Homebuilt ROVs Forum

What about running an extension cord for thruster power. What will the voltage drop be and can it handle only 12 volts of power efficiently enough to run 100 to 150 ft.

Short answer:
viewtopic.php?f=15&t=1191

Good advice ROVER3D . I'm hoping that KBG is only thinking 12 volts though! KBG, you have to know the gauge or alternatively the cross-sectional area of the wires inside the cable to be able to answer the question. Below is an example of how to work it out for 12 volts at the surface, 16AWG wire, 50 metres long, and a current draw of 3 amps

16 AWG has a resistance of approximately 0.013 ohms per meter (from a table off the internet)
50 metres of two-conductor cable has a total circuit length of 100 metres
Total resistance = 0.013 ohms X 100 =1.3 ohms
Voltage drop = current X resistance, or V=IR
=3 amps X 1.3 ohms
=3.9 volts
So if running off 12 volt battery on the boat, the motor will get 8.1 volts.

Problem with extension leads is that the wires inside are thin compared to the outer sheath diameter, so will add more drag and mass than say speaker cable with thinner insulation. The tether is one of the more challenging aspects of homebuilt ROV projects, especially if you are feeding power down it as well as having other wires for camera, data and control.