Which coil fitted?

[petegardner_901]

Hi

Electrics not my strong point but can anyone tell me how I can identify what type of coil I have fitted to a 1979 Spitfire 1500?

I suspect the previous owner may have changed it and I'm not sure if it's the correct one for a ballasted system.

I understand a non ballast coil is a 12V..?  and a standard, original ballasted one would be around 6 to 7V..?

No markings on the coil so how do I find out?

 

Thanks

[dougbgt6]

Pete

With a multi-meter.  A ballasted coil will be 1.5 ohms, non ballasted 3 ohms.  A ballasted coil although running at 6 volts most of the time gets a 12 volt boost at start up, it may have 12 volts printed on it, not sure why! 

Doug

[Guest]

16 minutes ago, dougbgt6 said:

A ballasted coil will be 1.5 ohms, non ballasted 3 ohms

Hello Doug,

It was only recently that I discovered via the Aldon site that it is possible to get a 1.5ohm NON-ballast coil - equivalent to Lucas DLB110.

https://www.aldonauto.co.uk/ignition/coils/lucas-equivalent-coils

Regards.

Richard.

[Pete Lewis]

yes there are ballast coils out there with 12v marked on, (as the base vehicle voltage)  

running a 6/8 volt coil on 12-14 volts doubles the HT and current at the points ... impending failure anytime soon.

running 1,5 ohms with a coil suited to 12v is ok but you double the current the points have to deal with , so points and condensers can fail due to overload, then what is the HT 

voltages produced , the std set up is around 22KV if halving the resistance boosts the HT to much higher voltages then rotors and caps all start to fail 

they are just not designed to handle much more than the std  output .

many past dizzy /points/ elec units /rotors have caused problems when wrong spec coil outputs and current loadings are employed 

 beware going to a lower resistance does not seem Utopia , just headaches 

Pete

[johny]

Without regapping the spark plugs (to what?) I not even sure theres much advantage in using a lower resistance coil. Surely the maximum voltage youre ever going to achieve is that necessary to jump the plug gap?

[Guest]

50 minutes ago, Pete Lewis said:

running 1,5 ohms with a coil suited to 12v is ok but you double the current the points have to deal with , so points and condensers can fail due to overload,

Hello Pete,

Unless the car is running a set of twin points - such as some V8 variants. Due to the dwell of that cylinder configuration the 1.5ohm recycles faster and supplies the correct level of charge to meet the demand of those 8x cylinders as a result of the reduced dwell.

Regards.

Richard.

[petegardner_901]

Tested the coil with a multimeter and got 1.9 ohms.

should I replace it...?.

[Pete Lewis]

if  you have std points  I would   as if you still have  the ballast feed  ( normally a dull white/pink) with a yellow trace from the solenoid  you will be getting a weak HT 

with the 6-8 ballast supply . running a 1.9ohm coil     use  a 1.5 ohm  eg  DLB102 https://www.autoelectricsupplies.co.uk/product/98/category/21

if the ballast has been removed/bypassed  then get a 12v 3 ohm coil  like GLB105     https://www.autoelectricsupplies.co.uk/product/96/category/21

Pete

[petegardner_901]

Hey thanks Pete

I have no history with the car but it has a sports exhaust and other ‘tweaks’ so I’m thinking it may have had a 3 ohm coil fitted but still has ballast wire so not quite right in all.

it runs out of power uphills and struggles to get to 70 even on a level road so I’m hoping a new coil would help

[Pete Lewis]

the ballast is just a  1970.s  aid to starting giving a boost to the HT when cold and low battery states exist , helps the spark when the starter is taking

all the battery capacity to crank  it up.

if you fit a 3 ohm you need to make a new feed from the white pigtail off the ign switch to the coil and dump the murky white/pink ballast wire 

you wont need the white/yellow that links the stater solenoid  to the coil when cranking

if you use a 1.5 ohm then leave all alone ...providing it does use the white/pink  and the white yellow,s to ballast /drop the running voltage 

Pete

 

[petegardner_901]

Thanks Pete