Charging Speed Limits of EV Cars Explained
As we can see many doubts and misunderstandings of real-life charging speeds, I decided to write this blog post. Here I try to explain, what does that mean, that EV car has a single onboard charger or double-speed onboard charger.
Common information we can find about the speed of charging is, that single charger can charge 3,6 kW and double one - 7,2 kW accordingly. But a real speed is slower. Why?
If we divide 3,6 kW through 230V (standard EU voltage), we can find, that current will be around 16A. This is a maximum current for 16A 3-phase socket (per phase), and also popular maximum current for private homes in EU. Every phase of such energy grid connection is protected with a B16 breaker (fuse). Because there is an obligatory gap between maximum permitted current and EV onboard charger (factor is 0,9 of maximum current), this means, that single charger would not charge at 16A, but 16A * 0,9 = 14,4A.
This current we see while charging of 3,3-3,6kW onboard charger (sometimes it is declared to be 3,3kW - what is true because 14,4A * 230V = 3,3kW, sometimes 3,6kW - what is not true).
Double (or 6,6kW - 7,2kW) chargers will have exactly 28,8A - that means, that a real power would be 6,6kW and not more.
For compensating that 0,9 factor we have used a voltage boost - Accelev uses +20V, but not more than 250V as standard voltage output (what is absolutely legal and permitted). This increases charging speed by about 10% over a standard voltage and fully compensates 0,9 factor. So single chargers will charge with a speed of 3,6kW, instead of 3,3kW, and double chargers will achieve 7,2 kW instead of 6,6kW.
Of course, there is no free energy and both phases powering Accelev will be loaded at 16A instead of 14,4A.
These fully loaded phases can still be used, if Grid Monitoring in Accelev is on. It reduces charging speed or stops it when additional load is detected and this protects fuses (breakers) to be turned off.