Creating a waterproof project enclosure

Question

I recently got an otterbox drybox for my phone. I was sitting and thinking that its waterproof, crushproof, and big enough to fit what I need as well protective foam. I realized this would make an amazing project enclosure...

My only problem is that I can't get the wires out of the box without negating the waterproof aspect of the box. I was thinking to drill appropriately sized holes in the box, insert bolt style contacts, and seal it with a mix of silicone caulk and gorilla glue but im not sure if the mixture would be conductive...

normally I would just go with the idea but I figured I would ask if anyone has had this problem and solved it. I want it to still be water proof up to 100ft and crush proof up to 1000lbs (as the product is advertised to withstand) and I'm not sure if I have the right idea...

Question: How do I seal a project enclosure to be water and air tight using a non-conductive seal that can withstand greater forces than a grommet?

EDIT A more specific description of what i am getting at seems to be in order... I want to use an Android device and an open source project called "IOIO" (a link to the landing page can be found here) to construct really any kind of unmanned, WIFI/Bluetooth/3G/4G/LTE/USB enabled, waterproof, and crush proof vehicle. Since submersibles are not out of the question, I got curious about maintaining the water resistance of the aforementioned product. With land vehicles being a possibility, crush proof sounds nice.

To answer a question from the comments which was what exactly I would need outside of the submersible to be connected. Everything expensive is exactly that, expensive. I will be using a relatively expensive android device, as well as the IOIO for each one of the products. Motors and frames and even overkill waterproofing can be made to happen cheaply if done correctly, but a $700 android phone is $700. So my desire is to protect the majority of the expense in a single well protected unit. (Just imagine the insurance package i can sell on my products if I know for a fact that there has been no significant damage to the real expense). So to answer the question directly, I would want to run circuitry from the box to all forms of input and output that may or may not be applicable to the intended circumstance.

Answer 1

As already mentioned, 100 ft is a lot. IEC 60529, which is a standard for ingress protection, tests their IP67 rating at 1 meter depth for 1 hour. IP67 is generally considered to be equivalent to a NEMA 6 enclosure, I think.

There are a number of companies that make multi-hole, water-tight cord grips. Two examples that come to mind are Heyco (IP68) and Sealcon (IP66/IP68). There are other companies that make similar things, too, so look around.

One thing to keep in mind is that if your lead wire exiting the box is stranded, you have a leak path through the wire (between the insulation and the copper strands). One solution to this is lead wire manufacturers can fill that space between the insulation and copper to prevent leaking. Another option is to have a water-tight connector on the other end of your lead wires, too.

Answer 2

I think what you're looking for is a "bulkhead connector". You want this enclosure to withstand 100' water depth, though? Without pressure compensation? You're asking a lot! You may have to opt for a spherical enclosure instead - the flattish sides of the OtterBox aren't likely to be able to withstand that sort of pressure differential.

Answer 3

You could use waterproof connectors, but they can get quite expensive by the time you buy the mating pair.

Your idea of penetrating the enclosure with fasteners used for contacts is a good one if the electrical conductivity of whatever they're submerged in doesn't matter, and you can do it all with seelskrews and no glue.

Answer 4

My approach to the problem would be to do an end run around passing signals & power through the wall since, as others pointed out, 100' is pretty darn deep and a lot of pressure.

To send/receive data, use a transparent/translucent box and communicate with the outside world through infrared. Signals can be sampled and transmitted via LED/photodiode. Loss won't be an issue if the receiver and transmitter are immediately on either side of the enclosure wall.

Supplying power is a bit more difficult, but you should be able to inductively couple through 0.1" of plastic without much loss.

But if you're looking for a cheap, watertight material to make small enclosures, I'd start with PVC pipe and plumbing fixtures.

Answer 5

Depending on what sort of connections you'll need in or out of the box, you can use standard panel connectors or feed-throughs and cement them in. Provided the pin connections are solid (not hollow) and you use good strength epoxy, the result should hold up pretty well, although I'm not running the allowances for pressure at 100ft depth in my head.

If you need a more generic connection where it won't suffice to use something like an Ethernet or USB panel, then you may want to check out if you can find a supply of MIL-DTL-38999 connectors. These are round panel connectors, circular, high pin density, and the -38999 standard deals with connectors for harsh environments, namely swamp and water and the good stuff. These connectors lock via an outside screw mechanism.

Granted, they're filthy expensive but you get a large amount of pins that can be used for anything from bit-banging to GPIO to more advanced protocols.

You can find a more generic list on DigiKey of -38999 connectors here. To find out what they're rated for in terms of exposure you might want to consult the standard of which the closest link I can find is here.

Comment on this and let me know what you're looking for specifically and I can suggest options that are less likely to make your wallet (and wife, if applicable) hate you.

EDIT: Also, don't mix caulk and Gorilla glue, as the mixture/resultant slurry may not hold. Use one or the other, and a hard epoxy or the Gorilla glue is most likely the preferable route. Keep in mind that Gorilla glue has a tendency to foam up when it's curing so take that into consideration if attempting to work in tight spaces or tolerances.

Answer 6

if you use it in sea water you can use goldplated contacts for the pins in the housing. (they will not oxidize like most others will) and you can use some strong magnets in the housing to make it easy to click the cable side on. (that side then need to have some iron our magnets with the right pole to the encloser side)

Answer 7

I have had great success creating underwater enclosures with PVC endcaps, and have detailed the development of my underwater housings over time on the Cave Pearl Project blog: (note: reverse chrono order)

http://edwardmallon.wordpress.com/category/a-diy-underwater-housing/

I considered the otter boxes back a the beginning of the project, but as an earlier poster mentioned, they bow in significantly at depth. I also did not like their anemic little O-rings. I have tried several epoxies for the hull penetrations, and so far Loctite E30CL has been the winner for mounting sensors on the outside of the hull (JB weld has also stood up well over time). Be sure to score the smooth pvc surfaces to help with mechanical bonding, as many epoxies have low shear strength on polymers.

Many of my housings have spend several months down in the 100 ft territory. 3" pvc caps are more than strong enough for this, but I have seen a fair amount of compression on 70duro EPDM orings over that time at depth. I wet sand the oring seats down to 800 grit (starting at 200 grit after cutting) and that has proved sufficient for a good seal.

I recently started building cheap underwater connector cables with Nibco PEX swivel adapters from the local hardware store. These have not been depth tested yet, but I suspect they will be good to 100ft as long as I make sure the mating oring seat is clear of any casting seams that might let water sneak by the cone washer.

http://edwardmallon.wordpress.com/2015/01/29/a-simple-diy-underwater-connector-system/

Links to the various parts are embedded in the post, but there are at least a dozen different brand names you could choose from.