How to save a lot of money when installing electric vehicle charging in your home


Often when you attempt to install an EV charging station in an older home, you find that the old 100 amp service on your panel is not enough, and the electrician may quote a very large price to replace the panel and upgrade the service.

There are ways to avoid paying thousands of dollars by putting in a modestly smaller circuit, and you may find it charges you just fine. Here is a guide to how to get away with less than a 50 amp plug and save many thousands.

See Don't spend a fortune installing charging at the Forbes site.


I have a Hyundai Kona EV with a 64 kWh battery. I drive it to work every day, usually totaling about 200 miles per week including some weekend driving. I have a 7.5 kW L2 charger, usually only charge once per week, and can completely recharge during the midnight until 6:00 am super off-peak period. This leaves six days per week to charge a second EV once my wife is ready to dump her ICE Honda. The charger actually was installed for free as part of a "smart home" demonstration study.

But it's pretty clear you would have done fine even with Level 1, which is free for many people.

But this is the point of my article. A lot of people imagine they need enough power to recharge their car from 0 to 100 in one night. They should realize that is nice but not necessary and not worth spending a ton of money on.

Thanks for the article!

“ But you may find when you call an electrician and ask to install a nice Level 3 charging station with a 50 amp circuit that they present a very expensive estimate — perhaps $5,000 or more ‘’. Level 3 chargers (also known as “super-chargers”) require 480 V or more, cost around $30k, and are usually only found at public charging stations.

Level 3 chargers are also not 50 amps! This was just a typo, corrected before you even left this comment (which makes me wonder where you saw it.)

The North American primary mains voltages have been 120Vac/240Vac (split phase) since 1967, 110V dates back well before WWII.

Has Anyone else driven over 150,000+ miles in less than 3 years and recharged it over
4,000+ times already? I have. GOOGLE Me:
* comments of speculation versus EV REALITY are HILARIOUS!

I have been charging my Leaf on 120 for years. 50 k a day. Works great.

Having a smarter main panel (which might be accomplished not by replacing the panel but by adding things on to it) seems like the long term solution. Not only are you not likely to have everything turned on at once, but many homes also have two or more inputs. If you have solar and grid inputs, you might be able to use everything all at once while it's sunny out, but not at night. Given the practicalities that might not be as useful as having solar, grid, and powerwall inputs. Then if you happened to run the dryer and the oven and the air conditioner and the car charger all at the same time for 10 minutes at night, you might be able to draw from the powerwall.

I'm not sure if the panel would be smart enough to handle that, though, and I'm not sure how to find out. The picture at gives me some idea of how everything is hooked together, and the setup with the "essential loads" panel (I assume it's a breaker panel) could probably handle it without violating the electrical code. The setup on the left seems to be the smarter one, but only if the system is smart enough to coordinate all the loads and inputs.

What exactly is the purpose of the rule in the electrical code? If you overload the main panel, the main circuit breaker will pop, and there isn't any harm done or dangerous condition, is there? Seems like it'd just be an inconvenience, and one you could handle by knowing not to run the dryer and the oven while the car is plugged in.

I'm not sure what the cost savings would be by foregoing the "upgrade" to the utility meter and the connection between the utility meter and the main panel (or, in the setup on the left, the gateway). It does seem wasteful to upgrade that connection if you plan on using solar and powerwall(s), though.

If you think upgraded service between the grid and the home is the way of the future, I wouldn't sweat making that upgrade. Yeah, it costs some money, but it'll add to the value of your home. On the other hand, if you think at-home generation and lower reliance on the grid is the way of the future, the costs of going that way might pay for themselves over time. If you don't think either one is the way of the future, I guess you don't think fast home chargers are a good investment.

Generally, the electrical code wants breakers never to blow in ordinary operation. It is designed that this should be extremely rare. The rules don't make it absolutely impossible but it is quite a low chance. Now, some practices are grandfathered in. When you have a room with several plugs, you can obviously plug several appliances in at once, so they are a bit practical about it (though most kitchens are wired with multiple circuits for that these days with high current appliances getting their own circuit.)

I think if the car charger or car is smart, there is no reason to draw power for the few minutes that everything is on at once. It's easy for the car to scale back. Electric chargers are a sign of new thinking in the codes, where the current is limited not by physical things but software. While your electric car can draw 30 amps you are allowed to plug it into a 15 amp circuit, as long as it has been configured to know it's on a 15 amp circuit and not to draw more than 12 from it.

It's easy for the car to scale back when everything else is running, as long as it knows when everything is running.

Maybe a sense energy monitor ($300) would be able to detect that?

But then would you be up to code? Or does there have to be a local, physical system that prevents overusage?

I still don't understand why the code "wants breakers never to blow in ordinary operation." Is there an actual danger that is being prevented, or is it just a rule that exists for obsolete historical reasons?

I think it probably took a lot of work for the code to adapt to the idea of current limiting through an encoded pilot signal, so it may take more time for advanced concepts.

Yes, it's trivial to measure current in the main wires if you can get access to them, or even just to the dryer by putting a small device on the plug. You then have to get the signal to the EVSE or car. (You do it in a deadman switch style, so if the signal stops coming, charging stops.) There are a lot of ways to think of doing it.

Another idea would be the smart meter. My car could actually talk (via Zigbee, if it had a Zigbee radio) to my smart meter and regularly read the total power in the house. A cheap zigbee to wifi gateway would let the existing Tesla do that if it wanted.

