Hi,

This is my first electronics project and I am seeking validation for my assumptions. I'm planning to build a LED grow lamp from 3W beads (FV 3.6, 700mA) set up on an aluminum casing. The LEDs themselves will be soldered to connection strips that I will stick to a 5mm (0.19 in.) thick aluminum plate (bottom of the casing 575mm x 400mm or approx. 22.5 in. x 15.5 in.) with thermal tape. The strips hold 10 LEDs each and I plan to put 10 of those strips on a box, for a total of 100 LEDs (please see schema attached). The strips will be wired in parallel (with 18 AWG solid copper wire) and connected to a constant voltage (36V) switching power supply (built for LEDs). I plan on protecting the power supply inside the casing, above the LEDs plate, jacked on two pieces of aluminum so it clears the plate by about 10mm (0.39 in.). Vertical space inside the casing is 120mm (4.72 in.). I will cut openings on both ends of the casing and set three cooling fans (60mm x 60mm, each is 12V, 160mA) in the holes of one of those ends. The power supply is 400W and has 3 outputs. I plan on using one output for the LED array and a second output for the three fans. My assumptions are as follow:

• A 400W power supply will safely provide for both the LEDs (252W) and the fans (6W).
• Three fans should generate adequate airflow to keep both power supply and LEDs in a safe temperature range.
• The different outputs of the power supply can provide different currents (7A to the LEDs and 480mA to the fans).
• A one Ohm resistor at the end of each LED connection strip should be sufficient to protect the lights.

Did I get anything wrong?

Thank you in advance.

 

Looks OK assuming the fans are powered by a separate 12 volt output on the power supply.

 

Looks OK assuming the fans are powered by a separate 12 volt output on the power supply.

Thank you for your reply.

What if I connect the fans in series instead of Parallel? The second output could then be 36V?

 

What if I connect the fans in series instead of Parallel? The second output could then be 36V?

That would work but if one fan opens up then other two will also shut down. The same for the LED strips.

 

That would work but if one fan opens up then other two will also shut down. The same for the LED strips.

Right.

Thanks!

 

For a safer design, I decided to add a small 12W power supply in order to keep the fans in parallel. My main power supply could not send 12V from one port. I will now try to find a design to shut down the LEDs' power supply if ever the fans' power supply fails. Thanks.

 

I will now try to find a design to shut down the LEDs' power supply if ever the fans' power supply fails.

Connect the LED supply through relay contacts. Use a 12 volt relay coil powered by the Fan supply.

 

Have you compared your heat-sink arrangement with what is suggested in the application data from some of the companies that produce high powered LEDs? That is a chaep and easy way to gain a lot of good information.

 

@sghioto: Thanks again, you saved me research time and headaches!

@MisterBill2: Thanks for the tip. I have checked with some online heatsink calculators, but I will take a second look at the data sheets.