I have had many ups and down, successes and failures! (Like an action movie. But less gripping and with fewer fist fights)
You can click on the pictures to get the full size.
As suggested by Chris I soldered, added liquid electrical tape and heat shrunk wires on the outer side of the cap. I will leave the end naked on the other cap as a test, to see if stripping a gap in the wires (for potting) is enough to stop water ingress.
Alexander suggested I put a thin layer of silicone on the ends of the e-tube to help the seal, particularly for shallow water where the pressure is basically nil. I did this by placing a bead of silicone around the edge then placing it face down on a ziplock bag (which I knew to be silicone immune).
The ziplock bag was great for pealing the e-tube off effortlessly once it cured but those baggies are not as smooth as you might at first think! check out those lines.
I used two methods to test the seal:
1 - Place the cap on one end of the e-tube and hold it in place while pushing that end under water (in my sink) and then letting go so the water pressure was the only thing keeping the cap on.
2 - Place both caps on, attached with the elastic band inside.
(3 - squeezing tight with fingers. Finger strength was enough to fully seal every time)
Method 1 leaked (small bubbles of water formed in 2 or 3 places and grew steadily). failure
Method 2 leaked but more slowly. failure
O-ring and silicone (cured) to the edge:
Method 1 leaked more slowly than without silicone. failure
Method 2 leaked but again more slowly than with out silicone. failure
Worried that the small lines in the silicone was letting the water wick through, I tried putting the bead around again but using a rigid plastic packaging material instead of the baggie, to get a smoother layer. (I tested various materials by adding a bloob of silicone to each and then trying to peal it off after it cured.)
This improved things with both methods but didn't stop the leaking completely. failure
I hopped to achieve a water proof seal with water pressure only and without adding grease, but that would require a (more) perfect edge than I have and/or differently shaped o-rings.
The o-rings I have are wide and flat. That is good for strength, but it is bad for a low pressure seal. Thankfully grease does exist!
O-ring, silicone and grease:
All methods kept water out. success!
I don't have pictures of the 'one cap' method so you will just have to imagine it.
Fred is helping.
I used petanque balls for weight (like bocce but French!) I used just 1 which was just barely enough to keep the e-tube underwater. I left it for many hours and no leaking.
The grease won't help once the pressure gets too high but by that point the o-ring should be compressed more than finger strength! And since we know finger strength is enough...success!
Sorry if this post was a bit long winded, but this (sealing the tubes this way) is one of the main points of this test. :)
The next post will cover the oil filled light modules and the 'rig' it will all be attached to.
Here is a sneak peek:
This is upside-down.