Even easier is just to track the voltage drop on the lines, and learn what current they correspond to. No new hardware needed. But harder to get the codes to adapt to that as valid. Perhaps if an electrician did the training. It's well established that if there is a heavy load on the house, voltage is going to drop, and a very simple system could tell the car not to draw so much current as to let the voltage get below a threshold which could be calculated by an electrician or even figured out by the car watching the house for a while.

The coils to measure this cost $1, it's getting them in place that is the issue.

All very interesting. As I've been looking at it more, it looks like 200 amp service has been the standard for most houses for decades, so I guess just making the upgrade is the easiest answer for most people.

Circuit Breakers are Over Current Protection devices, which means they only "pop" instantaneously at short circuits/ground faults. A 200 amp main breaker can hold at well above 200 amps, this can cause the insulating jacket on the conductors to melt and cause a fire. The main purpose of the electrical code (NFPA 70) is to prevent fires, NFPA stands for national fire protection agency.

Only an overload protection device would "pop" as soon as the load (amps) is exceeded.

I wonder how much it'd cost to install a charger on your street in front of your house.

I wonder what kind of permitting you'd have to go through to do that. The legal fees would probably be expensive unless you were willing to go through the permitting process yourself. In most places I think it'd be theoretically possible, though. The local jurisdiction usually has a process for building things in the space between the sidewalk and the street.

Installing a charger at your office would probably be easier permission-wise, if you park on private land. Get permission from whoever owns the land, and set it up. You can have your own private parking spot, and there's probably a way to get some nice tax credits, either for yourself or for the owner of the office complex.

You might pay more for power at your office. Then again, you might not. My office complex has solar panels all over it. We don't pay anything for electricity (the cost of electricity is included in the monthly rent). I bet if I asked them to let me have a dedicated parking spot and build a car charger on it that they wouldn't charge me for electricity but would include it in the monthly cost of the parking spot. Of course I wouldn't be installing a supercharger. (I suspect the reason they don't charge for electricity is because then they'd be regulated as a utility company.)

You don't own the street spot in front of your house, so somebody else can park in it. The hard part would be running your cord over the sidewalk. However, many cities have curbside chargers for curbside parking spaces run by the city -- but these are built and run by the city, and are public.

Maybe cities could be convinced to let people install those, but I don't know if they would let you get any ownership rights in parking there. They might fake it with a "EV parking only for residents with local permit" so that it's 99% likely the space is used by you or a very rude neighbour.

I definitely do own the land under the street in front of my house (to the center of the street). It's a right of way, so I can't build on it without permission, and people are allowed to park there, but I do own it. For instance, if the county ever decided to give up the right of way (and, presumably, the setback), I'd then be allowed to build there. Some states work differently, though, and depending on how your development was built and platted it may be different.

I wasn't thinking of running an extension cord. I was thinking of a professional installation. Get permission the same way the utility company gets permission to put stuff there. Quite possibly I could even piggyback on their permissions.

The trickiest part would be keeping the parking spot restricted for my use only. Actually that wouldn't be a problem where I live, as people generally don't park in front of my house anyway, but then I already have a driveway and a garage do this wouldn't be something I'd do anyway. "EV parking only for residents with local permit" might be the easiest, but it depends who's on your zoning board. If you live in a crowded city, the free market solution might not even be a consideration, and you're better off lobbying for government-owned charging stations.

Getting permission from my office complex owner would be a lot easier. The drawback there is what happens if we change locations after a short period of time. The office complex probably won't be interested in paying for the improvements I've made. This will probably change in several years, as EVs become more widespread, though.

And most of this is just a thought experiment. The right way to do it would be to set up a company, to do it for lots of people and not just one. Maybe even a non-profit. That'd make the deals with the local governments easier. Maybe for-profit REIT would make more sense, though.

If you live somewhere with a well-developed homeowners, you probably want to work with them. You might even have to work with them if there are deed restrictions. (Then again, those places tend to be garage places, or at least driveway places.)

The states could probably facilitate this quote a bit by setting statewide laws forcing local governments (and homeowners associations) to allow this. But absent state or federal preemption, it's basically a question of real estate and zoning law.

Because cities seem very willing to pass laws to boost EVs, I think you might be able to get something done. Probably not a law saying the space is exclusively for you, but something that amounts to the same thing. The "EV parking only with residential permit" of course would work if you are the only guy on your street with the permit. Particularly if the charger only works for you, who else is going to park there?

There are also spaces marked "EV Parking while charging only" which would exclude everybody but you since nobody else can activate the charger -- but then technically you would need to vacate the spot when full. Not that this would ever be enforced against you. On a quiet street I am sure it would work, but on a popular urban street, where parking is always hard to find, I don't think any sort of reserved spot is going to work -- in fact you might need to make the charger available to anybody (who pays) and your neighbours with EVs could park there. My street always has ample street parking, and somebody else not visiting me parks next to my driveway maybe once a year. Some streets you can never find a parking space, even when you have a resident permit.

As EVs become very popular, I think the answer will be they drive themselves off to some charging in the night. It requires a very simple robotic connection -- easy because the car is a robot and does all the moving, the station just needs some plates on the ground or similar setup.

The other alternative -- much more expensive -- would be to install curbside charging along these streets that are heavy with EV owners with no garage. Presumably at their expense. Ideally in a multi-car design because now you'll have to hunt further to find a spot with charging on your street. In general it's tough because on those streets, it's only rarely you grab the spot in front of your house.

