EV ChAmp

Copyright © 2015 DC & Co.
All Rights reserved.


EV ChAmp calculates the lowest charge amperage setting needed to replenish your electric vehicle's battery by a given time.

A typical scenario is at home where you would charge your electric vehicle (EV) overnight when electricity costs may be lower and such that by the time you need to leave for work, your battery has a full charge.

You can either login to add your vehicle(s) to the menu or use the calculator.


By using the lowest charge amperage (e.g., current) to charge your electric vehicle's battery, you realize the following benefits:

  • Minimized heating of the battery. Reducing unnecessary thermal stress to the battery prolongs its life.
  • Minimized waste heat. The higher the current, the more waste heat is generated due to increased electrical resistance. This waste heat is wasted electricity.
  • Minimized need for battery thermal regulation. When the battery temperature rises to a certain point, the battery's thermal regulation system works to cool the battery, using extra electricity.
  • Maximized charging efficiency. By using a lower current, the input voltage generally increases because of reduced load on the electrical utility service. A higher input voltage results in increased charging efficiency.
  • Reduced amount of time the battery spends at a high state-of-charge (SOC). Lithium-ion batteries that stay at a high state-of-charge for prolonged periods of time have reduced life. By charging at the minimum possible current, the battery only spends a short amount of time towards the end of the charging session in the higher SOC region. Presumably at that time, you will actually drive your electric vehicle and in the process of driving, the SOC of the battery goes down.
  • Minimized impact and disruption to the electrical service. This is especially important for residential electrical service, where the service was not designed for high continuous electrical loads, as happens when an electric vehicle is charged at high amperage for several continuous hours, resulting in voltage drops and possible overloading.


On the Login screen, enter the email address and password for your "My Tesla" account. The app signs in to your "My Tesla" account using the provided email address and password and receives back a session token that allows the app to retrieve vehicle information for up to three months without you needing to login again. The app does not save the email address and password anywhere.

Assuming the login is successful, the app retrieves the list of vehicle(s) under the account, listing their names (if set) and vehicle identification numbers (VINs). Tap OK to add the vehicle(s) to the menu. If the vehicle does not have a name, the last six characters of the VIN name the vehicle in the menu.

Select a Vehicle

When you select a vehicle from the menu, the app retrieves the vehicle's range and the state-of-charge limit for charging. The Start range and End range fields, respectively, get these range values, which are in units of rated range miles.

Presumably, when you start the app is the time that you want to start charging, so the Start time gets set to the current time. The End time gets set initially to 7:00AM. You can change the end time to the usual time by which you want charging to complete. Any change you make to the end time is saved for the vehicle. Thus if you have more than one vehicle, each can have a different saved end time.

With the above range and time values, the Charge at field displays the minimum charge amperage needed for charging to complete by the set end time. Set your vehicle's charge amperage to this value.


The calculator provides an easy way to calculate the minimum charge amperage without having to login to an account. The difference between using the calculator and selecting a vehicle is that the latter sets the starting and ending range values automatically based on the vehicle's current state, whereas using the calculator requires manual setup of those values.

To use the calculator, set the following fields:

  • Start range: The vehicle's current range.
  • End range: The vehicle's target range.
  • Start time: The time when charging will start.
  • End time: The time by which you want charging to complete.

With the above range and time values, the Charge at field displays the minimum charge amperage needed for charging to complete by the set end time. Set your vehicle's charge amperage to this value.

The app saves values you set for the start range, end range, start time, and end time fields so that you do not need to set them up again the next time you use the calculator.


The app makes the following assumptions:
  • The vehicle is a Tesla Model S.
  • The vehicle reports range in rated miles.
  • There is no difference in energy required to charge one rated mile among different vehicle models.
  • The input charging voltage is 240V AC.
  • The charging session lasts less than 24 hours.
  • Thermal regulation is not factored into the calculations.

©2015 DC & Co. All rights reserved.