Remote Sense: Compensating for Cable Voltage Drop

A power supply regulates the voltage at its own output terminals. Your load sees whatever is left after the connecting leads have taken their share — and at low voltages and high currents, that share is rarely negligible.

Where the volts go

A 1.0 mm² copper conductor has a resistance of roughly 0.017 ohms per metre. A load two metres away needs four metres of copper once you count the return path — about 0.07 ohms. Draw 10 A through that and you lose close to 0.7 V. On a 24 V rail that is a rounding error; on a 5 V rail it is 14% of your supply voltage.

What remote sense does

Remote sense adds a second pair of wires from the supply’s sense terminals to the load itself. The supply then measures at the far end and lifts its output just enough to compensate. The sense pair carries almost no current, so it drops almost no voltage — it reports the truth about what the load is actually receiving.

Using it properly

• Respect the compensation limit. Supplies state how much drop they will correct, often a few tenths of a volt per lead. Beyond that, fit thicker cable — sense is not a substitute for copper.
• Never leave sense leads floating on a supply that expects them. If you are not using remote sense, link each sense terminal to its own output terminal at the supply.
• Run the sense pair as a twisted pair, away from switching and motor cables. It is a measurement circuit and will happily pick up noise.
• It corrects steady drop, not fast transients. Keep decoupling capacitance local to the load for that.

Not sure whether your run needs it? Tell us the current, the distance and the rail voltage and we will tell you whether sense or thicker cable is the better answer.