All very reasonable. I'd say that curbside charging probably makes more sense than you think, though. I don't see how it's more expensive than charging all in one centralized location. In fact in some ways it'll probably be cheaper as it spreads the power requirements out more.

If the cars can drive themselves then they can drop off in front of the destination and then park at an available curbside spot.

But the big question is which becomes ubiquitous first, the EV or the self-driving car. I'm kind of assuming that level 2 or 3 EVs will be widespread long before level 4 cars are.

If I'm wrong about that, dropping people off at the curb and then heading to a parking garage where you can park and charge (moving between the charging spots and the non-charging spots when done) will probably make more sense in some crowded locations.

Maybe not all, though. Many places rely heavily on street parking, especially street parking with time/day restrictions. Putting a row of chargers on some streets, like those that are "no stopping or standing from 8-6 M-F" or whatever, might be appropriate. I guess if you did that you could take reservations and have an attendant that plugs everyone in at 8:30 PM and unplugs everyone at 5:00 AM. (Maybe the car could at least unplug itself when it needs to, by releasing a lock and telling the charger to roll in the cable.)

What I definitely think you have to do in locations where parking is at a premium is combine parking with charging. At least unless and until charging is a 10 minute thing, and probably even then because you won't want to do 10 minute charging every time. If you want to do 1-hour charging rather than 6-hour charging because the capital cost of charging stations is too high, that's fine. I still think that's going to require a lot of space. So much space that you're really selling parking, with a side of charging, in crowded areas (the areas where people don't have garages or even driveways).

With that said, parking will become much less of a problem once we have level 4 self-driving. Lots of parking in the business districts goes unused overnight. Even there, though, a lot of it is street parking.

Who pays the upfront cost for all of this is kind of irrelevant. Probably governments and/or corporations, though. It's capital intensive, with the payoff taking many years.


P.S. Did you see that Lyft is going into the car rental business? Great move. It might just save the company.

Full robocars may take longer than heavy deployment of EVs, who knows? However, I am talking about a car that can wander about a mile in the middle of the night on empty roads at low speed. That's something I think that can be done very soon, well before major EV deployment. At low enough speed even a Tesla can probably eventually do it.

The challenge with parking/charging is that people need to park and charge for different amounts of time. You either want to charge much longer than you park, or park much longer than you charge. Rarely are they just the same (as at a supercharger.) So it's generally a mismatch.

And no, you don't want to charge for just an hour. I don't charge for just an hour in my own home. Why bother? Maybe I would if I knew I had a super long drive coming up. Topping off is just not a thing in cars with >200 miles.

A car that can wander about a mile in the middle of the night on empty roads at low speed probably exists today. One that can do so legally and is owned by enough people to be worth hiring someone to plug them in when they get there, is possibly very far away. (I'm not even going to consider I stalling technology to plug and unplug the cars automatically, as that's obviously a long long time away, if ever.)

You say the "challenge with parking/charging is that people need to park and charge for different amounts of time." That's a problem that's solvable if the car can move itself a few hundred feet autonomously. But that's only if it's a problem in the first place. Level 2 chargers are fairly cheap. You'd install enough of them so that people can park at them for the entire night. If they're only charging for part of the time they're parked at the charger, because they don't need a whole lot of charge, it's probably okay.

My comment about whether you want to do "1-hour charging rather than 6-hour charging because the capital cost of charging stations is too high" was about that. Basically, you can install 6 level 2 chargers and have the cars use them for 6 hours, or you can install one fast charger that charges 6 times as fast and have the cars use it one at a time through the night. In most cases installing 6 times as many level 2 chargers probably makes the most sense, as swapping through the night is going to be a hassle.

No, you don't charge for just an hour in your own home. You don't have a supercharger in your home.

I assume your idea of having cars drive themselves to the charging station at night was talking about using superchargers. If you're just using a level 2 charger, why bring the car to the charger rather than bringing the charger to the car?

What do you mean when you say you "don't charge for just an hour"? Do you plug the car in every night, or only once in a while, when you need a lot of charge? If you get home and only need an hour of charge, what do you do? (I don't think it really matters, but I'm curious.)

You want to bring the car to the charger because some fraction of buyers can't install charging at their home -- we were just having a thread about that. Or they can't install Level 2 -- another thread.

However, remember the average car only needs 90 minutes of level 2. Some need more, some less. So you can get a 5 times as many cars through so it's less cost to install those chargers. Alternately, you could have only one car per night to reduce labour.

I don't know what the governments will do, but I think if Tesla put a focus on the specific problem of the car driving to charging stations at night on slow roads, I think they could delivery that within a couple of years. (Especially if they added a lidar :-)

As to how it plugs in, there are a few options. One is that the station is large enough to justify an attendant. If you go to the "one car per night" you could say, "All cars must be present at midnight, and leave after 6am" and then only need a gig attendant (such as somebody already on shift or somebody who pops over) to plug in at midnight and unplug at 6. In a 60 charger lot like the one near me, the plugging may only cost $10 of human time, less than 20 cents each.

However, better is to redesign the tesla charging port and put it on the front or back so the car can plug itself into a fixed charger. Plus a small number of stations with robotic charge plugs for the older cars that can't do that.

This could be up and running fairly quickly. The car can go 15mph at night or whatever the minimum speed is. It can keep to back roads, do no unprotected turns, pull over if traffic is too complex. I think you could make 15mph operations safe, even without lidar, as long as you have HDR cameras.

I'm sorry. Where's the thread that says that some fraction of buyers can't install charging at their home? You can install charging just about anywhere. It might be expensive, but installing a bunch of chargers all in one central location is probably even more expensive.

