What is an EVSE and why do we care?

What is the device shown in the photograph at right? My quick answer, and you might say the same thing, is that it is “an EV charger”. But my quick answer is wrong. The device shown at right is a mere “EVSE”, not an “EV charger”. This fact, it turns out, explains why a Hyundai Kona (Wikipedia article) charges at a mere 26 miles per hour, when plugged into this 48-amp device, instead of as much as 42 or 43 miles per hour the way some other EV might do. 

I know, because I installed it, that the Chargepoint Home Flex device shown above receives 240 volts AC through a 60-amp circuit breaker.  This means that an EV, when connected to this device, can charge at 11½ kilowatts.  In most EVs this would work out to around 42 or 43 miles per hour.

I say “can” charge at 11½ kilowatts but that does not mean that any particular EV, when connected to this devices, will actually charge at 11½ kilowatts.  And this is what forced somebody, a few years ago, to coin the awkward initialism “EVSE” which stands for “electric vehicle supply equipment”.

If you define “EV charger” as “the thing that charges up the big battery in an EV”, then it turns out that the EV charger is not the thing in the photo above.  The EV charger is somewhere inside the EV where you can’t see it.

The EVSE (seen for example in the photo above) is actually a very simple device that you can see, that merely provides AC power to the EV charger that you can’t see, but that is somewhere inside the car.

Why, exactly, is it that a Hyundai Kona (Wikipedia article) charges at a mere 7½ kilowatts, when plugged into this 11½-kW EVSE, instead of making use of the full available power namely 11½ kilowatts?  The answer turns out to be that the Hyundai company saved a few dollars, and saved a bit of vehicle weight, by scrimping on the EV charger in the Kona.  Some EVs, including the Tesla Model S, have an 11½-kW charger inside the car.  Those EVs can charge at around 42 or 43 miles per hour if plugged into this 11½-kW EVSE.  But the Kona, as just mentioned, has a smaller EV charger inside.  It is only able to charge at around 26 miles per hour.

This, then, prompts the alert reader to ask “okay, so if the device shown in the photo is not an EV charger, but is only a mere EVSE, then please tell me what does an EVSE actually do?”  I am glad you asked that question.  Here is the answer, after a bit of throat-clearing.

The first thing that we all have sort of figured out by now is that for the people of any particular country to give up their ICE (internal combusion engine) vehicles in daily life, one of the things that absolutely must happen is those people getting accustomed to the notion that EV charging happens at home, at night when people are sleeping.  Having the charging happen at home, when people are sleeping, serves several extremely important shared goals:

  • The charging happens at night when this counts as off-peak power for the electric company.  This is not during the day when lots of people are running their air conditioners and lots of factories are smelting aluminum and such.  The electric company does not need to construct new power plants to serve such night-time EV charging.  The existing electrical power transmission infrastructure is more than up to the task and the night-time EV charging does not require spending more money on electrical power transmission infrastructure.
  • The charging happens at night when this counts as off-peak power on the electric bill of the EV owner.  Instead of paying 35¢ or 45¢ per kilowatt-hour at some public charging station, the EV owner is paying maybe 12¢ per kWh (or less) on the home electric bill.  By the way, we can compare this with what it would cost to purchase gasoline for an ICE car that would drive a comparable distance.  If gasoline in a gas station costs, say, $3 per gallon, then the equivalent amount of driving distance, purchased as electricity at home, might add up to an equivalent of 75¢ per gallon.  Yes, it can be much cheaper to drive an EV, in terms of cost per mile driven, than to drive an ICE car.
  • The charging happens (at least in some cases) at a privately owned residence or forward-thinking apartment complex where the owner can simply “make it happen” that a charger gets installed, instead of waiting for somebody else to construct a charging station in some public place.
  • The charging happens when people are sleeping which means that the people sort of don’t care if the charging takes quite some time to finish.
  • Some home owners have solar panels.  They can sell their excess electricity to the electric company during the day, and can charge their EVs at night, and then the “price per mile” for the EV driving activity might drop to zero.  It would be as if a local gas station had reduced the purchase price of gasoline to zero.

