Bullet camera in PVC pipe condensation problems -- Help please

[NickatNite8724]

I had to installed some IP bullet cameras in some PVC pipe on a Hopper dredge to protect it from the salt water spray. They are outdoor cameras but they are made out of aluminum and they will rust if left unprotected. I sealed them in the pvc and used a cgb from the wire as well as sealant on the threaded end cap (for access to the connection). After being installed a few days later it started to form moisture on the inside of the lens. I added desiccant packs and also ended up adding a pressure compensation device on the bottom thinking it may have needed some ventilation since the camera generates heat and causes a pressure difference. After making the changes the moisture cleared up and they seemed to work fine for a few months while in the shipyard with no issues. The dredge left the shipyard in Louisiana and went to the jobsite in Delaware and now the problem is back but only on a few of the cameras and not all the time either. I figure it is more likely temperature changes (it's pretty nippy out here) not to mention the high moisture content from being out in the Atlantic ocean. I was thinking of adding heaters but since it is POE cameras I would need a way to first not exceed the total wattage of the 48VDC power injected and have a way to pull the power out and split it between the camera and the heater in each location. (I have seen older style RJ45 couplings that I could use for this that punch down like a phone connection). I would like to know if anyone has any thoughts on if that would work or have a better solution that I haven't thought of. Any help would be greatly appreciated. I would have liked to go with stainless steel housings for the cameras and not have to deal with all of this but my bosses wouldn't go for the price tag. Three of these cameras are critical to operation and really need a solution. Thanks in advanced for your help.

 

[CWatters]

I don't have a solution but I've experienced similar problems trying to keep water out of a transformer. If there is any air in the enclosure temperature cycling causes changes in air pressure that can suck in damp air if not water. I found the only answer was to fill any air spaces with potting compound which isn't practical in your case.

You mention a pressure compensation device. Is this just a air vent or something more exotic that doesn't allow air in/out?

 

[CWatters]

Can you tell if the desiccant is being used up?

If so perhaps filling the space between camera and pipe with bubble wrap might reduce the volume of air exchanged with the outside due to heating cycles giving the desiccant pack a longer life?

Perhaps use a vent with built in desiccant..
http://www.agmcontainer.com/desiccators/custom_desiccators

 

[NickatNite8724]

The pressure compensation is is a small 1/2 npt plastic piece that looks much like a cgb but has a small hole for air flow on each side and a stuffing that only allows air flow in one direction (out). I may try the bubble wrap. I will climb up there in a few minutes and see about the packs. Thanks for the input.

 

[NickatNite8724]

Here's a picture of the setup

 

[mrspeedybob]

Would it be practical to seal each unit completely and pull a vacuum on it?

 

[CWatters]

The pressure compensation is is a small 1/2 npt plastic piece that looks much like a cgb but has a small hole for air flow on each side and a stuffing that only allows air flow in one direction (out). I may try the bubble wrap. I will climb up there in a few minutes and see about the packs. Thanks for the input.

I think i was getting air sucked in through cable glands that were otherwise IP rated.

 

[Mech_Engineer]

I think the secret will be desiccant packets, possibly a lot of them, in combination with an environmental seal such that no new exterior air can get into the PVC enclosure you're created. Condensation will form on the interior of the unit if the interior air is humid and the window is cooled by the outside air, but if the interior air is very dry no condensation can form. My guess is that when you first assembled the units the desiccant you added was able to dry out the interior of the enclosure, but over time humid air leaked in through your cable gland and eventually overwhelmed your desiccant and raised the humidity inside. A better-sealed cable gland paired with some new desiccant ought to fix the problem.

You can estimate the dew point and other relevant parameters of the air you're working in using a Psychrometric Chart and two thermometers to create a "sling psychrometer." You can build your own sling psychrometer using these instructions: http://www.flinnsci.com/documents/demopdfs/Earth'sci/es10301.pdf .

 

[CWatters]

On a sealed home heating systems an expansion vessel is used to accommodate changes in the volume due to temperature. I'm wondered if there was something similar you could put inside the enclosure that would help keep the pressure constant eliminating the need for an air vent. That way you don't get an exchange of air with the outside.

 

[JBA]

On a sealed home heating systems an expansion vessel is used to accommodate changes in the volume due to temperature. I'm wondered if there was something similar you could put inside the enclosure that would help keep the pressure constant eliminating the need for an air vent. That way you don't get an exchange of air with the outside.

One way to achieve the above would be to integrate an elastic impermeable diaphragm on the rear cover (the standard method for pressure compensation on waterproof equipment enclosures for shallow diving).

 

[Tolklein]

I've used devices with vents, http://www.gore.com/en_xx/products/venting/protective/protective_vents_lighting.html
As well as Replicable desiccant cartridges as shown by CWatters