what is “smart” electric car charging?

There’s a steep learning curve on electric cars, because our brains have been molded for generations to think of mobility with gasoline engines. But once you switch your mode of thinking, it’s not too hard.

“How long does it take to charge?”

The answer is always… it depends. You don’t regularly drive your electric car around until it’s “empty” then try to hurry through a fueling station, like we’re all trained to do.

Another answer is a question: “How long does it take to charge your cell phone?”

How many watts does this cord pull? I have no clue. It just works.

I don’t know the charging rate of my phone, because I just charge it overnight and it’s full in the morning. Same with cars. Each garage with an outlet has a mini “gas station” that slowly fills the “tank” up while we sleep.

Or maybe it’s an army of helpful little electric gnomes. I haven’t checked.

I remember getting in my car one morning and seeing that it had gained 20 miles of range over night. What? Gained? That doesn’t make any sense! I’ve been driving for almost 20 years… you just go until you’re almost out then you have to go to the gas station. Cars don’t magically add range while you sleep! But my mind finally flipped, and I realized I can skip the gas station routine altogether if I spend 5 seconds plugging it in every day.

The reality is that if you have a garage with an outlet, you’ll probably never need a public charger unless it’s a couple counties or more from your home. That’s why the comparisons with gas stations don’t make much sense.

Anyway, the “real” answer is that there are various levels/speed of charging… and that there are two types of cars with plugs (full electric and gas/electric hybrids)… I already gave my too looooong explainer here, after my 1st year of driving.

But let me get to the main point.

In researching for our first grant-funded public charging station (thanks Marshall Co Community Foundation!), we determined the most affordable option was to use existing underground conduit that ran to the electrical panel. Ironically, it was first laid to run a pump used to clean a leaky underground gasoline storage tank. One more reason to go electric!

The conduit diameter predetermined that maximum size wire we could safely pull through, 6 gauge. This size uses a 60 amp breaker. The rule for continuous loads is 80% of the breaker size, so we can only run 48 amps continuously through this line.

The JuiceBox Pro 40 by eMotorwerks had just what we needed. They are WiFi-connected, which allows me to control the units from an online dashboard, view charging history, set maximum amperage and charging times, etc. Now I can also download data and use it for educational purposes

But the best feature was pairing the two 40 amp units on a single line. 40+40 = 80, which exceeds the 48 amp maximum for the wire. I set a rule such that each unit could individually go up to 40 amps, but they could never exceed a combined 48 amps if two cars were plugged in at the same time (they’d drop to 24+24, or 15+33, etc). This eliminated the need to run an additional wire/trench, while maximizing charging speed at the stations.

It’s not often we have two cars charging at the exact same time, but I noticed that there were on Dec. 21.

The image below is the charging profile of the Honda Clarity. The time is on the X-axis, and the energy and power are on the Y-axis. Focus on the orange line, which is power (the charging speed).

It is plugged in at 8:03 AM and ramps up to it’s maximum charging speed of 6 kW (29 amps).

At 9:10 AM, a Ford C-Max is plugged in. The C-Max is an older model and can’t draw as many amps as the new Clarity. It ramps up and peaks at 14 amps. Remember… we have a 48 amp maximum. Ok, technically I had set the limit at 40 amp maximum because I was nervous (without reason)! So 40 – 14 = 26 amps remaining available for the Honda. Sure enough, if you look at the first green arrow, the charging rate drops a bit, from 6 kW (29 amps) to 5 kW (26 amps).

It continues like this until 9:31 AM. At this point, the Honda is almost full. For reasons I’m not smart enough to explain (but you could Google), batteries have to “top off” their cells with decreasing speed. At the 2nd green arrow above, you can see the charging rate slowly drop over the last 15 minutes, then stop completely.

Meanwhile, the C-Max keeps humming along. The image below is the 2nd charger, used by the Ford C-Max. It charges at it’s maximum 3 kW (14 amps) until it is unplugged at 9:47 AM.

Ok, now that you see how these things can work… imagine the possibilities. Namely, we can change the vehicles’ charging rates and times based on our goals.

The price of electricity on the grid can change dramatically throughout the day (and you can watch it in real time here). We can program cars to charge so as to minimize cost. BMW already ran a pilot study. In fact, NIPSCO is planning to replace some of it’s coal capacity with “demand side management,” in which customers are paid to adjust their electrical demand.

There is also software available that watches the fuel composition of the grid and prioritizes charging when there are high amounts of renewable energy being produced (software is not yet available in Indiana).

Taken in one sitting, this can all sounds pretty overwhelming. But it’s an exciting time to watch the energy transition and figure out how to do it efficiently, affordably, and quickly.