gpsman wrote:How come on a cool 45 degree day I can regen at the full 70 kw but I can only DCFC at 32 kw?
I know charging warms the pack, but after 30 minutes I was only at 38 kw on a 50 kw DCFC.
My car was in the 26% to 50% range.
There are two types of "50kW" DCFCs. They can either be 100A / 500V or 125A / 400V.
If it's the former, your car is limited by the charger. The Bolt will pull 100A as the battery voltage slowly rises to about 370-380V before tapering down to about 66A. This means the max you can actually charge your car is the 38kW you have seen. I'm guessing this is what is happening.
Actually, the car is limited by the charger in both cases that you stated - it's just that in one of the two cases the car is limited more. The Bolt appears to be limited to a max of 150A when using DCFC (based on reports of fast charging posted from Europe, where they have 100 kW+ CCS charging stations).
Yes, the Bolt aggressively steps down the amperage when fast charging at multiple points : somewhere around 55% SoC (dropping from "up to 150A" down to "around 100A") and then again around 70% (dropping down to "about 65A") and again near 85% ("about 45A"). So, if you are using a 100A DCFC, it will charge at a rate of 32-36 kW until it reaches about 70% SoC (the voltage goes up during DCFC charging while the amps remain constant, and thus the kW rate slowly increases). If you use a DCFC that can provide 150A (or more) then you will charge at a rate around 52-54kW until about 55% SoC, when the charging will drop to 100A.
Now, if your question was more "why did GM do it this way
, since the battery will charge at 70 kW during regen", instead of "why can I only DCFC at 32 kw" - the answer is "because GM programmed it that way". My guess is that they did it that way to prolong battery life (but that's just a guess - nobody told me). The battery should be able to take short burst of very high-level regen (measured in seconds) with very little harm - much, much, much less harm than charging at the same high rate for 30 minutes or longer.