If you randomly pick 100 people who drive cars in daily life, and if you track their driving habits, you find that for 98% of those people, they spend 98% of their driving time within maybe 100 miles of home.  For those 98% of people, they lead a life that 98% of the time does not rely upon cross-country EV charging stations.  For those 98% of people, if only they can charge at home, that is just about the only place they will ever need to do any charging at all.

Yes, I get it.  Lots of people who cling to an ICE car do it because twice a year they drive cross-country and this means they would have to find an EV charger outside of the home.  But here I am focused on the 98% of the time that they are not driving cross-country. They are driving to work or they are driving to a grocery store.  The entire trip fits very comfortably within the driving range of any EV, no matter how small its battery may be.  Indeed the entire trip could be driven twice and would still fit within that driving range.  The relatively inexpensive Hyundai Kona (compared with much higher prices of some other EVs) has a driving range of around 250 miles which covers most grocery store trips at least twice.

And yes I get it.  Plenty of people live in apartment houses where they cannot install anything at all, let alone an EV charger.  And yes, I get it, lots of people lead lives where the only place they park their car is on the street somewhere, and there is no EV charger in that street parking spot.  Maybe those people will never escape a life of oil changes and spark plug replacements and a drive train with 20,000 moving parts instead of 12 moving parts.  I am not able to solve that problem in this blog article.

Back to the EVSE which I predict will eventually become a completely ordinary part of just about every privately owned home in the US.  Back to the EVSE that some landlords already provide in newly constructed apartment complexes.  Given that the EVSE is not, apparently, an “EV charger”, then what exactly does it do?

What the EVSE does is this.  When the plug of the EVSE gets plugged into the charging port of the EV, the EVSE sends a simple message to the EV, letting it know how many amps of electricity are available.  The EV charger that is inside the EV makes use of this very simple message to refrain from drawing so much current through the EVSE that it trips the circuit breaker.

That’s it.  From a functional day-to-day point of view, that is the only thing the EVSE does.  It tells the EV how to avoid tripping a circuit breaker by sucking too much electricity from the charging plug.

We have now completely described the main thing that EVSEs do.

There are a few other things that EVSEs do, and I must mention them to be complete about this.

  • The EVSE provides a ground-fault circuit interrupter (GFCI) function.  It very carefully measures exactly how much AC current goes out and comes back through the charging plug.  If those two numbers are ever non-identical, then this means that some of the current is leaking to ground through some other (perhaps uncontrolled) electrical path.  In such an event, the EVSE instantly cuts off the power.  In this way it is just like an everyday GFCI electrical receptacle such as might be installed in a kitchen or bathroom or an outdoor area.
  • The EVSE provides blinky lights to signal what is going on.  One color of blinky light might mean “charging is going on” and another color might mean “the charging has finished”.
  • Some EVSEs (including the Chargepoint Home Flex shown in the photo above) do lots of additional things.  The Chargepoint Home Flex can, for example, be programmed to delay the actual start of charging until off-peak time.  This helps the homeowner minimize the electric bill.
  • Some EVSEs connect to a cloud and thence to an app on the user’s smart phone.  This can permit the user to be notified when charging has finished.  Some clouds log the charging activity and permit the user to review the charging logs.
  • Some EVSEs can be installed in groups, with the group powered by a single load panel circuit.  They can coordinate with each other to share the capacity of the circuit among the EVSEs as needed.

So we can now circle around to the question that inspired this blog article.  Why does the Tesla Model S, when connected to the EVSE shown above, charge at 42 or 43 miles per hour, while the Hyundai Kona, connected to the same EVSE, only charges at a much slower 26 miles per hour?  And the answer is, the Hyundai people saved a bit of money and a bit of vehicle weight by putting a crummier EV charger into the Kona.

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