Thursday, March 24, 2022

Tesla Model Vision-only Autopark - Alternate Parking Space Target Selection!

While testing whether our October 2018 Model 3 was indeed now using Vision-only for Autopark (it does, and is apparently no longer restricted to Autoparking between adjacent vehicles using ultrasonic sensors), it was discovered that by creeping rearward with throttle after engaging Autopark (by pressing the blue "Start" button when presented), the system will (sometimes) sequentially re-target the next empty marked parking space. Experimentation suggests that this will occur a maximum of twice, for a total of three spaces consecutively selected. This was tested on both right and left sides of the vehicle (depending upon which side of the vehicle was positioned closest to passing available spaces).

Attempting to acquire beyond a 3rd targeted space resulted in cancellation of Autopark sequence in several attempts. Applying brakes at any point after engaging Autopark cancels the sequence (as always). This is likely not a feature, but an unintended behavior. Despite the slightly manual "override" nature of this behavior, the selection of a particular parking space is still determined by the vehicle system, and while the selection of a given empty space is possible, it is not certain - especially in circumstances where expediency matters.

Tuesday, August 18, 2020

Charging Your Tesla at Home: How Long Does It Take? How Expensive Is Home Charging Equipment?

A friend recently asked: "How long does it take to charge your Tesla at home -- and how expensive was the home charging station?"

This was my response:

I configured our Tesla Wall Connector (an “EVSE” - more about that in a moment) to report that it can provide 40A at 240VAC (9.6kW). At that rate, it adds charge at a nominal rate equaling about 37 miles of range per hour of charge. So if we’ve driven, say 70 miles on a given day, then it will take around two hours to replace that charge. If our ~75kWh battery were at 0% (something you do NOT want to subject a battery to, much less plan that close - though I’ve arrived home with <6%), it would take over 8 hours to top off (assuming you wanted to charge to 100%, which no EV owner should be doing unless it’s absolutely necessary for the next leg of a trip), with the charging system going quite gently near the 0% and 100% charge capacity of the battery (lithium-based batteries do not take on charge well at these extremes).

Our car’s on-board charger is capable of charging from AC sources at a maximum of 48A, or about 44 mi/hr. But the 240VAC service for our EV charging can’t handle that load. When we first installed an Aerovironment 30A, 240VAC “Level 2” charging station, we had an electrician run a service line from our breaker box to the breezeway of our home. The electrician told me that he installed a 50 amp line, so if I needed more current in the future, I was set. But when I removed the Aerovironment EVSE to install a Tesla Wall Connector, I found the wires disappointingly small in gauge. After no small amount of research and measurement (no visible markings on the wire), I determined that the 8 gauge wire over the 50 foot run could only safely support 40 amps. Statistics of charging sessions indicate no apparent thermally-related voltage drop, so I’m happy with that.

Regarding costs: in addition to the $700 to have an electrician run the original EV line, the Aerovironment EVSE was $1,100. However, we received a $750 rebate from LADWP for installing an EV charging station. We charged the Tesla from the Aerovironment using an included J1772 adapter for a while, until I discovered that LADWP would rebate us the entire $500 of a Tesla Wall Connector. Not only could the TWC charge at a higher rate, but I no longer have to handle the J1772 adapter daily. Best of all, the Tesla charging handle has a remote charge port button (it could be fussy to sometimes have to open the trunk to wake the car to unlatch the charge handle). We’ve also benefitted from three Federal $7,500 rebates and three California $2,500 cash incentives for adding three zero-emission cars to the state’s rolling stock.
“EVSE” stands for Electric Vehicle Supply Equipment, the “charging station” which incorporates a ground-fault system and an intelligent controller which is interrogated by an EV upon connection, reports it’s available current limit, and only while handshaking with a connected vehicle allows current to flow via big contactor relay. The charger in the car determines how much current the vehicle will attempt to draw based on the interrogation step. 
All contemporary EV’s AC charging is intimately managed in the car itself, monitoring charge and temperature and in the case of all of our EVs thus far, both heating and/or cooling the battery to optimize the charging process. Tesla cars even pre-heat or pre-cool the battery while on the road if the user sets a Tesla Supercharger as the navigation system destination, back-timing the thermal management so that the battery can immediately take on maximum charge. (Currently the highest Supercharger power is 250 kW - yes, more than most motion-picture generators, and capable of peak rates adding 1,000 miles per hour to a Model 3 or Y.
An EV owner’s commitment to upgrading home charging infrastructure should be consistent with their driving habits, lifestyle, and characteristics of the vehicle. Your Volt is the perfect example of NOT benefiting from the investment to upgrade to Level 2 (L2) charging equipment: 1)The longest possible L1 (120VAC ~12A) charge is almost achievable with a typical overnight parking period (~10-12 hrs); and 2) In an emergency, you can simply operate the Volt as a hybrid.

