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High power LED flashlight power supply questions Answered

I'm currently in the process of building a high power LED flashlight from scratch. I've decided to go for AA batteries as a source of power, however, I am not sure as to whether 2 AAs will be enough to drive my LEDs.

The LEDs are from a 5W LED bulb putting out ~360lm. I'm assuming the bulb itself has 5 1W LEDs connected in some sort of configuration, but I'm going to run them in parallel.

I'm planning on running it on either Alkaline or NiMH. However, I'm not quite sure if there will be some sort of voltage drop with the load I'm going to place on the system (~1A @ 200mA each). Also, 2 NiMH will only have a combined voltage of 2.4v making me a bit skeptical as to whether it would even run.

I already have a design for the flashlight for 2 AA batteries. Adding a third battery would complicate the design though, maybe requiring me to make a battery pack or something.

So, will a 5x1W LED array in parallel run from a 2.4v NiMH power supply? Or do I have to go with 3 batteries plus a current limiting resistor?



Best Answer 4 years ago

Do you have a link/datasheet for the LED, even if its was a bulb to begin with?

Most LEDs won't run at full power below 3.6V, so as a general rule, 3 NiMH batteries would generally work by themselves, or if you used a 18650 battery, or two 14500 batteries in parallel (one MIGHT work, but it would have a very short battery life).
If you don't have any of those batteries, you can get them at DX.com fairly cheap, but very low quality (literally NOTHING is name brand, or the stated capacity).

Mainly, get a datasheet, and find out what voltage you can dirve the LEDs unregulated at, or just buy a step-up regulator.

Yeah, looks like I'm going to have to go with a 3 cell NiMH design..

As for the datasheets, the bulb is pretty much an unbranded china-type LED bulb. The datasheet is virtually nonexistent.

I think most run on 3.5 volts so the third battery may be your only choice.

Try to get the strongest AA batteries 1300 mah or more even then you may only get 30 to 40 minets.

A voltage regulator connected as a current regulator works best as a driver.



4 years ago

All the 5 and 9 LED flash lights I own are powered by
three AAA batteries in a triad series bundle..

And when the batteries are low the LEDs are diminished in such a manner that
makes me believe the LEDs are in parallel with one single series resistor.


Unless you insert a current limiting circuit you will need a resistor. When on an LED is almost a dead short across it's power supply and will draw as much current as it can up to destruction.

You should try to find out the data sheet for the LEDs - often cree units - so you know he max voltage and current you can apply.

I assume you have removed the AC circuit that was driving the LEDs

Yes, I will remove the guts of the bulb only to retain the heatsink and LEDs.

Would 2.4v be enough though?