LED's are wierd componets. They are diodes, so yes you pretend that they are not there when you do your ohms law to figure out resistance. I use 220 or 330 ohms in series for each LED. If you have no resistor, you will have glorious light for awhile but they will burn out. With the resistor they should never burn out.
If you hook up the batteries by putting an alligator clip on positive to positive and the other clip on negative to negative you double the Amps, if you hook up the battery so that the alligator clips are positive to negative and the other is positive to negative, you double the voltage. If you want the battery to last longer, you can double the Amps so that it has more juice.
I think you should put your LED's in parallel. You can buy resitor bars. They are a bar like thing with lots of pins along it. It would allow you to save space. Because one resistor bar can have I believe 4 to 8 or maybe even 10 resistors all on one small component. There is a painted dot on the bar which indicates the common pin. That pin would go to ground or positive and all the others would go to the LED's.
Gee, batteries for me are a weak point, I am just getting into them myself. There are major differences between kinds of batteries and they do affect how long they last. I can't really remember the acurate names of batteries, so I can't really help you. I will likely just confuse you with misspelled names.
You can look into the lastest Robot Builders guides at Chapters. They will have a chapter on batteries and how to power robots. They may be up on the new batteries out there and could give you some useful information.
Jessica
>From: "Demetrius Anger" <danger@xxxxxxxxx>
>To: <arg-list@xxxxxxxxxxxxxxx>
>Subject: ARG: Power optimization and some (stupid?) LED questions
>Date: Wed, 18 Aug 2004 11:47:24 -0500
>
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>
>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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