw a line under this unfortunate incident, but thanks once again to all that replied.

Martin

[mobylette]

Quick update to this story. Whilst trying to get my money back from the RAC who supplied the coil that lasted 10 miles, I checked ii's specifications. Turns out to be a "ballast resistor" coil with a specified resistance of 1 ohm across the LT terminals. Nothing on the coil or its packaging tells you this of course. I presume the extra current being pulled by this coil fried my electronic ignition, so mystery solved.

I don't suppose that they will pay for that, but I will give them hell anyway.

[Ufudu]

Thanks for the feedback; it sounds like you are correct.

I would recommend anyone that buys an electronic ignition or compete electronic distributor buys a compatible coil from the same reputable manufacturer, just to be safe. And check your charging voltage.

I'm not sure about modern coils being worse than originals; in my experience (of a one man survey ) new coils are fine if all else is well.....

[bmcecosse]

Absolutely! And sue them for the inconvenience/distress/missed appointment etc etc.. A 1 ohm coil is HOPELESS on a Minor - whether on points or transistors... it MUST be 3.2 ohms or therebye.