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304 North Cardinal St.
Dorchester Center, MA 02124
There are a lot of possible choke spots for power flow between the grid and your new car when charging with 240 volts, or Level 2 in the EV world. The following five factors will mostly determine how rapidly your electric car’s range increases when you charge it at home:
Even if you give an electric car enough of power, it can still be a severe bottleneck, despite the fact that it may seem like we’re beginning from the wrong place. Alternating current (AC), which includes both 120 volts and 240 volts, also known as Level 1 and Level 2, has a maximum charging rate for each plug-in vehicle. (There is a different and significantly higher rate for public DC fast charging if the car is capable of it; however, it does not apply to what you can do at home.)
The rate of charging for the car is specified in watts, specifically in kilowatts, which just eliminates a few zeros. Currently, pure EVs with greater ranges are increasingly prevalent and typically have around 7.2 kW. The car can charge more quickly the more power it can handle. This step is important since the grid is AC and the batteries are DC. Why aren’t all of these onboard charging modules 19.2 kW, which is the maximum allowed under Level 2? Because the modules’ cost, size, and weight increase as their capacity increases, automakers are parsimonious with these resources.
The manufacturer may occasionally offer additional capacity as an option or combine it with a larger battery pack in order to ensure that it can be filled rapidly enough. Typically, a given model will have one rate.
We haven’t yet discussed how much miles an hour you can add, so let’s do that now. That’s because it depends on the power input to the vehicle and—more importantly—the efficiency of the vehicle. In addition to the issue of how quickly an electric car charges, the efficiency of the vehicle affects how many miles it can travel on a given amount of power. In gas-powered vehicles, the same is true, but this was never a problem because you can add hundreds of miles of range in a matter of minutes at a fueling station. But consider if you were only able to add fuel for five minutes through a drink box straw. After that time, which gas-powered vehicle—a Toyota Corolla or a pickup truck—would have a greater range?
The same is true for electric vehicles (EVs), though significant size differences are not necessary for one model to charge more quickly than another. For instance, Teslas typically have very high EPA mpg-equivalent ratings, which means that when given the same amount of power, they may charge more quickly than comparable, less efficient vehicles. We bring up this efficiency problem in part because automakers have started raising charging rates to offset inefficiency. One issue is resolved, but not the fundamental one.
Let’s just assume that charging at 6.6 kW is twice as quick as charging at 3.3 kW, thus whatever the automobile in question is capable of at one level, raising it should result in an increase in kilometers added proportionately. We provide a broad notion of the times required for Level 1, Level 2, and DC rapid charging in our charge level explainer.
As you can see, we referred to it as the charging hardware. That’s because, technically speaking, the charger—not the box on the wall with the long cable—is the module mentioned above that is integrated into the automobile. Electric vehicle service equipment or supply equipment is what the box is, which may be why everyone just refers to it as the charger.
One other possible choke point is this Level 2 unit. Although the term “Level 2” implies consistency, it regrettably only refers to voltage. A specific unit may supply between 12 and 80 amperes (amps) of current at 240 volts, which translates to between 2.8 and 19.2 kW in terms of the kilowatts we’ve already discussed.
There is no easier way to calculate watts than to take 240 volts and multiply it by the amps. For instance, if your Level 2 charger has a 32 amp rating, multiplying 240 by 32 results in 7.7 kW, or 7,680 watts. A car with a maximum charging rate of 7.2 kW or less would benefit from using this charger. Giving an EV too much electricity is never a concern because your car is protected by the EVSE and onboard charger. Our focus on maximum charging rate is entirely focused on charging as quickly as possible, not on overcharging or otherwise “damaging” the automobile.
Why is the Level 2 rating system so difficult to understand? There is, sort of, a reason, though. Only that the machine will pass a specific current can be guaranteed by the hardware manufacturer. Depending on the electric appliances you and your neighbors are using, the voltage, which is the responsibility of the electric company, may not always be exactly 240 volts. The voltage entering your property may be above or below the nominal rating of 240. Therefore, you should be able to understand why they want to sell you a 32-amp EVSE rather than a 7.7-kW one: In actual use, it may be 7.5 or 7.8 kW. We’ll get to that shortly, but sadly some manufacturers still struggle with Nos. 3 and 4 below.
We get 9.6 kW by multiplying 40 amps by 240 volts, which is less than the maximum output of both cars. Not a good thing, that. However, 48 amps translates to 11.52 kW, leaving nothing on the table.
Voltage is only one component of the equation here as well, just like with the charger. We won’t get too deeply into the theory of electricity, but the fundamentals demonstrate why this is necessary: Poor wiring causes too much resistance to the flow of current, which causes heat to be produced and increases the possibility of damage or fire.
The one appliance that consumes the most power when plugged into your home is undoubtedly an electric automobile. The required amounts in kilowatts are already known to you. For comparison, 240-volt appliances such as a common electric clothes dryer consume roughly 3 kW, an electric water heater uses 4.5 kW, and a sizable central air conditioner uses 3.8 kW. Hair dryers and space heaters typically have a maximum output of 1.5 kW. Only an electric tankless water heater gets close, with high-capacity devices requiring demands beyond 30 kW.
This indicates that, unless you’ve been doing some heavy welding, you’re not likely to have a 240-volt circuit in your home or garage rated high enough to utilize the full charging capability of today’s EVs. Simply said, the wire must be strong enough to support the current requirements for vehicle charging, and strong wiring may necessitate larger conduit than you now have. The electrical code, which differs by state, is what determines everything (even though there are national standards). A 40-amp circuit breaker is necessary if the Level 2 charger has a 32 amp rating. A 50-amp breaker is needed for a 40-amp device. Approximately 25% of headroom is always provided by the circuit breaker.
Unfortunately, this can lead to even more confusion when it’s time to buy or install a charger because you have to figure out whether the rating is for the circuit of the charger or for how well the unit operates. It would be quite simple to believe you were purchasing a charger with a 40 amp rating when in fact you were purchasing a 32 amp charger for a 40 amp circuit. 1,920 watts of charging power are different. In the piece, we go into greater detail about charging levels.
Because each affects what you can install and how future-proof an installation is made, we are counting the circuit and breaker as two separate elements of the same topic. It’s easy to change a breaker or outlet, but it may be more difficult to swap wire gauges because every situation is unique.
There is nothing wrong with utilizing overrated wire and a certain breaker, but using underrated wire and a given breaker is a formula for disaster. You should only notice a small price difference, and labor will only cost you once. All you have to do to upgrade your charger to one with a larger current capacity is change the circuit breaker to match, which is a straightforward process.
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