Ballast Resistor on Coil

[rjahunter]

I see reference to this being necessary where you fit Lumenition (think it might have been in the Rimmers catalogue).

Could someone enlighten me as to what it does, and how it's wired, and more importantly, do I need one if I have an electronic distributor fitted ?

Sorry for the usual novice question but I "like to understand things" !

Richard

[V Mad]

How it is wired:
All stags were fitted with a ballast resistor and a 6 volt coil. The Mk1 resistor was a discrete component situated by the coil. The Mk2 resistor is not a component that can easily be identified because it is part of the wiring loom. Instead of the loom having a copper wire going to the coil, it was made of resistance wire (constantan). The ballast is connected in 'series' with the coil, so it normally drops the 12 volt supply down to 6 volts. However, during cranking, the ballast is bypassed so the full battery voltage is applied to the 6 volts coil. This was done because during cold weather the battery voltage can drop quite a lot. I hope that makes sense?

To be safe and avoid overload, you should normally keep the ballast in circuit with electronic ignition UNLESS the manufacturer advises otherwise. For example, Accuspark advise using a 12 volt coil, obviously with no ballast, although they say it will work with the original 6 volt coil + ballast.

Sorry if that's long winded.

[rjahunter]

Thanks Chris - very interesting. I have a Lucas DLB198 12v coil fitted now, which obviously doesn't need a ballast resistor. I am still getting pretty ropey starting. Is there any chance that I accidentally have the inline ballast resistor still wired which would be causing a problem ? Where is it on the wiring loom ?

Richard

[V Mad]

To check whether you have the ballast fitted, connect the coil neg (-) to chassis, switch on ignition and measire the voltage at the coil POS (+). If it measures the same as the battery voltage you have no ballast. It is measures about 2/3 battery voltage ( 9 volts approx) then you have the ballst fitted.

[rjahunter]

To check whether you have the ballast fitted, connect the coil neg (-) to chassis, switch on ignition and measire the voltage at the coil POS (+). If it measures the same as the battery voltage you have no ballast. It is measures about 2/3 battery voltage ( 9 volts approx) then you have the ballst fitted.

OK Chris - you already know I'm pretty ignorant at this stuff, but when I do that and measure the voltage acorss the coil terminals (I assume that is what you meant ?) I get a reading of about 3.75 ! I did look at a wiring diagram and note the reference to the "ballast resistor wire" which runs from the coil to the Rev counter ? It's the pink one with a white stripe. Should that be connected or not ?

[V Mad]

Yes measure across the coil with NEG shorted to ground, but as you would expect 3.75 volts is much too low. I dont know how you are getting spark at all! What wires are connected to the coil POS??

The DLB198 is a special electronic ignition coil with a 1 ohm resistance. The Mk2 ballast should be about 1.4 ohms. So if the ballast is connected, and your battery is 12 volts you should get about 5 volts across the coil. I suspect the remaining 1.25 volts is lost through the igntion switch and connectors.

My guess is that the set up you have should not be used with a ballast, but should run from the full battery supply so the coil gets more current. If the coil is a 12 volt coil then it will not give much of a spark with a ballast.

By the way, if you look, at the wiring diagram the pink/white wire is the ballast wire, and this is normally connected to the coil POS, but it doesnt go to the rev counter (that is white/slate and is connected to the coil NEG) . The other wire connected to the coil POS is the white/yellow; this comes from the starter solenoid and applies the full battery voltage to the coil when cranking.

Best I can help without seeing it.

[rjahunter]

Yes measure across the coil with NEG shorted to ground, but as you would expect 3.75 volts is much too low. I dont know how you are getting spark at all! What wires are connected to the coil POS??

The DLB198 is a special electronic ignition coil with a 1 ohm resistance. The Mk2 ballast should be about 1.4 ohms. So if the ballast is connected, and your battery is 12 volts you should get about 5 volts across the coil. I suspect the remaining 1.25 volts is lost through the igntion switch and connectors.

My guess is that the set up you have should not be used with a ballast, but should run from the full battery supply so the coil gets more current. If the coil is a 12 volt coil then it will not give much of a spark with a ballast.

By the way, if you look, at the wiring diagram the pink/white wire is the ballast wire, and this is normally connected to the coil POS, but it doesnt go to the rev counter (that is white/slate and is connected to the coil NEG) . The other wire connected to the coil POS is the white/yellow; this comes from the starter solenoid and applies the full battery voltage to the coil when cranking.

Best I can help without seeing it.

Thanks Chris - you're right of course - I misread the wiring diagram. The ballast resistor wire comes off the fusebox I think ?

Not sure why I have such low voltage, but may be down to the coil as you say. I will get an original stag one and see what that's like.

The other issue is that my starter motor supplied by my engine builders only has one terminal, so that coill feed wire is not currently connected, which could be part of my starting problem. The voltage I reported to you is just static of course, not when cranking, so it could be worse during cranking, leading to really poor spark.

I'll discuss with my engine guy and see what we think but would appreciate any further thoughts you may have.

[DJT]

Stag coil is 6 volt ISTR.

http://www.ldparts.co.uk/shop/shop.php?c=viewproduct&pid=481&cat=3&sid=sid8b19953e85f4ac27a56860d6260ea912

Dave

[rjahunter]

Yes measure across the coil with NEG shorted to ground, but as you would expect 3.75 volts is much too low. I dont know how you are getting spark at all! What wires are connected to the coil POS??

