Design considersation for outdoor PCB - Page 1
Forum section: electronics / projects

author: anishkgt
author_rank: Frequent Contributor
timestamp: November 07, 2018, 08:18:07 pm
content: Hi All,I've an idea for a product that would be used to monitor several AC loads if they fail or consume more current and notifu me via a buzzer and if necessary switch on another load running on battery via a 5v generic relay. This would be placed outdoors. What should i consider when designing something like this as in components to be used and there placement on a pcb ?

author: capt bullshot
author_rank: Super Contributor
timestamp: November 07, 2018, 08:30:16 pm
content: You'll have to protect your circuit from moisture, rain and dust. Usually one does this by using an appropriate IP rated enclosure.https://en.wikipedia.org/wiki/IP_CodeDepending on the environment, a conformal coating might be necessary or useful.Then you'll have to consider the operating temperature range of your device, say from "cold nights in siberian winter" to "hot sun in the sahara". Especially sunlight can heat up your device to rather undesirable temperatures, plus the internal heating of the components power dissipation. For example, industrial designs for such environmental conditions use 125°C rated components, automotive also does.If your conditions are tighter specified, often 85°C rated components (industrial standard) will do. These are the typical ratings for semiconductors and similar, other components have other rules, e.g. an electrolytic capacitor rated at 85°C won't stand for a long time if it is exposed to 85°C.

author: anishkgt
author_rank: Frequent Contributor
timestamp: November 07, 2018, 08:42:21 pm
content: my components are resistors and ceramic capacitors. Crucial components include two Aluminum caps for ac filtering, one microcontroller, 4 Allegro SOIC-8 current sensor. Are Tantalum caps better than Aluminum caps when considering high temperatures ? I will be placing these in a Distribution Box or something similar.

author: Apollyon25_
author_rank: Regular Contributor
timestamp: November 08, 2018, 07:29:52 pm
content: In terms of considerations for the PCB itself - AC voltage creepage/clearances, and channel separation distances, input transient protection, and as it's outside some lightning protection is also probably in order.If you are connecting to extra low voltage (ELV - typ <50Vdc) interfaces for monitoring, you should probably have opto-coupler/isolators between your HV side and ELV side.Ensure all your components are suitably rated for line-line or line to neutral/earth use (assorted X and Y classes), and as noted above, consider the environmental conditions it'll be exposed to. You may need to conformal coat or encapsulate (pot) the board, or as also noted put it in a suitable IP-rated box (IP67 probably minimum here, but mounting considerations also play a part and you may get away with IP-56).Local part dissipation becomes critical once in a sealed box so your caps will need to be at least 85degC rated (though I'd simply use 105degC rated) and pick the higher reliability parts too (2000hrs+).Then post up the schematics and proposed layouts so others can check over your work. You don't want to kill yourself and having someone else review your design likely finds issues you haven't considered.Good luck & Enjoy!