Introduction: 84W PC Chassis LED Grow Light
Second Prize in the
Hydroponics and Indoor Gardening Contest
- 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
- Tap wrench
- M3 tap
- #6-32 tap
- assorted drill bits (with 2.5mm and #36 bits)
- center punch
- drill driver
- soldering iron
- 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
- 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 Aluminum Base Plate
Most 3W LEDs are soldered to 1-LED base plates. 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 4 red LEDs. The LEDs from the beads must be desoldered from their original base plates before soldering them to 4-LED base plates.
Step 3: Heatsink Marked for Drilling
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 heat conduction, the base plates should be positioned so that the LEDs are directly above the heatsink's flat surfaces. The screw sizes for the LEDs should be M3 x 10mm. Nylon washers are used to prevent shorting and the split ring washers keep the screws tightened.
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
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.
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
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.
Step 19: Cable Ties for the ATX Connectors
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