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Greetings, oh sage ones,

my 1974 CF is eating coils. To be precise, Flamethrower coils. I have now bought a Bosch red coil, which comes with a resistor.

So, is this a reasonable choice?

should I do a bit of re-wiring, bypass the old resistor wire and incorporate the ballast resistor?

Thanks for the advice.

Austin

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Either you have been rather unlucky with poor coils Austin, or perhaps something is wrong.  Maybe your ballasted coils have been getting too much supply voltage somehow. That could be a problem with the harness ballast wire (unlikely) or perhaps a fault in the starter relay or its wiring which keeps 12v on the coil instead of switching it off after starting.  Have you confirmed that the coil supply drops to around 9V when running?

Have you fitted electronic ignition or is the car still on points?  What spark plug gap are you using?

Genuine Bosch coils have a good reputation so that should be OK.  If the existing set-up does have the correct voltages there's probably no need to use the separate ballast resistor instead. 

 

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With my little experience with electrics, I have come across quite a few friends coils that do get hot, and this I have usually found to do with the condenser, and/or the dwell period of the points, and perhaps thirdly the condition of the points.  I have fitted many Accuspark electronic kits to other BL cars that have had hot coils and have cured the problems, and reusing the same coils, so I feel it must be those two/three items at fault.

To be sure you get the very best condensers I would only recommend getting them from Distributor Doctor.  There are so many dud ones out there.

There is also the possibility that the wrong rated coil has been fitted. Ballasted and non ballasted. 

Sure this must have been covered before, but could one of the super electricians on this forum put together a simple trouble shooting guide, which coil fits what models, and how to know by testing what volts should be found at the coil at different points of the ignition key, could it then be saved as a locked item/post on the forum please?

John

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22 hours ago, John L said:

With my little experience with electrics, I have come across quite a few friends coils that do get hot, and this I have usually found to do with the condenser, and/or the dwell period of the points, and perhaps thirdly the condition of the points.  I have fitted many Accuspark electronic kits to other BL cars that have had hot coils and have cured the problems, and reusing the same coils, so I feel it must be those two/three items at fault.

To be sure you get the very best condensers I would only recommend getting them from Distributor Doctor.  There are so many dud ones out there.

There is also the possibility that the wrong rated coil has been fitted. Ballasted and non ballasted. 

Sure this must have been covered before, but could one of the super electricians on this forum put together a simple trouble shooting guide, which coil fits what models, and how to know by testing what volts should be found at the coil at different points of the ignition key, could it then be saved as a locked item/post on the forum please?

John

+1 for Johns suggestion above, would be very helpful for a written seminar on "all things coils".

Colin.

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Hi,

 I doubt very much that a a bad condenser could kill a coil. Heat kills the coil. Heat can age the condenser. Condensers fail open & closed.
I went distributor-less ten years ago. In the last years of the distributor it was fitted with a 220nF 1600V capacitor that would last forever. 

Cheers,

Iain. 

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On 5/15/2021 at 5:08 PM, John L said:

With my little experience with electrics, I have come across quite a few friends coils that do get hot, and this I have usually found to do with the condenser, and/or the dwell period of the points, and perhaps thirdly the condition of the points.  I have fitted many Accuspark electronic kits to other BL cars that have had hot coils and have cured the problems, and reusing the same coils, so I feel it must be those two/three items at fault.

To be sure you get the very best condensers I would only recommend getting them from Distributor Doctor.  There are so many dud ones out there.

There is also the possibility that the wrong rated coil has been fitted. Ballasted and non ballasted. 

Sure this must have been covered before, but could one of the super electricians on this forum put together a simple trouble shooting guide, which coil fits what models, and how to know by testing what volts should be found at the coil at different points of the ignition key, could it then be saved as a locked item/post on the forum please?

John

Another +1 from me, it would be great to have a definitive reference.

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Coils and a 6v supply. The ballast wire or resistor does not supply 6 volts it depends on the coil fitted.

Could we assume a coil has a 3 ohm resistance, and the ballast resistor has a 3 ohm resistance, when current flows in the circuit through 6 ohms( 3 + 3) and the voltage supplied to the coil will be 1/2 of the battery voltage( engine running 14v) or 7 volts.

If you fit a coil of 1 ohm then the voltage is divided proportionally across 4 ohms (3+1) and the coil will be supplied with 3.5 volts.

If you fit a coil with a 6 ohm resistance the the voltage will be supplied proportionally across 9 ohms (3+6) and the coil will be supplied with 9.5 volts.

What is needed is a coil that matches the ballast wire resistance, or drop the ballast wire and use a 12v coil if you cannot obtain a coil that matches the resistance(ohms) of the original fitted to the car. Fitting "any" unmatched  6v coil may lead to problems and rapid burnout.

Alan

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On 5/15/2021 at 4:44 PM, RobH said:

Either you have been rather unlucky with poor coils Austin, or perhaps something is wrong.  Maybe your ballasted coils have been getting too much supply voltage somehow. That could be a problem with the harness ballast wire (unlikely) or perhaps a fault in the starter relay or its wiring which keeps 12v on the coil instead of switching it off after starting.  Have you confirmed that the coil supply drops to around 9V when running?

