On 19-May-17 8:08 AM, Chris Jones wrote:
On 18/05/2017 11:31, Aussie wrote:
On 17-May-17 8:45 PM, Chris Jones wrote:
On 16/05/2017 17:47, Aussie wrote:
I'm playing around potting some electronics for immersion in water
up to
10 metres.

A cable with a polyethylene sheath and PVC insulated wires connected to
a circuit board are embedded in some rigid setting epoxy.


I know I'm not going to get the epoxy to adhere to the polyethylene.

What can I do to enhance the bond between the epoxy and the PVC wire
insulation to keep the water from wicking along the wire to the circuit
board?


I've read that brushing with PVC pipe glue primer (MEK) can help, as
well as flame treating.

Flame treating is impractical as the job is too small & tight to get
into the area where the PVC insulation is.




Any suggestions?

Is the MEK priming likely to help?

Perhaps painting on some sort of low viscosity RTV silicone that might
form an intermediary seal?


You can get cable that is filled with a hydrophobic gel, so that even
if the cable does have a leak somewhere along the length, water won't
wick along it.

If your device is being potted, you could put a short section of
single strand bare copper wire between the circuit board and each
stranded wire. The epoxy should form a good seal to the bare copper.
Liquid water in the stranded wire ought to stop at the solder joint
between the stranded and non-stranded wire. Probably some water will
diffuse through all of the plastics and resins eventually though.

You could try corona-treating the polyethylene and PVC which is much
like flame treating but may produce less heat.






I've not been able to find jelly cable or water block treated cable at a
viable price. The inexpensive type is solid core conductors and I need
multi-strand unfortunately.

I bought some UV sensors from this Australian company:
http://www.monitorsensors.com/
and they came with stranded gel-filled cable IIRC.

They seem to be a small company so maybe they will sell you some cable
if the minimum order quantity is too large from usual suppliers.

I'm not sure I would take their advice on waterproofing though: one of
the UV sensors went intermittent and then stopped working not long after
it was installed outdoors.


Thanks Charis, I'll have a look.