Tesla is not going to put a focus on the specific problem of the car driving to charging stations at night on slow roads. Mainly because it's not a good idea. You have a 60 charger lot near you. You want to use it to charge 60 cars per night. According there are currently about 15,000 open supercharger stalls in the entire world. So Tesla is going to "put a focus on the specific problem of the car driving to charging stations at night on slow roads" so that they can charge 15,000 cars a night? It makes no sense. They will, of course, continue to work on a general level 4 car, and at some point, maybe in the next couple years, it might be able to drive headless around town at night with no human supervision and with minimal risk. Even then, though, it'll probably be several more years before most governments actually approve this.

(By the way, you can't get out of my development without going onto a 45 mph road, where it is illegal to drive at only 15 mph. This would be more feasible if the charging station was in my development. You bring the charger to the car, not the car to the charger.)

No, the 60 charger lot can charge 300 cars per night, since the average car needs under 90 minutes.

If you don't have a driveway or garage, or if you live in an apartment or condo that does not assign parking spaces or won't let you install charging in the lot or will only let you do it for $20,000, there are a lot of people who can't install charging at night.

It's not just cheaper to use this charging lots, they are free. The ones in question, like many, are there at companies to charge employees during the day, and sit empty at night.

You were suggesting one car per night, "to save labor." But okay, 5 cars per station per night. 75,000 cars a night in the entire world. And hiring a worker all night for every location. All in a hypothetical world where all these people have cars capable of driving completely autonomously from their home to a supercharger station at night. (Where do you get 5 from? What are the hours of operation? Are you factoring in that double-superchargers run at half power when both sides are in use simultaneously?)

Maybe it's easier to see this way. The USA has an urban population of 250 million in 100,000 square miles. So you want to put a supercharger station in every 4 square miles or so (1 mile radius). 25,000 locations, each serving 10,000 people. Let's say a quarter of them have an EV car. 2,500 cars. Let's say 20% want to charge on Friday night. 500 cars. 5 cars per station. 100 stations per location (all running at full capacity all night! That's a lot of power consumption!). Is that your vision?

My vision is that sure, we use the superchargers that'd exist anyway when we can do so cheaply, but the vast majority of charging is going to be done slowly (less destructive and easier on the power company) and in places where cars are parked anyway (more efficient use of land, more convenient, and less unnecessary driving). If 25% of the population is going to own an EV, that means a large fraction of all parking locations are going to be electrified. Yes, it's going to cost a lot to do that. I think it'll cost a lot less than doing it with superchargers, both in upfront capital and in ongoing costs. And level 2 chargers can be installed a lot easier. Installing a supercharger station is a huge investment. Installing a level 2 charger in a parking lot is something just about every parking lot owner can afford.

As I've said, you can always install a charger. The question is the cost. Even if it costs $20,000, that's less than one fifth the cost of just the supercharger equipment, let alone the installation of the incredibly large power service plus the cost of the land to build the station on. (You suggest later that it's free, but it's only remotely close to free for 15,000 stations in the entire world, and even for them it's not entirely free, especially if you're hiring someone to plug and unplug cars all night.)

It simply makes more sense economically, in almost all situations, to have level 2 chargers where people park at night rather than having superchargers in a location a mile away. Sure, there are exceptions, but not enough to create a market. You've said yourself that supercharging should be infrequent. I'm not sure why you're changing it. Supercharging makes sense when you're driving long distances in a short period of time. It doesn't make sense when you're using your car 50 miles a day.

I'm not sure what you're saying in your last paragraph. Maybe you weren't talking about centralized supercharger stations after all? How many of these "free" stations are there?

I do agree that it'll often make sense to use office park parking lots at night both to provide parking for residents and to provide charging for residents. This will be useful once we have autonomous cars that can handle this. Even then, you probably don't want superchargers. It's just a subset of charging in the places where cars happen to be parked anyway. And it's many many years off.

What I'm suggesting is to gradually put level 2 chargers where people park for long times anyway. Offices, of course. Residential areas, definitely. Shopping centers, maybe. At the beach, at the amusement parks, etc. You start slowly. 30 spots in a large amusement park lot. 2 spots in an office park. But over time you have built charging in 10%, maybe even 20% of the places where people park anyway (eventually, the places where cars park themselves anyway).

Public charging stations tend to be much more expensive than home ones, though I think that could be changed in time to some degree. But I don't know why you are citing the current numbers.

The question is, how in the future might millions of electric cars charge. One way would be to install a combination of a million home chargers and office chargers. Say 800,000 home chargers and 200,000 office chargers.

However, if the cars are able to wander off at night to office chargers, and do 5 per charger per night, well then you only need the 200,000 office chargers and NO home chargers. How can that not be a cost win?

In reality, you would not do that, you would still get lots of home chargers. But every office charger that can be reached by a car at night maps into 5 home chargers you don't need, particularly good for those who can't access either office or home charging.

Now, you could also have superchargers and each supercharger could handle 100 cars per night, but at some cost in battery degradation.

The use of attendants is a temporary approach. For automated driving to make sense, you want to move to a world where the cars can connect themselves. Because the cars are robots, that is not hard. For example, if a car can extend 3 contact plates down below it onto a small box with contact pads, and the car can position itself with high accuracy, then the charging box can be super cheap. (The box could also have the actuator and the plates could be in the car, but we need to keep them clean so it makes more sense the thing on the car retracts behind a cover.)

