>I recall a Bob Nuckolls article which had a diode which does what you
describe.
>My memory says that with this component in the circuit there is always some
>power to the bulb (kind of warming the elements) and when you turn it on they
>will have less tendency to shock the filament.
There are two ways to mitigate the inrush current to
a lamp filament at turn on. One is to keep some amount of
current flowing in the lamp filament equal to about 1-2%
of it's full operating power at all times. This keeps the
filament above the bittle/ductile transition temperaure
(more resistant to vibration) and elevates the resistance
of the filament so that application of full power has a lower
inrush value.
The "keep warm" power can be from a small DC-DC converter
that puts out about 3 volts which can be diode distributed
to all of the aircraft's lighting circuits. The other technique
involves the use of resistors in parallel with the control
switch of each lighting circuit such that a small but significant
amount of current flows to the lamps even when the switch is
open or OFF.
The other technique involves incorporation of an inrush
limiter in series with the lamp. These are educated
resistors that have a significant resistance value when
cold (.2 to .5 ohms) and drop to an in-significant value
(.005 to .01 ohms) when warm. When operated in series with
the lamp, their cold resistance keeps the inrush to a lower,
more desired value but a few seconds after application of
power to the lamp, their resistance drops due to the
warming effect of lamp current flowing in the device.
NEITHER of these techniques is particularly significant
in terms of lamp life for wig-wagged landing lights. This
is because the lamp filament doesn't have time to cool off
between flashes so after the inrush current for second
and subsequent flashes is MUCH lower than the first.
Bob . . .
////
(o o)
< Independence Kansas: the >
< Jurasic Park of aviation. >
< Your source for brand new >
< 40 year old airplanes. >
http://www.aeroelectric.com
|