Enrichment · Passion Projects · Travel

How many stops
to get there
with charge to spare?

Type the trip, the battery and how you drive. The calculator turns the battery into miles per percent, ends each leg at your reserve, and plans the fewest stops with the minutes each one takes.

Plan the stopsWhat you get

The charging stop planner

The worked example is a made-up 420-mile highway drive in a car with a 75 kWh battery. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
The number of stops, each leg’s miles and arrival charge, the minutes at each stop and the total charging time. It prints as a trip sheet and downloads as a spreadsheet.
Who it is for
Families planning a road trip in an electric car, new EV drivers, and consumer math and physical science classes.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Type the trip distance from a map.
  2. Type the usable battery and your usual miles per kWh.
  3. Pick the conditions for the day.
  4. Set the departure charge, reserve and charge-to level.
  5. Read the legs, then find chargers near each stop point.

Plan the stops

How the stops are planned

Miles per percent, then one leg at a time.

The worked example: 420 highway miles in a 75 kWh carMiles per 1%2.2975 kWh × 3.6 × 0.85 ÷ 100Leg 1172 mi90% down to 15%Each stop149 mi15% → 80%, 33 minTotal2 stops54 min chargingThe worked example: 420 highway miles in a 75 kWh carMiles per 1%2.2975 kWh × 3.6 × 0.85 ÷ 100Leg 1172 mi90% down to 15%Each stop149 mi15% → 80%, 33 minTotal2 stops54 min charging
Turn the battery into miles per percent, and the plan becomes simple arithmetic.

Miles per percent

A 75 kWh battery at 3.6 miles per kWh holds about 270 miles, or 2.7 miles per percent. Highway speed adds air drag and cold makes the battery and the heater cost energy, so the same car may get 15 to 30 percent fewer miles on a winter interstate. The conditions setting scales the efficiency to match.

Why stop at 80 percent

Fast chargers deliver their highest power when the battery is low and slow down as it fills, often sharply above about 80 percent. Two short stops from 15 to 80 percent are usually quicker than one long stop to 100. The last stop charges only enough to reach the destination with the reserve.

Sources

  1. U.S. Department of Energy and U.S. Environmental Protection Agency. fueleconomy.gov: electric vehicle range and the effect of speed and temperature (fueleconomy.gov).
  2. U.S. Department of Energy, Alternative Fuels Data Center. Developing infrastructure to charge electric vehicles; charging levels and speeds (afdc.energy.gov).
  3. National Renewable Energy Laboratory. Electric vehicle fast-charging behaviour and charging curves (nrel.gov).
  4. Federal Highway Administration. Alternative fuel corridors (fhwa.dot.gov).

The worked example is made up. Conditions factors are rough; your car’s trip computer is the better guide after a few trips. Your entries stay in this browser. Support: team@caveatacademic.com.