High-Power LED Resistor Calculator
Resistor ballast for 1 W and 3 W LEDs — honest wattage math, thermal-runaway warnings and where the constant-current driver wins.
Preset: 3× 1 W white in series from 12 V at 350 mA → ~6.8 Ω at 0.84 W (fit 2–3 W wirewound). If the wattage readout exceeds 1 W, read the last FAQ before soldering anything.
High-Power LED Resistor Calculator computes ballast resistors for 1 W / 3 W emitters — where resistor wattage and thermal stability decide the design — free, instant and private in your browser. Lighting modders and prototypers running 350 mA+ emitters use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About High-Power LED Resistor Calculator
High-Power LED Resistor Calculator computes ballast resistors for 1 W / 3 W emitters — where resistor wattage and thermal stability decide the design using the standard engineering relation: R = (Vs − n·Vf)/If at 350–700 mA; P(R) = If²·R lands in the watts, fit wirewound at ≤50 % rating. Worked live: 3× 1 W white in series from 12 V at 350 mA → ~6.8 Ω burning 0.84 W — a 2–3 W resistor. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use High-Power LED Resistor Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use High-Power LED Resistor Calculator?
- ✓Implements the real formula — R = (Vs − n·Vf)/If at 350–700 mA — with the substitution shown, not a black box
- ✓Built for lighting modders and prototypers running 350 mA+ emitters
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate high-power led resistor?+
Ballast resistors for 1 W / 3 W emitters — where resistor wattage and thermal stability decide the design follows R = (Vs − n·Vf)/If at 350–700 mA; P(R) = If²·R lands in the watts, fit wirewound at ≤50 % rating. For example, 3× 1 W white in series from 12 V at 350 mA → ~6.8 Ω burning 0.84 W — a 2–3 W resistor. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why keep at least 20 % of the supply voltage across the resistor?+
Stability. White-LED forward voltage falls a few mV/°C; with only 0.6 V across the resistor, a routine 0.2 V Vf shift swings the current 33 % — and a hotter LED draws yet more current: soft thermal runaway. With 2.4 V across the resistor the same shift moves just 8 %.
When does a constant-current driver beat the resistor?+
At 700 mA+ (where the resistor wastes whole watts), on battery supplies (current stays constant as voltage sags), and in anything you'll duplicate or leave running. A $2 buck CC module delivers the same current at ~90 % efficiency. Resistors remain legitimate for bench tests and ≤350 mA one-offs with proper headroom.
Is the High-Power LED Resistor Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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