# LED electrical/wiring help

Discussion in 'The Projects Forum' started by samrozzi, Feb 10, 2009.

1. ### samrozzi Thread Starter New Member

Feb 10, 2009
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hey. for v-day I wanna make an led heart with a on off switch. I bought some LEDs about 15 and wiring and a 9v battery. I know im prob burnign out the led instantly because when i attach it to the battery it flashes then doesnt relight. am i burning it out? and how can i prevent this?

I am using a 9v battery
a rated 300 volts, 20 gauge stranded wire.
and a SPST Momentary Submini Pushbutton Switch at 0.5A at 125VAC/250/VAC

I wanna light up about 15 red LED's

idk what to do. i didnt use a resistor or capacitor because idk what those really are (new to LEDs)

and i dont want to chain together them all incase it blows all of them.

the LED's are rated at 2 - 3 V, 10-20 mA leds (it is these http://www.radioshack.com/product/in...d...

any help? I think I just need a way to stop the battery from over powering the LEDs? and control the power? idk :/
48 minutes ago - 4 days left to answer.
ok i understand i can add more. but how many? I dont wanna blow it but is it possible to do to many?
32 minutes ago

so also say each led is 3v and the battery is 9. does that mean 3 LEDs?

so if i had a 24v power does that mean 8LEDs?

I just want to power about 15LED's and have a on off switch. thanks

2. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Ah! Romance!

Your battery will power three or four of the LEDs in series. No more.

To keep the LEDs from burning out, one must limit the current to not more than 20 mA.

I suggest five parallel strings of three series LEDs each, with a current limiting resistor on each string. Assuming worst case numbers (2V and 10mA) the resistors (five of them) should be 1000 Ohms. Use quarter Watt resistors or larger.

Don't expect the battery to last more than six or twelve minutes.

For a crash course in "parallel" and "series," check here: http://www.allaboutcircuits.com/vol_1/chpt_5/1.html

Feb 10, 2009
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4. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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The switch in the link is "on" when pushed and "off" when not pushed. The switch contacts close only momentarily, thus "momentary contact."

Five series strings of 10 to 20 mA LEDs in parallel will draw 50 to 100 mA total current from the battery. Once battery voltage drops below that required for the LEDs (6 to 9 Volts, average of 7.5) the string won't light. Have a look: http://www.powerstream.com/9V-Alkaline-tests.htm

You could, of course, wire several batteries in series. Or you could choose a different (and heavier) battery.

5. ### samrozzi Thread Starter New Member

Feb 10, 2009
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well i guess a heavier battery :/ didnt want it to big. but sorry and thanks for helping. im so new i dont really understand any of this. i thought id be easy. wire together some batteries attach to a battery then done. i guess not.

so is their anyway I can link all 16 LED's together then attach to a switch then to the battery? what size battery would I need? im guessing atleast a like 48v power supple? since each led is 3v i think and 3 times 16 is 48? is that right?

6. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Okay, slow down a bit....

Look through the link I provided earlier on series and parallel circuits.

15 2or3V LEDs in parallel will have a voltage drop of 2or3V total, and draw 10or20 X 15 = 150or300 mA.

15 2or3V LEDs in series will have a total voltage drop of 30or45V and draw 10or20 mA of current.

Either way, we need to limit the current through each LED to keep it from burning up. We do this with a resistor, called a "series limiting resistor" because it is wired in series with whatever it is limiting the current to.

To choose the most sensible combination of series and parallel LEDs, we have to first decide on the supply voltage. This means we need to decide on a specific battery or combination of batteries. Or a plug-in supply, sometimes called an "adapter" or more erroneously a "transformer." (Adapters do have transformers in them, but calling one such is like calling your car an "engine.")

7. ### Audioguru New Member

Dec 20, 2007
9,411
896
I think you need a gasoline engine powered generator to power all those LEDs continuously all night long.

My Ultra-Bright LED Chaser projects blink 10 LEDs in sequence brightly for months when powered from 2 or 4 AA alkaline cells. Because they blink each LED for only a moment and rest for a long time in between blinks.

Mar 24, 2008
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9. ### samrozzi Thread Starter New Member

Feb 10, 2009
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thanks bill. reading guide i hope it helps. I am wondering if its possible to just be able to plug it into the wall? like a night light? is their such a adapter?

and im reading this guide hoping to find something i udnerstand lol. hoping to see a picture i can go after

10. ### samrozzi Thread Starter New Member

Feb 10, 2009
5
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and also if a wall power supply is to hard. maybe just have an on/off switch so it can stay on for 5-6 mins at a time?