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TR2/3/3A TR3A Blowing Bulbs!!

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Quelch

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Hi Everyone, I'm having a problem with my 1959 TR3A blowing bulbs. The ones that seem to be to be most effected are my reproduction Lucas spot lamps which I'm using as day running lights, the only other casualty has been a sealed beam unit, all the others are fine. On close examination the glass is quite discoloured & burnt on the ones that have blown. This isn't happening on a daily basis, maybe every two or three weeks I get one go. Last season the car was fine with no issues at all, just seems to of started recently. I'm running a generator on positive earth. Can anyone suggest a good place to start looking for the cause of the problem. Regards, Neil.
 
I would start by seeing what voltage I'm getting, esp at high RPMs.

Specs are in most manuals and in particular in the Lucas manual. That same manual has the tests & adjustments for the generator and control box which may be your next step.
 
Unfortunately, the specs given in the manual are ridiculously high. They are supposed to be measured with the battery totally isolated from the voltage regulator, so no current is flowing.

With the battery connected and fully charged, you shouldn't see more than about 14.4 volts at the battery.

Also check that the ground connection for the control box is secure. If it is intermittent, it will let the voltage go too high.

And if that does turn out to be the problem, I would suggest removing the battery and wiping down all the surfaces in the area with a solution of baking soda in water. The battery will have been spraying a fine sulfuric acid mist out the vents, which will promote corrosion like crazy, especially under the battery. That's why so many TR3s have the battery box rotted out.
 
Good advice from Geo and Randall above. I don't know what bulbs you are using in the Lucas spotlight but I have noticed a very short lifespan on some recent halogens even with acceptable voltage. Tom
 
Thanks everyone for the advice, Finally, after two evenings I've found the cause of the problem. Turned out the coil of the voltage regulator required a little adjustment. But, boy did I have trouble isolating the snag!! Kept on taking meter readings across the battery terminals with the engine running, recoded wildly fluctuating readings of between 12.8 to almost 17 volts. Disconnected the "F" terminal from the voltage regulator going to the generator field coil and was still getting readings over 16 volts when revving the engine. At this point I was thinking there was a fault in the generator, so removed it from the car & tested the resistance, that was good, 6 ohms. reinstalled the generator. Now I'm really stumped!! What could be making the generator keep showing 16 volts plus with the field coil wire disconnected!!!!! Finally out of sheer desperation I tried another meter and noticed that this one started going crazy as soon as the engine was started. I then noticed that the closer the meter was held to my Crane electronic ignition module the more the meter gave hugely erratic readings!! Well I borrowed a more expensive meter from my neighbour and hey-presto, everything was looking good, had to adjust the coil on the voltage regulator 1/2 turn and there was my 14.4 volts across the battery terminals. The moral of this story, beware of cheap meters picking up interference from your electronic ignition!! Many thanks again for all the tips, just need to wash the battery box area with baking soda in he morning, then I'm good to go!!Neil.
 
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