----- Original Message -----
Sent: Monday, March 14, 2005 12:23
PM
Subject: Re: (ET) Batteries and
lighting
I talked to a friend of mine that is familiar with incandescent bulbs and
he was also sayying that the lifespan will decrease logirithmically as you
raise above the rated voltage.
He also mentioned that when you reduce the voltage by not much, the light
output drops off dramatically.
Things are all worse the quartz halogen bulbs, which is the version of
landing lamp that I intend on using.
It really sounds like I should use a switching supply, which will be
impossible to find, or design one, and I do not have the time for that. So it
looks like I will be wasting a little power and putting a resistor in
series.
I might sacrifice a bulb to see for myself how badly it kills the
lifespan.
I work for an automotive supplier here in Deetroit and the 42v stuff is
just about dead from what I hear.
Kevin
--------------
Original message --------------
> - Greetings -
>
>
The question recently developed about the lifetime of incandescent bulbs
> running on voltages other than the rated voltage. Many moons ago in
a
> lecture I learned that bulb life varies approximately according
to the
> following formula
>
> (actual life/nominal
life) = (nominal voltage/actual voltage)^11
>
> That is,
voltage ratio raised to the 11th power. The lecturer suggested
> that
a 230 V bulb rated for a thousand or so hours would last about 3000
>
years running on 115 V.
>
> If the auto induestry starts
producing cars with 42 V systmes (with engine
> running) the actual
on-board battery voltage, fully charged, will be the
> same as many
of our tractors, about 39.6 V. Sounds like a ready supply
> of bulbs
at a very useful voltage.
>
> Incidentally, since a bulb burns
more brightly with increasing voltage,
> and since tungsten has a
very large coefficient of resistance as a function
> of temperature,
increasing the voltage on a 12 V headlamp from 8 V to 11 V
> to 14 V
results in a very small increase in current. Because of this, I
>
find a headlamp quite useful as a load for testing the lifetime of a lead-
> acid battery (Peukert curve). Just read the voltage every so often
and note
> that the current has remained almost constant.
>
> Keep on Elec-Traking.
> Rhett George
>
>
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