If a Volt owner was determined never to operate the gas engine (keeping in mind that it must periodically run a maintenance cycle), and the owner’s lifestyle benefited from charging at 22-25 miles/hour during the day at home before once again using the battery, that might be a case for investing in L2 infrastructure, but there’s hardly a financial argument.

Our choice to spend $1,100 (after rebates in installing L2 charging was clear: we would attempt to go Cold Turkey on Internal Combustion (we never used our Dodge Caravan “backup” vehicle for local driving, and we do drive a small diesel RV for long-distance road travel). I decided that we would want our EVs topped off as soon as possible, in case an unexpected journey was necessary. The economic benefits of charging off-peak were pretty comical, as our annual fuel bill was something like $500. (I calculated that it would take 7.5 years to offset the $1,100 we were quoted to install the dedicated utility meter LADWP required to offer a discounted EV off-peak rate, and both of our first two EVs were inexpensive 2-3 year leases.)

(The friend commented about this article about the development of new battery technology.)

Battery technology is economically improving, especially now. And the financial rewards of owning the Next Great Electric Battery tech represents a modern Gold Rush. The Lithium-ion batteries that power our mobile devices and most EVs have fallen in cost by an order of magnitude in a decade. The 23 kWh pack in our 2013 Focus Electric was probably worth $20K. Our 2016 BMW i3’s 22kWh battery was probably almost half that cost, and our Model 3’s 75+kWh pack was probably only around $13K in 2018.

So even this old battery tech will continue to herald much of the early EV adoption, as its cost per kilowatt-hour makes prices of electric vehicles on par with ICE-powered (understanding the operational envelopes are not the same). A battery technology with twice the energy to mass density at similar energy/cost will yield lighter, more efficient, less expensive cars, while also increasing the potential range.

(It important to recognize that replacing the internal combustion fossil-fuel paradigm for local, urban travel addresses a huge percentage of consumer transportation needs, and that long-range travel requiring short-turnaround refueling might need to be compartmentalized as something not every owner needs or wants.)

Wednesday, June 5, 2019

Tesla Model 3 - 12 Volt Power Socket "Circuit Breaker" Auto-Reset


The 12-volt Power Socket in our Tesla Model 3’s console stopped working.

It subsequently appears to have “reset” itself (after some unknown interval, up to but probably less than 20 hours), and is functioning normally.

I wish I could know if and when it would reset itself in the future.


If the Power Socket fails (or maybe any 12 volt circuit on a Tesla Model 3), leave it empty and check back after (perhaps) a few hours. It will hopefully have automatically reset.

But exactly how long to wait, and whether this procedure will always work, is at this point uncertain to me.


I discovered that the 12 volt Power Socket in our Model 3 was not supplying power.

In retrospect, I think it may have been dead for a while, but we do not currently depend upon the Power Socket on a regular basis, and I hadn’t had a reason to notice whether it was actually working. I think I’d attempted to charge a rechargeable flashlight from a 12VDC-USB power adapter some weeks ago, and determined there was something amiss with part of the charging chain: the socket, the USB power adapter, the Micro-USB cable, etc. But I got distracted from the task, and forgot about it. When I attempted to test-power a 12-volt cooler for a road trip, I discovered that the Power Socket was dead.

When I went to plug in the 12-volt cooler, I had to remove a 24 watt 12-volt dual-port USB adapter which had been in the socket (this may be important). This typical auto adapter to charge mobile devices via USB claims a maximum output current load of 4.8 amps - 2.4A per device. Tesla’s Model 3 Owner’s Manual claims that the Power Socket is capable of “up to 12A continuous draw (16A peak),” so this single device, if operating correctly, should use well under half the available current rating for the Socket. 

