I’m connecting a sonar unit and an iPad cord to a 12V SLA 8AH battery for use on my float tube. The battery and cigarette lighter/USB adapter setup fits nicely inside a Lock&Lock pasta container. I have marine connectors for the 12V power to the sonar unit and the iPad cord is a long one and simply reaches from the battery box to the iPad.
The two 12V wires are just slightly larger in diameter than the iPad cord, and the three of them need to go from inside the container to outside the container. If I pierce any part of the lid or body, the hole would have to be big enough to pass the USB connector through it, so I’m thinking a better alternative would be to cut a small slot in the top of the body and lay the three wires in it and then glue the piece I cut out to make the slot back in place, minus a small piece off the bottom of it.
I have a fine blade jewelry saw to make the cut, but there will still be gaps when I put the cut piece back in, so whatever I use has to have enough body to seal the gaps so the o-ring in the lid works and the whole deal is seriously watertight. I was thinking aquarium sealer, but I don’t know if it will stick to the poly-whatever the L&L is made from. The plastic is kinda slippery, so I don’t how well a silicone type sealant would bond to it.
So recommendations for glues/solvents/gooey stuff?
Needless to say, space on the tube is extremely limited and a commercial waterproof car battery sized marine battery box is not going to happen. I need to DIY this thing.
Make the hole, then fashion a custom grommet around the cable out of Sugru or Proto-Putty. Neither will stick to the plastic (few things will) but you can over-engineer a grommet so that it makes a seal by fitting tightly into place, and having flanges that sit flush with the surface that is to be pierced.
The problem with the plastic is that it is very low surface energy, and very difficult to glue. Even installing a through hole socket would benefit from some silicone grease to help maintain the seal.
There is no big deal about chopping the USB connector off the iPad cord and soldering another one on on the other side. Indeed no real need. Just chop the connector off and use the power wires as appropriate inside the box. Then you could use a suitably sized cable gland.
True - it’s the same attribute that gets it chosen as a material for making these containers - it doesn’t tend to react with foodstuffs, or get stained or damaged by them.
There are glues that work on polypropylene: JB Weld PlasticWeld is highly rated. Another trick is to use a glue with a primer, like Loctite 401 + Loctite 770. Loctite claims their 3032 two-part adhesive works well on LDPE, but it’s apparently not been tested on HDPE. Some swear by Amazing GOOP plumbing adhesive.
You might consider melting instead of gluing - very carefully, with hot air if you can.
I’ve had modest success getting silicone adhesive to stick to polypropylene with a quick flame treatment. Basically, the surface oxidation provides some polar and charged groups for adhesives to stick to.
However, I had a whole case of “expired” syringes that I was trying to glue together. It took a fair amount of trial and error to get enough flame on the surface to make a difference, without melting or igniting the plastic…