Unusual charging on a 5,000 mile electric car road trip


Rounding out my 3 part series on doing a 5,000 mile international road trip in a Tesla, I talk about the times I used slower chargers. The world installed vast numbers of slow chargers at huge expense in a giant waste of money, but they do have virtues on a road trip, and eventually all hotels will have them. On a road trip charge and range become very important and sometimes they save the day.

See the story and analysis at: Unusual charging on a 5,000 mile electric car road trip


An interesting view of this subject from a US perspective.

I would add leisure facilities (movie theatres, gyms, etc) to places where there should be a row of 50-100kW DC chargers for those who can't charge at home or work.

If you can't charge at home or work, yes you will seek places you stop for 30-60 minutes. Movies usually mean a 2 hour stop (does anybody even go to those any more?) which is too long for 50kw chargers, but you can design them to let 2-3 cars plug in and charge in sequence if you want to go there. Problem is movie theatres are mostly popular at night. The ideal location of a charger will see use all day long, and for that, grocery stores are the obvious win. People go to them regularly, they drive, and they spend 30 minutes but not more than an hour. Gyms might be a decent choice though usually people spend an hour there, which is a bit too long.

A key error many make is they presume people want a "full" charge. Nobody ever does a full 0 to 100% charge, a full charge is actually from 20% to 80%, or about 35kwh or less on a city car. But normally you don't want to let it get down to 20 if you can't charge at home or work, so you may want more like 20-25kwh. Which is under 30 minutes on a 50kw charger if it can do full rate.

It's OK if you don't have to unplug your car as soon as it's done. Most fast chargers are designed to require that, but future ones can and should be designed with extra cords so you don't have to do that.

I regularly charge at the supermarket for free. Nominally it is 50 kW DC (there is also 43 kW AC but the Tesla is limited to 11), and I usually get about 35. Ideal.

Why do you say that no-one ever charges to 100%? I‘ve done it a few times.

I should say that I am in Germany. 230V three-phase power is in every house. Usually normal plugs are 16 amps (some older ones just 10) and most houses have mostly one-phase plugs, but not all are on the same phase (which can make ethernet over the power lines a bit tricky). Home chargers are usually 11 kW (e phases at 16 amps and 230 volts), but even a normal plug will give 3.6 kw, which is often enough for overnight charging.

I bought my house from an electrical-hardware guy, and there is a three-phase connector in the cellar. Unfortunately the garage is not connected to the house and has no electricity, but that might change. At the moment, though, I don‘t need it.

Free charging at supermarkets is a bit of a prisoner‘s dilemma for the supermarkets: no matter what the competition does, they are better off offering it (the increased profit more than offsets the cost), but if all offer it, they generate less profit than if none offer it.

It is easier when the base voltage is up higher like that. I was not aware everybody had 3 phase, not ever having seen anything but the standard plugs. 3.6kw is definitely enough. With 3.6kw the typical driver might find they need to top up at a fast charger 1 or 2 times a year, making it non-economical to spend a lot to put in a 3-phase.

We talked about those free 50kw chargers -- those are rare here (I used some in British Columbia) and I would have to imagine over time they will go away, but I could be wrong on that. Germans pay about 30 cents/kwh, and if people are going in there for 40kwh fill-ups, that's 12 euros and is an expensive perk for a grocery store or restaurant to give. Particularly with the large cost of installing such chargers. Level 2 is much easier to give for free, but also not very useful.

However, yes, in the future, you should see grocery stores perhaps offering 50kw charging at cost. I predict though, that most drivers will be able to charge at home or the office -- leaving only those who park on the street and don't park at an office or commuter lot during the day as strongly in need of fast charging. That becomes less something you must have to get customers, but there will be a segment of customers who will choose their store based on that.

Essentially all buildings have three phases, but most plugs are just one phase (but not necessarily the same one). Some heavy-duty appliances tap into more than one phase.

