Is anyone in this forum experienced with ROV builds in which (the thrusters at least) are powered by DC supply via a tether? I’d appreciate any pointers (and especially words of warning 
Advance thanks!
@Ed,
You might want to review the posts on the homebuiltrovs.com Control Systems and Tethers Forum
Regards,
TCIII AVD
14 AWG stranded wire is approximately 1/2 ohm resistance per 200 feet. Just Google resistance of stranded wire.
Assuming 2 motors are drawing 10 amps total, the voltage drop is 5 volts (I’m sure you know all of this). To run the T100 efficiently, you probably need at least 10 volts. From this you can see the usual 12 volt Lead Acid battery on the boat isn’t going to work. Two batteries in series (24 v) and running T200’s might work (they can take more voltage than the 100’s).
Unless you only need a very short tether, you’re basically restricted to using high voltage transmission and voltage converter on the ROV.
There are a few voltage drop calculators online that are very useful. We’ve made one that’s great for calculating voltage drop in tethers:
Even at 48V, the power loss is pretty substantial. Most pro-grade ROVs use 300-3000V for power transmission.
-Rusty