I got a field report of a product which is sealed in an IP66 aluminum die cast body. it was observed that water/moisture had condensed inside the enclosure over and over and creating some white marks inside (see attached). The product was installed in a US region about a year ago.
It was reported the top cover was screwed on properly, and there is no way water can get in. However one question in my mind is: we install this product on a street light pole, and the top cover is screwed on in the field only after the power cable gets in. So what if the atmosphere is already full of moisture during installation? That moisture will be trapped in the enclosure and sealed after covering the top. And due to the weather changing over and over that moisture gets condensed over and over and creates the problem. How can I get out of this? One way I think would be to use some kind of silica bag to absorb moisture. Any advice?
Best Answer
Here's what happened to a product I designed that was IP69K (Protection against powerful high temperature water jets). It was installed in China and failed after about a couple of years. When looked into there was about 1.5 inches of water slopping about. Seemingly a mystery.
However, it turned out to be a progressive build up of humidity. Every night the product was turned-off and internally it started to cool over night. During that period the internal pressure lowered (because the internal air cooled) and it sucked-in high-humidity air from the surroundings. That settled out on top of the microscopic layer of water that was ingested the previous night. Gradually it built up until it reached a switch mode power supply then bang.
The way we got out of this was selling the option of having a drain plug fitted and each order was processed with attention to that humidity problem.
Silica gel will work but only has a limited lifespan before it needs to be replaced. A positive pressure inside will help - if it's sealed as good as you suggest you can buy slow leak gas cartridges that keep the pressure positive - they are used in the petrochem industry and are akin to flameproofing by using pressure to stop volatile gases entering and potentially being ignited.