stevey_frac t1_j7khymq wrote on February 7, 2023 at 1:34 PM

Reply to comment by boganknowsbest in So How Long Does It Take To Slow Charge a Hummer EV? (10 days) by hi9580

The problem here is that a lot of the energy is going to keeping the battery warm enough to accept charge, because they're charging the battery outside, in the cold. Of the 1500 watts from the plug, less than 500 watts is actually going into the battery, with 1000 watts going to heat.

Move up to 3000 watts, and you're still throwing 1000 watts to heat, but 2000 watts will be going into the battery, and your charge time drops to like, 2.5 days instead of 10.

drweird t1_j7kshis wrote on February 7, 2023 at 2:56 PM

Actually, assuming the Hummer is correct in its estimation, only 18.79% of the energy cannot be accounted for, and might be heat...?

Given 49pct charge on 250KWh battery, we have 122.5 KWh to charge. Standard 120v outlet has a max utilization of 1500W continuous, regulated by NEC, so the charger maxes out at that; this gives us 1.5KWh/h charging. IEEE has done studies EV chargers and found on average Level 1 charging is 83.8% efficient without heating present. This is not specific to this vehicle, so it's a rough number. Given 83.8% efficiency, our charging drops to 1.257KWh/h. At this rate, we have 122.5KWh / 1.257KWh/h, giving 97.45h. This is 4.06 days. Assuming that the video is roughly 1030AM on Sunday (he says Sunday morning) and we know the charge finish was projected as 1030AM Friday, we can roughly assume a 5 day charge period. 4.06 days being the optimal estimated charge period, and 5 being estimated gives us an estimate that is only 82.12% as fast as we expect. That gives us the unexplained 18.79% slower than expected charging.

I agree that in extreme cold Teslas and such will use heat to keep the batteries warm enough to charge, but at least if we trust the Hummer computer, it isn't cold enough to significantly heat the batteries, if at all. The unexplained slowness could be heating, or an incorrect estimate about the Hummers onboard inverter charging efficiency, or the Hummers ancillary charging equipment like cooling pumps pulling more power than the average car in the IEEE study. OR it could be as simple as the Hummer being wrong about 1030 on Friday.

My 2 cents