At first, when you want an attendant, this will mostly be for people who can't have charging in their house, which is quite large in urban areas. Later, once you don't need the attendant, it is economical for everybody.

Inductive charging is also possible but it's more expensive and really not needed by robots. it is more useful for humans who will not park with perfect precision.

Truth be told, if a Tesla had its current charging connector on the back or front, and horizontal, you could build an automated Tesla plug in just by having a charging plug out on a poll with a small amount of spring load and sway. The car, tracking targets, would drive to that and push the plug in just right. Pretty cheap. Most cars do not mount their charging plug to go in horizontally though.

What kind of office charger do you need to handle 5 cars per charger per night, compared to handling only 1 car per charger per night? That answer might make it "not a cost win." What kind of electric service do you need for the faster office chargers? That answer might make it "not a cost win." How much extra destruction is done to the batteries by charging them 5 times as fast? That answer might make it "not a cost win." How do you plug and unplug the cars at night? That answer might make it "not a cost win." How much power are you using to "wander off at night"? That answer might make it "not a cost win." How much time are spending writing software to enable cars to "wander off at night" and to license them to be allowed to do so? That answer might make it "not a cost win." How much extra power do you have during the day compared to at night? That answer might make it "not a cost win."

I could keep going, but I think you see the point. Over time, equipment costs are a small and diminishing fraction of the total cost of deployment. I think it'll make sense to have extra equipment in exchange for much more efficiency. Maybe I'm wrong. As you note, I am basing some of my thoughts on this on the current numbers. Obviously the current numbers aren't going to be the current numbers in the future. But you have to start somewhere, and starting with the current numbers and extrapolating from them is better, in my opinion, than just randomly making up numbers that fit your beliefs.

You say that "every office charger that can be reached by a car at night maps into 5 home chargers you don't need." Perhaps one day that will be true. Perhaps not. I'd lean toward that not being true any time soon, because the technology to automatically plug and unplug the cars likely won't be widely deployed any time soon. Furthermore, it depends on how fast the office charger can charge, and how much charge the cars need. Because of the expense of automatically plugging and unplugging the cars and the extra destruction done by charging more quickly, I think it'd make more sense to only charge one car per charger overnight, at whatever charging speed enables the car to charge however much we want to charge it over the entire period of the lowest electricity rates. Most cars wouldn't need to be charged every night, though there would probably be higher demand on certain nights, like Thursday or Friday nights, where a large portion of the population wants to fill up at once. Perhaps only on those high demand nights we could hire people to plug/unplug cars so that we can handle more cars in a single night.

That's only one possible scenario, though. Maybe there will be enough electric vehicles on the road at night doing other tasks (we could switch package delivery to nighttime if we had robots that could do it) and we could use the office to handle their charging needs. By all means we should use the office chargers that are already there, if we can do so without too much re-engineering. And not just office chargers. The chargers at the beach, the chargers in residential areas, the chargers at shopping centers, the chargers at amusement parks. Use them all, once we have self-driving technology. But probably use them slowly. Slow charging causes less battery destruction, and if we're going to use humans to plug and unplug them, it also saves the cost of plugging and unplugging them. (I do wonder if some release mechanism could be inexpensively produced so that at least unplugging could be a humanless process. Probably so, though perhaps only on new models.)

Tesla doesn't have its current charging connector on the back or front, and horizontal. I think it's unlikely they're going to complete re-engineer things to change that, in large part because I still don't see the point. It's okay to have more chargers than you absolutely need. Long in the future, we'll of course have equipment deployed for cars to plug and unplug themselves. Tesla already has a prototype, and it doesn't involve making any changes to the car. But by the time these are widely deployed, much of the charging infrastructure will probably already be in place, and the gains from having fewer chargers don't seem to be worth the costs of redoing the infrastructure. Additionally, slower charging will probably be less destructive than faster charging for the foreseeable future. Furthermore, having lots of extra chargers helps when there are spikes in demand or issues with supply. If a natural disaster is approaching and everyone heads towards the 200,000 office chargers all at once, that's going to be a problem. If there are 800,000 "home chargers" in residential neighborhoods in addition to the 200,000 office chargers, the process will go a lot more smoothly.

The same office charger. 5 cars/night is because the average car drives 40 miles/day, which takes about 80 minutes for the average session at 7.2kw. Same electric service, same chargers, not any faster.

If the wandering trip is 1 mile one way at low speed, about 0.5kwh energy wasted (5 cents at night.)

The time writing the software? It's the same software Tesla wants to write for FSD. And it's spread over all the cars.

The only actual question in your list is how you plug and unplug. If it's a human attendant, that is a real cost. To make it cost effective you either want a fairly busy lot. A lot with 100 chargers and a $10/hour full time "pump jockey" would cost 20 cents/car.

That's one reason to move to robotic plug in. However, 25 cents every 2 days, under $40/year, can be quite a bargain compared to the cost of installing home charging if you can do that at all.

I think you just misunderstood and thought I meant fast charging.

So you are proposing that every car charges every night? At an office 1 mile away (presumably this is not the office where they work, but just some random office somewhere). Is 1 mile away realistic? Do most people have offices, where parking is available, within 1 mile of their house? I'll assume for now that it is.

