IP65 Plastic vs Alu. enclosure and condensation

[hcglitte]

Hi,
I currently use an IP65 plastic enclosure for my product with a membrane ventilator installed.
The product is taken out/in from cold/warm to warm/cold environments (cold=below freezing temp).
Currently there has been no issues with moisture building up inside and condensation.

I am currently thinking about moving to a custom CNC machined IP65/67 aluminium enclosure.
My worries is that the aluminium may cause condensation inside.

I have read that plastic enclosures provide better heat insulation than metal enclosures, and with lower heating capacity.
This means that when air temperature changes quickly, plastic enclosures adapt faster, which in turn means less condensation.

I was wondering if anybody has experienced that alu enclosures have caused more faults than plastic in this respect.

[Jackster]

Not an expert in this field but have designed product housings for my own stuff. Here is what I know from research.

Plastic has a much lower thermal conductivity and thus will transfer heat a lot slower than (raw) aluminium.
We are talking orders of magnitude of a difference with plastics around 0.02-0.05 W/mK vs aluminium which is 204 W/mK.
This is for direct contact temperature changes though. Air will transmit heat a bit less depending on a few factors.
IR is another thing to consider. Plastics (some if not all) will absorb and radiate it more than uncoated metal. (someone please confirm/correct this if this is wrong)

Your membrane vent should prevent any large buildup of moisture inside the enclosure. That is one of their primary purposes after all.
If it fails to do this, you might not have a large enough vent hole in the housing or not enough vent holes that would allow the air to pass through.

I am currently thinking about moving to a custom CNC machined IP65/67 aluminium enclosure.
My worries is that the aluminium may cause condensation inside.

If it ain't broke don't fix it?


Personally, I would go on eBay and pick up an aluminium project box, some moisture sensors and an Arduino and test it in a real-world environment.
Install one or more vents in it and see what happens. Do it with the plastic box at the same time ideally so you only have a single variable, that being the case material.

If moisture is of high concern and you want extra protection, consider conformally coating any PCBs and exposed wiring inside the case.
This way if moisture does build up and due to temperature change you hit due point, you are better protected.