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Re: Power optimization and some (stupid?) LED questions

From: jim ruxton   cinetronpassport.ca
Date: Wed, 18 Aug 2004 11:06:26 -0700

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As Sandor said no such thing as a stupid question.  You'll probably get
different opinions on this but I would put 2 LEDs in series with one
resistor. These resistor 2 LED modules could then be wired in parallel.
If you put 2 in series it gives you some headroom. ie the battery can
die down to 4 volts before you get nothing. As Sandor suggested 1 LED
with a resistor would work also but you are burning up some power. The
resistor value would be calculated (6-4)/.020= 100 ohms 

> I have some questions about battery power.  I'm making lighting for a
> scultpure that uses LEDs.  I'm going to (try to) make a dark-activated
> switch so it only runs at night, but it needs to run for about a week.  I
> can always go switch out batteries but I'd rather just make something that
> doesn't need any attention so I'm trying to figure out if there are
> different ways to do things to optimize the power use.
You can probably buy one of those lights that turn on at night and just
use the relay that is in it. Remove the AC going through it. duh...
guess you don't have power there or you wouldn't use batteries right. 
> 
> I got a couple 6 volt lantern batteries that I was going to use.
> 
> Also, does it make a difference if I set the batteries up in series or
> parallel in terms of power use?  Or does it make a difference in power how
> much the LEDs are in parallel or series?
As Sandor said put them in parallel.
> 
> I want to run about 20 of the LEDs. 
This means you use about 10 x .020 = .2 amps .
Batteries are rated in Amp Hours. For example if your battery had a 5
amp hour capacity your battery would last approx. 5/.2 or 25 hours. Do
some research and find the amp hour capacity of your 6 volt batteries
jim


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