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From: email@example.com (carltons)
Subject: Re: powering a bulb or led(s) with audio amplifier?
References: <3DB1323B.1F9EA4F0@stanford.edu> <firstname.lastname@example.org> <3DB929D1.F8551A8C@stanford.edu> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sun, 27 Oct 2002 00:12:57 GMT
Date: Sun, 27 Oct 2002 00:12:57 GMT
In article ,
firstname.lastname@example.org (N. Thornton) wrote:
> "Bevan Weiss" wrote in message
> > The current being drawn from the amp by the load (speaker and bulb) will be
> > the sum of the currents drawn from each device. Hence if your amplifier is
> > rated at 100Wrms(@say 14Vrms) then you can draw ~7.1A rms in total.
> 14v 7A... thats 2 ohms. Most home stereos dont do 2 ohms. 8 ohms is
> typ, some do 4 ohms.
> > If the
> > speaker is a 4Ohm speaker (typical car speaker) then the current drawn from
> > it would be 14Vrms/4Ohms = 3.5A rms. Hence you could draw 3.6A rms through
> > the bulb. Allowing for a 50.4W bulb.
> Well, I'd disagree with the figures, I'd change the figures for power
> and impedance, giving different Vs and is for the bulb.
> Also audio doesnt spend much of its time at peak power output, so that
> will change your bulb ratings somewhat.
> > You could use a resistor in series with the bulb to limit the current to
> > this level, and then place this is parallel with the speaker. I'm just not
> > sure whether the bulb would then get enough power to illuminate correctly,
> > and the resistor might need to be capable of dissipating a lot of heat.
> > However these values will all change for different voltages etc...
> > To ensure the brightest light, use the highest power dissipation in the bulb
> > that you possibly can (up to the bulbs rating), note however that this will
> > reduce how much power you can put into the speakers...
> I'd recommend taking it above the bulbs rating, long as youre not
> using halogen, that way you'll get more significantly more brightness
> and faster speed. Bulb speed does tend to be sluggish if you dont pay
> attention to that.
> > "Adam Bowen" wrote in message
> > news:3DB929D1.F8551A8C@stanford.edu...
> > > thanks everyone for ideas on how to get leds to work, but i've decided
> > > for aesthetic reasons to go with a simpler lamp setup, as dmb suggested.
> > > i forgot that with leds' on/off nature, it won't glow with variable
> > > brightness. so a simpler question: how do i hook up a bulb so as to
> > > ensure the brightest peak light without damaging my amp? put the bulb and
> > > a resistor - relative to the impedance of the speaker - in parallel with
> > > the speaker?
> We'd need to know power output and impedance of your amp.
> Regards, NT
Incandescent bulbs vary in resistance depending on how much voltage is
applied and how long it is applied. They have a positive temperature
coefficient, which means that when cold they draw lots of amps and when
they heat up at their rated voltage, they draw the correct amps to match
their rating at a lower current than start up. Designing with a lamp is a
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