But the cooler didn’t start. Eventually, I tested a few other 12V-USB adapters in the Model 3’s socket, then took the entire collection of cooler and USB adapters to another 12-volt socket in another vehicle and they all functioned normally. A 12-volt accessory socket voltage tester plugged into the Model 3 Power Socket also confirmed that it appeared to be dead.

I read long ago that the Tesla Model 3 does not incorporate traditional fuses to protect its low-voltage (12 volt) circuits, but uses solid-state current control and monitoring infrastructure, which temporarily interrupts current flow when the system measures excessive current for the designed load of the circuit. These “virtual fuses” or “virtual circuit breakers” would presumably reset automatically. In searching through the Model 3 Owners Manual, I’ve thus far found no mention at all of the topic, except to mention a maximum current rating for the Power Socket (“12A continuous, 16A peak,” pg. 21 of the Dec 2018 Model 3 Owners Manual).

I tried resetting the Model 3’s user interface from the steering wheel (hold both scroll wheels until the screen goes black). No change. (The owners manual says of the socket: “Power is available whenever the touchscreen is powered on,” so it seemed as though that would cycle the power supply to that circuit, and perhaps reset the current protection mechanism.) I tried using the Controls > Safety & Security > Power Off command, waiting 3 minutes and then waking the car with brake pedal. No change. 

While all this was taking place, the Power Socket was sometimes empty, and sometimes had a USB adapter plugged in, its LED pilot light serving as a visual indicator of when the power was restored. It occurred to me that even though the USB adapter that had been plugged in for months seemed to work fine in another vehicle, that it might still have malfunctioned enough to trip the Model 3’s circuit protection system, and that even though the overcurrent condition might no longer be present, that the circuit might not “reset” until it was convinced that there was nothing connected. Even an empty USB adapter probably flows some current all the time. So I deliberately left the socket empty for several minutes, then tested it again.h I also tried two other different USB adapters.

The socket never worked that day. 

I found no useful information from online forums about how/when/if the Power Socket circuit would reset (some Tesla forum posters said that they’d experienced a reset, but gave few clues as to how much time had elapsed). One poster mentioned “36 hours,” but I couldn’t tell if that was a suggestion or experience. 

I contacted Tesla Support via their web-based chat system. I explained that we were preparing for a cross-country journey, and that we were depending upon the 12-volt socket, and asked what I could do to reset it. The chat agent responded that there was NOTHING I could do but schedule a Service appointment. I responded that we were imminently departing, and that I’d never been able to schedule a Service visit in less than several weeks. The agent responded that they had [changed their Service strategies], and that perhaps a mobile Tesla service rep would come to my location (we’re in Los Angeles, where I’d expect more Tesla Ranger visits, but so far, I’ve never even had one suggested). I said again that we were anxious that this might delay our travel plans, and the agent wrote, “I mean you can try a powercycle, but I don’t think it will help if the outlet is dead.” The chat rep pasted Power Cycle instructions into the chat window, asked if there was anything else they could help me with, and I said thank you and we ended the chat.

The provided instructions:
“Power Cycle:
1. Select the car icon on the bottom left of your screen
2. Select safety and security
3. Select power off (may be under Emergency Brake and power off)
4. Are you sure you want to power off? --> Yes
5. Wait 3 minutes
6. Open and close the door to wake the car up
7. Hold both scroll wheels on the steering wheel until you see the Tesla T logo appear.”
I tried the slightly different variation to what I’d already tried (opening and closing the door, and doing a “two thumb salute” reset afterward), but it made no difference. This was probably 30 minutes after my last testing session with the Model 3 Power Socket.

Defeated, I made an appointment with Tesla Service via the Tesla app. The scheduled appointment was 8 days away - delaying our departure by a couple of days, but I had no choice, and I hoped that perhaps a mobile service would be suggested after evaluation of my request.


The next afternoon - 19-20 hours after my last test of the Power Socket - as I was about to begin the day’s errands, I tested the socket again. It worked! I wasn’t completely surprised (after all, I did test it again), and I’m happy that it’s working, but I still have NO idea whether the circuit performed an automatic reset during the night, or something else happened. And assuming that it did automatically reset, how long did that take? And were any of the other conditions (i.e., plugged into charger; Sentry Mode; devices charging from Model 3 USB ports) important?