I won't assume your 5 cents a night figure is correct, because at you say 4 cents a mile, which would be 8 cents a night. Add 11-20 cents a mile for depreciation and 6 cents a mile for insurance (both your figures, again). So 21-30 cents a mile, or 42-60 cents a night in incremental cost. Let's say 50 cents a night. Times 365, times 7 years, equals about $1275. That's just from driving, and might surpass the cost of a charger in itself. Add the 20 cents/car per night for the human attendant (robots doing it would be more expensive for the foreseeable future), for another $500 over 7 years, though I think your estimate of 100 chargers per lot is overly optimistic. You say the charging isn't any faster, but if you're charging in 80 minutes instead of 6 hours, that's faster.

If it's the same software Tesla wants to write for FSD, then I think we are at least several years away, and possibly many years away, if you include the time for governments to make it legal.

I guess if people have an office full of chargers (enough to service 1/5th of the cars parked on the street) within 1 mile of them, it comes out about break-even, at least at today's prices (which no doubt will come down quite a bit over time). So I think maybe we should look at how realistic that 1 mile distance is. I'm not sure how to get a good random sample though.

Looking at the last apartment complex I lived in, there are not many offices within a one-mile radius. There's a church, and a school, and a supermarket, and a strip mall. You could put chargers at any of those locations. But probably the best place to put chargers to serve the people who live in that apartment complex would be right in the parking lot for the apartment complex. You could, if you wanted, serve 5 cars for every charger, and have the cars drive themselves to and from the chargers overnight. You wouldn't need government permission for this, as the cars would stay on private land the whole time.

I think that's much more realistic, as well as more efficient.

My apologies, I thought you were asking about the loss of energy. Yes, the car suffers other costs in driving a mile. And no, a lot of cars would not charge every night. A decent number of cars don't drive in a given day, Probably anybody under 20 miles won't bother charging. You can set it as you like, many people would be just find saying wait until down 50 miles (or longer drive planned for tomorrow) to charge, which might mean 150 or so charges/year.

It is a subset of what they need for FSD, and a fairly small subset, since speeds are low and roads are empty and limited to just a few classes of roads. If you live on a busy street at night this may not be an option for you. Would admittedly be better with LIDAR's night vision but not happening with Tesla.

Many would still prefer to install home charging. But for those who can't, and those who face a bill of thousands of dollars to put in home charging, it's a win. It can be a further win in that the office park may have industrial night energy prices that are better than those at home. Finally it's a win in that you don't have to do the plugging. Plugging is not a huge amount of work, but it's something. Your car is just magically always loaded with energy while you sleep.

The same thing would run in the day for employee cars, too, once they can do the basic parking lot manipulation and plug in. No travel distance for those cars. Today, EV drivers at companies have to have little mailing lists where they announce that a spot is free, and need to go out to parking to move their cars.

Not every residential area has an office near it. But many do.

Unless you truly bought your EV as a “city golf cart”, don’t skimp on the charger. Life can be unpredictable and you may need to use the car for long distance travel when you hadn’t planned to. There’s nothing worse than having a great EV and knowing it “won’t be ready” for a certain distance trip until 4pm today. Buy and install a fast Level 2 charger as it’s cheap insurance in the long run. If you live in an area with potential disasters like hurricanes, floods, or fires, you also may want that car at 100% charge quickly.

Again, for the average car owner, the car is almost always at full every day. For people who drive above average amounts, that's not true and they want more charging. For the rare days when you are a bit low and need to do a long trip, you spend a short time at the fast charger. Not ideal, but better than spending $6,000 which is not cheap.

I have a Clipper level 2 charger for my Leaf. Cost $800.00 for the whole deal installed. I have no problems with the supply current.I think your numbers are off.

Some people can install a charger for well under $800. For others, the quote to do it legally can range to $8,000 or more.

I think if you live in a home with only 100 amp service you're not likely to be purchasing an EV until the prices become even with an ICE car. Just sayin.

There are homes costing millions of dollars with 100 amp service. It is just a factor of when they were built.

Show me one.

One? Around here, hundreds of thousands. Most of the older homes in Silicon Valley qualify. 100A service was the norm 50 years ago. My last home back in Canada came with 60 amp service. Doubt it's worth millions but still enough.

Also understand that electric cars are not that expensive. With the federal rebates, a car like the Kona or Soul can be about $24,000. When you add the savings in gas and maintenance that makes it one of the cheapest cars you can buy. Any homeowner can afford one of those. Even the Model 3 SR is comparable in cost to a Camry after the savings -- again any homeowner can afford one. Not everybody can afford a Model S or i-Pace perhaps.

But nobody wants to find out it will cost $6,000 to charge their car at home, even a millionaire. In the Facebook thread on my post, people have reported estimates over $8,000.

There are some technical errors, omissions, and code issues in your article (which vary by state). Are you a graduate electrical engineer from an accredited engineering college? (I am)
At least a licensed electrician for your particular state maybe? Was the information reviewed by an EE or licensed electrician? If not, you should not be giving this kind of advice to people however well intended especially given the voltages and currents discussed. A house in our neighborhood burned to the ground due faulty charger wiring.

Please feel free to point out errors rather than saying they are generically present. The article contains no instructions on how to wire, but rather on what to ask your electrician about. (BTW, university level electrical engineering classes, which I have taken, are not generally about electrical codes for residential wiring, so I am not sure why you cite that.)

Codes do vary by location of course. But it remains true that there are panels where the code would not allow the addition of a 50 amp 240v circuit but which would allow a 20a or 30a, thus vastly lowering cost. The article is not about how to wire, it's about understanding just how much current you actually need.

