Fast Charging with DCFC’s
written by Howard Ashmore
Do you seem to get slower than expected charge rates at the fast chargers? It says its a 150 kw charger but you only seem to get 30-40 kw speeds or less?
Its probably you!.. Okay not only you but it is a lack of preparation on our part…its not the car or the charger. Its all about the preconditioning, let me explain.
Typically we arrive at a DCFC (Direct Current Fast Charger) with a low SoC (state of Charge) on the battery and want a fast fill up. However if you just got in your EV from being parked all night and want to get a charge to start your day, it will be a slow charge. If you have been driving for a couple hours and want a fast charge, it too may be a slow charge. Lithium batteries can accept large flows of DC electricity but only when they are properly prepared, this is called “preconditioning” or pre-heating the battery to the optimal temperature to receive high capacity flows of power, as can be delivered by a DCFC.
So how do we pre-condition our EV’s? Well that too is a tricky question. It depends on the EV. For example, Tesla EVs will automatically precondition if the car knows you are headed to a DCFC (or supercharger). A Chevy Bolt can be preconditioned by starting the car and warming up the interior which will also warm the battery. Other EV’s have similar ways to precondition however the owners manual may not call it that.
The trick to getting high charging rates at the DCFC’s is to give your EV lots of time to precondition (warm up the battery). Lots of time depends on the temperature outside, the present temperature of the battery and the SoC of the battery.
Rule of thumb would be 30 minutes minimum even in summer, 40 minutes in the fall and spring and a full 60 minutes in the winter (here on the sunshine coast) and have a SoC below 30%
A few tricks and tips.
- Tesla – Use the navigation feature and key in the supercharger of your choice. Be sure to give the car at least 30 minutes to precondition, more if its cold, below 16ºC.
- Chevy Bolt – Use the MyChevrolet App and start the car, the battery will automatically warm (precondition) but give the car lots of time to warm the battery. It may be warm in the cabin but the battery will take at least 30 minutes, more if it’s cold, below 16ºC.
- Nissan Leaf- Look for pre-heating under the Zero Emissions button. Give the car lots of time to pre-heat, at least 30 minutes, more if its cold, below 16ºC.
A little more detail, Tesla EV’s will not precondition the car unless it is told to or knows it’s going to a DCFC. Therefore if for instance you are on a long trip and stopping at the superchargers without using the navigation, then you will get slow charging rates because the car will not have warmed the battery to the optimal temperature. If however you use the navigation feature to tell the car you are going to stop at a given supercharger, then the car will automatically precondition the car for the estimated arrival time. You will see high charging rates depending on the capacity of that supercharger, usually 75 to 150+ kw.
The Chevy bolt looks after itself quite well on a trip because it has a battery heater that keeps the battery warm at all times while the car is on but it will require a least an hour of uptime or driving to reach the optimal temperature for fast charging.
Read your owners manual to familiarize yourself with the system your EV uses to keep your battery warm. If you can arrive with a warm battery with a low SoC, you will experience fast charging rates at the DCFC’s. 😎
Both of the following shots were taken at the Sechelt supercharger:
Cold battery w/o preconditioning – 37kw fastest charge
Preconditioned battery for 40 minutes (drove fom Sechelt to Gibsons and back) max 175kw charge