I am trying to make an automatic garden gate unlock that runs on a timer. I plan on running an arduino uno 24/7 with a software timer that activates a motor to release a bolt lock. I am going to fit all the electronics and extension cord into a waterproof junction box. Will this cause over heating? Is there a need for some kind of waterproof cooling system? Has anyone ever built outdoor electronics and ran into this problem?
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3Arduinos don't generate that much heat - except maybe the 5V regulator. Use an efficient switching regulator instead of relying on the 5V regulator on board and there will be little to no heat.– MajenkoCommented Aug 18, 2020 at 10:09
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If you do need to actively cool something then use a metal enclosure and thermally connect that component to the casing.– MajenkoCommented Aug 18, 2020 at 10:10
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I wouldn't worry all that much about the Arduino itself, but, depending on what you use, the power supply and especially the motor driver may generate some heat. It won't be on often, or for very long, though. Somebody somewhere could do the math given your exact set-up; speaking for myself, I would just try it and experiment.– ocrduCommented Aug 18, 2020 at 10:32
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@Majenko good point I'll look into that.– MyDisplayNameCommented Aug 18, 2020 at 11:34
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@ocrdu no the motors won't be on often likely twice a day for a couple of seconds, but the arduino will be running always but not performing any tasks until the time– MyDisplayNameCommented Aug 18, 2020 at 11:35
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2 Answers
The linear regulator on an Arduino works by converting excess voltage to heat. If you power it with 12V and draw a full amp from it it will turn (12-5)*1a or 7 watts of power to heat, and quickly overheat even if it's not in a box.
If you power it from 6.5V and only draw 300mA from it, it will turn (6.5-5)*.3, or a little under half-a-watt. While the Arduino is idling it will probably only draw 50mA, so less than 1/10th of a watt of heat.
For infrequent, short bursts of a few seconds you can probably get away with drawing 500mA of power without overheating.
Or skip the internal regulator and use a buck style voltage regulator. Those generate a LOT less heat.
Edit:
For a project I did recently, I used an external 5V regulated supply for everything. I cut a USB cable and soldered the red and black (+5V and ground) to the 5V supply, and plugged that into the Arudino's USB connector. That feeds 5V into the Arduino.
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I normally use a SEPIC converter and low RDSon MOSFETs. I usually set the output of the converter to about 8 volts. I am assuming the motor is powered by another power supply not the one on the Arduino. I typically use the plastic Euro boxes without any problems. Keep it out of the sun and you will be OK.– GilCommented Aug 19, 2020 at 19:18
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"I usually set the output of the converter to about 8 volts." Wait, what? You then feed the converter into the VIN and still drive the Arduino's voltage regulator? Why not set your converter to 5V and use it's output to power the Arduino directly?– Duncan CCommented Aug 20, 2020 at 10:59
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If you use a converter to generate 8 volts and feed that into the Arduino's VIN, you'll still turn 2V to heat.– Duncan CCommented Aug 20, 2020 at 11:52
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Sorry, you'd convert THREE volts (and whatever current is drawn through the Arduino's regulator) to heat.– Duncan CCommented Aug 20, 2020 at 14:40
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Using the Vin adds additional filtering and stability and it is free. I do not like inductive loads or lines leaving the enclosure to be on the same power supply as the microprocessor, they are great antennas. That is a lot less heat with an 8V feed then with a 12V feed. The proper choice of MOSFETS will have a big impact on the heat. Most of my designs do not use heat sinks, Low RDSon FETs cost more but are generally much cheaper for me then installing heat sinks.– GilCommented Aug 21, 2020 at 16:00
The simplest selection is Aluminum water proof box.
You can make it yourself, using aluminum U profiles, and mount arduino heat generator parts on the internal surface of the box.
