That's interesting data, but it's not complete. At least with some data, like from @David99, there are at least 2 types of pack readings, nominal full pack, and usable full pack, along with full remaining, and usable remaining. There are multiple SOC readings also, SOC, SOC Min, and SOC UI, and they are all slightly different, so you should designate which one you are referring to, or show the table. For example, your chart shows SOC = 6.5%, but your 4.3 / 70.8 = 6.1%. So they don't match in that case.
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I think my car is lying to me...
- Thread starter supratachophobia
- Start date
I like the analogy of efficiency loss like evaporation. I think it's accurate in the sense that it is calculable, but perhaps not quite relevant during a 100% to 0% trip.
BMS data = CAN bus data. What you get on the CAN bus is what the car's computer and BMS uses. There is no difference. The difference is counting the energy taken out vs what is left. Those are two different data sets, that's all. Their difference tells you the battery internal losses.
I like the analogy too. Like all analogies, it's not perfect. For example, the internal losses in the battery(I2R, in part) are the direct result of drawing current from the battery, whereas the evaporation from the barrel occurs whether or not you are draining the barrel of water.
But that's a small nit for an otherwise good analogy.
There are a lot of factors that apply to energy loss of a battery, as long as we don't go crazy into the discussion being a little general helps. The pack impedance is the largest factor of performance but there are a lot of other things that can cause issues with our packs. I see people here asking about their packs not charging up to 100% and I think this is mostly temperature related rather than condition of battery.
I just want to add that the amount of energy lost in the battery is basically impossible to predict. Ohmic losses increase exponential with current. There is no way the BMS can predict how you will drive. Even if the average is the same, it is not the same to drive at 20 kW constant or 30 kW for half the time and then 10 kW for the other half. Losses will be higher in the second case. Temperature affects resistance as well.
The best overall number I have is the total charge vs discharge energy measured by the BMS. The BMS keeps track how much energy the battery has been charging and discharging and after 5 years the difference is 6.6%. This leads to the conclusion that when charging you lose 3.3% and when discharging you lose 3.3%. But given the fact that our batteries are optimized for discharging (you can discharge at a much higher power than charging), I would think the discharge losses are lower than the charge losses. Maybe a 3:1 ratio.
The best overall number I have is the total charge vs discharge energy measured by the BMS. The BMS keeps track how much energy the battery has been charging and discharging and after 5 years the difference is 6.6%. This leads to the conclusion that when charging you lose 3.3% and when discharging you lose 3.3%. But given the fact that our batteries are optimized for discharging (you can discharge at a much higher power than charging), I would think the discharge losses are lower than the charge losses. Maybe a 3:1 ratio.
So if that is the case, which I know it is, then you would think that supercharging losses would be higher than say, home charging, since the charging rate is so much faster. Is that observable in any way? I don't do supercharging so I have never looked into that.
Interesting because I thought charging at 240v was actually *more* efficient than charging at 110v?
I have not done any tests or measurements. I'll try next time I'm on a supercharger.
Yes 240 Volt charging is more efficient. Tesla used to have it on their website in the charging section. It showed that the most efficient charging is at full power rate the charger can handle. There are two reasons. The charger itself is just optimized for full load. It is slightly less efficient at partial load, especially when running at 120 Volt instead of 240. That's actually pretty common for power electronics. The other reason is that when you charge at a lower rate, the supporting systems (battery pump, cooling fans, ...) are running longer because of the charging session taking longer.
Tacking onto those reasons, the pack is 350 to 400V, so having an input voltage closer to that also increases efficiency.
Plus you get less cable loss (I^2*R) for the same power at a higher voltage.