Features

Expandable to 240W or 480W (depending on power supply limit)
4 modes: Red; blue; red and blue; green
Red and blue LEDs for growing plants
Green LED suitable for viewing plants at night without disturbing them
Controlled with lamp timer

Step 1: Tools and Materials

Tools

Tap wrench
M3 tap
#6-32 tap
assorted drill bits (with 2.5mm and #36 bits)
center punch
drill driver
soldering iron

Grow Light

1 x ATX power supply
PC chassis (with drive bay removed)
1 x 120mm case fan or 2 80mm case fans
1 x 5V power supply
1 x outlet timer
1 x strip board
thermal paste
2 x 1N4001 diodes
8 x IRFZ44N N-channel MOSFETs
9 x 2N3904 NPN transistors
8 x 100k resistors
8 x 0.82 ohm 1W resistors
2 x 10M resistors
1 x 10k resistor
2 x 1k resistors
2 x 3 ohm 2W resistor
16 x 3W deep red LEDs
12 x 3W royal blue LEDs
1 x 3W green LED
8 x 4 LED aluminum base plates
1 x 2.1mm panel mount jack
1 x DPDT on-off-on rocker switch (2A)
3 x push button on-off-on DIP switches
lead free solder

Fasteners

10 x M3 x 10mm screws
10 x M3 nylon washers
10 x M3 split ring washers
6 x sets of M3 nylon stand-offs
4 x #6-32 x 2 1/2" screws
4 x #6-32 x 2" screws
4 x #6-32 cap nuts
4 x #6-32 nuts
8 x #6 split ring washers
4 x #6 flat washers

Step 2: LEDs Soldered to 4 LED Aluminum Base Plate

To save space on the heatsink and simplify wiring, solder the emitters to a 4-LED aluminum base plate with thermal paste on their cooling surfaces. For a 12V power supply, each base plate can have up to 3 blue LEDs or four red LEDs.

Step 3: Heatsink Marked for Drilling

Mark the heatsink for mounting its parts and indent the marking with center punch. I used an aluminum CD rack as the heatsink.

The tap and drill bit sizes are:

3mm and 2.5mm for the LEDs and circuit board
#6-32 and #36 for the fans, stands, and air deflectors

Step 4: Heatsink Drilled and Tapped for Fans

Step 5: Heatsink Drilled and Tapped for LEDs

For maximum cooling, install the base plates so that the LEDs are directly above the heatsink's flat surfaces. I used M3 x 10mm screws, nylon washers for insulation, and split ring washers.

Step 6: Heatsink Drilled for Cable Ties

The cable ties will be used to hold the LED's wiring.

Step 7: Heatsink Drilled and Tapped for LED Driver

To keep the wires short, I mounted the circuit board on the heatsink. Nylon standoffs were used because they are non-conductive.

Step 8: Heatsink Drilled and Tapped for Stands

The LEDs are delicate so the four #6-32 x 2" screws serve as a stand to protect them while you are working on this project.

Step 9: Heatsink Drilled and Tapped for Air Deflectors

The air deflectors increase the airflow through the heatsink. You can use them if the heatsink is too hot or more LEDs are used.

Step 10: PC Chassis Drilled for Mounting and Ventillation

Drill the chassis for the toggle switch, DC jack, ventilation, and grow light mounting screws.

Step 11: LED Driver Circuit

In this circuit, LED drivers were used for four strings of deep red LEDs and four strings of royal blue LEDs which were the wavelengths growing plants. Only two strings were shown to simplify the diagram. SW3 controls the blue LEDs and SW4 controls the red LEDs which uses the +12V rails. The current limit is around 15A. Some PSU's even have dual +12V rails for higher output! The +5Vsb rail is on during standby and allows the green LED to be used at night. Plants do not detect green light as daytime and is less dazzling for viewing your plants. All three wavelengths of LEDs have their own fuses.

An external 5V source can be plugged in to a 2-prong lamp timer to control daylight hours. Some plants depend on daylight hours for flowering. Turning on SW2 or supplying 5V through the DC jack turns on Q1 which shorts PG-ON to ground.

In the zip file, I have included the ExpressPCB files with a printable sample for the stripboard.

ATX grow light.zip
Download

Step 12: Stripboard Track Cutting

Step 13: Soldered LED Driver Circuit Board

For the strip board sample, I used green lines for the wire connections, red lines for the copper cladding strips, red circles for the stand-offs, and red squares for the track cuttings. To solder the ATX connector which has 18AWG wires, the mounting holes need to be enlarged by drilling. SW1 and the DC power jack will be screwed to the case.

Step 14: Soldering the LEDs

Step 15: LED Base Plates With Thermal Plaster

Step 16: Hot Glue As Wire Strain Relief

Step 17: Rewiring the ATX Power Supply

You will need the wires +5Vsb (purple), +12V (yellow), 0v (black), 3.3V (orange), 3.3V sense (thin orange or brown), and PG-ON (green). You should keep two or three sets of connectors to power more grow light units in the future. The remaining wires can be clipped. The 3.3V wire must be connected to its voltage sense wire.

Modify a four pin connector so that:

One black wire is connected to PG-ON
One black wire is connected to 0V
One red wire is connected to +5vsb (not +5V)
One yellow wire is connected to +12V

For the expansion connectors, you only need the +12V and 0V rails.

Step 18: Rubber Washers for Spacing the Fan

To keep the fan from touching the chassis while running, space it with 4 washers. Use #6-32 x 2 1/2" screws for the fan. It will be used for attaching the grow light to the chassis. With only one 120mm fan, the heatsink did not get too hot.