Neither, I’m considering an EV and just wanted to understand if charging at home would work with that outlet and what I’d need to buy/install. I’m also renting so I don’t want to invest a bunch on an install.
I commute about 22 miles each way to work, primarily highway driving at around 75-80mph
So, let's take this from the top so it all makes a bit more sense. I'm going to hit you with some concepts, then some math.
First: Energy is (usually) measured in Joules and is a
quantity, like a bucket with a gallon of water.
Second: Power is the
rate of usage of energy. A Watt (another one of those white-haired gentlemen from long ago) is the unit of power; and, at a steady rate of usage, 1 W = 1 Joule/second. That 100 W lightbulb in your overhead? Yep, it's using 100 J/second.
For various historical reasons, the power companies of the world decided to express energy in terms of Watt-Hours. 1 KW-hr (1000 Watt-hours) is 3.6 MJ, exactly. When you get your electric bill, they charge your for how much energy your houses has used, and they charge you so-many-cents per kW-hr. The electric car guys follow suit, so battery capacity (i.e., how much energy a battery can store) is measured in kW-hrs. For example, my Model 3 has an 85 kW-hr battery in it, or at least it held 85 kW-hr when it was new.
Going along these lines, then, electric cars' efficiencies are measured in W-hr/mile. (That is, how much energy it takes to move the car a mile down the road.) That rating is pretty much exactly the same as (you're going to love this) Gallons/mile. Which is upside down to how the EPA usually measures things, but go figure.
So, let's take a couple of typical Teslas: A Model 3 and a Model Y. The Model 3 uses 250 W-hr/mile; the Model Y uses 280 W-hr/mile. Let's stick with the Model 3, you can substitute in the EPA efficiency by looking at the car you're planning to buy at epa.gov, looking it up, and getting the efficiency from there.
So: How fast will a Model 3 charge when hooked up to a source of 240 V? Back to Power.
Let's say you've got a NEMA14-50 and a Tesla Mobile Connector. The latter comes in a cloth bag. One end of the TMC plugs into the car; the other end takes a number of adapters and lets say you get the NEMA14-50 adapter. Plug the adapter end into that NEMA14-50; the TMC has a limit of 32A, and the Power from that is
P = 240 * 32 = 7.68 kW.
What you want to know is how fast the car will charge, in miles of charge per hour. Watch this:
Time = 7.68 kW/(0.25 kW-hr/mile) = 30.7 miles/hour. Note how the "kw's" cancel, and you end up with miles per hour in the units.
So: a Model 3 LR has about 320 miles of range or so. How long would it take to charge a completely empty one?d
320 miles/(30.7 miles/hour) = 10.4 hours. That is: Overnight.
Nobody sane runs around with a completely empty car; it's typical to wait for the car to get down to 20% charge or so, but, it being a Tesla, one typically charges it up to 80% for typical running-around-the-landscape tasks. The difference is 60% of 320 miles, or 192 miles; let's call it 200 miles. That would take
200/30.7 = 6.5 hours. Which also qualifies as "overnight".
If you're commuting 44 miles a day, you'll probably charge once or twice a week, although there are various reasons in the winter when you might like to pre-heat the car before driving out the garage door, in which case you might leave it plugged in.
Now, the
other choice you could do is get a Tesla Wall Connector. (Or, if you're getting some other kind of BEV, something like a Juicebox or what-all; there's lots of different brands.) Nearly all of these are designed to be directly wired to the breakers in a breaker panel. The advantages these things have over the Tesla Mobile Connector (or the equivalent from other car manufacturers) are two fold:
- They can do more current. With the right car a TWC can do 48A at 240V.
- Convenient. The cable coils around the box on the wall. And if you have a TMC, you leave it in the trunk, where $DIETY intended .
If you do the math for 48A @ 240V, you get a charge rate of 45 Miles of charge per hour. That's more than the 30 or so you'll get from the TMC; but, when you look at the times, while it's a couple hours or so shorter, it's still comes under the classification of, "overnight".
Now for a couple of snivveys. If one is putting in a NEMA14-50 into a garage,
new (which you're not doing), current NEC code says you have to have a GFCI breaker in the breaker panel. If one adds up the costs of a good NEMA14-50 and a GFCI, turns out it's about the
same as a TWC, which doesn't need the GFCI. So, a lot of people around here have the advice, when asked about NEMA vs. Wall Connector, to state, "Wall Connector, of course!". But you have a
pre-existing NEMA14-50 there; the one you've got can handle the 32A from the TMC; so, well, you're done, stick a fork in it.
Second snivvy is kind of weird, but true. Turns out that if one looks at the possible NEMA connectors out there, there are 15A connectors, 20A connectors, 30A connectors, and 50A connectors. And
no 40A connectors.
However, there
are 40A loads - like clothes driers and electric ovens. Next bit: Copper is EXPENSIVE. So, the general rule is that the breaker, the wire, and the connector all have to have the same rating: If you've got a 120 VAC 15A circuit, then the breaker is 15A, the wire can handle 15A, and the wall sockets in your house handle 15A. So, what to do about that blame clothes drier? Electricians don't want to put that 50A wire in, it's $$. So, the NEC gave them an out: With a 40A load, it's code to put in a 40A breaker, 40A wire... and a NEMA14-50 socket, that one is supposed to label as
only being good for 40A.
Ha. As if (a) that label is going to be there after 20 years and (b) $RANDOM user isn't going to plug a 50A load into it anyway. And if one actually runs a 50A circuit with 40A wire, there is the Real Possibility Of Setting The House On Fire. Which is not a good thing.
So, back to Tesla. They have a NEMA14-50 adapter for their TMC. But they people at Tesla have no clue whether that's being plugged into a true, 50A socket, wire, breaker collection (in which case, it's allowable to draw 40A continuous) or if it's plugged into a 40A breaker, 40A wire, but 50A socket. In which case the maximum allowable current is 80% of the 40A, or 32A.
So they play it safe. Max current on a TMC is 32A. Safety first!
Hope this helps.