2 Questions from new Tesla owner after first long trip…

[father_of_6]

I thought you could set your max charge and that would be it. Like if you are charging at home overnight and set it at max 80%. is this not possible when at supercharger? I know You-tubers say they got delayed eating lunch and charged more than the app said they needed to reach next charger but could that be because they didnt care or didn’t bother to set a max charge? Trying to learn as much as I can before I get my MX. thanks

Hmm... the SuperCharger *does* honor the limit set in the car, as far as I recall.

 

[RTPEV]

I thought you could set your max charge and that would be it. Like if you are charging at home overnight and set it at max 80%. is this not possible when at supercharger? I know You-tubers say they got delayed eating lunch and charged more than the app said they needed to reach next charger but could that be because they didnt care or didn’t bother to set a max charge? Trying to learn as much as I can before I get my MX. thanks

Yes, what you are saying will work. If you want to limit the charge at a Supercharger to say 80%, you can set the car's charge limit to that and it will stop charging.

But that's not what the OP was talking about. When you charge at a Supercharger, you generally only charge to whatever you need to get to your next stop (or final destination). No need to sit and wait for it to get to 80% if you only need it to get to 55% to make it to the next stop.

When you put in your final destination to the nav system, it will tell you that you need to stop at Supercharger X for 15 minutes to make it to your final destination with 10% (or something around that). And when you get to the Supercharger and start charging, it will give you that 15 minute countdown. But the OP was wishing that instead of giving you the number of minutes, it would instead give you the goal SOC it was trying to reach (say 55% in this example). I would agree that this is useful information, because if you feel like you'd like say an extra 5% buffer above and beyond what the car has already determined is an adequate buffer, you would know to go to 60% instead of 55%. If you only have a minute countdown timer, once it gets to 0, you don't really know how much longer to stay.

Of course, once you get used to the car, you may come to realize that the countdown timer is actually pessimistic and you really don't have to wait until it gets down to 0 and still have an adequate safety margin, but particularly for new drivers, knowing the target SOC would be helpful.

 

[drtimhill]

I thought you could set your max charge and that would be it. Like if you are charging at home overnight and set it at max 80%. is this not possible when at supercharger? I know You-tubers say they got delayed eating lunch and charged more than the app said they needed to reach next charger but could that be because they didnt care or didn’t bother to set a max charge? Trying to learn as much as I can before I get my MX. thanks

yes the max charge applies to all chargers (though at some busy superchargers there may also be a max allowed charge, in which case your car will charge to the lower of the car setting and supercharger setting).

 

[Tronguy]

So, as in All Things Tesla, there've been some changes since this thread got started. In no particular order:

• In many, but not all states on the East Coast (I know for sure with New Jersey, Massachusetts, and Maine) Telsa has been changing over many of their Superchargers to charge different rates depending upon the time one is charging. Charge from 12 noon to 9 p.m.: Pay max rate, $0.43/kW-hr. Charge from 9 pm. to 12 midnight, pay, I dunno, $0.35/kW-hr. Charge from midnight to 12 noon: Pay $0.28/kW-hr. No question, they're they're trying to get people to charge at off-peak hours.
• SC's at high-usage locations tend to have higher rates.
• The Tesla Mapping function definitely is playing what I tend to call, "Operations Research". Say you're an airline company. To make it simple, say that you're doing freight, a la FedEx. You've got hundreds of airports, thousands of planes; the airports take certain size airplanes, the planes have different load and distance capability. Quick: It's a make or break decision for the profitability of the company and how well one competes, complete with how much one charges: Which airplanes does one route where at what time of the day, taking into account fuel prices, weather systems, airplanes, and all? And one has to solve this complicated problem on a daily basis based upon who's shipping what to where, which also varies madly. Answer: Huge square matrices with millions of terms and repetitive optimization. People get their PhD's in this field and, no, I'm not joking. And that Monster Math Problem has to be solved, every day, probably as Everything Is Happening At Once.

On that third item, take Tesla: Superchargers scattered across the landscape, Some of them are inevitably broken. Different power levels. Different levels of historical usage, varying by time of day, day of week, and season. On a given day, there's a bunch of Teslas that have loaded a variety of destinations that pass Superchargers, and one would like to get all these Teslas to their destinations at (a) minimum cost to Tesla and to them (remember, Tesla's paying for the electricity - and the cost varies as per the time of day, and load!), (b) minimum cost to the users, and (c) minimum time to the users.

