Headlamp blowing

[Billington]

Hello, I hope you can help. The headlamp bulb on my on my 1932 BSA clouds over and blows as soon as I turn it on. The bulb is 6v 36/36W D10 my battery is a 6 volt 4Ah / 20Hr. Any ideas how to solve this? Many thanks

[rgsjohn]

May I ask, from where did you source your lamps? I worked in the lighting industry for many years, and the symptoms you describe are associated with air inside the glass. Going cloudy accompanied by rapid failure is a sign that either the seal is compromised by a capillary leak or that during the manufacturing process the lamp was not flushed properly to purge out the air leaving the fill gas contaminated. The presence of air will cause the filament material to quickly evaporate due to excessive heat. All incandescent lamps are normally filled with argon to inhibit this process a few others are vacuum lamps. Halogen lamps work in a similar same way the main difference being when the lamp reaches operating temperature the filament evaporation particles are recycled back to the filament. Internal clouding is indicative of air contamination.

[Billington]

Thank you for your reply, it is interesting. I got the bulb from Kidderminster Motorcycles, who are BSA and Triumph part specialists. I though it was something to do with my bikes electric system. I will try purchasing a bulb from elsewhere.

[R]

Interesting problem - and reply.
Someone probably needs to notify Kidderminster, so they can contact the manufacturer ?
If this is more than a few isolated examples.
And just one example is already flagging a problem ?

I worked in the computer industry, and apparently the art of manufacturing hard drives was hard learnt.
Some days they were 99% good, and other days 99% rejects. Or worse.
Without 100% testing this was impossible to determine - a very expensive process.
And this was before shifting to low cost manufacturing centres...

[Rex]

Hello, I hope you can help. The headlamp bulb on my on my 1932 BSA clouds over and blows as soon as I turn it on. The bulb is 6v 36/36W D10 my battery is a 6 volt 4Ah / 20Hr. Any ideas how to solve this? Many thanks

But is the engine running when you turn the lights on? Maybe try a known good  lamp with the engine off, then on, before blaming the lamps themselves. Use a DVM to test the reg output and battery voltage with engine running if you have no spare bulbs.

[Billington]

I've now ordered two bulbs from two different places and will run some tests with a digital volt meter. I know the bulbs cloud over and stop working when the engine is not running.

[iansoady]

If it happens with the engine not running it's almost certainly the bulb. If it was running I might suggest voltage regulation as you'll have a 3 brush dynamo which can be tricky to get right.

[Billington]

Success! I purchased two bulbs from JB vintage spares, a new German bulb and a new old stock bulb. I put the new German one in first and went for an eight mile ride. The bulb simply works. Thank you for your advice everyone, I had convinced myself the problem must be with my wiring loom; however the problem was due to me purchasing new old stock light bulbs. I think this is may be a lesson for me, do not assume new old stock electrical components will be okay. Next time I will look for modern production alternatives first.

P.S the bike is running just great thanks to the help from this forum.

[rgsjohn]

I'm glad the problem is resolved. Lamps in long term storage are unfortunately prone to leaks. In the days when I was involved in lamp making all lamps were put into a 7 hold before being tested as an insurance against capillary leakage. It is also worth knowing that frequent use of the headlamp flasher will cause halogen lamps to fail because the lamp is not lit long enough for the tungsten filament cycle to reach operating temperature.