What gauge tether to use?

[Sea Searcher]

I have never done anything like this before, so please be patient with my ignorance and questions that may seem very basic. I'm a bit confused about how to choose the most appropriate tether/power cord. My thrusters are 600 gph Seasense bilge pumps. It has been difficult for me to find specifications that state the amp draw for these, but I figure that when running two at once, they should draw about 5 amps.

I looked at a voltage drop converter and it looks as though I will want to use at least 18 gauge wire to get a decent amount of thrust. Again, I am a beginner at this, so I have been starting out by following the instructions on MBARI's site, which has a lot of good photos and step-by-step instructions. One thing they have not made clear, however, is what is the gauge of the wires in the 6 core tether they suggest using. I bought one already, and the wire in it is stranded 24-guage. This just seems too narrow to be powering thrusters that are 50-feet away (huge voltage drop). I don't need the thing to go fast (I think going fast could make it more difficult to control), but I think I might have bought the wrong gauge tether cable.

I just assumed there would be an additional, thicker wire that would supply power to the thrusters, and that these narrow ones in the tether were just for sending instructions of what to do (i.e., send power to this thruster or that thruster). Now, it appears as though I was wrong, and that the tether is the sole source of power for the thrusters.

It seems like it would make for a pretty heavy tether, if all six, or eight wires inside it were 18 gauge or thicker. Does anyone have any recommendations or thoughts about this. I really don't want to waste a lot of money through trial and error.

Thanks,

Kevin

[CLYON]

I am a newbie also and I am sure others will comment, but For me I chose to have on board batteries for this very reason. You can have the correct gauge for the current you will need. There is just to much of a drop going through 100 feet or so of cable for me to even consider going that route.


Chuck

[Sea Searcher]

Thanks, Chuck,

I'm leaning in that direction, too, at this point. It seems to add a fair amount of complexity to the design, however, and without some guidance from people who are familiar with transmitters, servos and such, I feel a bit intimidated. I can't afford to do a bunch of trial and error these days, as I'm living on a very low budget and going to school full time.

I bought some design plans from a guy in England. He made a pretty nifty sub that uses an on-board battery and some other electronic doodads that I've never messed around with before. Once I get familiar with the electronic aspects, I think I will be able to come up with some good ideas. I currently live in a custom camper I built, and I have improvised many projects over the years (it is a way of life for me), but I know very little about electronics.

I appreciate you responding to my query, and I hope to collaborate in the future. Here is a link to the site that inspired me to want to build an rov http://www.rovrobotsubmariner.com/pages/pictures.htm
I've already thought of several ways to improve the design, but, again, first I need to understand the electronics.

Best wishes, and good luck with your project.

[bikerbones1968]

Hi Guys welcome to the forums. I am using onboard batteries to reduce tether size and big bulky batteries on the surface. There are many guys on here that run topside batteries so hopefully someone will pipe up and help ya out.

[Sea Searcher]

Thanks for the welcome. This is such a fun and educational project, so much to learn.

For my first go at this, I plan to use a tether that supplies power from above, so I can see what that's like. However, in order to reduce the amount of wires going down to the rov, I'm wondering if I can just use a single ground wire that splits in a junction box, at the rov, to connect to the thruster ground wires. If so, do I have to make it a heavier gauge than the power wires? What gauge would be the equivalent of two 18-gauge wires?