A circuit breaker designed for electric cars to lower costs
While I was watching a rocket lifting some of my friend's satellites into space from my driveway yesterday, my new electric Tesla car was delivered to that driveway.
Now that's a sentence that says you're truly in the 21st century. The SpaceX Falcon9 was launching 64 different micro satellites, some of which were from my friends at Planet Labs. What used to be the province of countries is now done by the startup down the street. And it was just an extreme coincidence that the Elon Musk Tesla arrived at the exact same minute as the Elon Musk SpaceX launch. You do have to hand it to Elon, even with the differences of opinions we have on LIDAR and other issues.
If the opening sentence sounds like it says "look at how fancy I am" (and it does) consider:
- The friends are not billionaires. Cubesat lauches are in the tens of thousands of dollars, not the millions.
- The Tesla Model 3 medium range model without autopilot is $46,000. After $10K tax credits it's $36K. After gasoline savings (if you get them) it's $32,000 -- and it's a really great car for that fairly ordinary price.
- Anybody in most of California can see launches from Vandenburg from their driveway.
So you'll see more posts from me about electric cars in the near future, I'm sure, so let's start about the question of home charging. In the robocar world, cars will be able to drive off to find charging when they are low, so you won't need to install home charging, but today you want it.
This means having some sort of "charger" with the big car charging plug. We call it a charger, but in fact the charger is in the car, the home unit is just an interface between the car and the grid which tells the car about the power available. It is surprisingly expensive considering that's all it does. Wall units tend to run $400 to $600 (and even more.) Tesla's mobile unit is a surprisingly cheap $300 compared to those. Almost always, you will need to run a new dedicated high-current circuit from your parking place to your power panel, and for most people that means a professional electrician install, possibly even with a city permit, and you can hit $1,500 in costs without much effort.
But worse, older homes that only have 60a or 100a of service may need to do a full panel and service upgrade. That's on top of the EVSE (the real name of the "charger") and can readily run $4,000 or more here in California. That pretty much uses up several years of the money you planned to save on gasoline with your electric car. (And I do want to stop burning gasoline or buying anything from Mohammad bin Salman. In California, my energy company offers a 100% renewable option that is cheaper than the non-renewable price from PG&E.)
Some cheaper alternatives
Some lucky people may already have a spare high current circuit or plug in their garage or near their parking, most commonly the one for their clothes dryer, or sometimes an unused one for an electric range. If you don't use those (for example you have a gas dryer or range) you might be able to just use them or put a very special extension on them. And some people sell special switches you can put in these sockets which split out into two plugs, but turn off the car socket when the dryer is running. This assures your house never uses more current than it originally would. These plugs are 30a, meaning they can charge a car at 22 amps, which is slower than the higher end cars can handle.
Smart sharing of power
This led me to an idea for something that should exist. There are partial forms, but offerings could be a lot cheaper. The car is smart, can control its current, and has wifi. The EVSE may not be that smart, but has the ability to interrupt the current and tell the car how much current it can output. And in the main power panel, there are many things, including the circuit breaker for the EVSE which also has the ability to disconnect the power, and there's also a smart meter which knows how much power the house is using, and the ability to put loops around the conductors there to know how much current the house, or any given circuit is using.
Instead of putting in extra, expensive capacity, the smart devices should be able to learn how much spare current is available at any given time, and only draw that much current.
Here are a bunch of ways that could be done. Some are easier to install, some are cheaper, some give better results.
Smart meter and smart car
I have a smart meter. You can connect to it over Zigbee Smart Energy and get a stream of information on real time power usage. The Tesla doesn't have Zigbee but it could talk to an inexpensive gateway on the home wifi and get this information. Then it could track house energy usage, and decide when to charge. If other appliances are drawing lots of current, the car could stop or scale back. It would leave a large enough margin so that any one appliance (oven, dryer, air conditioner, hot tub) could get turned on and not overload, and then it would scale back so that any new device would not overload. If the stream of data stopped for some reason, it would stop charging. If it stopped for long, it could send an alert to fix things.
One problem -- a car visiting your house would not know to follow this protocol and could overload the panel. UL probably would not approve that. So in the end, while the car is nice and smart, some change to the EVSE is needed. This could be a fully smart EVSE, described below, or a minor modification that it does not offer power to any vehicle that doesn't identify that it knows and follows the protocol. Tesla has a protocol to negotiate with their EVSEs, but other cars don't have this.