Here are my observations, speculations, and hypotheses about the experience so far:
  • The 12-volt circuit protection system may reset itself: 1) after a certain period of time has elapsed; 2) if the overcurrent condition is no longer present; and perhaps 3) if the circuit is completely unloaded.
    • Regarding item #3 above: I suspect that having the USB adapter plugged in for weeks or months may have prevented the protection system from resetting. Perhaps it waits for a period of time (1 hour? 2 hours? 6 hours?) after the overcurrent fault, and tests for presence of a load-carrying device. If it finds none, it resets. If it finds even as little load as an idle USB charging adapter, it waits to try again.
  • While I’d LOVE to establish the exact amount of time one has to wait for the system to reset, I don’t currently have time to risk continuously triggering the Power Socket’s shutdown mechanism - especially if it might ultimately lead to a Tesla Service call. This would entail:
    • Deliberately and repeatedly tripping the circuit protection by plugging in a device which attempts to draw more than 12A continuous/16A peak. I’d like to think the overcurrent protection system would protect the car’s systems from damage resulting from multiple overcurrent events, but that’s part of the risk of not having enough information.
    • Testing a variety of periods of time to establish the threshold at which the circuit is still found to be dead. (This is tricky: trying shorter intervals first and making them longer is somewhat self-defeating, if the act of testing resets the delay period. But starting at 19 hours and progressively lowering the intervals would take days as well.)
    • After writing most of this document, I discovered this Tesla Model 3 blog post from mid-2018 titled Model 3 “Fuses” where “Pete” writes:
      • The good news is that the fuses are self-resetting, which means that after the current on the circuit has settled, they'll normally reset themselves; this can take 60-90 minutes, we've yet to determine an exact time frame...
  • Why didn’t Tesla Chat Support know about this? They could have just scripted a response for the user to unplug all devices and wait overnight or a few hours, and then schedule an appointment for service if that doesn’t restore power to the circuit, rather than essentially saying “it’s broken, and there’s nothing you can do about it” which is pretty much the opposite of the actual answer.
  • While it may be a positive that the Model 3 can automatically reset its 12-volt systems without any action from the user, it’s important that we users identify the difference between a system that’s “going to eventually reset itself,” and one that won’t be working for another three weeks. For 19 hours, that’s where my wife and I were: changing our travel plans and figuring out a way to manage the trip without any 12-volt accessories.
    • (While this may seem trivial to those who don’t use 12-volt devices, consider that there may be Model 3 owners powering important health-related devices like oxygen concentrators and CPAP machines.)


The good part about the Tesla Model 3’s 12-volt circuit protection system is that there are no fuses. The whole system is protected by solid-state systems that function as circuit-breakers, interrupting electrical flow to a circuit which has exceeded its safe maximum current load.

Also good: that the system appears to automatically restore power to the affected circuit when the overload condition is resolved.

I just wish I could be confident that the Power Socket - or any of the Model 3’s 12 volt systems - would automatically restore themselves in the future, and I would like to know with any certainty just how long we’d have to wait for the self-reset if this reoccurs, to determine whether the symptom was the result of a protective action or a system failure.

So far, I’ve found no explanations, only read theories and speculations from unconfirmed sources. I hope that can be remedied.

I’d love to hear the Straight Scoop from Tesla about exactly how this is supposed to work, and what Model 3 owners should anticipate if they trip one of the current protection devices. I think their corporate attitude is that as far as users/owners are concerned, it’s just “automatic” and takes care of itself (like windshield washers, and headlights, and other things over which I which we could take control, or take control more easily). And despite the fact that this is NOT reflective of a Tesla product failure (indeed, the “breaker” trips because of an external device failure or because the operator attempted to connect a device with an excessive current draw), it may be that Tesla thinks this makes some sort of negative association with users - as though the car’s systems were substandard or incapable.


Voltage is a measure of the potential for electricity to flow between two parts of a circuit. It sort of represents the readiness, if you will, of electrons to go from one place to another. Our homes have 120 volt and 240 volt devices. Traditional automobiles and the some of the Tesla’s systems, like lighting, audio entertainment and HVAC, are 12 volt. Our Tesla’s propulsion battery packs and motors operate in the 350-400 volt range.

Current, measured in Amperes or Amps, represents how much electric charge actually passes from one place to another in a circuit. Devices which use electricity will attempt to take as much current as they can without regard to whether the circuit can safely supply it - it is the responsibility of the user and the designers of the power distribution infrastructure (wires, connectors, fixtures, etc.) to appropriately select and design them for the intended loads. Components are initially selected based upon an economic balance of cost versus required performance. Put another way: wiring is only as big as it needs to be to confidently assume liability risk. 

