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From: "Boris Nogoodnik"
Subject: Re: Current draw of several light bulbs?
Organization: KGB, Ltd.
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Date: Wed, 11 Dec 2002 02:00:55 GMT
NNTP-Posting-Date: Tue, 10 Dec 2002 21:00:55 EST
"Rileyesi" wrote in message
> I need a rough and dirty way of estimating how much current I
will need to
> drive a set of light bulbs. The situation is that at some
> will be 6 light bulbs in parallel while at others, there will
be as many as 42.
> These are #47 incandescent bulbs rated at 6.3 volts and 0.15
amps. I assume
> that this means it will draw 0.15 amps at 6.3 volts when
illuminated (so each
> bulb is 42 ohms).
> My first guess would be to simply add the current draws (i.e.
6 bulbs in
> parallel would draw 6 x 0.15 or 0.90 amps). Can I assume that
42 bulbs will
> draw 6.30 amps (i.e. 42 x 0.15 amps)? I don't have any of the
bulbs yet (so I
> can't do a bench test) and want to get started on designing
the power supply.
> I also looked at the resulting resistance of a network of 42
bulbs in parallel
> assuming that all have a resistance of 42 ohms. This
calculation also leads me
> to a total current draw of 6.3 ohms, but that calculation
might be simply a
> re-arrangement of my first attempt since they are based on the
> Another question, what is the difference between driving them
with DC rather
> than AC? I know that the bulb doesn't care and I'd like to
use AC because it
> simplifies the power supply. Are there any advantages or
> the two?? Any safety issues?
Yor calculations seems to be correct. What is the input power
source? AC line? Looks like a simple transformer is all you
need. Safety can be an issue in outdoors applications. In this
case it's always better to use the isolated supply - same
transformer. Making a fancy switching supply just to drive few
bulbs looks like an overkill to me.
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