The more correct way to do this is to put these smarts in the EVSE. Let it learn what load is present in the house, and adjust the current it offers. It could learn that from the smart meter -- it could speak Zigbee Smart Energy protocol.
Current measurement at the panel
It's easy to measure current in AC wires. You just put a small loop around the wire and it induces a voltage. Electricians could install these loops. They could either feed to the EVSE over some extra wire put in the conduit at the same time the big current wires are run, or it could tap off a little power to run a digital device which would read the loops and send the value by RF or signal on top of the powerline. This signal would get to the EVSE and let it know the current with no smart meter.
Current measurement at appliances
For those unable or unwilling to measure current at their panels, a small device could be made which would be built into a unit which would be inserted into dryer or range plugs. For example, you could get a unit that plugs into your dryer plug, and then the dryer plugs into it. The unit would read the current used by the dryer and transmit it, via RF or signal over powerline, to the EVSE (or the car.) The EVSE would now know when the dryer was on, and signal reduced or no power available while this is so.
A special circuit breaker
It would be most elegant perhaps to put all this into the large circuit breaker which controls the car charging circuit. That's because that breaker is, of course, in the power panel box where it's easy for it to run loops to measure the current on other devices there. It's also because that breaker has the ability to cut the power on the main current lines to the car, eliminating the need for the EVSE to do that. (A proper EVSE offers no current until the amount has been negotiated.)
This would mean the EVSE would be almost nothing. It need only generate the pilot wave to tell the car how much current to use. It could perhaps not even have to generate that. A 5 6 wire convention could be developed for the run from the power panel (and smart breaker) to the EVSE, which would really be mostly just a pass through to the charging connector.
The circuit breaker could also enhance safety by cutting power if the car does not reduce the current when it is told to.
Smart load management
Almost all the big loads in a house except the electric car are actually intermittent. Air conditioner and refrigerator compressors, oven heaters, dryer heaters etc. all turn on and off. Likewise the car can take current in the low cycles and refuse it in the high cycles. Pool pumps often run all night, but new modern pool pumps usually are multi-speed, and run at low power (just 2-3 amps) during their night circulation mode.
As noted, the system could also put current measurement rings on the big loads. This would let it learn their maximum load, and know which particular appliances are turning on and drawing power, to help it adjust the current.
Some day we'll have smarter panels that do this for all circuits. And it makes sense for all appliances to talk a protocol like this to manage power. A house where all the major appliances listed had a system to "take their turns" could get by with a vastly smaller connection to the grid. And by evening things out, they would be doing the grid a favour. The hot tub doesn't care when it heats (unless you are in it.) The pool doesn't care when it pumps. The air conditioner and fridge can wait a few minutes to cool if needed.
This makes the charging point electronics very simple, and much cheaper. In fact, I believe this design would eventually make the whole install cheaper once it is made in quantity. The main downside is you must make breakers for all the major panel designs if you want to use them to interrupt the power. Code requires there be no voltage in the main pins until the handshake has been done with the car. The circuit could also go in a small box clamped to the side of a main breaker box.
But even if this circuit cost a lot extra, as it might to start, it would be far less than the cost of upgrading your whole house electricity, which is something many will face as they buy electric cars.
Do you need Level 2 charging?
Home charger installation can get quite expensive -- as I will detail below, it can involve $5,000 or more for many people. But as the batteries get large, it is no longer necessary to keep a car fully charged, unless you know you are going on a road trip the next day.
This means that it is practical, but not as nice, to charge with an ordinary household plug with 15a or 20a max. These are plentiful, though you want one that is on its own circuit. They charge very slowly -- anywhere from 3 to 5 miles of range are gained with an hour of charging.
But the average car in the USA is driven only 32 miles per day! My 220 mile range Tesla could do a week of average charging on one charge, and would do just fine ordinarily gaining only 50 miles each night from the wall plug.
The problem of course is that cars don't drive exactly 32 miles every day. Some times I go to San Francisco (100 miles RT) two days in a row, and this would be barely doable and put me in the "range anxiety" mode. So this is where fast DC charging can save the day. It can mean a 30-50 minute pause, eating a meal at a supercharger, but it probably only needs to be done a few times a year. It might be a much simpler alternative than adding expensive high current charging in the home.
One problem is that if you use only 12 amp charging, you are very tempted to charge not just at night. Here, the electricity costs 3 times as much in the day as in the night if you have the EV plan. That gives up a lot of the savings you might have hoped for.