Load Voltage Calculator

1) Purpose of a load voltage check

Load voltage is the potential difference across a device while current flows. It can be lower than the supply’s open-circuit rating because the source and wiring have resistance. This calculator estimates that drop for design and troubleshooting. It also supports acceptance testing, where minimum operating voltage must be demonstrated.

2) Typical ranges and practical resistance

Many systems run from 3.3 V to 24 V. Output resistance may be milliohms to several ohms, depending on the supply and cabling. Batteries add internal resistance that changes with temperature and state of charge. Even 0.5 Ω at 2 A causes a 1 V drop, which can push sensitive electronics out of tolerance.

3) Voltage divider mode with numeric insight

Divider mode uses V_load = V_s·R_L/(R_s+R_L). If V_s=12 V, R_s=10 Ω, and R_L=40 Ω, current is 0.24 A and the load receives 9.6 V. About 20% of the supply is lost in R_s.

4) Thevenin view for complex sources

Thevenin mode expresses a network as V_th in series with R_th. Measure open-circuit voltage for V_th, then estimate R_th using a known test load and a second voltage reading. The same divider equation applies.

5) Current and resistance mode for field checks

If current is known, Ohm’s law gives V = I·R. For 300 mA through 20 Ω, V_load=6 V and P=1.8 W. This helps verify resistor ratings and spot unexpected wiring losses quickly.

6) Power-based estimation when voltage is unknown

When you know dissipation and resistance, use V = √(P·R). For P=2.5 W and R=10 Ω, V=5 V and I=0.5 A. This supports resistor sizing, heaters, and controlled load testing.

7) Design checks: droop, heat, and tolerance

The tool reports total power and an efficiency ratio (load power divided by total). Larger R_s increases wasted heat and reduces headroom. For tight limits, consider 1% resistor tolerance and typical meter error around 0.5%–1%, then apply safe margins.

8) Reporting and repeatability

Export CSV for comparisons and PDF for documentation. For repeatable results, keep the same wiring and connectors, because contact resistance can vary by tens of milliohms and change droop at higher currents. Saving multiple runs with dates makes reviews and audits much easier.

1) What is load voltage?

Load voltage is the voltage measured directly across the load terminals while current is flowing. It can be lower than the supply’s rated voltage due to source resistance, wiring resistance, or protection circuitry.

2) When should I use Thevenin mode?

Use Thevenin mode when the upstream network is complex but can be represented by an equivalent Vth and Rth. It is especially helpful for modeling sensors, regulator outputs, and battery packs under load.

3) Why does my load voltage drop when current increases?

Higher current increases the voltage drop across series resistance (Vdrop = I·Rs). That resistance may come from the source, cables, connectors, or internal device protection, causing delivered voltage to sag.

4) Can I compute load voltage from power alone?

Only if you also know either the load resistance or the load current. With resistance, use V = √(P·R). With current, use V = P/I. Power by itself is not enough to determine voltage.

5) How do units affect the results?

Units are converted internally to base volts, ohms, amps, and watts. Selecting mV or kΩ changes the interpretation of your input numbers, so confirm the unit dropdowns match your measured quantities.

6) What does the efficiency value mean here?

Efficiency here is load power divided by total power from the source, expressed as a percentage. It shows how much power reaches the load versus how much is wasted as heat in the series resistance.

7) Is this calculator valid for AC circuits?

It targets DC or steady-state resistive equivalents. For AC with reactance, you must use impedance and RMS quantities. If your load has significant inductance or capacitance, results may not match reality.