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I've built a remote control for my 3W power LED with an Arduino UNO and I'm powering the Arduino with a USB cable and the LED with 4x AA NiMh batteries (1.2V). Is it possible to power both my Arduino and my LED with the same power source (meaning batteries)?

I haven't found anything on here for my case. Most questions that revolve around using the same power source are for 5 or 10 high power LEDs with a source of 12V, but I'm only using 1 and I need it to run on batteries.

Specifications of the LED:
Max. Current : 750 mA
Forward voltage : 3.5 - 4.5 V
Max. Working temperature: 60 °C

P.S.: total newb in electronics so sorry if it's a simple question

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  • \$\begingroup\$ What are you using to regulate current to the LED? Hopefully not just the battery internal losses! Your battery voltage is probably too low for an Arduino Uno's regulator, but it would work for a 3v3 variant of an Arduino. Depending on the precise cell details at full charge you might or might not be able to use a bare ATmega without a regulator. \$\endgroup\$ – Chris Stratton Dec 17 '18 at 20:57
  • \$\begingroup\$ Just using a resistance setup to regulate current to the LED, I know it's not very efficient but as I'm new at this I keep the setup easy for testing purposes \$\endgroup\$ – B913 Dec 17 '18 at 20:59
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Specifications of the LED:
Max. Current : 750 mA
Forward voltage : 3.5 - 4.5 V Max.
Working temperature: 60 °C

These specs are not good for a battery powered LED.

3.5 - 4.5 Vf says it is a horribly inefficient LED.

When battery powered, always start with an LED with the highest efficacy possible. Today that LED is a Cree XP-G3 XPGDWT-01-0000-00ME3. High efficacy means more light and less heat. This White, 5000K Cree LED has a efficacy of 180 lm/W.

At 750 mA this LED's Vf is 2.85V. See Pg. 18 of datasheet.

Just using a resistance setup to regulate current to the LED, I know it's not very efficient

This is not always true. You can easily power this with the Arduino UNO's 3.3V. You cannot do this with a 3.5-4.5V LED. With a 2.85V LED powered by 3.3V with a current limiting resistor would give you an efficiency of over 86% no matter what current you run at.

I'm powering the Arduino with a USB cable and the LED with 4x AA NiMh batteries

Powering a 5V Arduino with 4.5V batteries is not good. The Arduino wants at least a 5.1V input. The Arduino Vin is run through a 5V NCP1117ST50T3G LDO regulator. The minimum input voltage for the 5V NCP1117 is 4.950V.

You should just use a 5V USB power bank to power the Arduino and use the Arduino's 3.3V to power the LED. You probably cannot run it at more than 250-300 mA without a heatsink. At 250 mA the Cree Vf is 2.7V so a 2-2.4 Ω half watt resistor would give you better than 80% efficiency. Well, minus the the efficiency of Arduino's 5V and 3.3V LDOs.

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    \$\begingroup\$ "3.5 - 4.5 Vf says it is a horribly inefficient LED." - Or that it's multiple LEDs in series. \$\endgroup\$ – Reinderien Dec 18 '18 at 23:25
  • \$\begingroup\$ Do you know of an LED with a forward voltage of 1.75 - 2.25V so when two are connected in series the Vf will be 3.5-4.5v? Unlikely. Are there LEDs with 3.5-4.5 Vf? Many. And the OP used the term "Specification of the LED. So I'm going to stick with horribly inefficient, The way efficient LEDs are made, is by reducing the Vf. \$\endgroup\$ – Misunderstood Dec 19 '18 at 1:06
  • \$\begingroup\$ Digikey has 8100 results (give or take) for LEDs with Vf less than or equal to 2V. \$\endgroup\$ – Reinderien Dec 19 '18 at 5:46
  • \$\begingroup\$ @Reinderien that's actually a little low. But that is a useless statistic. Try how many LEDs with a 750 mA or more max current and are visible (i.e. less than 700 nm). More than zero? Nope. BTW, the 60° C operating temperature is also a good hint it's a horrible LED too. And again when the OP wrote: "Specifications of THE LED", kinda says single LED. Keep in mind the Chinese have to wait 18 years for the patents to expire so much of their LED technology is 20+ years old. Twenty years ago white LEDs Vf was in the 3.5+ range. Today white lighting (700 mA) LEDs are rated at about 2.8V. \$\endgroup\$ – Misunderstood Dec 19 '18 at 6:31

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