Hi, I'm Tom, the creator of the site. Before buying an electric car, I spent about 12 months researching, there were plenty of questions I had - namely in regards to range and charging. With charging, I was surprised that I couldn't find any simple tools for calculating charging times online. So I decided to build one and contribute something back to the community which I hope is helpful to others.
It's far from perfect, so if you spot any mistakes, glaring errors or just want to say hi, you can contact me on twitter.
How the calculation works
The basic calculation is the simple theoretical one: Battery capacity ÷ Charging rate = Time to charge.
Charging rate is based on the charger and the acceptance rate of the vehicle in question, along with battery size these are all properties stored for each vehicle. Charging rate has a small reduction in the calculation based on an efficiency value, which varies between chargers, but it's mostly around 90%.
However, this theoretical value is completely unrealistic in the real world, as charging time isn't normally linear, it generally takes longer the closer that the battery is to being full. To account for this, I apply a logarithmic curve to the theoretical value. The greater the power rating, the greater the curve. It's not dissimilar to charging curves in the real world, but it's not identical either - these vary between chargers and vehicles so it is a generalisation.
I'm not an engineer or a mathematician, I simply compared the theoretical results to real world results and attempted to get a reasonable estimate by creating and applying a formula. It's not accurate and to be honest I'm not sure it ever could be, considering the number of variables involved, but it's better than the theoretical calculation.
Why no hybrids?
This site is intended as a tool for electric vehicle owners and hopefully to help a few would-be owners understand the basics of charging. I've decided to include electric vehicles only, with the simple aim of promoting them.
It is still possible to use the calculator for other vehicles - if you know the battery capacity and on-board charger size, just choose "Not listed" from the homepage.