Have you fitted electronic ignition or is the car still on points?  What spark plug gap are you using?

Genuine Bosch coils have a good reputation so that should be OK.  If the existing set-up does have the correct voltages there's probably no need to use the separate ballast resistor instead. 

 

Hello Rob, and thanks for coming back. I have monitored the voltage, and it looks like I’m getting around 9 volts, except during start - when it’s 12. 

It does have electronic ignition (Pertronix), but I’ve bought a 123TUNE distributor in order to retard the ignition under boost (the engine is supercharged). I’ve had to replace the Pertronics twice, and the coil three times within about 15k miles. It does seem excessive. I’ll check the voltage at the coil again. The coil is rated at 1.8 ohms, but there is no resistance rating on the resistor.

Austin

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1 minute ago, Austin Branson said:

I’ve had to replace the Pertronics twice, and the coil three times within about 15k miles.

That is odd Austin. It points (!) towards excessive current or perhaps something else........    The standard Pertronix doesn't like being left with the ignition on and the engine not running, and neither does the coil. If the engine has stopped at a point where the contact is closed, the Pertronix and the coil have current flowing all the time the ignition is on and can overheat. Could that be it?

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Sorry, I don't mean to hijack this thread, but has anyone any experience of the Pertronix 2 ? It's meant to have circuitry that prevents overheating/burnout if the ignition is left on.

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6 hours ago, barkerwilliams said:

Coils and a 6v supply. The ballast wire or resistor does not supply 6 volts it depends on the coil fitted.

Could we assume a coil has a 3 ohm resistance, and the ballast resistor has a 3 ohm resistance, when current flows in the circuit through 6 ohms( 3 + 3) and the voltage supplied to the coil will be 1/2 of the battery voltage( engine running 14v) or 7 volts.

Alan

Alan,

Resistance of a Ballast Coil is nominally 1.5 Ohm, same for the resistive feed wire I believe.

Bob

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Bob,

Sorry but coils do not have a "usual" resistance, Pertronix supply Flamer thrower in 1.5 or 3 ohm, and Flamethrower2 in 0.6 ohm. Bosch Black coils are 3.4 ohm

http://www.pertronixeurope.com/coils.php

I haven't looked at other coil manufacturers, all I was suggesting is that the choice of coil needs to be matched to the value of the resistance wire in the car as it makes a great deal of difference to the working voltage and the longevity of the coil.

I have never seen if Triumph always used the same value of resistance wire in all of .their cars or they used what was to hand (never heard of that before). and I have no idea what happens to the resistance wire after fifty years; probably increasing resistance which will reduce the voltage supplied to the coil.

If you have coil eating problems I  believe that it is far better to use a coil with an external ballast resistor, or a 12v coil & supply. Then you are dealing with known values.

Alan

 

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Alan there are indeed two 'standard' coil resistances. 3 Ohms or thereabouts for a 12V coil and 1.5 Ohms or thereabouts for a ballasted coil These are available from a number of manufacturers and will work on any car with the appropriate system.  

The other odd values such as the one you quote are special coils for use with the same maker's more sophisticated electronic ignition systems which have fixed dwell periods and other complications. They will not work on a standard car ignition.

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16 minutes ago, jerrytr5 said:

How about coil polarity, would that affect longevity?

In a word - no Jerry.  Sorry -  good thought though. 

Edited by RobH
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2 hours ago, RobH said:

Alan there are indeed two 'standard' coil resistances. 3 Ohms or thereabouts for a 12V coil and 1.5 Ohms or thereabouts for a ballasted coil These are available from a number of manufacturers and will work on any car with the appropriate system.  

The other odd values such as the one you quote are special coils for use with the same maker's more sophisticated electronic ignition systems which have fixed dwell periods and other complications. They will not work on a standard car ignition.

I have a 73 car with a ballast wire and am running a Bosch (red) 1.5 Ohm coil. The operating voltage is around 9V.

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13 hours ago, barkerwilliams said:

Bob,

Sorry but coils do not have a "usual" resistance, Pertronix supply Flamer thrower in 1.5 or 3 ohm, and Flamethrower2 in 0.6 ohm. Bosch Black coils are 3.4 ohm

Alan

 

Presumably Alan you have read Rob's clarification regarding the varying resistances you have listed, and since you haven't challenged his post then I think we can safely say 1.5 Ohm and 3 Ohm are in fact the 'usual' resistances.

Every day is a school day eh?

Bob

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On 5/17/2021 at 8:29 PM, RobH said:

If the engine has stopped at a point where the contact is closed, the Pertronix and the coil have current flowing all the time the ignition is on and can overheat.

Sorry me, from my own measurement I know:

with the Pertronix "the contact" is cloesed in any position when the engine stopped,

So with the ignition switched on (again) and the engine not running there is a constant current of 4A (12V / 3 Ohm coil) over this tiny part - and it fails,

On the installation guide of the Germany supplier this is a special matter.

From my own testing the open/close function by the "magnet ring" only works when the engine is running.

This is why you can't adjust the Pertronix with the engine not running, and not by spining the crankshaft manual.

Ciao. Marco

 

Edited by Z320
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Thanks for that Marco. Useful information. 

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