LED Christmas Village lighting help needed!

[SandiH]

Background: My husband paints our Christmas Village buildings. We add 5-6 new buildings each year. Currently we have about 100! The lighting systems they have for villages require night light bulbs and lots and lots of plugs and electricity. I'm done with that crap!

My idea: Using 3w warm white LED's(still waiting for them to arrive, so no idea on volts or amperage yet) set up a series circut with as many LED's as possible connected with white bell wire and plugged into the wall with as few plugs as possible. Saving money, electricity and my sanity! Not to mention making the whole display look nicer.

Help I need: I can solder. I can do math. But, what I need is 1) The equation/details to figure out how many lights can be in a series and what size resistor(s) I need. 2) Can I run several series strings and attach them at the end just before a plug and have multiple lines out with one plug? 3) Advice on what kind of adapter to use to plug into the wall (I have some model train power packs, but I'm new to this and not sure how those would work just yet with this). Fir instance, can iigo purchase a plug that is designed for something like this or can I just run down to Goodwill and buy an adapter from some electric something or a universal adapter of some sort and make it work? And in either case, what should I be looking for? (As in voltage, wattage, amperage or variable? Or does it matter? An 4) If I have lost my mind and this is a worthless cause, please tell me!

I know I am asking a lot, but I know it can be done! I just don't know where to begin. It has been 30 years since I played with this stuff. And I'm not really sure that high school counts!

Thanks in advance for any assistance you can give.

Sandi

 

[kellys_eye]

Chose a power pack that can deliver AT LEAST the wattage total of the LEDs you plan to use i.e. 30 LEDs at 3W = 90W so you need a power pack that can deliver at least 90 (I'd advise getting one that is 50% larger than the intended consumption) so around 120W. Old laptop power packs ar egood for this purpose, easy to obtain and cheap if you know where to ask - try your local PC repair shop.

The output voltage is irrelevant as this can be countered for with the series resistor calculation.

You can wire the LEDs as series/parallel combinations - series up to the total voltage of the power pack (with a little overhead) so based on each LED taking 3V and a 19V laptop power pack you could put 5 or 6 in series (15V or 18V total) and fit a resistor using:

R = (V_supply - LED_{total volts in series}) divided by LED current (usually 20mA) so 0.02. Oops, the 3W LEDs will draw 100mA each!!!

For 5 LEDs (15V and laptop PSU of 19V this gives (19-15)/0.1 = 40Ω. Nearest 'real world' value would be 47Ω. Resistor WATTAGE would be (I²R) therefore 0.1 x 0.1 x 47 = 0.47W so any 1W resistor would suffice).

Other combinations of LED would require simple adjustment of the calculations.

The 5 LEDs in this example total only 15W so you could parallel 6 strings (identical) before encroaching your 90W limit.

Remember to observe the LED polarities when wiring in series (positive to negative to positive etc).

 

[BobK]

Agree with @kellys_eye, using mains directly would be dangerous, especially with something kids would be around and probably want to examine.

Bob

 

[SandiH]

Thank you so much! This is exactly what I needed! It will take a little effort, but this is going to make the village so much nicer!!!

I really appreciate your help!