And then throw into the mix areas of the country where people want to live in apartments and don't have wall connectors. They'd like to use the SC network, too - but they sure don't like that $0.43/kW-hr charge. How about when the long distance travelers are sleeping - send the locals out for a twice-a-week SC visit! Hence, the rates vary as per the time of day. And, for what it's worth, it might even be cheaper for Tesla to buy the electricity in the wee hours of the morning.

On the last couple of couple-hundred mile trips I've taken in the M3, one can see hints of this going on. Stopping at a SC in CT for five minutes, then continuing on, but skipping a heavily used one in Central Massachusetts and getting to a lightly used one in SE MA, instead.

Fun stuff. But could you imagine this with gasoline? Charging half the usual rate at 6 a.m. and doubling it at noon? Whee!

Thing is: I wonder how, or if, ABRP is going to compete with this Tesla initiative. Or how Tesla's computers will handle $RANDOM variations due to ABRP. Stay tuned.

 

[RTPEV]

I don't know if Tesla is going to the trouble of optimizing costs for customers. At best they are probably just trying to maximize the customer experience by trying to discourage peak (most congested) charging and diverting to less crowded Superchargers, but more likely they are simply trying to recover their own costs which are higher during those peak times.

ABRP can continue to "compete" (if they even consider themselves in competition with Tesla--remember, they support other EVs as well!) by simply offering features and functionality that Tesla doesn't. It took Tesla this long to just add waypoints and it still doesn't give a great view of upcoming charger utilization. But I wouldn't worry about ABRP: they are offering a Tesla-like experience in vehicles that have no prayer of ever having such capabilities built into their vehicles.

 

[avs007]

One thing to add, that I noticed on my return trip from California last week... When I was sitting charging, I was looking at the energy graph, at the estimated arrival %. I don't think that updates in real time, I think it updates every few minutes or something like that... I remember watching it, while it was negative, and looking at what my current SoC was, and then figuring out how much SoC I need.... Then as I watched it, I noticed it didn't always rise linearly with my current SoC, it would jump up in spurts. One time I remember thinking it was odd, so I actually exited out of the energy graph to something else, and then came back. When I came back, the estimate on the energy graph was in line with what I thought it should be. So with that being the case, I can see how it might jump up a few percent when you start to drive, as the OP noted.

But yeah, as others have said, if this is your first road trip, your car doesn't have all that much data on your driving, etc... It'll get better over time. I go on road trips all the time for work every month, so found it to be pretty spot on... Even after I swapped out the tires to a slightly bigger size. After a week or so, the range estimator self adjusted, and is back to being pretty spot on... As far as roadtrips tho, there is still a lot of variability, particularly if you have a lot of altitude changes. I found that for the most part, I tend to drive with a constant speed, but when I get in to the hilly portions, I'm all over the place, depending on traffic... Sometimes I end up only driving the limit, sometimes I end up driving much higher, etc... That can really throw off the range prediction. One time when I was driving thru Shasta, I found myself driving much faster than I had been, and my range estimate dropped below 8%, so I decided to just use AP for a while, and the range estimate went back to 15% after a while... On the way home, there was a traffic jam going thru Shasta, so I ended up having to drive much slower than normal... That time the range estimate went from 15% all the way up to 27%.

 

[Genie]

I think the 'sell electricity by the kWh' law was intended to prevent master metered apartment owners etc from marking up their electricity and selling it for a profit instead of passing it thru. It was written before EVs and so probably too broad.

Even residential power is sold by time in some states? I am curious to see a bill, my house uses some power 24/7.
As lights etc go on and off are you constantly going to different rates?

 

[Tronguy]

Even residential power is sold by time in some states? I am curious to see a bill, my house uses some power 24/7.
As lights etc go on and off are you constantly going to different rates?

My understanding is that, for residential properties, there's two options:
1. The energy is free from the landlord. (There are apartments like this; they make it up on the rent)
2. You're metered and billed by Ye Electric Company.

