Simple Homemade Led Strings

Overview

Have you ever wanted to start going led but after looking at the prices, you have a hard time like me spending the money? Well with the help of tonypgst who posted the original word document on the full wave rectifier, i was able to create my own strands of lights. I did this using 100 ct mini lights, leds, diodes, and resistors. It really is easy and very cost effective way to go led if you have the time and patience to solder every led. So this page will be filled with all the useful info you will need to make your own led strings. i hope to make this the best page to find the info. i have spent 2 years trying to find out how to do these and im glad i finally found out how. So i hope i can help some out.

How it Works

Doing this method allows you to connect these led strings directly to standard 110v SSR's. This is very nice b/c it is alot easier to power an you do not need to have seperate power blocks to run. I will touch on this a little later in pros and cons. Since LEDs only run on DC they will not work on standard AC without a rectifier or an adapter with DC output. The simple rectifier on each end allows the leds to be full wave and feed it the direct current it needs to light. Since the leds act as resistors themselves it allows you to run a much smaller resistor on each end of the diodes to allow you to safetly run them on AC power.
With this method you will also be able to piggy back string to string. So this is a very nice feature because most strings you will only be able to do so many per string. So some of your strings will only be 34 leds long, you will need longer so you can just add to it to make it longer until you reach your max amps per channel.
More to come in this section

Calculating your Resistor Values

You will need resistors at the end of each diode. To figure out your resistor value you will first need figure out your needs for each string. Heres a list of questions you need to ask yourself before you find out what you need. I hope to have a Excel sheet soon to allow you to input your values and figure out what you need.

1. What color are you going to use? You need to know this b/c each color has a different voltage. This will determine how many you can have per string. IE - Blue is 3.4, Red is 2.0

2. How long will the string be? If you wanting to use any less than the max you will need to know how many. You will input this as this is the biggest determing factor on the resistor value.
There are a few more i will be adding.

Here is some info from tonypgst's write up he did to modify a manufactured led strand. You can use this method if you do not want to use an online calculator.

LED Calculations

1. Peek Voltage - Peek voltage out of the full wave rectifier from 120VAC RMS equals 170V minus the voltage dropped by the diodes. This would result in about 167V.
a. Rounded voltages, 120VAC *1.414 = 170V.
b. 170V - 2.8V = 167V
2. LED Voltage and Current
a. Voltage varies by manufacturer and color for LEDs. The most common current is near 20mA. You must look up the specifications for your LED string.
b. In my examples below, I’ll be using: Red = 2.0V, 17mA or 0.017A
3. Resistor Calculation (Example using a shortened string of 26 Red LEDs.)
a. Calculate voltage drop of LEDs
i. 2.0V x 26 = 52V
b. Calculate peek voltage minus voltage dropped by the LEDs
i. 167V – 52V = 115V
c. Calculate Resistor(s) needed to drop remaining voltage
i. Ohms - 115V / 0.017A = 6.764KOhm (Use next higher standard value, for example, 8.2KOhm)
ii. Watts - 115V * 0.017A = 1.955Watt (Use a minimum of 2 watt resistor)
4. Rectification – You will need 4 diodes per string to make the full wave rectifiers.
a. I use 600V/1A diodes. Mouser part number 821-1N4005
Limitations: This example does not utilize any voltage doubling circuits. You are limited to using the number of LEDs that add up to or just below 167V. For example, I could build a string using a maximum of 83 Red LEDS which drop 2.0V each. This would utilize 166V of the available 167V. Other LED colors drop higher voltages. For long strings, you must divide the string in half and build full wave rectifiers for each section.
Tip: When purchasing resistors, you can use one or more. Rather than just using the one 8.2KOhm resistor, you could use two resistors, one on each end that adds up to at least 6.8KOhms or just over that value. I’d also recommend purchasing resistors in bulk where you can. I calculated the resistor sizes needed for each of my strings based on number or LEDs and voltage differences based on color. I then purchased resistors with a value common to all of my strings, but within the closest range of my requirements. This allows me to use the same resistors for most strings, and I commonly only use two different resistor sizes. For example, I have purchased both 3.6KOhm/2watt and 2.7KOhm/2watt resistors for all of my strings. I may use one, two, or a combination of these values depending on my needs.