Charging speed - why can't the following be done....

[FloridaSun]

I'm not an expert in battery and charging technology, so this question may be dumb but I have wondered about the following.

Let's say that a 100kw Tesla battery pack charges in 45 minutes to 80%.
Now, if you can apply the same charging speed to a 33.3 kw, a 33.3kw battery pack could charge to 80% in 15 minutes.
Why isn't it possible to divide the battery pack into 3 individual 33.3 kw units for charging and re-connect them as one unit once they are all charged up to 80% in 15 minutes?
Any engineers on here that can explain why this is not done or is not possible??

 

[DucRider]

There are technical reasons (research "C rate" for one example), but the big drawback is that your scenario would require you to hook up to 3 DCFC units simultaneously to charge all three packs at the same time (I believe the Tesla Semi currently uses this method).

 

[bwilson4web]

Fast DC chargers have two limits: kW and current. The “kW” is a function of the grid service agreement. The current is a function of the charger-to-car.

Now IF you had a 50 kW, battery pack charging limit, in theory you could split the pack and parallel charge them at 100 kW only if the current was within the charger maximum current. But the charger kW rating is typically at the higher traction battery voltages. For all the complications of splitting and paralleling to halves, the current limit could make it moot.

Still, I like seeing thinking like this!

Bob Wilson

 

[electriceddy]

I also would expect a surge current the moment of connection until the cells equalize the voltage differences. You would not want to try this if one or more cells were not up to spec. or for example different internal resistance.

 

[FloridaSun]

There are technical reasons (research "C rate" for one example), but the big drawback is that your scenario would require you to hook up to 3 DCFC units simultaneously to charge all three packs at the same time (I believe the Tesla Semi currently uses this method).

If indeed this could cut charging speed, someone could come up with a new connector that has 3 different 400 volt/150 amp currents..

 

[FloridaSun]

I also would expect a surge current the moment of connection until the cells equalize the voltage differences. You would not want to try this if one or more cells were not up to spec. or for example different internal resistance.

My line of thinking was to electronically separate them for charging and once they all reach 80% and charging finishes, the battery packs are connected back together.