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Author Topic: Powering 100 LED's. Possible?  (Read 3585 times)

Tank

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Powering 100 LED's. Possible?
« Reply #10 on: September 06, 2004, 12:08:31 AM »

Quote from: Skylined
70 Ohm 10% doesn't exist.
In 10% you only have 68 and 82


I'm sorry, it was a 75 Watt, a typing error on my part. here is the link, it is towards the bottom of the page.

http://www.electronicplus.com/content/ProductPage.asp?maincat=RE&subcat=REG
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linear

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Powering 100 LED's. Possible?
« Reply #11 on: September 08, 2004, 03:09:03 PM »

Uh, why aren't we considering series combinations? And 12V supply.

How about 33 parallel strings of 3 resistors in series (with one resistor per string)? now we're down to 33*0.02 = 660mA. Each resistor would be a 68ohm, 1/4W.

Even if you wanted to got the single-resistor route, you're talking R = (12 - 10.8) / 0.66 = 1.8 ohms P = 792 mW, so you're dealing in a radically smaller resistor. And throwing less waste heat.
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Psycho Clowns

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Powering 100 LED's. Possible?
« Reply #12 on: September 08, 2004, 03:27:20 PM »

Thank God we know for a fact that linear knows what he is talking about cause I sure as hell don't.
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Tank

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Powering 100 LED's. Possible?
« Reply #13 on: September 08, 2004, 07:59:18 PM »

Quote from: linear
Uh, why aren't we considering series combinations? And 12V supply.

How about 33 parallel strings of 3 resistors in series (with one resistor per string)? now we're down to 33*0.02 = 660mA. Each resistor would be a 68ohm, 1/4W.

Even if you wanted to got the single-resistor route, you're talking R = (12 - 10.8) / 0.66 = 1.8 ohms P = 792 mW, so you're dealing in a radically smaller resistor. And throwing less waste heat.


Linear, this seems like the route that I want to take. I am serious about doing this project, but to be completely honest, I don't understand 100 percent what you mean. I think what you are saying is that I would wire the led's in 3 parallel chains, then wire the chains in series? Do you think, linear, that you could simplify your solution a bit for me? I really want to understand this.

EDIT: Iv'e been thinking about this, and here's my best guess. There will be essentially 3 chains of LEDs, all wired in parallel, with 1 resistor for each of the three chains. Then , the resistors will be wired in series to the 12v rail. So, the voltage will be split three ways (4v per chain?). More or less, then, I just need to use resistors that will protect 33 leds off of a 4v power source? I am thinking that because the leds are in parallel off of the resistor, that they will all get equal amperage.

Am I getting close?
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modnut

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Powering 100 LED's. Possible?
« Reply #14 on: September 08, 2004, 08:08:30 PM »

Quote from: Psycho Clowns
Thank God we know for a fact that linear knows what he is talking about cause I sure as hell don't.


i don't either...oh well, at least it looks right.
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Firespark

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Powering 100 LED's. Possible?
« Reply #15 on: September 08, 2004, 08:29:42 PM »

I wouldnt use the 5v rail. there is a sticky somewhere in here that points out why it is better to use the 12 v rail and resistors/a resistor. also, 5 and 3 share the same source or something like that and runnin it on the 12 is just better...

http://forums.gideontech.com/viewtopic.php?t=24341
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viridius

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Powering 100 LED's. Possible?
« Reply #16 on: September 08, 2004, 09:43:59 PM »

No, that was saying that you shouldn't be slapping a 5 volt LED onto the 5 volt rail without a resistor.  If the LED's Vf is less than 5 volts, it's perfectly fine to put it onto the 5 volt rail with the appropriate resistor.  The 5 volt rail usually can pump out more current, anyways.
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Daneel

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Powering 100 LED's. Possible?
« Reply #17 on: September 15, 2004, 06:48:58 AM »

For people still nutting out what linear said, here you go:

He's is saying that you could have 33 parallel strings, each with 3 leds and one resistor.

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Tank

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Powering 100 LED's. Possible?
« Reply #18 on: September 15, 2004, 10:29:54 PM »

Thank you, Daneel! I was hoping someone might post and simplify the concept a bit. I think I understand now. Thank you for that input.
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linear

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Powering 100 LED's. Possible?
« Reply #19 on: September 17, 2004, 03:02:48 PM »

Sorry not to be around to clarify, but Daneel gets it exactly right.

All I'm doing with the power calculations in my original post is comparing the efficiency of my solution with the other alternatives.
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