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

From: Sandor Ajzenstat   sandorinterlog.com
Date: Wed, 18 Aug 2004 10:26:28 -0700

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Hey Demetrius,

I should mention that I don't think there is such a thing as a stupid
question.  I should also mention that I don't really have a proper answer
for you.  I hope someone else can perhaps give you more information.  I will
only say, that if it was me doing the project I would wire the batteries in
parallel, (because 6 volts is sufficient to operate an LED, and batteries in
parallel will last longer than a single one as you know).  Then with the
LED's I would certainly wire each LED with it's own resistor, and wire all
the  LED-resistor groups in parallel.  (In the event that only one LED will
be on at a time, then all the LEDs can share a single resistor).  I'm not
sure how long the LEDs will remain illuminated in this configuration, but my
guess is longer than a week.

Sincerely,
Sandor



----- Original Message -----
From: "Demetrius Anger" <danger@xxxxxxxxx>
To: <arg-list@xxxxxxxxxxxxxxx>
Sent: Wednesday, August 18, 2004 9:47 AM
Subject: ARG: Power optimization and some (stupid?) LED questions


> A! Sent via the Art & Robotics Group mailing list:
arg-list@xxxxxxxxxxxxxxx
> R! Use your "Reply All" to  reply to the list, "Reply" for private
response
> G!
>
>
> I don't know if these questions are way off topic or not - it's not really
> about robotics.  It is just the beginning of learning for me though so I'm
> trying to start simple.  Let me know if it is totally off-topic.
>
> 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.
>
> I got a couple 6 volt lantern batteries that I was going to use.
>
>
> Okay stupid question(?) first - if the battery is 6V and the LEDs have a 2
> volt drop and want to run on 20mA do I need to put a resistor in there if
I
> use three LEDs in series?  This is totally confusing me.  Do I calculate
the
> resistance as if the LEDs weren't there?  Like the ideal LED is without
> resistance right, but then there's a voltage drop so then it's got to be
> doing something right?  I am feeling stupid about this because I think
> someone has explained this to me before.
> Aaa!
>
> 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?
>
> I want to run about 20 of the LEDs.  I'm just trying to get a general idea
> of whether or not it matters how I set it up.  Like 2 batteries in series
> with parallel sets of 6 LEDs in series.  Or 2 batteries in parallel with
> parallel sets of 3 LEDs.  Or should I put every single LED in parallel for
> some reason?
>
>
> Anyone done battery powered stuff?  Should I get more batteries or are my
2
> 6V batteries going to last the week?  I can't find any information about
how
> to calculate battery life.
>
> The only thing I can find is that battery life is longer at lower rates of
> discharge.  I went to some of the battery manufacturer sites and can't
find
> anything about amp/hours (which is what someone told me how battery
> discharge was measured) or battery life at all.
>
> Thanks for any help!  If these are too many questions or whatever anyone
> have a source I can read up on?
>
> -aaron
>
>
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