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How do i go about choosing LEDs for a project? Answered

So i'm planning on building a battery bank to charge my phone and other usb devices . I wanted to also use it as a flashlight, My size is limited, since i was planning on using an altoids tin, and i'm already stuffing two 18650 batteries inside. What i want to know is what is the brightest led i can use that wont need a heat sink? or at least one that will dissipate enough heat into the tin alone.

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Wired_Mist

Best Answer 3 years ago

Well a board like this will do the Heavy Lifting for you

https://www.sparkfun.com/products/11231

Wire you bats in parallel so you can double you Ah capacity. The board above has whats called a boost converter in it. It will take the 3.7v from the batteries and boost it up to the 5v you need.

It also has a built in Charger (only 100ma per hour but it still works)

For the Led, like Max said, you don't need to drive the Led at full power. I would suggest a 3W cold white Led and use a resistor to limit the current from the maximum 750ma to say 250ma (for 5v source, use a 4.7-Ohm 1Watt resistor)

Mount it with some heat sink compound and a few dabs of super glue around the perimeter.

Btw are you using apple products?

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Tomahawk92Wired_Mist

Answer 3 years ago

That's great, I wonder if i could find that exact board. It looks like it has usb ports for both charging the battery, and a cell phone.

If i get a pre made board for charging an 18650, do you think i can use it to charge multiple 18650s in parallel.

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Wired_MistTomahawk92

Answer 3 years ago

Definitely !

Check for Sparkfun Distributor in your Aria, there's a few. Otherwise just buy a cheep USB Power bank (like in the I'ble I Linked to) and harvest the components !

As long as all the cells are the same Voltage,Yes you can wire them in Parallel :)

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iceng

3 years ago

I see them sold as 3000mah to 4000mah 3.7volt batteries.

If you want to charge an iPhone you will need an up-verter to 5 Volts or are you putting the batteries in series ?

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Tomahawk92iceng

Answer 3 years ago

i'm using them in parallel, and i have an "upverter" that gets anything from 3-14 volts and converts to 5v. It already has a mounted usb port.

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-max-

3 years ago

For charging the phone, if you can cram a 3rd battery in and still have space, and wire everything in series, then to charge the phone, you can use the buck converter to regulate the output to 5V for the phone. (these are found in USB car chargers, and as descrete units and chips online.) However, you should check to see if the low voltage cutoff works on the charger. When the input voltage goes below 9V, it should cut off power to prevent over-discharging the battery.

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-max-

3 years ago

What you can do is pick up a cree XM-L LED, they cost around $6, but they are really good LEDs. They can be driven up to 10W, which is 1000LM, and at lower power, they do not dissipate much. Maybe a 1W to 5W LED driver that is variable, and you can set it so that the LED does not get that warm while still providing plenty of light. High CRI one's are also avalible.

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-max-

3 years ago

Any LED can be used without a major heatsink. Even a 100W one. It is how many watts you decide to push into it that counts. You can control the watts by controlling the current through it, or the voltage across the LED. (less volts = less amps = way less watts)

The advantage with using a larger LED is that when large LEDs are underpowered, they have higher efficacy (measured in lm/w.)

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iceng-max-

Answer 3 years ago

Very Informative especially about prolonging LED MTBF with less then peak drive.

But, he asked "what is the brightest led i can use that wont need a heat sink?"

How are you answering his primary inquiry ?

What specific LED do you recommend ?