THE Battery
previous: Electricity
Electric vehicle (EV) is a catch all. The correct terminology would be battery electric car (BEV) since there is not a generation source as there are with hybrid models (HEV) which have the battery, electric motor but then also have a fossil fueled engine which is used to recharge and some hybrid vehicles can take that one step further with the ability to plug-in. (PHEV). Everyone understands that batteries must be charged. The hybrid is a compromise to this end. A hybrid is an easier transition for manufacture who are reluctant to go all-in with this pure electric idea This uncertainty is of course driven by consumer demand but realize that for traditional makers of internal combustion engine (ICE) powered vehicles; they must take a significant risk. Their production facilities have engineering, tools, infrastructure and supply chains all with major capital investment that don’t translate easily. It would cost them dearly to make the switch-over. It’s probably cheaper to build a new factory from scratch as Tesla has done.
The Long Range Model 3 has an (estimated) 77.5 kWh battery. This big battery is also known as the traction battery or battery pack or just Pack; meaning package container of cells. It is the single most expensive component in the Model 3 and the entire assembly weighs in at 1,054 lbs. There are 4,416 individual type 2170* cells clustered in groups and these groups into modules within the pack. They are arranged so that they can be heated, cooled, monitored and controlled by a sophisticated computerized battery monitoring system (BMS)
*2170 is a form factor describing a single cell’s dimension 21 mm diameter x 70 mm in length
Each cell when fully charged is rated at 4.2 V but considering that there are so many and that they are wired in series the total voltage at the end point connection becomes 360 V* nominal. The rated max is 400 V and a minimum at about 242 V. Keep in mind that due to the constraints of the chemistry and the desire to maintain a stable system to insure safety and long equipment lifespan, that this arrangement can never be allowed to fully drain itself. You’ve heard the term “dead battery” this could be 0 V but in our case 242 V is considered depleted** At this point it must be recharged***
*360 V is a great deal of pressure. How many amps can we flow? This depends on the size of the pipe (wires) and the ability of the system(s) to handle the heat. Ultimately there is a very high capacity fuse (a type of CB that cannot be reset) and it’s limit is 1200 amps. A discharge anywhere approaching this could only be for short duration, possibly milliseconds because — boy that’s a lot of watts! Max continuous rate is about 1027 A or 370 kW. (360 × 1027= 370,080)
**It’s the same with your 12 V ICE battery. It would be considered to be quite flat by the time it was drawn down to ~11.6 V and it would be abusive to have this happen routinely. The number of times that a battery can fully cycle like this is finite.
***Note that we are using voltage as a unit of measure. This after we just said that kWh is the measure of choice for quantity. Voltage can be easily determined and it is used to derive the kWh available. There isn’t really a gauge that quantifies kWh (like a float gauge measures gasoline in a fuel tank does) The range display on the instrument screen of a Tesla is actually a derived assumed (guess) calculation. See the section on “Nice to Know” at the end.