Would any of you care to speculate on what caused the drop from 7 Kw to 4 Kw here? Normally I see it just stay high until it gets close to charged, then drop. I think this one was reading about five bars on the battery when I plugged it in. This is from a JuiceNet charger.
I see drops like that on Chargepoint chargers, but as they only update the data every 5 minutes, it is hard to say if it happens sharply like that 7 -> 4 kW drop. If the area was chilly and the battery was cooling down, it may have throttled back on the power draw to manage the charging better for long term life. At low temperatures and low SoC, the battery can manage a faster charging rate, but as the SoC goes up (at the same cold battery temperature), the maximum charge rate will decline somewhat. The fact that it drops suddenly like that is surprising, if that was indeed the cause. Could you have been using climate control during the early stages of charging? When that turns on and shuts off I would see sudden changes like that. But since you didn't mention it I'm guessing that was not the case. Interestingly, the curve at the end of the cycle is where it changes from controlled power to constant voltage to avoid overshoot. I have a reference somewhere on Honda charging technology that I can link after I find it. It may also contain some details which explain the behavior you are asking about.
Is this a public charger that someone may have plugged into the other side of the charger? There may be a maximum total amperage for the two.
To answer the second one first ... no. I drove into the garage and plugged in the charger. Just as I always do. But I think you may have it on the first postulate. The garage was cold (~20°F). The battery was probably relativey warm from providing energy for the recently-completed trip. But as time passed, the battery cooled. I have observed abysmal charge rates into a cold battery, and as I remember it the signalling protocol for the charger is based on steps. I wonder if the battery cooled to the point where the car controller decided that the next step down of charging rate was appropriate, and signalled the charger, slow down to 4 kW.
My Charge Point Home always charges at a steady 7.1 to 7.2 kW rate until the ramp down at the end. The only time I ever saw it drop down to 4kW was once when I charged immediately upon arriving home instead of waiting for the middle of the night scheduled charging. I speculate that it’s battery temperature related.
