5 ms·
Look at charging rates in watts (watt hours per hour) instead of in percentage; those semis have much larger capacity batteries, so they need a higher charging
by jepler 9y ago
Look at charging rates in watts (watt hours per hour) instead of in percentage; those semis have much larger capacity batteries, so they need a higher charging rate in W to charge 80% in 30 minutes than a vehicle with a smaller battery.
- cperciva 9y agoThey don't have larger capacity batteries. They have batteries with more cells. Sure, the total charging rate is a higher Wattage, but you can charge cells in parallel. The scaling here is exactly the same as with the "larger battery" versions of the Model S having more horsepower; higher capacity = higher throughput when you're dealing with battery banks.
- kumarvvr 9y agoWait, are you concluding that having batteries with more cells is not the same as increasing the capacity of the system? For any battery system, the capacity is the product of the number of cells and capacity per cell.
- cperciva 9y agoMy point is that having a larger capacity battery automatically increases the wattage at which you can recharge. It's not like a gas tank where a 100L tank takes longer to refill than a 50L tank.
- kumarvvr 9y agoNo, capacity of the battery isn't what determines the wattage at which you can recharge. It's the physical power supply constraints. If I have a 250v, 25 kWh battery, I can charge it at 250 V, 100 Amps for 1 hour or at 250V, 1000 Amps for 6 minutes. What charging rate I select depends on the voltage and chemistry in the battery. Can the battery support charging at such a rate. The charging current rate is limited to the max operating current of the battery. If the above battery can supply a max current of say 50 amps, then you will have a max charge rate of 250V, 50 Amps for 2 hours.
- petre 9y agoWhat makes it confusing is that the charging rates are given as 10C, meaning 10% of nameplate capacity.
- kumarvvr 9y agoMight be fererring to nameplate power capacity.
- zAy0LfpBZLC8mAC 9y agonC means n*capacity/time, so 10C for 10kWh is 100kW
- jsjohnst 9y agoThat’s wrong. 10C means 10x the nameplate capacity. If I have a battery that outputs 40Ah, 10C means I can give it a charging current of 400A.
- jsjohnst 9y agoHere’s some napkin math based on a few assumptions. Assumptions: The article is correct and it’s an 800KW battery pack for the semi. I’m also going to go with a conservative assumption and assume 2C charging rate for the battery pack. I’m also going to assume that the semi will have the ability to take in a 480V charging current because it simplifies wiring and is easier to get in an industrial capacity. With those assumptions, you’ll need 1.6MW of power, something that can be easily delivered with less than eight 500MCM cables (roughly 1” copper cables including insulation that weigh about 2lb a foot and are still rather flexible). This seems in line with the charging port photos I’ve seen for the semi. Neither the cables or the power needs are that dramatic, there’s wind turbines that put out that much power individually along I-70 in Kansas for example where there is thousands of them.
- nbanks 9y agoThis makes sense--it explains why it takes as long to charge my mobile phone as a model S. Obviously different chemistries can charge at different rates, and the power supply and cooling needs to scale with the battery capacity, but if these are scaled then two batteries which use the same cells will recharge in the same time regardless of how many cells are in the battery. I suspect Tesla's grid storage already proves this point.
- foota 9y agoI would imagine that the difficulty in charging is proportional to the cell's capacity, so charging 2*n cell shouldn't be any harder than charging n cells, as long as the cell's capacity is the same. If you increase the capacity of a cell, then you might have to innovate.