Backyard Aquaponics
A place to discuss aquaponics

OK, so its not aquaponics, but I know theres some some electrical guys around.

my wife wants to add some LED's to our christmas tree (a custom, timber, minimalist tree), and after seraching commercial LED solutions, we have decided that we need to wire it ourselves.

so, my questions are:

a) how many watts of driver will we need to run ~110 LED's (5mm white)
b) am I safe to simply wire these in series in groups of 3 with a 270 ohm resistor

is there anything else I need to add to the circuit?

any help would be awesome, my DC electronics is way rusty.

I am assuming you are using a 12v power supply?
How did you come up with a 270 ohm resistor? I would think 100 ohm.
You need to know voltage drop and current draw of the leds.
Normally they are 3v and 30mA.
So, if that is the case, with 3 in series they drop 9v, 12-9=3v to drop across the resistor.
Ohms law v=ir, so in this case 3/.03=100 ohm resistor.
I would recommend a 24v DC power supply, that will run 7 leds in series and still use the 100 ohm resistor.

To work out total current draw, divide total number of leds by the number in each string, times that by the mA of each string.
Your 12v example is 110/3= 37 strings drawing 30mA.
37x.03=1.2 amps.
So use a 1.5a power supply.
Ohms law, p=vi, so 18w power supply.

Andrew.
Ps rounded up where necessary.
Pps typed on phone, sorry for spelling

before you invest too much time into making up stuff, have you checked out www.dx.com ?
Look for "led string" or something.

It might be too late to get something for christmas though, sorry I only just seen this thread

http://dx.com/p/led-string-lights-red-blue-green-10m-23845