I have also charged to 99% a few times on road trips when I knew I had the need. The reason "no one" (really meaning it is rarely done) does it is that it takes as much time to go from 90% to 100% as it does to go from 20% to 60% and cars will warn you to not do it very much, for good reason, though it's better if you are going to immediately drive after the charge so it doesn't stay at 100% for long.


I agree 350kW everywhere is overkill and government and state subsidies need to be to help apartment complexes and homeowners install at least 24 amp, 240 V stations. I believe 5.8 kW is the bare minimum, especially as battery packs get larger, and also a convenient way to make a 30 amp circuit servicing a clothes dryer serve double duty, as long as it is near where cars park. There are now companies that make "smart" switches that give priority to the dryer but at all other times let the car charge at 24 amps, and there is no risk of tripping the breaker. What are your thoughts about 10-11 kW at places where at least a 2 hour stay is probable (48 amps, either 208 V or 240 V)? More and more BEVs are coming standard with 11 kW on board chargers and I think this speed is extremely useful and fairly speedy for the cost - a 60 amp circuit is needed but not three phase power.

It is a common error to believe that 6kw is a bare minimum. I mean, faster is always nice, if it doesn't cost any more, but the average car drives under ~40 miles/day (15,000 per year) which is 10kwh and you can fill that in under 2 hours at 6kw, and almost every car parks 10 hours overnight.

People fixate on filling a car completely, which you almost never do, or even on the "optimal" fill-up of 20 to 80% which again, you almost never do in your home town. On road trips, sure, you do that a lot. Hotels should have 10kw at each station.

Even level 1 (12kwh in a night, or 18kwh at 20a) is enough for most cars almost all the time, especially if the pack is big enough.

You say we need more as packs get bigger. Actually we need less as packs get bigger, because you can tolerate more deviation from the average. What perhaps you meant is we need more as cars get less efficient, and that's more true. A pickup truck would like a bit more than a car, regardless of pack size, as it uses more kwh per day.

That's why I say that for an office or apartment building, you want mostly 3kw stations, because they are cheap. Put in mostly 3kw stations, and put in a few 7kw stations for those very few cars who need it. Discourage use of the 7kw stations by people who need less than 30kwh (120 miles) unless all the 3kw are full, to save them for the people who are down more than 40kwh.

You see, you only need a 40kwh fill up if you are both down that much and need to be able to go full range tomorrow. Except almost nobody is going full range tomorrow. The average person is going 30-40 miles tomorrow.

And anybody who is going full range tomorrow is almost by definition on a road trip and can use fast charging in that situation. And in the rare situations when there are too many cars that need 7kw stations, local fast charging will do the job.

Now, in hour house, putting in 7kw often costs only a little more than 3kw. So you might as well do it there in that case. If it doesn't, don't do it. But if you are putting 40 stations in a parking lot, no way you want to put in 40 7kw stations, that is going to cost a lot more in terms of your service level than putting in 5 7kw stations and 35 3kw stations. As a result, you might see people putting in just 20 7kw stations, which means half the people don't plug in or have to play games going out in the middle of the night to swap plugs.

Charging every other night does work, but you need a system to manage that. Simpler to just let almost everybody charge at their regular spot, or at one of the fast spots if they are very low.

Another option which works OK is to have paired 7KW stations with two plugs that will charge one car then the other. But you have to now plan, don't park two empty cars at the same paired station etc.

Only staying a short time, like 2 hours at a movie? Then you want as much as you can take. That's the paradox. The longer you will be at the charger, the less powerful it needs to be. Particularly if you will be there every day. The charger at your home is fine at 1.8kw (Level 1) for almost all days because you are there every night for 10 hours or more, often much more if you don't commute in that car.

The one problem not fully resolved is offices on Monday. There will be extra demand there from the people who have no other place to charge. To resolve this, offices might need to beef up a little more (Level 1 is not enough) or those people might use fast charging from time to time if they drive a lot on the weekend. Unless they have a large pack, in which case it's not a big problem, they can handle the extra burden of the weekend most weekends.

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