Menu

Power station runtime calculator

Add what has to run and how long it must last. Every power station in the data set gets a verdict, with the math behind it.

Updated

How the calculator works

  1. Running watts. It adds the running watts of everything on your list, as if all of it runs at the same moment.
  2. Starting watts. It lets one motor start on top: the appliance whose start adds the most swaps its running watts for its starting watts.
  3. Watt hours a day. It adds what each appliance uses in a day: watts × hours, or the published daily energy for refrigerators and freezers.
  4. Each station. It keeps 85% of the rated capacity, checks the output against your running watts and the surge rating against your starting watts, then divides the usable watt hours by your daily total and multiplies by 24.

A station is Enough when it passes the power checks and lasts at least your goal. Runs it, but not long enough passes the power checks and runs out sooner. Cannot power it fails a power check, and its line names the numbers. Inside Enough, the smallest capacity comes first because it is the closest fit, then the lower price, then the lighter unit.

Reading a result card

  • The large number is hours of your routine: how long the station lasts while you use each appliance for the hours you entered. It shows minutes under an hour and days above 48 hours, and it is the number compared with your goal.
  • The small number is the time with everything running nonstop at once. It is there for reference.
  • The line of math shows the rated capacity, the usable watt hours and what your list uses in a day.
  • Output used and Start surge show your running and starting watts against what the station can supply.

The methodology states every formula and assumption. Nothing here was tested: the figures come from published specifications and appliance data, and each station and appliance page lists its sources.

Questions

Why can a station with a big battery fail?
Capacity and power are separate limits. The output check compares the continuous output with your running watts, and the surge check compares the surge rating with the starting watts needed. A failed check puts the station under Cannot power it however many watt hours it has, and the line prints both numbers. Watts vs watt hours explains the difference.
Why does each card show two runtimes?
The large number is usable watt hours ÷ the watt hours your list uses in a day × 24: hours of your routine, with the use spread through the day. The small number is usable watt hours ÷ running watts, the time with everything on at once. Only the first is compared with your goal.
What does the 85% under Assumptions and solar mean?
It is the share of the rated capacity that reaches the outlets after the inverter and conversion losses. 85% is the default; you can set 75% to 95%. Plan with less for a cold location or an older battery. Why you get less than the rated capacity has the details.
Why does a refrigerator count less than its watts times 24 hours?
A compressor switches on and off, so the calculator uses the published energy per day for refrigerators and freezers instead of running watts × 24. If you enter label watts for a fridge, those watts count for every hour you enter, so set the hours to the time the compressor runs. How to read an appliance label shows how to work that out.
What does "starting watts not published" mean?
The appliance has a motor or compressor, but no source gives its starting watts. The calculator checks its start at running watts, so it does not reject a station on a guess, and the note stays on the line. A label figure entered as your own appliance gives a firmer answer. See starting watts explained.
When does a goal shorter than a day mislead?
The runtime spreads each day of use over 24 hours. With a 4 hour goal, it counts a sixth of the day's watt hours. If all of the day's use falls inside those 4 hours, a television at a tailgate for example, set the goal to 24 hours so the full day counts.
How does solar change the result?
Enter panel watts under Assumptions and solar and each card adds the energy a day from the sun (panel watts, capped at the station's solar limit, × sun hours × 0.75), whether that keeps up with your list, and the hours of sun to refill. The verdict does not change: it describes how long the battery lasts without recharging.
What if an appliance is not in the list?
Add it under Your own appliance with the running watts from its label and, for a motor or compressor, its starting watts. A watts figure you enter for a listed appliance replaces the typical value through Use the watts on your label.
Is the list stored or sent anywhere?
Your list stays in the address of this page, so Copy link shares the same result. Nothing is saved in your browser's storage, and there is no account behind it. Our server logs leave out the part of the address that holds your list, and the visit statistics never see it. The site counts tool use without cookies: how many appliances, a band of total watts, the goal and which appliance types were added.