What is immersion gold plating

Circuit for controlling a 5 watt LED via 18650 battery


The Cree XP-G3 V f will be ≈3.1V, probably less.

I have to take back the 0.13 Ωn resistance. I now recommend a 0.47Ω

The Cree is specified at 2.73 V at 350 mA at 85 ° C
with a maximum of 2000 mA, where V f = 3.06 V at 85 ° C.

An 18650 at 2000 mA has a maximum voltage of 4 V.
The voltage drops to less than 4V pretty quickly.
Now that I have the V f (3.06) at maximum current (2 amps) of the LED and the maximum voltage is ~ 4 V.

97 resistors that work: Digikey 0.47 3W + resistors
I would use the Yageo PSP400JB-0R47

This spot lens is designed for a Cree XP LED. LEDil is a very good company.


Here are 108 more: Digikey Spot Lenses

Heat will be a big problem here.

I would make a custom printed circuit board for this. These guys do a very good job and small boards under 4 "x 4" (100mm x 100mm) are very cheap, $ 5 for 10 boards. Shipping to the US is $ 21. PCBway

If it's in your budget I would use 2 ounces. Copper, 2 sided FR4 with the immersion gold plating would be a good option for thermal management. It's much flatter (smoother) than HSAL and it helps a lot with heat conduction between the PCB and the heat sink.

Lot of 10 with 1 ounce copper: $ 5
Lot of 5 with immersion gold over 1 ounce copper $ 39
Quantity 5 with HASL over 2 ounces of copper: $ 41
Lot of 5 with immersion gold plating over 2 ounces of copper $ 66

I would then place the circuit board between two sheets of copper or aluminum with a handle big enough for the LED and lens. I would flood the top of the circuit board with copper for the XP-G3's thermal pad. I would flood the bottom with copper and drill lots of vias near the LED to connect the top and bottom thermal copper.


An 18650 battery is a very good choice for powering an LED.

A 3.3V LED f works very well with an 18650 and resistor.

You did not provide the lumen part number for your LED. My choice would be a Cree XP-3G, the most efficient (185 lm / w) white high power LED. Over 600 lumens and 3.1 V at 1500 mA. Costs around $ 1 in small quantities. At 1500 mA, 4.65 W you drive hard, so the effectiveness drops to 130 lm / w.

There are LED drivers that are specifically designed for a single Li-ion cell. For example the TI TPS63030DSKR, which has a maximum of 800 mA. It will be very difficult to find a higher amperage driver.

The current limiting resistor isn't as bad as you'd think. 3.3 V at 1500 mA will run hot. Hot lets the V f fall a little. And the LED light intensity also drops.

The midpoint in the discharge curve is 3.5V, so this is the value to use when calculating the resistance. This results in an average efficiency of 94%. At the beginning of the discharge curve at 4 V, the efficiency is 83.5%. At 3.4V 97%. You can't beat 94% with a switcher power source.

Source: hobby-hour.com Resistance calculator of the LED series

A good flashlight is very difficult to make. The flashlight I'd like to have is the Coast HP314R, one rechargeable $ 500 flashlight .
The non-rechargeable HP314 costs just $ 330 and is powered by four D-cells.

This shows that these people are charging $ 170 for the Li-ion batteries and mini USB charger. Getting 1200 lumens out of batteries for 3.25 hours is not easy. You must use top quality Li-ion batteries.

Batteries last 3.25 hours at 1200 lumens, length = 17 ", weight 1.4 kg, b beam spacing 2762 FT / 842 M.

I also like their $ 150 AR25R and am seriously considering buying one.

You're probably better off buying one than making one. The look is the key.
LINK: Coast Flashlights
Home Depot has great prices on Coast Flashlights.

Make sure to check out Battery University to learn how to get the most out of a Li-ion battery. For example, do not let the battery discharge below 2.8V. Do not charge more than 4V for longer life.


This is a great answer. Thank you for being thorough. First clarifications: 1. Yes, the LED is a Cree XP-g3. 2. Using a resistor instead of an LED driver for this spec is easier and cheaper, but finding a 0.6 ohm resistor ??? I will supply my LED from 2 18650 Li-Lion cells in parallel with a charge protection module and a TP4056 for charging via micro USB.


Can I also ask where you got the screenshot from? It seems like a great resource!


@Euphoria added a source link in response.