I have put dessicant bags into some DotWorx enclosures that were installed in rainy/humid weather just as a precaution that some moisture definitely got inside the housing during install. We never went back and replaced them as there was never moisture buildup on the dome.
IPVMU Certified | 02/05/13 07:43pm
Hello, Soeren: Interesting question! My climate is neither wet nor as humid as yours, but we never added desiccant to housings. Even in semi-arid environments, the difference they make was not worth the cost.
We did frequently specify outdoor enclosures with heaters/blowers. If I'm not mistaken, a blower simply equalizes humidity inside the housing to what it is the same as outside conditions, and the heater keeps that humid air from freezing into frost and damaging electronics when the temperature drops.
In the case of a camera housing, a desiccant would work like crazy to remove (absorb) all moisture, not work for equilibrium. I'm not sure even the most aggressive blower and heater 'dehumidify' the air. To that end, any 'delta' between the inside/outside ranges could cause the lens glass and housing glass to fog or condense.
For corrosion control, most housings are painted or powder-coated.
It's an interesting querstion, and I'll ask some enclosure manufacturers for feedback on this.
IPVMU Certified | 02/05/13 08:34pm
All: I asked Videolarm for feedback on Soeren's question, and their response was helpful:
"We do have some experience with Desiccant bags. Our general practice is not to use them, but there are cases where it makes sense for us. Most of our housings and cameras we do not include them, we rely on the seals built into our products and/or heaters to deal with moisture. If you have an outdoor camera that is having a problem with condensation on the viewing window or dome, most of the time a desiccant packet will not solve the problem in our experience. The desiccant packet absorbs all of the moisture it can and then you still have a moisture problems most of the time. We focus on the incoming wiring and make sure that it is sealed for water, but also for air circulation.
Where we do find them useful is with a our IP67 sealed cameras/housings, like a pressurized or Stainless Steel domes and housings. Once the product is installed, any moisture inside has not place to go. A small desiccant packet (2"x4") works very well since it only has to absorb the moisture that was in the air at the time the product was closed up.
So adding a desiccant packet does not hurt anything and might help some, but it is not a permanent solution from our experience."
So, like Sean suggests, desiccant bags are valuable in scavenging entrained moisture in air-tight housings (like IP 67), but aren't widely used as an alternative to heaters/blowers.
We include dessicant packs with our cameras (IP66 rating) and recommend they be installed in any humid environment.
Any sealed enclosure is going to have moisture trapped in it. Heaters and blowers won't really change that fact, though they can potentially help prevent condensation slightly in some cases. The dessicant packs will absorb the excess moisture and keep it from accumulating anywhere. The problem is really prevalent with our dealers in places like Malaysia, TT, Caribbean, southeast US, etc. In the more northern climates it's less of an issue, unless the camera was installed on a really humid day where higher amounts of moisture would have been trapped inside.
Thank you all for the answers.
At the moment the humidity is around 93% and 1°C.
I do alot of service on cameras and will be opening the IP66 enclosure, to adjust and check the heater, etc.
So I asume I will have to change the desiccant bag, right before closing the enclosure, as the existing bag can't consume more moist.
But at which humidity level is it nesesary to change the bag? If there is an answer to that... :)
We include 1 and do not have a recommended replacement schedule. The dome is fairly weather tight, so the purpose of the dessicant pack is to absorb any humidity that got trapped inside during installation.
However, if we suspect that packs in the Caribbean need to be replaced I supposed I'd have to fly down and check it out in person to be sure ;)
I don't think I've ever installed them pre-emptively in a camera, but I have used them in cameras that developed fogging problems due to air leakage (actual water leakage is a whole other issue - you have to actually FIX that, not just put in something to sop it up). I've closed up sealed cameras in humid conditions and NOT had fogging issues, but when they do fog, I'll go back and add the packs. On one site, we tried adding the manufacturer's heater modules to address fogging, to little success... adding the desiccant did the trick.
We had a beyotch of a time finding the pre-made packs, but we did find a couple sources of the bulk product so we can make our own.
$5 for a two-pack, sold for use in in-line air dryers for compressors.
I found the whole bottle actually fits right inside many of the dome cameras we use - poke a few holes in the lid and just drop it in.
I had to add some to a Dahua mini-dome recently, NO room at all for even a small baggie of the stuff... so I just poured the bare beads into the back section of the camera. So far, so good :)
IPVMU Certified | 02/07/13 04:37am
I was under the impression that desiccant needs to be periodically 'recharged' (dried out) if the media is used over time?
The silica beads will absorb a finite amount of water; if there's a constant influx of moisture, then sure, they'll reach capacity eventually. IF there's a constant influx of moisture, though, you may have a bigger issue.
If the housing is well sealed and it's just a matter of trapped humidity, then once the existing moisture has been absorbed, there shouldn't be an issue anymore - it will be held in the beads.
Not all desiccants can be "dried out" and reused, either - make sure you have the kind that can before you put it in the oven.
The only time we ever use the bags is when we are handling the camera's on a rainy day.
You always end up with moisture on the glass when the sun comes out.
So we place the bags in the house as either a precaution, or afterwards when we see the moisture build up.
But generally, the sealing of the houses should be sufficient enough.
I just remembered that a couple of the thermal cameras I've been testing use dessicant bags in the housing. DRS especially recommends them in the back of their housing. The only components back there are the Ethernet and power jacks, however, it's not open to the sensor or lens compartments.
On a related note: if your connections are in a damp area, especially if you're near the ocean where the air is salty and potentially corrosive, I'd recommend something like this:
Also sold in RV stores for putting on trailer connectors and the like... I've seen mechanics use it on automotive light bulbs before plugging them in.
The idea is to fill voids in the connections to prevent ingress of water, and to keep air away from the contacts. I've used this on outdoor coax splices (two cables connected by BNC barrell) that ended up laying in a pool of water, with no failures.
Some Panasonic unitized cameras have an electronic means to seperate the water molecule and then exhaust it from the housing.
We looked at this a few years ago when developing pressurized housings, here are a few things we learned. A liter of air (approximate size of a small camera housing) holds a maximum (at 100% relative humidity) about .03 grams of water at 30 degrees C. So not very much.
Desiccant bags are typically sold by “Unit” sizes. A 1/2 unit package will hold 3 grams of water at 20% relative humidity or 6 grams at 40% relative humidity. (Note the amount changes with a change in relative humidity.)
Of course if you have an IP 66 housing you are most likely not air tight and will have to deal with a constant exchange of air, so it's difficult to say for how long you will have the benefit of the desiccant.
One test that might be worth trying. Place a unit of desiccant in the camera housing, but also add a humidity indicator strip in there as well (a humidity indicator strip is like litmus paper except it test moisture- you can find them with a quick search on internet). Locate the humidity strip where you can see it without having to open the housing. The humidity level of the housing should initially drop and you can see for how long that level stays below 100% RH. If it’s a long time than your in good shape.
Actually we found desiccants very useful for pressurized housings in cold temperatures.
During testing we had condensation problems when the housing temperature was dropped from ambient (25C), to -40C. (I know this doesn’t apply to everyone.) Even with good purging of the housing, air at minus -40C simple holds almost no moisture. We found a unit or two of desiccant prevented any condensation. It’s easy insurance and sure is better than making a site calls when it’s -40 outside.
Thank you all for all the answers. Very helpfull.