# Lighting up a 5mm LED using a homemade battery

1. Jun 30, 2016

### Joel Kee

1. The problem statement, all variables and given/known data
I'm currently doing a mini project as an assignment in my engineering course. I tried replicating the coin battery, where I stack a piece of cardboard soaked in black vinegar (couldn't find white vinegar), a piece of aluminium foil, then a 20 sen
coin (Malaysian, cupronickel), and continue. I managed to get a stable reading of 6V. However, my 5mm LED did not light up when I tried connecting it. So, I tested the coin battery using the link multimeter and found out that it only produced 23microA. How do I increase the current? Or is that not the problem?

2. Relevant equations

3. The attempt at a solution

2. Jun 30, 2016

### Staff: Mentor

Hi Joel Kee.

If you look at the LED at night with the room in darkness you may discover that it is giving a faint glow.

But I see two ways you could go from here. You could try bigger coins or metal sheets, so there'd be larger areas for the electrochemistry to work with. This is equivalent to connecting multiple batteries in parallel.

Or, you could use what you have and drive a low-power flasher, an electronic circuit where a capacitor is slowly charged (over some seconds) by your micropower battery, then its accumulated charge gets dumped through the LED for a brief time, and the charging cycle repeats.

3. Jun 30, 2016

### Joel Kee

Thanks for the reply! I have almost lost faith in this project, so thanks for replying. I tried using a buzzer with this coin battery, yet no sound is produced. I shall try the LED in a dark room though. Any other advice?

4. Jun 30, 2016

### Joel Kee

UPDATE :
The LED lights up! But it's really dim. Any idea how to make it brighter other than add more coins?

P/s I still don't get why 5v isn't enough to make this LED light up brightly.

5. Jun 30, 2016

### Staff: Mentor

It's not the unloaded voltage of your battery that is important. If you measure the voltage across the LED when it is connected to the battery you will see that the voltage is nothing like a few volts.

There may be tiny lower-power more-efficient LEDs available.

6. Jun 30, 2016

### Joel Kee

Can you explain more on why? And why does a normal battery make it light up so bright then?

7. Jun 30, 2016

### Joel Kee

And how much voltage do you think I need to make it bright?

8. Jun 30, 2016

### Staff: Mentor

Across the LED itself when glowing brightly, between 3V and 4V.

9. Jun 30, 2016

### Joel Kee

Care to explain why the voltage of the battery doesn't really matter?

10. Jun 30, 2016

### Staff: Mentor

The battery voltage does matter. While powering the LED the battery voltage must of necessity be at least what the LED requires.

11. Jun 30, 2016

### Joel Kee

Any idea how much voltage should my battery be in order for the LED to be about 3-4V?

12. Jun 30, 2016

### Staff: Mentor

A battery of that voltage will work. With it connected directly to the LED then the battery voltage becomes the LED voltage.

It's not more volts that is required of your homemade battery; what is needed is more current. The only way for your voltaic pile to supply more current is to provide it with more metal surface for its chemistry to work with.

13. Jun 30, 2016

### Joel Kee

Will having multiple coins on one flat surface, piled on another set of coins on another flat surface on it, work?

14. Jun 30, 2016

### Staff: Mentor

You could try that. It will be an improvement.

15. Jun 30, 2016

### Joel Kee

Do you think that would work better, or wrapping copper wire with aluminium and salt water soaked tissue together, joined in series?

16. Jun 30, 2016

### Staff: Mentor

You have to try these to find out. It's not as straight-forward as you'd like.

17. Jun 30, 2016