Charging
previous: THE Battery
The primary rule is ‘always be charging‘ (ABC). This is the only guidance in Tesla’s owner manual (all caps and bold): LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. For battery health and long life, a car that is plugged in can automatically monitor health and optimize itself.
Secondary rule is to never deplete the battery to zero. This would seem to be self evident but you may not realize that the on-board computer that manages the magic is always on even when the car is parked overnight. Granted that during inactivity power use is minimal, one should know that the computer never sleeps and is always monitoring the wide area network (listening for the Mothership) and maintains self awareness should the owner return. (and operative security should the haters show-up) So, computed range is never static, your miles of range remaining will slowly disappear into the ether*. . Plugging in ensures that the BMS with help from the grid can mind the system long term.
*Early adopters coined a name for this — vampire losses. With the first cars it could be 5 to 6 miles daily but with the latest improvements it is more like 2 or 3
A bit of urban knowledge; the battery is thought to be happiest if it is not made to sit idle long term with a 100% state of charge (SoC). Thus it is considered bad form to routinely set your charge limit to greater than 90% unnecessarily. Of course, for a long trip when maximum range is desired a full battery is quite all right. Best to achieve this SoC just as you are about to set off as opposed to having the car sit 100% fully charged overnight.
Tesla has its dashboard charge display screen that displays the charging process. Assuming that you are plugged in, it shows the external volts value that is being supplied to the car and also the amps. Tip: While it is possible to charge an EV using only a 115 V circuit, as we have seen, 240 V will be quicker and more efficient. It’s a larger pipe with greater pressure.
Another tidbit about electricity: There are two types. Direct Current* (DC) and Alternating Current* (AC). You need to realize that large state-of-the-art motors are AC but that all batteries are DC. See a conflict looming? AC and DC don’t mix. They can be interchanged only after a conversion takes place. Your household service from the utility is AC. The battery stores, charges, and discharges energy in the form of DC current so… The AC current from the grid must be converted going into the battery and then converted yet again when output to the AC motor**.
*These two forms have been competing since early times with two different camps headed by Thomas Edison for DC and the other by Nicola Tesla a protagonist of AC.
**In case you are wondering why do I care? The reason has to do with the care and feeding; the mechanics of which is probably less complex then in the explanation of what happens to the gasoline on its path from tank to exhaust tailpipe. In either case we don’t need to know the nuts and bolts. Model 3 has a built in charger on-board that is responsible for the juice going in to the battery and it has an inverter that changes battery outflow to a stream that the motor is expecting.
We can measure charging. If you are in your garage then your charge source from the wall socket is AC*. An extension cord will allow you to access a convenient 115 V outlet but as we discovered we are not going to be able to pull significant amounts from it, at least over the course of a few hours duration. Whereas a PHEV such as Prius or Leaf will feed happily, the Tesla has a much greater appetite and charging from a 115 V source is unsatisfactory. How slowly might that be? A meager gain for the big Tesla battery of about 3 miles gain per hour of charge time. After a lapse of 24 hours you will only have added 72 miles of range. We can do better. Hopefully an electrician has installed a 240 V outlet for you.
It figures this way. Take your available volts (240) and amps (40) and multiply them to see 9.6 kW. Yes! Your Tesla charge screen window on the tablet will display to you that you are recharging at a rate of 38 miles per hour (mph). If the car charges for several hours overnight at this rate it will be good to go in the morning. It’s possible to go one step marginally better with a custom installation of a (240 V) Tesla Wall Wall Connector aka (HPWC) which supports 48 A or 11.5 kW which is a rate of about 44 mph. This is the best you can do with an AC charge source*.
Recall from the preceding that the battery is DC so we have to convert the AC to DC (AC to DC charger converter). One final point here, and that is, in any conversion process there is will be energy losses. The AC to DC converter itself uses energy and is recognized to be about 87% efficient. Therefore, if you were able to measure/monitor the energy coming from the wall outlet it would not precisely equal that going into the battery because of waste. In other words, add an additional 15% for your car’s share at your utility meter if you are trying to calculate the true energy cost of charging from your house.**
*The factory installed on-board charger is rated @ 48 amps maximum Home Charging NC Rates (taxes and fees inclusive)$0.14 /kWh equates to ~$0.05 per mile (charge conversion efficiency of .85 factored in)
**Other AC charge point sources include grocery store, office, library, restaurant and hotel parking lots* Unfortunately, there are several different flavors some with differing plug outlet types and with names like CCS, CHAdeMO, Level 2 but fortunately there is the Society of Automotive Engineers (SAE) that is working diligently to get a grip on this issue. Also, if your EV is not so equipped there are adapters or other work-a-rounds. Here’s an comprehensive list of public charge locations. See also the adapter fun section below.
Exit your residential garage and drive to a Tesla Supercharger (SC). Once in position you will enjoy DC Fast Charging. The vehicle’s own AC/DC charge converter is cut-out of the loop and not used. The Supercharger, also receiving energy from the AC grid but in the form of 480 V has its own bank of multiple AC/DC converters and the output funnels directly to your battery as DC. At present the available power ranges from 120 kW to as high as 250 kW. Compared to the 10 kW at home you can imagine that the charging process will be speedy. https://supercharge.info/map
*however the electric battery system is still very efficient. An ICE car is much less so and thus the need for large front end grille openings and radiator coolant system. The reason being is that one gallon of gasoline contains 33.7 kWh of energy. This amount of energy from a battery will deliver 120 miles of range so you can see how efficient an electric motor is. An ICE car can only hope to be 20-35% efficient. Thus, much of the energy stored in gasoline is lost to the environment.
The taper looks like the following where the percentage axis is state of charge (SoC).
Charge to about 60% for a fast getaway.
Other Charge Locations: There are public DC Fast Chargers being added but they typically supply DC at 50 kW. maximum. These can be made to function with Tesla (see adapter fun) and Essentials: Plugshare , Tesla’s Destination charging