DIY Christmas lights: Modify - Convert 120VAC set of LED lights to 24VDC PART 2

We'll continue the conversion of a 120VAC set of LED lights to operate off 24VDC.

Step 2

Now we have to divide the 30 series LEDs into 6 parallel lots of 5 series blue LEDs AND get the polarity right! Also we must find the existing resistors (for 120V) and remove them. This is easy to do if you carefully follow these instructions.

The letters show ends of series LED group; X shows the cutting spots.

Note: if the light string does not have an extension socket:

wire in a new A supply wire and connect to first LED at A (red wire);
wire in a new C supply wire and connect to last LED at C (black wire). See Step 2 diagram;
if wanted, continue these 2 wires to a new DC extension socket, as shown.

How to divide the 30 series LEDs

Get some masking tape and attach a label at LEDs: 1, 5, 10, 15, 20, 25, 30.

Now on the wire between 5th and 6th LED, attach a label marked C next to 5th LED; attach a label marked A next to 6th LED - see Step 2 diagram.

Repeat this between:  10th LED label C, 11th LED label A
                                    15th LED label C, 16th LED label A
                                    20th LED label C, 21st LED label A
                                    25th LED label C, 26th LED label A

Now carefully trace by hand down the supply wire from LED 1 [red wire in diagram] (not the series wire) down to the extension socket. When you arrive at LEDs 5, 10, 15, 20, 25, attach a label A at each spot.

Now carefully trace by hand down the supply wire from LED 30 [bold black wire in diagram] (not the series wire) down to the 120V plug. When you arrive at LEDs 25, 20, 15, 10, 5, attach a label C at each spot.

What you have done is divided the series lights into groups of 5 series LEDs and prepared to make 6 parallel lots - see Diagram Step 3.

Photo shows labelling before joining

Before cutting, I suggest checking the above labelling is absolutely correct against the Step 2 diagram. The above process will give correct polarity connections.

Find the existing resistors

Carefully look at each LED to see if a resistor was soldered to the leg of a LED. The photo shows a typical connection (one with insulation; one after insulation was removed).

For each resistor: You will have to cut off insulation, unsolder resistor, slide on insulation tubing, solder a wire extension onto LED, position tubing over join.

Step 3

Now it's a simple process to cut the series wires at X, and connect label A wires to adjacent A supply wire at LEDs 5, 10, 15, 20, 25. Repeat for label C wires to adjacent C supply wire and install resistors. See diagram and below for details.

How to do this:

It's less confusing to only cut one series wire and join it to supply wires one set at a time. To do this:
• Cut series wire between the 2 labels, eg LEDs 5 - 6. Strip each wire 12mm.
• Cut one supply wire, say A label and strip each wire 12mm. Slide on 6mm insulation tubing onto 1 supply wire.
• Twist the 3 A wires together and solder. Slide tubing over the join.

• Cut the supply wire label C and strip each wire 12mm. Slide on 6mm insulation tubing onto 1 supply wire.
• Solder a 330 Ohm resistor to C wire. Slide insulation tubing over the resistor and wire.
• Twist the 2 C wires and resistor lead together and solder. Slide tubing over the join.

Repeat above for each pair of LEDs, ie 10-11, 15-16, 20-21, 25-26. See photos for more info.

Photo shows correct joining of wires

For 120VAC supply
Also connect the transformer to the bridge rectifier's AC wires. This connection must suit the type of terminals on the transformer. You may want to:
• extend the wires between transformer and bridge rectifier to keep the transformer within shelter;
• if necessary, cut off the extension socket and change to a DC socket which suits your needs.

For 24V battery supply
Connect a 2A fuse holder to positive terminal of battery then connect it to one AC wire of bridge rectifier; connect other AC wire of bridge rectifier to negative terminal of battery. The bridge rectifier ensures the correct polarity DC is connected to LEDs.

Testing

Check the tubing covers each joint then energise the lights! Since it works, heat shrink the tubing and use cable ties to stress relieve the soldered joints.

HEelpp!!

one series group is dull: check again if an original resistor was not removed. It's resistance is too high and severely limiting current;
One series group does not light: check quality of joins and if the LED polarity is the same as other groups. If different, reverse the first and last connections to supply wires.