Heat management for Arduino light control system

Hi All,

I’v been working on a light system for my reef aquarium and have a question regarding heat management for my arduino control unit…

The system is designed as 8 separate units, each made of a high-power LED, a 12VDC fan and a DS18B20 onewire temp sensor. the LEDS are driven by a dedicated power driver which takes 120VAC and outputs dedicated voltage (42VDC) at ~ 2A each…

To control these units I have built a small project made of an arduino mega 2560, 2x 8 channel relay boards (rated at 10A 240VAC) and a CC3300 Wifi sheild.

The LEDs and drivers get 120VAC from a dedicated line which is only connected to one of the 8 channel relay boards (opto isolated) and the Arduino, relays and fans are driven by a dedicated 2A 12VDC power supply.

Initially I was having overheating issues that were because i was running the arduino from 12V and the voltage regulator was really not liking it… I first tried to compensate by putting a spearate LM317 based cictuit but that just moved the problem to that unit instead…

At the end I switched to a buck dc stepdown driver to move from 12V to 6V which handles the heat much better… also one BIG mistake i made was to feed the relay boards 5V from the arduino which ended up consuming 1.5A between 16 relays and the Wifi shield… once i moved the relays out of the Vin pin and into a dedicated line from the buck driver the usage on the arduino dropped to 175mA and its heat management is much much better…

Currently i have one issue still outstanding… My buck driver is running at average 110 degrees F which i think is OK?.. But the relay boards are generating a significant amount of heat… the relays which controls the 12VDC fans are around 125 degrees F while the relays which control the LED drivers (120VAC) are around 145 - 150F after running 5-6 hours straight… thats when running with the control unit box open… If I close the lid the heat ramps up faster even…

Im wondering if there are any options other than making more air space + fans to cool down the relays as the run?

Im attaching pictures of the control unit and the buck driver unit (PSU) - the control unit box is divided into 3 chambers… first is the 120VAC input + wiring, then in a separate chamber are the two relay boards stacked on top of each other… bottom one is the 120VAC relays (which might have been a mistake now that I think about it) and on top is the 12VDC fan relay board… the last chamber is the arduino + 12VD power input…
thx!

etay

I don't see any ventilation holes to let cooling air in and out, without them the fan motors are just heaters.

If you are referring to the small box with the buck driver and fan in it - then the air vent holes are under the fan (output) and behind the buck driver heat sink (input) - they are not visible in the picture but they are there...

The main unit box does not have cooling fan on it... I didn't plan for the relays to get so hot and so i didn't ventilate it... i am wondering if that will be all it takes to prevent the relays from heating up to 150F? just more ventilation?

thx!

etay

Metal die-cast box, not plastic.