The DLB198 is a special electronic ignition coil with a 1 ohm resistance. The Mk2 ballast should be about 1.4 ohms. So if the ballast is connected, and your battery is 12 volts you should get about 5 volts across the coil. I suspect the remaining 1.25 volts is lost through the igntion switch and connectors.

My guess is that the set up you have should not be used with a ballast, but should run from the full battery supply so the coil gets more current. If the coil is a 12 volt coil then it will not give much of a spark with a ballast.

By the way, if you look, at the wiring diagram the pink/white wire is the ballast wire, and this is normally connected to the coil POS, but it doesnt go to the rev counter (that is white/slate and is connected to the coil NEG) . The other wire connected to the coil POS is the white/yellow; this comes from the starter solenoid and applies the full battery voltage to the coil when cranking.

Best I can help without seeing it.

Hi Chris. Been thinking about this overnight (sad.....).

I think from what you're saying, I would be better to take the redundant coil feed lead which no longer connects to my new starter motor, and take it back to the fusebox, connecting it directly to the terminal currently supplying the ballast cable for the coil, and cut off and tape the ballast wire. What do you think ? This will then provide a non-ballast feed for the coil regardless of cranking or not, hopefully ensuring a more robust spark.

Interesting learning for me, but this may be a daft proposal !

[jbuckl]

Your stag will struggle to start without a 'ballast-resistor' and 6v coil unless a much larger capacity battery is fitted.

This is because the battery voltage drops upon cranking. (so fitting a 12v coil is a backwards step for starting even if you are not using the ballast resistor)

Sorry if you feel like I'm teaching you to suck eggs!

Btw the (pink) resisted wire is hard to get hold of but not impossible.

Also, beware, many '6v coils' are actually marked 12v based on the assumption that they were designed to be fitted on a 12v car with a ballast resistor.

Check the resistance of the coil windings againt the workshop manual.

[rjahunter]

Thanks for that. I spend my life on this car not only learning to suck eggs but frequently breaking them in the process, so I've learned never to take offence on advice offered !

Richard

[V Mad]

Your stag will struggle to start without a 'ballast-resistor' and 6v coil unless a much larger capacity battery is fitted.

This is because the battery voltage drops upon cranking. (so fitting a 12v coil is a backwards step for starting even if you are not using the ballast resistor)

True for the points system but not for electronic ignition systems because they have an internal circuit that is designed to work at a lower voltage.

Richard, before making any changes, check that Lumenition can work with your 1 ohm coil and no ballast; we would not want to overload it. I tried the website some time ago but it was not clear to me, maybe others here can say what works for them with Lumenition?

Then if thats OK to do then just bypass the ballast with a temporary wire and confirm that if its better. Don't cut off anything as its always nice to be able to go back to original later.

[DJT]

Check what Peter Howells says on his website about the DLB110 Lucas Sports Coil:

Lucas Sports Coil 6Volt for use with ballast converter situations or ballast wire situations.
These sports coils when used with Sports Electronic ignition, like for example Lumenition Performance Magnetic as opposed to standard Lumenition Optronic systems, can be asked to produce higher high tension voltage than standard.
They will produce up to 40,000 Volts.
To achieve this the spark plug gap is opened to 40K

This can improve performance

Normal coil output is 25,000 volts.

The ignition leads sold on this site can handle up to 30,000 Volts. If you wish to use the full 40,000 then it is wiser to invest in some ignition leads suitable for purpose.

We are also advised that it is likely the Rotor Arm and Distributor cap will need replacing more frequently when used with extra wide Spark plug gaps.

NOTE
Why a 6 volt coil in a 12 volt car?
With the points closed, current will flow as follows: battery to ign switch to ballast resistor to coil to points and finally to ground.
With an assumed charging voltage of 14 volts at the battery, we can measure voltage drops of about 8 volts across the ballast and 6 volts across the coil. THIS MAKES THE COIL OPERATE ON 6 VOLTS WHICH INDICATES THAT IT IS A SIX-VOLT COIL.

But why have a Ballast resistor? To stop points or Electronic seeing too much voltage and burning out.

However it is "by passed" by direct supply from the starter solenoid during engine start meaning a full 12 volts is applied to the coil increasing the spark voltage for quicker fire up.

This is what I have, along with Lumenition and a ballast wire, and starting is never a problem, even after a 2-week layup.

Dave

[elvimto]

Richard I don't know if you have Lumenition fitted but they do a coil for that set up its called a Mega spark sold by most suppliers i had this system when i got the car but it had a standard coil so I changed it to the Mega spark coil My car is a MK 1 with the ballast resistor no problems with the ignition system and really good starting etc after a bit of TLC.

cheers Stuart

[V Mad]

Hi Richard. As you seem to have the ballast in circuit, then as Julian pointed out to me, if the ballast bypass is correctly connected and working it should not affect starting (obviously because the full battery voltage will be applied to the coil).

Since your problem appears to be on starting, either check that the bypass is working or temporarily bypass it with a wire to see if it improves.

If still no joy, it could be a fuelling problem. Are your carbs propely balanced? Are both enrichment levers being equally moved with the choke cable?