The "Amazing-E" EVSE provides ~3.8 kW via 16 Amps at 240V. It comes with a 4 prong NEMA 14-30p (clothes dryer) plug, but, since it is limited to 16 amps should work with a 20 Amp 240V circuit that might reasonably be added to an older 100A service panel.

3.8 kW is more than triple L1 rate, and, last I checked, the Amazing-E cost well under $300

Brad, as an ev owner who struggled with the insane cost of a panel upgrade, I have also turned to a dryer splitter solution. EV-powershare is what I am using, it's safer than other solutions out there, as it has built in over-current protection that prevents someone who has no knowledge of the 80% rule misconfiguring their EVSE. Would you be willing to take a look, and add it as an alternative solution in your article?

Your comment is written like a user, but the links suggest you work for the company. That's not something that this site or other sites take kindly to, and a bad way to start things off if that's the case.

I looked at the site. The devices there have 14-50 sockets on them, which is dangerous unless the EVSE can be set to limit the current to 24 amps. With Teslas, their EVSE does not do this with that plug, you want to use one of the two dryer plugs. Odd choice when the competitors have selected the right plug.

The second issue is that I suspect most customers will want a unit that has a pass through for the dryer, but then a long cord to the EVSE, which usually does not go right where the dryer is a typical parking setup. I would need 35' of cord in my case, AWG10 or better of course.

I do like that you have the breaker switch, so users can assure it is off before unplugging it, I presume. Alternately, these would probably do better hardwired into the dryer socket, which most electricians could probably do for whatever their minimum work rate is. It's better if a high power plug can't be unplugged.

These boxes are useful (if configured correctly) though there seems to be an obvious win in just making a special EVSE designed to pass through to a dryer from its plug. Rather than just switching off the EVSE when the dryer is one, that EVSE can just reduce the max current in the pilot wave based on what the dryer is drawing. That can be important with some new dryers that also have low current modes. Of course, you would want to somehow get your hand on Tesla plugs since I don't want to add another $100 to put the adapter on a J1772 I will never use. I don't know if you can buy those.

I'm going to look at Dryer Buddy and Neocharge at some point, perhaps do a shoot out. When yours is safe, with 2 of the same plug on it rather than a 14-50, I could include it.

But please don't post a note like the one above, that says you "turned to" a solution that "I am using" when in fact you make the product. That's a very bad thing.

Brad, I didn't mislead you in anyway, I am one of the designers of this product and I do use it myself!
The safety issue that you have raised, where a 14-50 can draw too much power from a 30 amp circuit is exactly why I have added the overcurrent protection at 25amps via the breaker. So if someone doesn't understand the 80% rule and sets it too high, it will just cut off power way earlier than the house breaker would.
I have seen products like Dryer buddy that allows a 14-30 and 14-50 combo, and I didn't feel safe using it. Same way that you probably felt. Hence I worked to overcome that safety issue.

Lastly, having a 14-50 socket is purely for the convenience of the user. It kinda sucks having to buy another adapter that converts 10-30 to 14-50 just so that you can plug in the EVSE, when you already spent $350 buying a smart splitter. I would even dare to say that daisy chaining adapters is a bad idea. If you do a quick search on amazon, you will find TONS of those adapters, if they can be "deemed" safe, then I feel my product is actually much safer.

Anyways let me know if you want to chat more, I am a tinker and can talk about charging all day.

Also to add, having dual 14-30, or 10-30 sockets is very easy to make. I will ask for it to be offered.

Your idea of having a by-pass for the dryer (which it is currently), then an "extension" cable for the EVSE is a good idea. It is true, dryer socket is usually 25' to 50' away from the ideal location to install the EVSE.

I guess I won't convince you. The general rule for all online activity is that if you are the maker of a product, you identify yourself extremely clearly as that. You don't equivocate or make subtle truths. You say, explicitly, "Hi, this is Henrick the designer of ." Nothing less than that when you talk about it. Ever.

The breaker is good. To my mind though, the $35 adapter is a better choice as it tells the car what current to draw. The breaker (which has its own cost) is also not needed if that is used.

I am referring to the Tesla EVSE, which has switchable plugs, and each plug tells the EVSE what current it can handle. I realize other EVSEs take different approaches.

I am not a market or media person, thus I actually appreciate your candor about this type of etiquette.

Hearing yours suggestions, looks like offering multiple options to consumer is the best route for now.

Since we are conversing, how or can we keep in touch? what's the best way to do so?

is my preferred mode of contact, is my public address

Thank you for this. I’m buying a Tesla because it is the safest car on the road and I just realized I won’t feel safe riding Metro until I’m vaccinated - which could be two years from now. Next question - how to safely get a charger installed? Thanks to this article I think I can wait. My commute will be 21 miles each way. There are three chargers at work. I can charge at home at night and on weekends. The 110 volt outlet should do until it is safe to have someone in my home.

You can also order a and for $549.00 and about one hour of an electricians time (or you can easily install), you can have an auto switch of power between two appliances. An oven and an EV charger, a dryer and a sauna, a spa and bandsaw, etc. One source of power and two outlets. Or you can buy the simpleswitch EV that comes with the cord already attached. Please send me a pic of your panel for a free evaluation.

What I really want is better than that. I want an EVSE that knows how much current the other appliances are using, and adjusts the EVSE pilot signal up and down.

