How the calculation works
For each row, watts = entered watts × quantity, or voltage × amps × quantity. Peak connected watts is the sum with all included devices operating. Duty-adjusted average = the sum of each row’s watts × duty fraction. Total amps = total watts ÷ entered voltage.
Worked example
One illustrative 100 W light bar plus one 10 W GPS draws 110 W, or 9.17 A at an assumed 12 V, when both operate. At 50% duty for the light and 100% for GPS, the planning average is 60 W, or 5 A.
Use input power from the right source
Check the device label, manual, or measured operating draw. Marketing brightness and audio output ratings are not electrical input consumption. A phone charger’s USB output rating can differ from its vehicle-side draw because of conversion losses.
Peak versus duty-adjusted average
Use peak connected draw when considering simultaneous demand. Duty percentage is only a time-average assumption and does not reduce instantaneous current while a device is on. A known accessory budget should account for the machine’s own loads and engine-speed-dependent output; do not enter the entire charging-system headline rating without checking that basis.
Frequently asked questions
Can I add a device rated in amps?
Yes. Select amps on that row; the tool converts it using the voltage you entered.
Why is the power budget optional?
No machine charging capacity is assumed. An unknown budget produces totals only, not a claim of spare capacity.
Does a positive budget margin mean the wiring is safe?
No. Branch circuits, fuses, surge demand, connectors, and voltage drop need separate checks.