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Bulb slow burn.

1K views 16 replies 11 participants last post by  LarryGroves 
#1 ·
On a New York City subway car, the tail lights are 37.5 vdc. I have one which reads 36.5 vdc, and every bulb installed, does a slow (about 2 seconds) burn. It doesn’t pop instantaneously, but rather smokes and burns out.
Any ideas?
 
#3 ·
When you say "every bulb installed" do you mean the entire car? Multiple cars? Or just one socket on one car?

What I'm getting at is if you have a bad connection, you may read line voltage until you put the load on it. Then a bad connection results in voltage drop and there's your sign.
 
#5 ·
If the voltage at the problem light is 36.5 or 75.5 vdc then it may be a bunch of defective bulbs

If a bulb comes on and then burns out it usually means there is an air leak in the bulb-- no vacuum -- thus the bulb burns hot and dies quickly
 
#9 ·
Is it in series with something else? A shunting resistor gone bad?
They are not in series and no resistor.

When you say "every bulb installed" do you mean the entire car? Multiple cars? Or just one socket on one car?
Every bulb that I installed in that particular socket.

This. Did you measure the voltage at the socket?
Yes, measured the voltage at the socket.

If a bulb comes on and then burns out it usually means there is an air leak in the bulb-- no vacuum -- thus the bulb burns hot and dies quickly.
I thought that too, a leak, but every one?
 
#10 ·
If a bulb comes on and then burns out it usually means there is an air leak in the bulb-- no vacuum -- thus the bulb burns hot and dies quickly.
I thought that too, a leak, but every one?
Who & where were the bulbs made? Farfetched, but, why is it happening now? Do all the other bulbs work? Maybe a bad socket.
 
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