Making a Cheap LED PAR Light Safe and Quiet

I have bought some cheap LED reflectors for my band from e-bay. It was called "4PCS 36 X 3W LED PAR STAGE LIGHT DMX-512 DJ LIGHTING COLOR CHANGE AUTO STROBE". The price was around 32 EUR / 1 light. So I risked it and purchased.

The lights worked out of the box, but were also giving a quite loud sound coming from a fan cooler. Adding a heat sink would allow better heat dissipation and lower fan speed.

So I opened the case and spotted that the ground wire was not connected to the metal case. This means a serious flaw in safety. I would certainly not recommend using these lights without modification. The CE label is there, but for sure the safety requirements are not met.

I have decided to modify the lights by adding passive cooling (heat sink), lowering the fan speed and definitely connecting the case to the ground.

Check the video for difference in the sound of the original and light modified according to this instructable.

I wouldn't recommend buying these lights, but this instructable could help you if you already have some.

Skills required:

• electrical
• metal drilling, cutting, or alternatively gluing a heat sink

Tools required:

• phillips screwdriver
• flat screwdriver
• utility knife
• soldering iron
• hot glue gun
• saw for metal (to cut the heat sink, if needed)
• nut tap for 3 mm thread (for heat sink mounting)
• drill with a 2.5 mm drill bit (drill a hole in the heat sink)

Bill of material:

• 1 screws 4x6 mm
• 1 nut 4 mm
• 2 cable eyes 4 mm
• 4 screws 3x6 mm
• 30 cm wire at least 1 mm cross section (for connecting ground)
• 1 resistor 180 Ohm, 2 W or more
• heat conductive paste
• 2 heat sinks (my final dimensions were: 40 x 98 x 15 mm)

Warning: This project requires certain knowledge in electricity. Make sure to unplug the socket when working and discharge the capacitors at the power supply, which may keep dangerous voltage even after disconnecting the power. If you do not know what a capacitor is, I suggest to have an electrician friend to help you.

• Unscrew all visible screws and open the case from both sides.
• Disconnect the connectors from the PCB
• Loosen the power cable gland
• Unmount the power supply board from the LED board

• There have already been holes suitable for mounting the heat sinks in the LED. If you decide to drill new holes in the board, be careful - there are circuits on the board, which are likely to be damaged. You could also decide to glue the heat sinks. I did not know about a good glue to do this, so I just used threads and bolts.
• Prepare the heat sinks - cut it into appropriate dimensions, so they fit inside between the LED module and the fan. My dimensions were 40 x 98 x 15 mm, the distance between the bolt holes was 67 mm in my case.
• Measure and drill the 2.5 mm holes into the heat sinks at the appropriate places. Tap 3 mm threads.
• Apply the heat conductive paste
• Mount the heat sinks in place using 3x6 mm bolts.

Probably the simplest method is to add a series resistor.

• Cut one of the wires close to the fan motor
• Mount the 180 Ohm 2 W resistor in a way that the fan will be cooling it
• Solder in the wires to the resistor

The power supply gives 24 V DC. I have chosen the 180 Ohm resistor by experiment. The voltage over the resistor was around 15 V when in series with the motor, so the dissipation power from the resistor is 15 V * 15 V / 180 R = 1.25 W. So it gets warm during the operation, but will do.

The fan starts OK and runs quiet.

• Cut appropriate cable lengths (about 10 cm and 20 cm to reach the power supply)

• Solder them to the ground (yellow-white) of the power cable

• Solder the wire eyes to the wire ends

Scrape off color around hole for ground connection, for example using a flat screwdriver

Connect the ground wire using the 4 mm bolt and nut.

• Connect the ground at the power supply base (use one of the existing bolts)
• Use heat glue gun to fix the power wires leading to the power supply

Mount the power supply back to the LED module

• Mount the LED board with the power supply back to the can
• Replace the light reflecting plastic parts, if they do not fit because obstructed by the bolts, cut them a little to make it fit
• Reconnect the connectors to the PCB and tighten the power cable nut
• Mount the back panel

I have tested the modified LED light at full power (R = G = B = 255) for several hours. It heats up a little more than the unmodified one (measured temp. around 43 °C at the heatsink, the unmodified has 37 °C at the LED panel at ambient 20 °C). I think it is not a problem. If you do, you could use a slightly lower resistor value to make the fan turn faster.