LED Light Repair

[zooo]

I have three sets of LED lights that have half the set out. The LED keeper points to a 3-wire LED on all three sets. When I pull out the 3-wire LED, it tests fine on all 3 sets. Are these 3 sets repairable?

[Dennis Cherry]

Does the bad string have a module on the string before the LED you tested? You can have one or two modules per string, which do you have?

The module may be bad.

 

Edited December 27, 2018 by Dennis Cherry

[~DOC~]

On 12/27/2018 at 7:49 AM, Dennis Cherry said:

Does the bad string have a module on the string before the LED you tested? You can have one or two modules per string, which do you have?

The module may be bad.

 

I have the resistor in a little pack. 1 light out before it and all the others out after it until you get to the next resistor. Have three strings like this.

Edited January 5, 2019 by ~DOC~
Correction

[TheDucks]

28 minutes ago, ~DOC~ said:

I have the resistor in a little pack. 1 light out before it and all the others out after it until you get to the next resistor. Have three strings like this.

I hve some strings with the resistor bulge at the OUTLET end.  So verify that your string starts with a resistor. Technically, it can be anywhere in the section. Section separations only have 2 wires (hot and neutral)

[rcktpwrd]

I had a few strings that were half out like that, so I cut them up and connected the good parts together... then kept the remaining good bulbs as spares.

Edited January 6, 2019 by rcktpwrd

[~DOC~]

These are holiday time lights. All my lights have been repaired and packed except these three strings. They each have 5 resistors per 30 leds. 1 Led is before the resistor. Total 150 leds.  

[~DOC~]

My thing is the resistor figuring out the size.  I would rather Fix it.  Just call it my OCD getting the best of me. 

[beeiilll]

I use this to repair and modify my LED strings.  Not sure if it will help but will post it for the FYI factor.  This is part of a pdf that I found years back on modifying LED strings but the forum here won't let me post the pdf.

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 peak 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
5. Here is a link to a handy online calculator which I use:
http://www.horrorseek.com/home/halloween/wolfstone/Lighting/litlec_LEDCalc.html
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 the number of 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.

LED Colour	Forward Voltage Vf	Forward Current If
White	3.2 V to 3.8 V	20 mA to 30 mA
Warm White	3.2 V to 3.8 V	20 mA to 30 mA
Blue	3.2 V to 3.8 V	20 mA to 30 mA
Red	1.8 V to 2.2 V	20 mA to 30 mA
Green	3.2 V to 3.8 V	20 mA to 30 mA
Yellow	1.8 V to 2.2 V	20 mA to 30 mA
Orange	1.8 V to 2.2 V	20 mA to 30 mA
Pink	3.2 V to 3.8 V	20 mA to 30 mA
UV	3.2 V to 3.8 V	20 mA to 30 mA

[tlogan]

Thank you, beeiilll !!

I've been trying to figure out if it was possible to create a 10 LED string (several, actually) to swap out the incans in my old-school candy canes.  I've read several versions of what you posted, but all of sudden after reading yours, it clicked. I think I can do it, now!

I don't know what the hold up from manufacturers is in making/marketing these individual candy canes with LEDs instead of incans. I see several versions of candy canes with LEDs but they are sets of 3 or more all connected together. Makes it hard to control each one individually, like I can with the incans.  

 

[k6ccc]

Great reference Beeiilll

If you have the ability to measure the current before you start, I would recommend it - works better for a modification as opposed to a repair.  That also is especially handy on multi-color strings as it helps to avoid errors due to variations in LEDs