# LEDs powered from AAA battery

Discussion in 'LEDs and Optoelectronics' started by dorabud, Jan 30, 2018.

1. ### dorabud

12
0
Jan 30, 2018
I have an idea on a project that involves LED Lights and I know nothing about LED s. I would like to use 3 small clear LED lights that can be lit from a single AAA Battery, is this possible?

2. ### kellys_eye

4,275
1,147
Jun 25, 2010
Possibly. LEDs require anywhere from 1.2V to 3.6V (colour-dependent) so what LEDs are you using? If you can give a part number we can check the datasheets and see what the manufacturers say.

3. ### dorabud

12
0
Jan 30, 2018
Don't know what lights to get, I haven't got that far.

4. ### BobK

7,682
1,688
Jan 5, 2010
You would most likely need some kind of boost converter to run them off a single AAA. Look up "Joule thief".

You can run them without a converter from a CR2032 coin cell, which is 3V.

Bob

Merlin3189 likes this.
5. ### dorabud

12
0
Jan 30, 2018
what does a joule thief do?
I am a welder by trade

6. ### BobK

7,682
1,688
Jan 5, 2010
It boosts the voltage from a 1.5V cell to enough to run LEDs.

Most LEDs require about 2V or more.

Bob

7. ### Audioguru

3,115
696
Sep 24, 2016
A Joule thief boosts the voltage of a "run down and almost dead" single battery cell to dimly light a 3V LED.
I have many solar garden lights that use an AA or AAA rechargeable cell and a voltage boosting circuit.

An AAA alkaline cell averages 1.2V during a discharge and has a capacity of 800mAh for Energizer or 850mAh for Duracell. Then it can provide 1.2V x 825mAh= 1 Watt for 1 hour.
An LED is fairly bright with a current of 20mA. Three 3V LEDs need a power of 3 x 3V x 20mA= 0.18W but the voltage boosting circuit needs about 0.1W so the total is 0.28W. An AAA alkaline cell will power them for 1W/0.28W= 3.6 hours.

8. ### dorabud

12
0
Jan 30, 2018
Is it possible to stack 357/303 coin cell battery to do the job. I have limited space and a joule thief looks like it may not fit in the area available

9. ### Audioguru

3,115
696
Sep 24, 2016
The datasheet for a tiny 357 button battery cell (or a bunch of them in series) says it is designed for a load of only 0.2mA which is about 1/300th of what you need. It has a capacity of 138mAh at its tiny current but an AAA cell has a capacity of 825mAh at the much higher 180mA of current you will need.

10. ### BobK

7,682
1,688
Jan 5, 2010
What do you expect to do with these three ligths. Are they expected to give out significant light (like a flashlight) or just be visible (like an On indicator?)

If the latter, under what lightng conditions? For normal indoor lihting, a modern high-efficiency LED can be run at 1 mA.

Bob

11. ### dorabud

12
0
Jan 30, 2018
The area these lights are to used is normally unlighted but sometimes a light is required to make sure a part is in location, we use a small flash light now. I have 3 holes (about 1/4in Dia and on a 3" bolt center circle) through the punch that the lights can be placed. Normally lights are not required the light will give the operator a little better hands free check. The Area that I have to place the Battery and things is W3/4in x H5/8in x L2 3/8in the switch will mounted in an area about 6" away. this would be a normally off switch. The purpose for the lights is to free up the operator hands for safer operation. The lights will only be on for about 2 to 3 minutes at a time.

12. ### dorabud

12
0
Jan 30, 2018
If I changed to a 9 volt battery would that help?

13. ### BobK

7,682
1,688
Jan 5, 2010
OK, so you do probably want something like 20mA for each LED.
And you presumably want white, which require over 3V.

I would go with a small LiPo battery like these:

Small LiPo battery

I am using these same batteries for some LED strips and I am very happy with them.
And they are rechargeable.

These would run 3 LEDs at 20mA each for about 6 hours before needing recharging.

Bob

12
0
Jan 30, 2018
15. ### Audioguru

3,115
696
Sep 24, 2016
You also need a charger for the battery. Maybe buy a quadcopter and use its charger.
A name brand 9V alkaline battery will power two LEDs in series plus a third LED by itself for about 15 hours. Current limiting resistors are needed.

7,682
1,688
Jan 5, 2010
17. ### dorabud

12
0
Jan 30, 2018
Check my wiring, Battery - to light1, light 1 to light 2, light 2 to light 3, light 3 to switch, switch to Battery +, Completed?

18. ### dorabud

12
0
Jan 30, 2018
going to order the part that you suggested, is there anything else that I might need and thanks for all the help,

19. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,480
2,826
Jan 21, 2010
You need a resistor (or multiple resistors, depending on how you wire the LEDs) to limit the current through them.

LEDs are not like light bulbs.

In our resources section we have a resource about LEDs. Sections 1 and 2 would be the most relevant to what you're doing I think.

20. ### dorabud

12
0
Jan 30, 2018
Please be patience this is way above me. Now that I have the battery and the LEDs, I also need resistors?
How do I determine the correct resistor? Thanks you for the read but I'm still a slow on this hole thing, and may have to read this a couple of times.