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Author Topic: Powering 100 LED's. Possible?  (Read 3705 times)

Tank

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Powering 100 LED's. Possible?
« on: September 05, 2004, 04:19:59 PM »

I am planning a project right now that requires me to power about 100 LED's off of the 12 volt rail of my Antec 380 Watt TruePower. The project would still work if I use only 66 LED's, but I would like to use the 100, if it is possible. I know that LED's are efficient, but I dont know if that amount of lights is going to draw too much power.

I am using a Radeon 9500 Pro, one hard drive, two optical drives, and a 120 mm case fan, to give you an idea of what else is drawing power. Is the 100 LED's possible? Any help would be appreciated.
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viridius

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Powering 100 LED's. Possible?
« Reply #1 on: September 05, 2004, 05:12:41 PM »

Well, if you assume 20 or so milliamps per LED and multiply that by 100, you get 2 amps, which is 24 watts off of the 12 volt rail.  My guess is that it would work, but you'd have to find a 24 watt or higher resistor, which could be expensive.  Try Digikey.
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Tank

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Powering 100 LED's. Possible?
« Reply #2 on: September 05, 2004, 05:28:13 PM »

I am having a difficult time finding a resistor of that wattage. Is it possible to chain up several resistors of lower wattages to acheive 24 watts of effective resistance?

Also, could you explain, viridius, the correlation between 2 amps, and 24 watts? I don't think I understand.
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viridius

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Powering 100 LED's. Possible?
« Reply #3 on: September 05, 2004, 07:38:27 PM »

Digikey sells them.  Just go to digikey.com, search for 'resistors' and select 'power resistors'.  Power in watts is found by multiplying voltage in volts by current in amps.  Two amps, 12 volts, 24 watts.
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Tank

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Powering 100 LED's. Possible?
« Reply #4 on: September 05, 2004, 08:53:41 PM »

Would this mean that it would be a better idea to attempt to run them off of the 5 volt line? 2 amps x 5 volts= 10 watts?
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viridius

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Powering 100 LED's. Possible?
« Reply #5 on: September 05, 2004, 09:49:29 PM »

Yeah, I'd go with 5 volts and the appropriate resistor.
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Tank

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Powering 100 LED's. Possible?
« Reply #6 on: September 05, 2004, 10:15:57 PM »

So, If I plan to use 100 Blue LEd's at 3.6V, 20mA, off of the 5V line, then I'd need at least a 10 Watt resistor. So I am going to assume that if I wire these in parallel, then each LED will get the same amount of power, correct?

Brutal's LED calculator says that a LED of my specifications needs a 70 ohm resistor. Does this mean that I am trying to find a 70 ohm 10 Watt resistor?
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viridius

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Powering 100 LED's. Possible?
« Reply #7 on: September 05, 2004, 10:33:08 PM »

Yes, but they don't make 70 ohm resistors.  You'll have to go with 75.
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Tank

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Powering 100 LED's. Possible?
« Reply #8 on: September 05, 2004, 11:19:21 PM »

I found a 10 Watt, 70 Ohm, 10%, ceramic block resistor, for $2.50. Does that sound about right? Iv'e never seen a ceramic block resistor, so I don't know if it is wired any differently,  or if I'll need to heat sink it or not.

By the way, thank you for all the help, viridius, I really appreciate it.
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Skylined

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Powering 100 LED's. Possible?
« Reply #9 on: September 05, 2004, 11:33:10 PM »

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