Electrical calculator
Cable voltage drop calculator
Work out what a long DC run actually delivers at the far end — voltage drop, percentage, and the power burnt as heat in the cable — by conductor area or AWG.
Estimation tool, not design authority. This calculator gives a first-pass figure from the stated method and the assumptions listed below the result. It does not replace engineering sign-off, and it does not model everything a real build has to account for — see “Assumptions and limits” for what is left out. For a figure you can build against, send us the requirement.
Result
Why it matters
The tether is a resistor.
On an ROV the tether is often the longest conductor in the system and the least visible source of trouble. Thrusters that stall at depth, brown-outs when several units spool up together, and a vehicle that behaves differently on 50 m of tether than on 10 m are all voltage-drop symptoms rather than thruster faults.
The same applies to any long DC harness — a UAV power run, an instrument cable, a battery feed across a vehicle. The current goes out and comes back, so the resistance that matters is twice the run length.
How it is calculated
Resistivity, doubled.
Loop resistance is R = ρ × 2L / A, with ρ the resistivity of annealed copper at 1.724 × 10⁻⁸ Ω·m, L the one-way run and A the conductor cross-section. Voltage drop is that resistance times the current; the power lost is drop times current, and it all becomes heat along the cable.
Under about 5% drop is the usual working guideline for a continuous run. Above 10%, size up the conductor or raise the bus voltage — and raising voltage is usually the cheaper fix, because for the same delivered power, doubling the voltage halves the current and quarters the loss.
This is a DC calculation at 20 °C. Copper resistance rises about 0.4% per degree above that, so a tether coiled on a drum in the sun drops more than the figure here. It also says nothing about the cable's current-carrying capacity or insulation temperature rating, which are separate limits.
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