noob question: 24 5v led's at 120 vac?

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noob question: 24 5v led\'s at 120 vac?

I guess the title is pretty self explanatory...

Is it possible to to run 24 5v led's in series at 120 vac? Can you run them on ac at all? Do I need a capacitor in line?

What happens if the voltage to the series burps +/- 5v?

Any one done anything like this before? pics? plans? linkage?

thanks

 

[Streak]

Re: noob question: 24 5v led\'s at 120 vac?

Hey Stinky.
Yes this can be done using a bridge rectifier and then connecting the LED's in series.
Take a look at http://hometown.aol.com/xaxo/index.html
for a possible circuit diagram.

Be careful working with mains voltage.!!

My Land Rover Horror Story

 

[**DONOTDELETE**]

Re: noob question: 24 5v led\'s at 120 vac?

streak

thanks your schematic should help me flesh out my idea.

mabey some questions?

in your diagram of the line driven led, (is this a dumb question?)
where is the rectifier? ever build this?

thanks

 

[Streak]

Re: noob question: 24 5v led\'s at 120 vac?

The four diodes make up the bridge rectifier. This is not my circuit but one that I plan on using.
I have built one using only one diode but then it was for only one LED.

 

[**DONOTDELETE**]

Re: noob question: 24 5v led\'s at 120 vac?

Hey Streak, gotta question on this for you.

I'd like to power 4 LEDs (something small and bright, of course) and use them as a sort of "cool computer room" lighting fixture, similar to those halogen light bulb contraptions you see in lighting and hardware stores.

Ideally, something like 4 individual LEDs, each hanging from a ceiling connection by just a thin pair of wires.

Any idea how I would wire such a beast, and now to power this from 120V AC?

Just curious, and wondered if you could help. Thanks, either way.

kirkhere

 

[Streak]

Re: noob question: 24 5v led\'s at 120 vac?

Hey I am no expert but I would do it this way.
Buy one of the variable voltage AC/DC adapters, 110volt in variable DC out 500mA should do. Run your two wires across the room from this adapter.

Solder a resistor to each LED, the value will depend on what voltage you choose to run the system at. At 3.5 volts you would not really need any resistor but better to use one to balance the brightness of the different LED's.
You could rate the system at say 12 volts with the appropriate resistors and then switch the adapter to lower voltages to dim the system. Probably safer that than rating it at say 6 volts and then turning the voltage up to 12 and popping the LEDs!!

Hang the leds from your wires.

Have fun.

 

[**DONOTDELETE**]

Re: noob question: 24 5v led\'s at 120 vac?

Coolio, I can handle this... thanks for giving me the starting point.

Dumb guy question... "Solder a resistor to each LED, the value will depend on what voltage you choose to run the system at." How do I determine resistor values for the LEDs I choose? Point me there and I'll go do the legwork.

Thank you, Streak!

kirkhere

 

[Streak]

Re: noob question: 24 5v led\'s at 120 vac?

Kirk,
Here is the formula

R = (Vs-Vl)/Il

Where: R = resistance
Vs = supply voltage
Vl = LED forward voltage
Il = LED forward current

Typically for a white LED,
V1=approx. 3.4 check specs of led.
I1=20mA for normal or more (say 30mA) if you want to overdrive a little.

So, for a supply of 12v you would need a series resistor of 430 ohm per LED.

Good luck.

 

[Empath]

Re: noob question: 24 5v led\'s at 120 vac?

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