Leakage wiring harness


#1

Hi folks…
I want to share with you some possible leakage issues you can run into…
I live and dive my ROV in cold sea water… 3-11 degree C

I have now found my problem(s) to my leakages…

the cause seems to be:

  1. I had a end cap epoxy sealing that didn’t hardened… leaving the glue soft letting the water to slowly enter the battery tube. Then I guess the rush in current made the wires in the harness back to the ROV heating up and ruin some of the plastic cover and expose the copper.
    this gave the water a passage into the E-tube

OR The plastic cover of the wires in pic.1 were damage in the first place letting the water enter the battery tube AND the E-tube at he same time. Then the rush in current due to salt water in the battery tube increased the pressure in the tube pushing the faulty glue out and letting more water in the battery tube.

In my opinion there is two issues here:

  1. I mad a bad gluing causing the failure to happening.
  2. The quality of the wires/ solution of letting all the tiny wires be exposed directly in the water are a weak design. There are no second “barrier” if the plastic cover of the wires should fail some how. In my case cold environment makes the wire shield stiff and hard. If they get bent some how they just crack and are damaged.

It shouldn’t be a problem taking the E-tube out of the ROV with out the risk of damaging the wiring harness due to slite bending of the wires.
How about to design it as a whole cable with penetrators instead as other ROV’s have?


#2

Hi Tom,
Sorry to hear about your sealing issues with your wire harness. Operation in very cold water will cause the wire and the wire insulation to stiffen and make epoxy start to become brittle. I agree that the 2.6 configuration that you have does have some weaknesses.
The OpenROV 2.8 wire harness and End Cap routing is about as good a sealing method that you can get if done properly. Being able to anchor the DB-25 connector to the entrance of the wire harness trough (I used CA Kicker around the flange of the DB-25 connector to ensure that the connector flange would bond quickly with the CA spread around the periphery of the wire harness End Cap entrance) and then forcing the 2 Ton epoxy into the trough virtually guarantees an even distribution of epoxy around each individual wire and the elimination of all air pockets in the trough. Also, I found that routing the wires side by side in the trough instead of just a jumbled wire bundle helped to ensure that the epoxy coated all of the wires completely and forced the air out of the trough.
I have built several 2.8 End Cap assemblies and have been able to pull a 560 mm Hg vacuum on the WTC for over two hours even without the ends of the wires in the wire harness being sealed. I have found that attention to detail in the application of the 2 Ton epoxy to the wire harness trough in the End Cap is very important for a good waterproof seal.
Regards,
TCIII AVD


#3

Thanks for respond…
Yes, I agree that the 2.8 is a better way… now, since I have this 2.6 I can not use 2.8 end caps.
I have sent OpenROV an email wanting to buy new end cap and harness. This time the new colored version.
I guess the damage to the insulation may be caused by overheating in the first place due to the expected rush of current from the leaked battery tube. And then the ball started to roll…