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why does one bulb keep on blowing, while others on the same circut dont? Answered

I have a alarm system at home that turns on a 12v circut when the alarm is active.  Attached to this I have 3 12v globes (the kind you find in old car indicator lights connected in parallel.  The one globe keeps on blowing.  Each bulb lasts about 3 days (this would total to about 40hrs total on time tops. The other two lights never give me any issues.  Any hints on what to look for?


Can you tell us the wattage of the bulbs and the output wattage of the 12v circuit?

Also, is it a bulb on the "outside" or one in the middle the keeps blowing?

Either way, it sounds like your circuit is overloaded.  I've seen this several times.  You probably have to switch lower wattage bulbs that your 12v circuit can handle (all of them, not just the one that keeps blowing).

It was the one closest to the power source, I have now put in a new globe that is smaller (fewer watts) that the others and somehow that seems to have solved the problem.

Thanks to everyone who gave some input much appreciated.


8 years ago

Thanks all for the input.


8 years ago

I would put in a fresh bulb,
Switch on the power.
Test voltage at each bulb.
Even a half volt can make big difference in bulb life.
Also, if suspect bulb blows and is not replaced; will  a second one fail?
It can also be a problem of the bulb overheating.  Does it have adequate ventilation? 

What exactly is providing the 12V, how is it switched, and how are the bulbs wired (diagram would be nice)?


If the other two have bad soldier joints or long runs off wire then that resistance is what is protecting them and the other one is taking more of the current than it should be.