There have been many and varied ways of measuring energy usage. About seven or eight years ago I had to put an electric meter on the inverter output of the solar panels, so, being interested, I looked it up. Edison was the first, but by no means the last, person to come up with a way of measuring energy usage.

Current systems use a kind of motor that spins a wheel depending the magnetic field generated by the current, AC or DC, flowing into a house. Interestingly, these things are bidirectional. The back side of a residential electric meter in the US has four big lugs. Two of them are the split-phase hots from the city power; the other two go straight into the breaker box. When running solar, the two hots from the inverters are literally bolted on top of the two hots going to the breaker panel. So, if the solar panels are making more energy than the house is using, the difference between the two flows out of the meter. If the solar panels are making less energy than the house is using (at night, say), then energy flows through the meter from the city power guys into the house. In the second case, the disk inside the meter runs forward; in the first case (and I've seen this with my own eyes) the disk runs backwards. Really. Cool technology.

In any case, meters used for revenue purposes (i.e., you're going to get charged real money) have to be accurate to less than 1%, with the paperwork and testing to prove it.

Last thing. Let's be really clear about this: Watts are a rate, like gallons per minute. Energy is a quantity, like a gallon. The SI unit for energy is the Joule; a Watt is defined as the rate of one Joule per Second being used. (1W = 1J/s). That 100 Watt lightbulb lighting up your life right now? It's using 100 Joules per second, so long as it's on.

For $RANDOM historical reasons, energy companies like to charge for energy usage in kW-hours; one kW-hour is 3.6 million Joules (3.6 MJ).

So, if you leave that 100W lightbulb on for 24 hours, the amount of energy used is 100W * 24 = 2.4 kW-hr. In New Jersey, residential, that'll cost you $0.18 or so. Leave it on for half the time? Then, you get charged $0.09.

 

[Feathermerchan]

Reason for charging by the kWh is kWh = energy and energy costs $ to make. An it's easy to meter. Like gallons of gas.
New meters do not turn backwards. Electronic meters register consumption and generation separately. I have solar on my house. Sometimes it registers consumption, sometimes generation.

 

[Tronguy]

Reason for charging by the kWh is kWh = energy and energy costs $ to make. An it's easy to meter. Like gallons of gas.
New meters do not turn backwards. Electronic meters register consumption and generation separately. I have solar on my house. Sometimes it registers consumption, sometimes generation.

The electronic meters which don't use that reluctance motor are, you're correct, unidirectional. Over here, there was some confusion with paperwork when the solar panels went in and the local electric company didn't come down and put in an electronic meter. Said electronic meter actually contains two meters: One counts up when energy flows into the house while the second one doesn't move; the second one counts up when energy flows out of the house (middle of the day, solar panels are running) while the first stays still.

So, for the first couple of months I had ye olde-tyme mechanical meter in there and it ran backwards during sunny days. One month, the reading on the meter's little pointers was less than the reading the previous month. The power company's billing computers decided that this meant that that the meter had run forwards until it rolled over and back up to that slightly-less-than-the-previous-month's reading. The electric bill on the statement was, like, $20k or so.

A call to PSE&G was swiftly followed by hands slapping foreheads left and right. Turned out that NJ has this billing system for solar panel types called, "Net Metering", where one of those electronic meters goes in and the power company tracks how much one uses or generates each month. A quick phone call resulted in a truck showing up the next day with the new meter, and in it went.

Starting at the install date, excess energy in any month gets carried over to the next month as a surplus with no monetary charge; so long as that surplus exists (which it usually does, during the winter months) one pays a relatively cheap connection fee. At the anniversary of the install date, if there's still a surplus, the running total gets zeroed out and the homeowner gets paid wholesale for the energy (that's the "net" business). If in any month the running surplus goes negative, then one pays retail energy costs that month just like any other electric subscriber.

Fun thing was that the system here generated, over a year's time, roughly 2 MW-hr's of energy more than used, which meant that there was a payment of a couple hundred bucks to the account on the anniversary date. That surplus has kind of evaporated now that there's two Teslas in the garage; but it does mean near-free driving around for 2e6W-hr/(250W-hr/mile) = 8000 miles every year between the two cars, not bad.

Which is why those of us with Teslas and solar are making out like bandits. At least, for local driving around.