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Re: turn signal



"Curiously I had checked to see that both left turn bulbs were
blinking at double speed and they were. So I took the front one out
of its housing and then returned it, and the problem went away. Thus
it appears that corrosion or some poor connection (poor enough to
increase the resistance but not to the point of preventing the bulb
from lighting) was in fact the culprit."

Is this an example of the eyes' insensitivity to brightness measure
(either like absolute pitch or the log. response) or that the corrosion
activated a "bulb out" detector?


(Wouldn't it be great
to have a similar indicator for headlights? ....)



I'm not in favour of the proliferation of such devices that do little,
add to the price, and repair. I find it hard to believe an "out"
headlight is unobserved by the driver.

Regarding the design; vibration is, I think, more of a problem and
solved by the low operating EMF requiring a large diameter filament. I
suspect this also delays the time when variation in the diameter
(resistance) is sufficient for the higher resistance portion to become
overheated and evaporate.


"... magnetic stress ..."


That's a new one. The coiled filament flexes?


Here's very. approx. data * ; you figger: cold 2 Ohm ;
filament length 8 mm; 40 T; D 0.5 mm.

* 12 V; turn signal; stop-tail-parking. Philips 1157/1034. I assume
the higher power fil. is the turn sig.

bc








Carl E. Mungan wrote:

This is an indication that you most likely have either a burned out bulb
or a bulb with a burned out filament on the left side of your vehicle.

Another possible, but much less likely problem, is a corroded bulb
socket.



As many people pointed out, this is supposed to be an indicator of a
burned out bulb. The car manual verified this. (Wouldn't it be great
to have a similar indicator for headlights? I never fail to be
surprised by the large number of people driving around with burned
bulbs. Of course, maybe they know and just don't care. And don't get
me started on the number of people at twilight who drive around with
no lights on. How can they even see their dashboard?) I guess I
hadn't burned a turn signal bulb before.

Curiously I had checked to see that both left turn bulbs were
blinking at double speed and they were. So I took the front one out
of its housing and then returned it, and the problem went away. Thus
it appears that corrosion or some poor connection (poor enough to
increase the resistance but not to the point of preventing the bulb
from lighting) was in fact the culprit.

Thanks for enlightening me about what appears to be a common feature
of auto design, Carl

ps: Thinking about the turn signal makes me curious about another
point. Do turn signal bulbs, or in general all flashing bulbs, need
to be specially designed to handle the fact that they will constantly
turn on and off with the corresponding continuous temperature
changes? I understand for example that this is bad for tungsten
halogen bulbs, which need to be allowed to run warm for a while
before being switched off too soon (after turn on) to allow the
halogen cycle to work. But even regular bulbs generally fail at turn
on due to the magnetic stress when the current is high due to the
cold, low resistance filament.
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/