How to wire 300 blue LEDs?

Colt

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I would like to wire 300 blue LEDs to one power source in order to light up a tree. What is the best way to do this?
 

idleprocess

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What is the best way to do this?
If they're miraculously a perfectly consistent Vf, determine how much current that 300 will use, wire them in parallel then drop that over the surplus voltage across high-power resistor(s) on the positive or negative leg.

Of course this is not practical (the Vf's will vary from the factory enough to make a significant difference as well as change over time) and odds are the power supply is considerably higher voltage than the nominal 3V blue die operate at so instead the most efficient means is parallel strings - ideally each with its own series resistor sized to limit current using the voltage overhead not flowing through the LEDSs. So if you have LEDs that are 3V Vf and a 12V power supply that's 3V of overhead. If your current is 20mA then the logic is as follows: V = IR >> 3V = 0.20A*R >> 3V / 0.020A = R = 150ohms of resistance ... 3V * 0.20 A = 0.060W so a 100mW or 1/10th watt resistor should suffice. 100 strings will mean 2A of current so your power supply needs to be able to provide a minimum 2A of current.

But that's still a lot of fabrication - 100 strings. The market has solutions...

Best or easiest? I would just buy a string of holiday lights.
LED tape, fairy lights also potential options.
 

LEDphile

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You want a series string driven at constant current if at all possible. But for 300 LEDs, that puts you at around 1kV string voltage, so you're going to want to split that across multiple strings.

Me, I'd just buy the holiday lights
 

Dave_H

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I would like to wire 300 blue LEDs to one power source in order to light up a tree. What is the best way to do this?
What form does this take: what length, or multiple lengths; can you use ac power or use battery; how bright, and have you already acquired (the) LEDs? If yes to last point, specs of the LEDs?

Dave
 

Dave_H

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You can easily get strings of line-powered LEDs up to 400 or more, or shorter strings which can be connected end-end i.e. Christmas lights. They effectively are series strings connected in parallel. These are usually very power-efficient but usually shows some flicker; some people are more sensitive than others. And of course you need some place to plug it in, and need to take usual line voltage precautions.

I've seen battery-powered strings up to 200 or more but at some point the drain is too much to make it practical even with D cells. These are parallel wired, likely lower efficiency than series. Whether you can get 300 in the LED colour/style you want, would have to check around, and this long after Christmas is not the ideal time for stores (so online better).

You could hand-wire 300 LEDs, but pre-wired strings would be a whole lot easier. Challenge with low-voltage parallel is getting uniform current-sharing and brightness along the length; using one dropping resistor per LED would be a fun job.

Dave
 

alpg88

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add 30 pc. and do this, I've done it with less pieces, it worked. not the optimal way, but very simple.
assuming your leds are 3.6v leds, if not, recalculate for your voltage and adjust amount of leds in 1 string.
 

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Dave_H

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Assuming the "3.6v" LEDs have built-in resistors that could work, otherwise wiring raw LEDs to 120vac without current-limiting would be not a good idea. Blue LEDs are typically 2.5v to 3v Vf by themselves. OP needs to check this.

Dave
 

Dave_H

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Some of your numbers are off. Most small white LEDs are in the range of 2.6v to 3.2v at low current (say 5-10mA) etc. I worked on component 2nd-sourcing and went through this is detail.

In any case connecting LEDs directly across the line without proper current limiting is a bad idea, regardless of how you try to balance the voltages. Perhaps it worked for you, I do not recommend it.

Dave
 

alpg88

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Some of your numbers are off. Most small white LEDs are in the range of 2.6v to 3.2v at low current (say 5-10mA) etc. I worked on component 2nd-sourcing and went through this is detail.

In any case connecting LEDs directly across the line without proper current limiting is a bad idea, regardless of how you try to balance the voltages. Perhaps it worked for you, I do not recommend it.

Dave
They are correct for 3mm, 5mm and 10mm leds, and i have done almost same thing (just less leds) with such leds more than once. since OP never mentioned what leds he had in mind, but did mention he is is about to wrap a tree with 300 of those, i assumed it would be cheap 3 5 or 10mm leds.
current limiters are needed when you have excess of current, when you match power available with right amounts of leds, you eliminate that excess. this concept works with every type of led, and i have done it with many types. i've been designing and building flashlights and led light fixtures for longer than i'm on this forum, pretty much everything i recommend i tried myself, and i know it works.
 
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