The Triumph Dolomite Club - Discussion Forum

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PostPosted:Mon Jan 17, 2022 9:39 pm 
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Further to my previous question on ignition timing, I’ve fitted one of electronic modules in place of the points on my Sprint and now it won’t start, not even a kick. I get a spark on a plug fitted to any of the leads which suggests either the timing is out or a lack of fuel, although of course it ran well before the change over. I’ve carefully followed and checked the supplied instructions.
Reading my maintenance manual I note that a 6V coil is fitted as standard. Can anyone explain why a 6V coil is fitted to a 12V car? Is the ballast resistor the cause of my problems?
Thanks in advance.
Tilly, Canberra Oz (Don’t mention the cricket).


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PostPosted:Mon Jan 17, 2022 10:11 pm 
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The 6 volt coil was commonly fitted on British cars in the seventies. The power feed to the coil passed through the ballast resistor cutting the nominal 12v down to around 6v. BUT when you are starting the engine, that is cranking it on the starter motor, the ignition key switch sends the full battery voltage to the coil. The idea is that with the coil overpowered you will get a stronger spark and the engine will start more easily. As soon as you release the key, the ballast resistor is put back in circuit and the coil then operates on 6v.

It is my understanding that most, if not all, electronic contact breakers require you to by-pass the ballast resistor and provide the coil with full battery power at all times.

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PostPosted:Mon Jan 17, 2022 10:24 pm 
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Quote:


It is my understanding that most, if not all, electronic contact breakers require you to by-pass the ballast resistor and provide the coil with full battery power at all times.
I am about to fit electronic ignition to my 1850; does this mean that you run 12V through a 6V coil at all times or that you replace the 6V coil with a 12V coil?

Malcolm


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PostPosted:Mon Jan 17, 2022 10:26 pm 
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Thanks Mike. A very clear and simple explanation.
Regards,
Tilly


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PostPosted:Tue Jan 18, 2022 12:18 am 
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Still wondering why the OP's car won't run though!

A spark at the end of the plug leads would indicate the system is working, but is it a GOOD spark? ie a nice fat blue one? if so, i'd be inclined to have a look at the timing, i've had a couple of aftermarket kits that left the timing up to 20 degrees out. If not i'd try getting the power to the coil from the unfused (white wire) side of the fuse box and fitting a 12v coil and see if that helps.

To Malcolm, the coil must match the system if you have a ballasted system you must have a ballast type coil (Jeroen would flay me alive if I called it a 6v coil) If you run 12v through it on a permanent basis you need a 12v coil. I've run the Simon BBC product both ways, ballasted and unballasted and it doesn't SEEM to make any difference.

Steve

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'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
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PostPosted:Wed Jan 19, 2022 12:39 am 
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Quote:
The 6 volt coil was commonly fitted on British cars in the seventies. The power feed to the coil passed through the ballast resistor cutting the nominal 12v down to around 6v. BUT when you are starting the engine, that is cranking it on the starter motor, the ignition key switch sends the full battery voltage to the coil. The idea is that with the coil overpowered you will get a stronger spark and the engine will start more easily. As soon as you release the key, the ballast resistor is put back in circuit and the coil then operates on 6v.

It is my understanding that most, if not all, electronic contact breakers require you to by-pass the ballast resistor and provide the coil with full battery power at all times.
Hadn't much time to read lately but I see I'm just back in time.

Running 12v through a BALLASTED 8) type coil will have twice the amps through the electronic ignition module and will destroy it instantly or in case with a Lumenition within 10 minutes. Some quality products like the 123ignition can switch a 1 Ohm minimum coil so you can bypass to have advantage of the bigger spark during normal running. The Lucas BALLASTED coils, 1,5 Ohm, cannot handle the extra current itself and will go faulty but a Bosch BALLASTED coil, 1,2 Ohm, can handle the extra current without it's resistor and can be fitted this way on for example an 123ignition.

The Lumenitions and the cheap 25gpb points replacement kits made in China sold as made in UK cannot go lower than 3 Ohm resistance so these need a conventional 3 Ohm coil or a 1,5 Ohm BALLASTED coil incl. the 1,5 Ohm resistor to have a total of 3+ Ohm again.

The electronic ignition should be fitted on a 12v feed and not on a BALLASTED coil as this feed is reduced by the resistor.

You can check when starting there should be battery voltage during cranking on the white/yellow wire connected to coil positive. The white/pink is the ballasted feed.

Jeroen

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