Ballast System coil replacement

[PaulBSpit1500]

Had some issues driving the spitfire on a very hot day when she just stopped after showing symptoms of an electrical fault, ie under load loss of engine power and then dying, happened after I had driven some fifteen miles. Manage to get her going again after some twenty minutes after looking at fuel, no issues and fiddling with electrical connections reseating  them. Electronic ignition all ok.  The coil was extremely hot, and I mean hot, too hot to touch. Got to the TSSC meeting after another fifteen miles without incident but the coil was again to hot to touch. Same thing happened on the way home after fifteen miles or so she died with the same symptoms as before, got her going again and onto the drive. So I got a new  Accuspark Sport 1.5 ohm ballast coil as a start to try and resolve the problem thinking the coil may be an issue as others at the TSSC meeting had suggested. When I measure across the contacts it shows 2.2 ohms not 1.5 ohms. So does it go on the car and if so what is the effect of this coil being over the 1.5 ohms.  It has been suggested by he who shall rename nameless that these extra ohms may increase the spark hence the “sport” reference. All answers gratefully received.

Paul B

[GrahamB]

If the coil is too hot to to touch, this is indicative of a coil with a low resistance.  If it is 1.5 ohms it must be connected to the ignition switch via the white/pink resistance wire so that it only receives 6 volts during normal running.  Has this wire been bypassed to obtain 12 volts for the electronic ignition?  If so, then you need a 3 ohm coil.  Alternatively, has the feed from the starter solenoid been misconnected so that it supplies 12 volts continuously rather than only when the starter motor is actuated?

As for the coil, the extra 0.7 ohms may just be due to the resistance of the test leads.  If it is 2.2 ohms it will pass less current and run cooler, and for the same inductance, provide less energy to the ignition system. But the extra resistance could be due to more turns on the primary giving a higher inductance and more energy but at the expense of a longer rise time.  After saying all that, I think that the replacement coil will work fine provided it is only being supplied with 6 volts via the resistance wire.

[Pete Lewis]

just to add do make sure the coil polarity is right the coil neg- to dizzy/points    the pos+ to the white pink ignition  ballasted  feed 

having it back to front gives you what you describe stops and wait then restarts 

grahams idea of the link to the starter sol is on the 12v live side is well worth a check

Pete

[VixenPPP]

Is this a case of a faulty coil, my incompetence or a faulty meter ?

[Pete Lewis]

well   meter the ohms across the lucar /blade terminals  should be  1.5ohm on a ballast coil   and 3 ohms on a full12v non ballast coil 

Pete

[johny]

yes that reading is miles too high for the low tension side of a coil but I take it if you connect the meter leads together the resistance reading is pretty near zero?

Edited August 2, 2023 by johny

[VixenPPP]

Yes, that reads 1 and remains at 1 when disconnected. 

As you can see the connections and settings are correct. I've double and triple checked them.

It's an Delco D200 dizzy and I'm getting a weak spark with an online plug tester.

[johny]

2 minutes ago, VixenPPP said:

Yes, that reads 1 and remains at 1 when disconnected. 

Please explain?

[Pete Lewis]

dont discount the condenser has failed hence a weak spark 

Peyte

[VixenPPP]

  The meter must be faulty because after turning the dial backwards and forwards a few times I'm getting different readings on the same settings i.e 200m and 20k ohms. I'll take it in to my local garage and ask them to check it.

Understood about the condenser.

Thanks gents

[johny]

I get something similar with my multimeter and its probably down to not being a quality instrument. It seems the dial contacts oxidise a bit so I have to turn it back and forth vigorously quite a few times to clean them before the readings become repeatable....

[VixenPPP]

These readings are on DLB105 Lucas coil. I believe it's an oiled filled coil. Fitted to a 1970 Vitesse.

Is it worth investing in a modern more efficient coil ( so I'm told )?

[Pete Lewis]

to determine if this is the ballast  6v  1.5 ohm or non ballast 12 v  3 ohm you need to measure across the two blade terminal not the HT pole 

DLB105 is anon ballast should read 3 ohms 

perfectly good lucas sports rated coil and used by many  no need to replace it 

Pete

[johny]

Agree with Pete and that first photo shows its definitely a non ballast coil. As the terminals are marked +ve and -ve youre good to go👍

[Pete Lewis]

yes just make sure the +ve is on the white ignition feed and the -Ve is the  link to the dizzy 

pete

 

[VixenPPP]

Thank you gents.