What size cable to use for tether?

[Kjetil]

I`m planning to use 6mm2 (approx 9 AWG) cable for power supply to my ROV to minimise the power loss. Total length is 25 Meter.

Have been calculating that I can use to motors and ligth with at the same time with a power loss of 1 volt (using 12V supply)

2X rule 360 max 2,1 amp each + 63 led *0,02 A = 5,46 amp.

When I see on pictures of other ROV`s the power supply cable seems to be a lot smaller than mine.

What size of power supply cable is recommended on a 12V system?

[AHarris]

Hello Kjetil,
When selecting a power cable, you have two options... go for a thick cable and get the most amount of power running to the ROV but have a thick, bulky and heavy tether or go for a smaller one but compromise on how easy the electrons flow... smaller cables have more resistance.
I am no expert on this, I haven't completed a ROV myself but from the failed attempts I have done I would personally go for something mid range, I have an 18AWG wire which isn't much good to power something over a long distance but is great for connecting up switches e.t.c.
Steve (the owner of homebuiltrovs.com) has made yet another excellent page on this subject at:
http://homebuiltrovs.com/howtotethervoltagedrop.html

This explains it in excellent detail!

Good luck!

[Rover]

One last thought.... Keep in mind the larger the power wire, they heavier the tether will be. You dont want the tether to be a boat anchor, or have to add a ton of floats that will add drag.

I was shocked how heavy just the pvc insulation on the wire is. I went with teflon insulation, because it is thinner and lighter. Teflon wire is used on aircraft. I was able to buy it at a electronics surplus store.

[thegadgetguy]

Yes, you have to be carefull about the weight. I know with my ROV, the stiffness of the tether will actually twist the ROV sometimes. My ROV isn't very big, but any ROV will twist with minimal force if nothing is being done to correct it's movement. Stranded wire is better for a flexibile tether than solid.