Battery Runtime and LED Resistor Basics
Low-voltage DC projects often need two estimates: how long a pack lasts at a load, and which series resistor protects an LED. This guide covers the worksheet math and the hard stop before AC mains work.
Runtime from capacity
Idealized runtime hours ≈ capacity (Ah) ÷ load current (A), with derating for Peukert effects, temperature, and usable depth of discharge. Wh-based estimates use energy ÷ load watts. Treat results as planning numbers, not guarantees.
LED series resistor
For a simple DC LED string, R ≈ (Vsource − Vf_total) ÷ I_led. Power in the resistor is I²R. Forward voltage and current come from the LED datasheet—guessing them burns parts.
Project checklist
Confirm DC vs AC
These tools are for low-voltage educational estimates.
Size runtime or capacity
Use battery runtime/capacity calculators with your load.
Protect LEDs
Use the LED resistor calculator with datasheet Vf and current.
For household circuits
Switch to Ohm’s law learning tools only as theory; hire a pro for installs.