Condensation inside a close box

[Dalit]

I have an out-door cabinet (with PCB) that over time is being damaged due to condensation (humidity).
I would like to minimize these damages over time (corrosion, etc...)
The cabinet is closed but not 100% sealed. Cabinet size is 80X20X20cm.

How do I avoid the damages due to condensation of air inside the cabinet?
Changes I can implement are:
1. Changing the external geometry of the cabinet.
What would be the preferable geometry?
2. I can change the coating of the internal components (cabinet included).
Any recommendations?

 

[FredGarvin]

There is nothing you can do geometry wise to solve this problem. There are specific electrical enclosures and PCB meant for this kind of usage. You would be better off to get a PCB design that includes some kind of coating finish to protect it from condensation or getting a proper enclosure.

The only other thing you can do is to treat the air in the cabinet to ensure a constant atmosphere inside the cabinet.

 

[Dalit]

I can not ensure the atmospere inside a cabinet. I will have to use cooling system all year long. That would be very expensive.
I would like to chanel the water drops, after being condensed, in a pre-designed chanels.
I am sure electric cabinet, installedout-door, have the same problem, or should have...

 

[Bob S]

You could use a desiccant like silica-gel in bulk, and regularly recharge it. Or you could use a heater inside the cabinet to always keep the temperature inside the cabinet above the ambient temperature.

 

[MATLABdude]

Is it possible to weather seal the box? (Compressed) adhesive weather stripping, caulking, gaskets, etc.? If you have components that get hot, you have to be a little more careful, but you can heat sink these to the outside of the enclosure.

 

[Dalit]

MATLABdude, what do you mean by weather seal?
The cabinet can not be sealed, but the problem is with the air trapped inside the "box".
Hot/cold weather will cause air to condense inside, and I am trying to minimize the problem causes by the water drops accumulating inside the box.
I am not concern with the getting hot but getting wet.

 

[Dalit]

Bob, Silica-gel is not a long term solution for me, since I will have to change it in a regular bases, it is not very easy to open the cabinet.
It's like an out-door electric cabinet. I wonder what is their solution for humidity inside the cabinet.

 

[MATLABdude]

By weather seal, I probably mean environmental seal: things like gaskets and o-rings for things that open/close or fit together, and welding or silicone (or other) sealant for seams. Basically, measures which will keep moisture out of your box (save for when you're opening /closing the box), and allow your can / bag of desiccant to go that much further (get the kind that colour changes so you know when to replace / regenerate the desiccant). A not-as-good alternative may be to use the weather stripping (closed cell only!) that you buy in hardware stores, which will keep copious amounts of moisture (rain, snow, etc.) from seeping in if applied properly.

Outdoor electronics (that can't be completely sealed in) often have parts that *are* sealed in, with weatherproof connectors for electrical connections, and parts which can't be sealed are, as Fred Garvin says, potted or conformal coated. Then they're tested to ensure that they don't (have unacceptable) rates of failure. For more on these types of coatings, here's a handy app-guide from MG Chemicals (they make various types of electronic coatings):
http://www.mgchemicals.com/downloads/appguide/appguide0405.pdf

Given that your box is tough to crack open, you should consider a case redesign / reselection (say, one with environmental sealing) or some of the other measures we've presented.

 

[Dalit]

MATLABdude, thank you for the file.
The cabinet is not tough to crack as much as I want to keep it low maintanance. I don't want to open it every other day.
The cabinet is sealed in some level, but I can not remove (vacuum) the air trapped inside the "box".
Weather changes will condense the air trapped inside the "box" into water drops, these drops will accumulate on the surfaces of the internal "box" and encourage corrosion.
That's what I am trying to avoid.

 

[MATLABdude]

MATLABdude, thank you for the file.
The cabinet is not tough to crack as much as I want to keep it low maintanance. I don't want to open it every other day.
The cabinet is sealed in some level, but I can not remove (vacuum) the air trapped inside the "box".
Weather changes will condense the air trapped inside the "box" into water drops, these drops will accumulate on the surfaces of the internal "box" and encourage corrosion.
That's what I am trying to avoid.

But that's the point of environmental sealing. You don't need to remove the air, because the desiccant will absorb the moisture out of the air inside the box, and prevent moisture from condensing on your electronics. And since you open the cabinet so infrequently, you won't replenish the humidity.

As part of my work, I heat seal moisture-sensitive chemicals in polyethylene bags (ZipLocks with the tops cut off) with (fresh) desiccant packs. Then I freeze the ones that need to be frozen (at -20C), and no moisture ever condenses on the inside of the bags. I keep other chemicals (ones that don't need to be frozen) in a vacuum desiccator kept under (a low) vacuum, so that there is so little air that you have very little moisture. Nevertheless, I still keep desiccant inside the desiccator to remove what little moisture remains / leaks in.

 

[Dalit]

you could use a heater inside the cabinet to always keep the temperature inside the cabinet above the ambient temperature.

