mopitcher wrote:I have one customer who is adamant that his "internal charger" should be feeding 7.4 kW to the battery AT ALL TIMES when plugged into a Level 2 EVSE. He reports a max of about 6 kW. I informed him that it's more like "up to" 7.4 kW and that a lot of variables can affect the amount of energy that goes into the battery but he doesn't seem to accept this, and says that "he paid for 7.4 kW" or something to that effect. Is there an a solid answer I can give customers who inquire about why their charging rate isn't the maximum?
For any point in time during a charge, the power is the voltage times the current. It is not constant during a charge.
The max L2 charging is 240V at 30A, which is 240x30 = 7200 watts, or 7.2kW. However, any EVSE may be capable of supporting less than 30A. If the EVSE can support more than 30A, then only a max of 30A will ever be fed to the i3. Also, all 240V circuits have line resistance, and the more there is, the more the voltage drop will be to the car. A typical 240V circuit supplying more than a few amps will be showing about 220V, leaving the i3 with a more typical charge rate of 6.6kW. And, finally, as the i3 reaches full charge, the charge rate will slow down (the i3 will slowly reduce the current it draws from the EVSE).
One more issue is that many industrial (not home) circuits are 3-phase 240V where the EVSE will only see a max of 208V from any two of the three power legs, rather than the full 240V that a home 2-phase 240V circuit sees. So the max power on one of these circuits, as might be found in a large parking garage, for example, is 6.24kW.
So, the basics are the L2 charging power is limited by:
1) The supply voltage, which may be anywhere from about 200V to 240V.
2) The supply current, which may be anywhere from 0 to 30A, where the EVSE reports to the i3 the maximum safe current the circuit can provide, but which the i3 will never take more than 30A, as that it the most the internal i3 chargers can handle.
3) The i3 battery, which can only take the full 30A when available from the EVSE when the battery is not near full charge, and will draw less and less current as the battery reaches full charge.