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Author Topic: Best way to run power for LEDs (IR SPOTLIGHT)  (Read 15091 times)

REK636

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Best way to run power for LEDs (IR SPOTLIGHT)
« on: April 13, 2007, 03:34:20 AM »

This project I have been working on for at least a few weeks now and I am not sure how to run power to all the LEDs. The PCB is set up in 15 series of 6 LEDs and 6 series of 3 LEDs. The IR LEDs are rated at 1.5v @ 50mA each.

I thought about 12v because I have a few power supplies that went to rechargeable flashlights that died. But now I want to go portable and go with batteries instead of a power cord.

Thinking of several 9v ones for either 18v or 27v. Then I'll just need to recalculate for the resistors. I don't have capacitors, because I don't know how to use them or figure them in.


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REK636

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #1 on: April 16, 2007, 01:23:15 PM »

Anybody? Just need a power supply and I can get this done.
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trials_modder

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #2 on: May 01, 2007, 12:27:52 PM »

could you rephrase/explain further how that pcb is set up?
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REK636

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #3 on: May 01, 2007, 01:48:33 PM »

I didn't have room on the board for the resistors they are on another board. Each searies of leds gets power from a wire on the other board.

Not actual size.
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trials_modder

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #4 on: May 01, 2007, 02:28:37 PM »

correct me somebody if i'm wrong but:

to run the series of 6 LEDs,  you'll need 6*1.5 = 9 V, 300mA per series*15 = 4.5 A total
and the series of 3 LEDs is 3*1.5 = 4.5 V, 150 mA per series*6 = 900mA total
108 LEDs

total = 5.4 A of current required? that would mean a battery rated for 5.4 AmpHours would only last... an hour? if those calculations are correct then i think the bigger problem is finding a suitable battery (i'm not sure how portable it would be).

again, correct me if i'm wrong as this current seems rather large
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REK636

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #5 on: May 01, 2007, 03:46:42 PM »

That makes sence about the current not working well for a battery. Looking at taking out the 6 series of 3 leds and replacing with somthing with less mA or a diffrent color.

Still the  6 x 1.5 = 9 V, 300 mA per x 15 = 4.5 A fot the 90 LEDs

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trials_modder

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #6 on: May 02, 2007, 02:44:04 AM »

so say if you use a decent 12 v battery (laptop lithium ion maybe?) then...

on each series of 6 LEDs you'd need (12v-9v/0.3A) = 3 ohm resistor per branch = essentially no resistor?
and (12V-4.5V/0.15A) = 50 ohm resistor per branch

i think those calculations are set up so that the resistor lowers the 12volts to the amount needed by the LEDs in series to run
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viridius

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #7 on: May 03, 2007, 06:28:54 PM »

You might try strobing the LEDs to conserve power.  Other than that, infrared is the most efficient color in terms of electricity to light.  Don't run them without a resistor.
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REK636

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #8 on: May 03, 2007, 06:31:05 PM »

Strobe them. Using a 555 or somthing.
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viridius

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Re: Best way to run power for LEDs (IR SPOTLIGHT)
« Reply #9 on: May 03, 2007, 06:37:10 PM »

Strobe them. Using a 555 or somthing.

Well, 555s can only source a few mA, so you'd have to use a logic level MOSFET or something but yeah.
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