Shouldn't the temperature inside the cabinet be below the ambient temperature?

 

[russ_watters]

Shouldn't the temperature inside the cabinet be below the ambient temperature?

No, that's largely what causes the condensation!

 

[Dalit]

That way I might solve the condensation problem, but start a new problem of heat inside the cabinet, which might damage the components inside.

 

[MATLABdude]

Think about this for a second: would you leave the heater on all the time? How might you control this?

 

[Dalit]

This is not afeasible idea. I am very much aware of that. The cost for constant heating the internal volume of a cabinet will be enormous.
I can not avoid the condensation problem, therefore I am trying to design the cabinet to comply with humidity and water drops.
I am sure there is a mechanical design that I can drain the drops accumulating over time.
I just wonder if there is a thumb rule or know how I can follow.

 

[FredGarvin]

You can easily overcome and direct the drops in the cabinet. However, you still have to deal with the condensation forming on the electrical components to begin with.

What about some form of heat tape? Can you put a small electrical controller in there and use a heat tape do this?

http://en.wikipedia.org/wiki/Trace_heating

 

[Dalit]

The solution implementation can't be electrically controlled.
I am sure all the electrical cabinet on the streets have the same problem, I wonder what is the solution there.
Is it special coating on components, drain or what ever…?

 

[FredGarvin]

Nuts. Well, it was worth a shot.

I am sure that electrical boxes like the ones you mention have components in them that are rated for outdoors use. Like I said, I have seen some that have protective coatings applied to the PCBs and other components to protect them.

 

[junglist]

The solution implementation can't be electrically controlled.
I am sure all the electrical cabinet on the streets have the same problem, I wonder what is the solution there.
Is it special coating on components, drain or what ever…?

our major telco's pump masses of space-filler foam into their junction boxes to reduce the air volume and supposedly protect their wiring/componentry. This however, raises new (immense) problems in servicing difficulty.

 

[Dalit]

Junglist, it seems that you don't recommend on that idea.
Are these space filler are removable?

 

[MATLABdude]

...You would be better off to get a PCB design that includes some kind of coating finish to protect it from condensation or getting a proper enclosure.

Outdoor electronics (that can't be completely sealed in) often have parts that *are* sealed in, with weatherproof connectors for electrical connections, and parts which can't be sealed are, as Fred Garvin says, potted or conformal coated. Then they're tested to ensure that they don't (have unacceptable) rates of failure. For more on these types of coatings, here's a handy app-guide from MG Chemicals (they make various types of electronic coatings):
http://www.mgchemicals.com/downloads/appguide/appguide0405.pdf

The solution implementation can't be electrically controlled.
I am sure all the electrical cabinet on the streets have the same problem, I wonder what is the solution there.
Is it special coating on components, drain or what ever…?

They've already been mentioned twice in this thread! (Follow the link I provided, or Google for "Conformal Coating")

 

[Dalit]

Conformal coating is very expensive to apply on a large scale PCB.
I am looking for something I can implement when designing the cabinet.
For example, door geometry that will drain the water drops in such a way I can control and prevent them from spreading all over. I can even add a part in the design.
That way I keep the cabinet low maintenance.

 

[MATLABdude]

Conformal coating is very expensive to apply on a large scale PCB.
I am looking for something I can implement when designing the cabinet.
For example, door geometry that will drain the water drops in such a way I can control and prevent them from spreading all over. I can even add a part in the design.
That way I keep the cabinet low maintenance.

Eh? A (aerosol) can of (acrylic) conformal coat is around $15. While it'd be better to dip coat rather than spray coat, it'd still work. And it'd last more than one large-area PCB.

You can play with geometries all you'd like (slanted PCBs with bulky connections up top, allowing them to drain, some kind of high surface area fabric to wick up moisture once it piles up, etc.) but, if it's as you say, you'll always get condensation and moisture on every surface (including your boards). And you won't be able to (passively) drain this fast enough to keep your boards from getting wet. Nothing short of hermetically sealing your box will prevent that (and that's the only 'geometrical' solution that exists).

 

[Dalit]

Coating is additional cost, for mass production every extra dime makes it problematic.
But I guess there are no easy get a ways here.
Thanks!

 

[pontecorrea]

Hi, i just sign into ask something on this thread (sorry for my english, I am from venezuela), i'd like to cool down my pc hardware with a freezer, but i know there's things that can harm the components, such as humidity and others..(other thing is that i don't really know is some components can be damaged been frozen) the thing is, if i seal the components inside a plastig bag or something like that with a vacuum pump, extract all air inside to prevent humidity and figure a way to get the cables out without loosing vacuum, u guys think this can be done? (if u think i might make my own thread ill do it! sorry for posting here)
My pc is too hot inside and i don't want to try any usual way to cool it down.

 

[MATLABdude]

If you just hermetically sealed the box, and then put a big can of desiccant inside of it, you'd be able to remove enough moisture from the air to prevent substantial amounts of it from freezing out / condensing on your components.

