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If you want to avoid the seeming hassle of resistors, here's some simple math to consider...

Say your power source is a regular alkaline 9v @ 800mA. You know your leds are just about 3v and need 25mA each. If you resistored each led, you would have to kill 6v off each led (9-3=6). However you can do a serial-parallel wiring setup by wiring your leds in groups of three.

So: power source+ to led1+, led1- to led2+, led2- to led3+, led3- to power-. So that's 3x3 for 9v and 25x3 for 75mA. Now, you can wire 10 sets of 3 leds to give you up to 30 leds running on one 9v battery at full power for about an hour. Remember, that's 10 sets of 75mA for 750mA. Very close to your 800 ceiling, but it should work.

As each set of three leds is serial, if one goes, all three go. However, the other 9 sets of three will stay on. In this way, you can build a modicum of redundancy into your model.

With this basic math example, you can scale up or down to any size power source. Odd numbers get tricky such as two 3v on a 5v or 8v power source, but with some finagling, all should go well. And more often than not, leds will be 2.4v or 1.8v or 3.2v, so the math is never exactly simple, but is ballparked easily enough. But you do want to get into resistors sooner than later.

I highly rec. getting your leds off ebay. Forget Xmas lights. You gotta carefully slice the string up, pull each one out of there, there's tangles and all sorts of hassle. Also, you won't know the mA or v of each, though you could ballpark it. At 100 leds for ~$10 shipped of any of nearly 1 doz colors and all arriving within a week ina a nice little baggie. You've got no hassle and typically the seller lists the power numbers on the sales page and will tell you more important info like the degree of visibility, the candle power and more. That's stuff for another post.

And quite often, there are sellers that throw in the resistors for free. Just tell them the power source voltage you have and they will do the math for you. Just say you want 12v, 8v, 6v or whatever nd that's the apropriate resistor you get for that exact led. No resistor math involved, just ensure you have the wallwart to match. Later on, you can grow into the more complicated math. Just check the sellers rating and make sure you are comfortable with all the terms. I've spent about $100 on these sellers and not been burned yet. And if I am, I'm out $10. If I spent $50 on a seller and got burned, I'd be disappointed, but the buyer protection can help out on that front.

Have fun!

<blockquote data-quote="ModelMan" data-source="post: 3451" data-attributes="member: 397">If you want to avoid the seeming hassle of resistors, here&#039;s some simple math to consider...Say your power source is a regular alkaline 9v @ 800mA.&nbsp; You know your leds are just about 3v and need 25mA each.&nbsp; If you resistored each led, you would have to kill 6v off each led (9-3=6).&nbsp; However you can do a serial-parallel wiring setup by wiring your leds in groups of three.&nbsp; So: power source+ to led1+, led1- to led2+, led2- to led3+, led3- to power-.&nbsp; So that&#039;s 3x3 for 9v and 25x3 for 75mA.&nbsp; Now, you can wire 10 sets of 3 leds to give you up to 30 leds running on one 9v battery at full power for about an hour.&nbsp; Remember, that&#039;s 10 sets of 75mA for 750mA.&nbsp; Very close to your 800 ceiling, but it should work.As each set of three leds is serial, if one goes, all three go.&nbsp; However, the other 9 sets of three will stay on.&nbsp; In this way, you can build a modicum of redundancy into your model.&nbsp; With this basic math example, you can scale up or down to any size power source.&nbsp; Odd numbers get tricky such as two 3v on a 5v or 8v power source, but with some finagling, all should go well.&nbsp; And more often than not, leds will be 2.4v or 1.8v or 3.2v, so the math is never exactly simple, but is ballparked easily enough.&nbsp; But you do want to get into resistors sooner than later.&nbsp; I highly rec. getting your leds off ebay.&nbsp; Forget Xmas lights.&nbsp; You gotta carefully slice the string up, pull each one out of there, there&#039;s tangles and all sorts of hassle.&nbsp; Also, you won&#039;t know the mA or v of each, though you could ballpark it.&nbsp; At 100 leds for ~$10 shipped of any of nearly 1 doz colors and all arriving within a week ina a nice little baggie.&nbsp; You&#039;ve got no hassle and typically the seller lists the power numbers on the sales page and will tell you more important info like the degree of visibility, the candle power and more.&nbsp; That&#039;s stuff for another post.&nbsp; And quite often, there are sellers that throw in the resistors for free.&nbsp; Just tell them the power source voltage you have and they will do the math for you.&nbsp; Just say you want 12v, 8v, 6v or whatever nd that&#039;s the apropriate resistor you get for that exact led.&nbsp;&nbsp; No resistor math involved, just ensure you have the wallwart to match.&nbsp; Later on, you can grow into the more complicated math.&nbsp; Just check the sellers rating and make sure you are comfortable with all the terms.&nbsp; I&#039;ve spent about $100 on these sellers and not been burned yet.&nbsp; And if I am, I&#039;m out $10.&nbsp; If I spent $50 on a seller and got burned, I&#039;d be disappointed, but the buyer protection can help out on that front.&nbsp; Have fun!</blockquote>

[QUOTE="ModelMan, post: 3451, member: 397"] If you want to avoid the seeming hassle of resistors, here's some simple math to consider... Say your power source is a regular alkaline 9v @ 800mA. You know your leds are just about 3v and need 25mA each. If you resistored each led, you would have to kill 6v off each led (9-3=6). However you can do a serial-parallel wiring setup by wiring your leds in groups of three. So: power source+ to led1+, led1- to led2+, led2- to led3+, led3- to power-. So that's 3x3 for 9v and 25x3 for 75mA. Now, you can wire 10 sets of 3 leds to give you up to 30 leds running on one 9v battery at full power for about an hour. Remember, that's 10 sets of 75mA for 750mA. Very close to your 800 ceiling, but it should work. As each set of three leds is serial, if one goes, all three go. However, the other 9 sets of three will stay on. In this way, you can build a modicum of redundancy into your model. With this basic math example, you can scale up or down to any size power source. Odd numbers get tricky such as two 3v on a 5v or 8v power source, but with some finagling, all should go well. And more often than not, leds will be 2.4v or 1.8v or 3.2v, so the math is never exactly simple, but is ballparked easily enough. But you do want to get into resistors sooner than later. I highly rec. getting your leds off ebay. Forget Xmas lights. You gotta carefully slice the string up, pull each one out of there, there's tangles and all sorts of hassle. Also, you won't know the mA or v of each, though you could ballpark it. At 100 leds for ~$10 shipped of any of nearly 1 doz colors and all arriving within a week ina a nice little baggie. You've got no hassle and typically the seller lists the power numbers on the sales page and will tell you more important info like the degree of visibility, the candle power and more. That's stuff for another post. And quite often, there are sellers that throw in the resistors for free. Just tell them the power source voltage you have and they will do the math for you. Just say you want 12v, 8v, 6v or whatever nd that's the apropriate resistor you get for that exact led. No resistor math involved, just ensure you have the wallwart to match. Later on, you can grow into the more complicated math. Just check the sellers rating and make sure you are comfortable with all the terms. I've spent about $100 on these sellers and not been burned yet. And if I am, I'm out $10. If I spent $50 on a seller and got burned, I'd be disappointed, but the buyer protection can help out on that front. Have fun! [/QUOTE]

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