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### Topic: Power supply for my LED modules (Read 2409 times)previous topic - next topic

#### long_p1

##### Aug 14, 2011, 02:27 am
Hi, I hope someone can help me with this.
I'm a newbie to electonics, Ardiuno & ect but have been swatting up as much as possible whilst playing with my Uno.

I have some LED modules, 6, each with 5 Pirahana LED's so total of 30 leds, which i believe runin parrell, thay are basiclly these http://uk.farnell.com/jsp/displayProduct.jsp?sku=1693865&CMP=e-2072-00001000 in white.

I get the basic mathmatics of ohms law but cant figure out if a DC power supply i have laying about will power/blow these.

The string is 12volts & 6watts(1watt each) & (500mA?) in total, The power supply I have is AC/DC Adaptor, input:230-240v (UK) ~ 50Hz 150mA. Output:12v but 600mA (7watt?), 7.2VA. Will this supply work or can I get it to work (add in resistor/potentiometer?) .
In the sort term I just wanna check the LED's are working ect.

Hopefully someone can help me out and the law may then sink in finally!

Cheers

Paul

#### long_p1

#1
##### Aug 14, 2011, 02:50 am
There doent seem to be a datasheet for them but here are the items http://www.ebay.co.uk/itm/Car-Boat-30-LED-White-Superflux-Light-6-Module-String-/280721768121?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item415c523eb9.

Sorry, I think they are in series? They are already connected in a string and yes I wan them all them all to come on simultaneously.

P.s. How do I draw a diagram? Just use a basic art package?

#### long_p1

#2
##### Aug 14, 2011, 02:52 am
I should say connected in a continuous chain, one after the other.

#### long_p1

#3
##### Aug 14, 2011, 03:07 am
Does this help?

Thanks for your help and patience.

Paul

#4
##### Aug 14, 2011, 03:59 am
If you put 12V on the end of 1 string, do you have 12V on the other end too? That would tell us the strings are all wired up in parallel, so you need 12V & about 500mA of current.
6W/12V = 500mA.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Catcher

#5
##### Aug 14, 2011, 04:12 amLast Edit: Aug 14, 2011, 04:33 am by Catcher Reason: 1
I checked your ebay source. 12 volts at 6 Watts means 500 ma of current is needed (MAX). You have 6 modules with 5 leds each so thats 30 leds. 0.2 Watts per led. It would seem from the pictures that the leds are wired in parralel, meaning that they all get 12 volts and fight over amps. So voltage dropping isn't a problem. 0.2 watts/12volts gets you 16mA.

So if you're going to power all six, then you need 12 volts at no more than 500ma. If you're going to power one module, you need 12 volts at no more than 83 mA. If you're going to power one LED you need 12 volts at no more than 16mA.

EDIT: see next post.

-Catcher

#### retrolefty

#6
##### Aug 14, 2011, 04:19 am
Quote
For your 12 volt 700mA power supply, i would just use a 20 ohm resistor or greater. i would use 100 ohm just to be safe.

V=IR
P=VI

What are you saying? No need for any external resistors, that would only hurt by lowering the applied voltage to the modules. The modules are designed to be wired to a constant 12vdc voltage. The modules take care of current limiting for the leds inside the modules. A 12vdc @ 700ma power supply should power all the modules.

Lefty

#7
##### Aug 14, 2011, 04:25 am
Catcher,
I think the Piranha LED are already wired in series within the module with a resister, as Piranha LEDs drop 2 to 2.5V each.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### retrolefty

#8
##### Aug 14, 2011, 10:15 am

We're all just wasting our time shooting in the dark without any definitive information about the mystery LED modules.

Well the OP did link to where he bought them, and from the description given there, it seems a pretty simple wiring job to me, 12vdc to as many modules that you want to string together.

http://www.ebay.co.uk/itm/Car-Boat-30-LED-White-Superflux-Light-6-Module-String-/280721768121?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item415c523eb9

#### long_p1

#9
##### Aug 14, 2011, 12:53 pm

We're all just wasting our time shooting in the dark without any definitive information about the mystery LED modules.

Well the OP did link to where he bought them, and from the description given there, it seems a pretty simple wiring job to me, 12vdc to as many modules that you want to string together.

http://www.ebay.co.uk/itm/Car-Boat-30-LED-White-Superflux-Light-6-Module-String-/280721768121?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item415c523eb9

WOW, Thanks for the responeses guy & maybe it wasnt as stupid question as I thought.

They came prewired in the string of 6.
"I checked your ebay source. 12 volts at 6 Watts means 500 ma of current is needed MAX" + "For your 12 volt 700mA power supply, i would just use a 20 ohm resistor or greater. i would use 100 ohm just to be safe."
So adding a resistor will "draw down" (bad terminology?) the 700mA to under 600mA making it safe for the lights?
Will a standard 1/4 100ohm resistor be ok? Also, I just wire it in between power supply & 1st module?

Again massive thanks, I',m trying to read as much as I can but just couldnt find a direct answer to these questions & dont really wanna start a fire (or electrocute myslef) or anything ;-).

Also sorry my camera isnt working otherwise I could just post decent pics!

#### long_p1

#10
##### Aug 14, 2011, 01:38 pm
I also have a digital Multimeter (still dont really know what im doing with that either!0
but when I connect it at either end of the string/lights on 200ohm  I get a read out of 00.8 wether connected to pos/pos or neg/neg.

Paul.

I also know you can string more of these together on with a 12vDV power supply.

#11
##### Aug 14, 2011, 05:15 pm
"They came prewired in the string of 6. "
I believe you can just hook them up to 12V then, and they will draw about 500mA of current.
Adding a resister in series will only reduce the available voltage and then they might be dimmer, or might not all turn on.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### retrolefty

#12
##### Aug 14, 2011, 05:34 pm
Quote
So adding a resistor will "draw down" (bad terminology?) the 700mA to under 600mA making it safe for the lights?
Will a standard 1/4 100ohm resistor be ok? Also, I just wire it in between power supply & 1st module?

Forget the resistor, not needed, will only hurt. The modules will draw what current the require and no more. You could use a 12vdc power supply rated at 12 thousand amps and still only 600 ma would be drawn from the supply. At your home your typical AC power outlet is rated at up to 12 amps but you can still power a little 7 watt lamp, right?
The 12vdc power source just must be rated for at least 600ma, a little more (1 amp) give the power supply a little breathing space, got it?

Lefty

#### long_p1

#13
##### Aug 14, 2011, 10:30 pm

The other end of the chain will connect to nothing so if I just "cap" them off?

I will test them now, see what happens & post the result.

As a matter interest, how would you burn the LED's out? Over voltage?

Thanks again for your time & patience guys.

#14
##### Aug 14, 2011, 10:33 pm
Yes, overvoltage would lead to increased current, leading to overheating & burning up.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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