However, such cases exist, and many have been around for over a decade (I remember when Tomshardware or Anandtech or some such first broke the 1 GHz barrier using just such a case on an original AMD Athlon CPU). Most of which have a way to compensate / eliminate frost. For instance, this unit from OCZ:
http://www.hardwaresecrets.com/article/377 [Broken]

However, how are you so sure that your computer case is, in fact, overheating? It's a whole lot easier (and cheaper) to just add some additional 80 or 120 mm case fans and periodically blow out the dust in your computer / fans. Remember to arrange the fans so that you have air flow, and not have them working against one another:
http://pressf1.pcworld.co.nz/showthread.php?t=47317

EDIT: Welcome to PhysicsForums! However, you should post questions like this, either in a new thread, or in the Computer sub-forum

 

[stewartcs]

I have an out-door cabinet (with PCB) that over time is being damaged due to condensation (humidity).
I would like to minimize these damages over time (corrosion, etc...)
The cabinet is closed but not 100% sealed. Cabinet size is 80X20X20cm.

How do I avoid the damages due to condensation of air inside the cabinet?
Changes I can implement are:
1. Changing the external geometry of the cabinet.
What would be the preferable geometry?
2. I can change the coating of the internal components (cabinet included).
Any recommendations?

Install a purge air system that has an air dryer on it. The PCB should have a conformal coating on it as well. These coupled with the proper rated box (IP rating) should solve your problem.

CS

 

[PFsteve]

So in a simplistic way...lets’ say you have a sealed enclosure from the outside with silica gel inside and some heat generating electronic device inside the enclosure. Would that be enough to prevent condensation inside the enclosure from forming?

 

[Mary 4 Tek]

Hi, if your still looking for some help on this, check out www.ddbunlimited.com
They provide sealed weatherproof enclosures that reduce the condensation problem and are also secure against vandals and theft. They offer heat and cooling options. They are reasonably priced as well.

 

[Selectronix]

Where possible use a sealed enclosure - it stops water & dust getting in. You should then consider placing a VENT on the enclosure. A VENT will equalise the pressure inside the enclosure with the outside.
WHY? When you get a change in temperature you get a change in pressure. This difference places strain on the o-rings /seals of the enclosure - potentially damaging them - which could lead to future ingress problems. The VENT allows air to pass through the membrane without letting water or dust in. There are different VENTS with different air permeability & water entry pressure ratings.
The VENT also allows any 'moisture' inside to escape out of the sealed enclosure. We provide VENTS in a number of formats & sizes - depending on the size of the enclosure.
VENTS are used in outdoor wireless enclosures, in a sealed box with a battery inside, they are used on a car headlight - to stop condensation on the glass, on outdoor LED lights.

Additionally - you can consider heating your enclosure. We provide heaters which can stop your electronics/components from freezing and potentially failing. The heaters also prevent condensation. We have very small heater that is 5W - OD 10mm and 45mm long - & then we have larger ones... These connect to a small thermostat which regulates the heater.

We also have DRAINAGE VENTS: these are place in the bottom of an outdoor enclosure, and allows water to drain out through the vent, without letting water dust or bugs inside your enclosure.

So - don't rely on GEL packs, what you should be doing is preventing the condensation, not trying to do something about it once you've created the environment for it to happen...
see: www.selectronix.co.uk

 

[jim hardy]

"""I am sure there is a mechanical design that I can drain the drops accumulating over time.
I just wonder if there is a thumb rule or know how I can follow.""

I wonder if it's really condensation or rain.

in my low-tech industry there were simple rules:

1. All conduit enter from bottom, never side or top. Holes in the top ALWAYS leak.

2. All conduit have a drip loop just priior to entry. Drip loop is a bend that looks like a sink trap , with a drain hole in the bottom. That let's water that somehow got in the conduit by rain or condensation drip out the low point instead of filling up the box.

3. Use drip-proof boxes, ie they have a lip around trhe lid that diverts water away from the door seal. Small drain hole in the bottom. Make the hole, and the ones in conduit drip loops too, small enough that mud-dauber wasps won't fill them with mud in their breeding season. Or cover it with screen. The Swagelok company (Parker Hannefin) makes brass tube fittings for that purpose, ask for "Mud Dauber Fitting". Also handy as fuel strainers in your boat tank..


4. Mount the board high in the box just in case.

In extreme cases we'd run a trickle of air throough the box from our inhouse compressed air system. But be sure your air source is clean and dry, not at end of a long pipe run. A volume change every hour or so does the job.

 

[Stege]

If the cabinet is sealed, you might consider using an ionic membrane dehumidifier.

It is a solid state device that mounts on the side of the enclosure and reduces the humidity through electrolysis. Not the cheapest solution, but maintenance free, long lasting, silent, and inexpensive to run from a 3V dc source. The website is at www.rosahl.co.uk http://www.rosahl.co.uk