RE: headlight relays...

[Ernest Wong <esw5@cornell.edu>]

About this soft start for incandescent headlights,

Am I that much an idiot to turn on my headlights in the "high beam"
position to let the less often abused high beam filament take the higher
current load?


Another annoying habit like the one where I start my 5000s with the clutch
disengaged to lessen load on starter. . .

>
>The problem with incandesent (that includes halogens) lamps is that the
>resistance of the lamp when cold is several times lower than when hot.  Thus
>when you turn on an incandesent lamp, there is a huge rush of current thru
>the bulb.  Before the filament warms up and reduces the current thru the
>bulb, the smallest cross  section of the filament gets VERY hot and
>eventually acts like a fuse.  So, a soft start circuit needs to limit the
>current thru the bulb until the filament heats up then apply full voltage to
>the lamp.
>
>The simplest thing I can think of is placing a resistor (or another lamp) is
>series with the bulb with a time delay relay to short out the resistor after
>a second or two.  Of course, you have to add this to EACH lamp you want to
>soft start.  Unfortunately, most time delay relays are designed to only
>switch a fraction of an amp or so and you need to switch something like 5
>amps.
>
[snip]

>Robert Wheeldon
>'90 V8Q
>Principal Engineer
>Boeing Commercial Airplane



Ernest Wong
at esw5@cornell.edu