May 26, 2020
We are buying a Tesla 3 and get delivery 3 to 7 weeks after May 17, 2020. Enjoying your charging solutions at home in California. Taking the unused elec. dryer outlet through the wall to the garage and using the Mobile Connector, 10-30 connector plus a 10 ft. welder's extension cord to run the charger overhead to the rear of my Tesla pulled in front first. We also have 16 solar panels and am paying $30 month for elec. (Pre-panels it was $153). Southern California Edison has net metering, so I sell back extra above my use. Solar Panels product DC and Tesla takes DC, is there a way not to convert twice between my solar panels and my Tesla?

Note that the use of the extension cord is not strictly to code, but if you do it with care should be OK. You can also consider telling your Tesla to use only 20 amps instead of 24, just to add some more margin if you like.

No, there is no practical way to take DC from your panels and put it directly in the car. So yes, there will be some losses. I mean, it's physically possible to make a DC charger driven by solar panels, but the car needs a carefully controlled voltage and your panels don't put that out. While DC fast chargers are huge expensive things, in theory one could be built that was just a solar charge controller which might be a lot cheaper since it would not do very much current and not be meant to be that fast.

But then you would only be able to charge (with that) in the daytime, when your car is not going to be sitting in your driveway, is it? And it would need to be fancy, switching from solar to the car, to grid to the car, to solar to the house, depending on what's going on. All of which means more cost than the losses you will take using what you have now.


Is there a way to keep track of electricity used through my cord only used to charge my Tesla?

There are a number of ways. By far the simplest though is your car will tell you how many kwh it has used. Your trip odometers will tell you how many kwh you used over a given distance, and give you wh/mile which you can multiply by miles. This will not tell you energy lost to keeping the car computer on, or charging losses, though.

If you plug your car into level 1, you can get a kill-a-watt which is very cheap and will tell you everything about the electricity used. If you plug in level 2, there are lots of home energy monitoring systems they sell that will track usage of different circuits in your house, but they tend to be more involved to install, but there are electronics hobbyist devices that let you measure current in any wire, and you only have to snap them around a wire, you don't need to interrupt it. You can buy a "clamp AC meter" if you can get your hands on one of the conductors going to your car, and compare current in it vs. what the car says the current is.

More tricks: Do you have a smart meter that tells you the watts? Read what it says while your car is charging, then stop it charging with the app and see the difference. make sure nothing else in the house goes on or off in that few seconds.

Or if your power company breaks down power usage by 1 hour chunks, as mine does, just look at the reports from the night when you charge. At night your house current will stay pretty constant except your fridge or AC (or furnace) in winter. You can safely unplug a fridge for an hour or two if you keep it closed.

Just bought a used EV (BMWI3). Perhaps you can answer a main question re the charging of the battery. Is it best to “top off” the battery every night (level 1) or should I allow it to reduce to a certain level before plugging in. Thanks in. Advance for any guidance

This is hotly debated. Generally it is agreed that charging to 100% should only be done in advance of a trip that will need that which should be rare. Unfortunately, the i3 battery is so small that this could be many trips.

The "ideal" charge level is about 63%, in that it is estimated lithium ion will get maximum life at that charge state. However, you also don't want to take it too low so that's not a state most people use except when storing their cars. Some people charge to 90% each day, a lot of people like 80%. Since you don't want to go below 20% most of the time, going 80 to 20 on an 85 mile battery like in the i3 would only offer you 50 miles of range. If that is your normal day, it's a good choice. 90 to 20 gives you a little more.

There is no reason not to top it off to 80% though, except when storing. The minor downsides outweigh the benefits. The main reason not to is to save the trouble of plugging in if you don't plan much driving the next day.

Good practical points here, thay help me realize I don't need to invest powering up my 100-year old garage for a future level 2 EV charging station, but I couldn't help but do a double-take over your recommendation to use the electric clothes dryer circuit and then hook up natural gas for your clothes dryer. One of my main motivations for getting an EV is to get off fossil fuels. Now granted, reality today is that the electricity on the grid mostly comes from gas, so nobody is really going to be a purist, but if you are going to invest in electric car and maybe heat pumps, etc., then you would not want to go backwards by continuing to use natural gas in your home.

If your power comes from fossils in your area, using a natural gas dryer is the green thing to do. You will cause less fossil fuel to be burned if you run your dryer on gas instead of having them burn gas at a power plant to make electricity, that's only about 50% efficient. So you will double the gas burned if you use the electric dryer.

That's even true if you have solar panels on your house!

The only time its not true (barely) is if you buy grid power from solar/wind farms, but people even argue about whether it's true there.

But do the math. If you have solar panels on your house, and run your dryer in the day, you can pretend you put "solar electrons" into your dryer, but that means you did not feed them back to the grid. So a grid power plant had to fire up a little hotter, burning twice as much gas (or worse, coal) than you would have burned in your gas dryer, to serve the other people who no longer got your "solar electrons."

So if you want to increase global warming, use an electric dryer.

Until the day comes when we have an all renewable grid, that is, then junk your gas dryer and put in an electric one. (Or hang your clothes to dry.)

In theory if you buy your power from grid renewables, your money over time goes into building more renewable grid power. You will find arguments on this question in other posts on this blog.

Will the advice in your 12/19 article change?

It remains the same. Full 7kw home charging is "nice to have" but not worth spending a fortune on for most drivers. People with long commutes do need more than Level 1, as before. Once cars can drive to charge themselves, you don't need to install charging at home at all if it's expensive.

If you want to look at an alternative to the DCC energy manager check out Black Box Innovations.
There products are much smaller, faster and easier to install.

I think they call them ALMS for short around here. We use the Black Box EVEMS240-100 device and it works like a champ.

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