(NOTE: Modern electric vehicle charging represents an exception to the device current demand model, as EV's on-board charging systems actually communicate with charging interfaces, which report how much current they can safely supply, and the on-board charing system within the EV then safely limits its current draw below the reported amperage available.)

Circuit breakers and fuses are intended to protect distribution infrastructure from catastrophically and dangerously failing (i.e. wires in your home’s walls from heating enough to ignite surrounding structures) by interrupting electrical flow well below the current limits of the distribution components. 


From the December 20, 2018 “Model 3 Owner’s Manual” PDF file:
12V Power Socket

Your Model 3 has a power socket located in the center console's rear compartment. Power is available whenever the touchscreen is powered on.

The power socket is suitable for accessories requiring up to 12A continuous draw (16A peak).

Warning: The power socket and an accessory’s connector can become hot.

Warning: To prevent excessive interference with the vehicle’s electronics, Tesla recommends that you do not plug any non-Tesla accessories, including power inverters, into the 12V power socket. However, if you do use a non-Tesla accessory and notice any malfunctions or unexpected behavior, such as indicator lights, alert messages, or excessive heat from the accessory, unplug the accessory from the 12V power socket immediately.

⚠️Caution: Do not attempt to jump start Model 3 using the 12V power socket. Doing so can result in damage.

Thursday, October 26, 2017

"How to Prolong Lithium-based Batteries" Article

Here is a very nice article about issues affecting battery lifespan from Cadex Electronics, a Canadian company that specializes in battery technologies:

How to Prolong Lithium-based Batteries - Battery University

The short list of takeaways about consumer Lithium-based battery use (from this and other resources I've read about lithium battery technology):
  1. Avoid overheating batteries 
  2. Avoid deep discharging as much as possible (don't let the device run all the way down) 
  3. Frequent partial charging is desirable (charge whenever you can)

However, this document is not presented as a how-to guide for consumers using electronic devices powered by lithium-based battery technology. Indeed, in their own self-interest, many consumer goods contain sophisticated battery maintenance and management mechanisms, which apply many of the specific principles discussed in the above article.

In EV applications particularly, any significant procedural or parametric choices regarding battery charging are strictly controlled and limited by the charging systems which are built into the cars themselves (with the exception of "DC Fast Charging" solutions, which typically involve a combination of systems internal and external to the car). In order to be able to offer a product with acceptable performance and to have acceptable warranty risk, EV batteries are aggressively underutilized, masking their actual capacities. So the "empty" to "full" battery capacity available to the car and displayed to the user as "0 - 100%" may in actuality be, say, 22 - 90% (or whatever range the manufacturer has decided presents optimum cost/performance/risk for the given application). This ensures that their entire life cycles fall within a statistical sweet spot for longevity, never deeply discharging nor fully charging the pack. A user's deliberately preventing their car from achieving an indicated "100%" charge (which is actually something far less) is therefore unnecessary, as that has already been protected by this artificial capacity range. While there might still be battery longevity benefits to further conservatism, I wouldn't concern myself with trying to stop charging my EV short of an indicated 100% every day.

Likewise, battery temperature control is such a critical issue that most EVs both cool and heat their battery packs during charging and operation, actually using not-insignificant power (and therefore affecting energy budget) to protect the battery pack and optimize its range performance. There's little that a user can do to improve upon this thermal management - indeed, many EVs will defend themselves with warnings and shutdowns when faced with conditions which threaten damage to their expensive propulsion battery pack.

That said, experts appear to agree that frequent "topping off" of a lithium-based battery pack whenever practical does contribute to prolonged capacity performance. Because we attempt to exclusively use our EV for transportation, my choice is to charge it whenever I'm home, regardless of its state of charge when I return. My sensibility is that in the event of an unexpected transportation need, I want as much range as possible as soon as possible.

When we got our first EV four years ago, I made spreadsheets to compare and evaluate several charging options, and determined that choosing to charge our EV on an automated schedule during off-peak utility hours when rates were lower yielded minimal benefits - on the order of $200/year if we drove 10,000 miles. This was my financial justification for Always Plugging In. Likewise, the cost of installing a separate utility meter so that we could qualify for an EV discount from our utility was so high that we wouldn't break even from the $1,100 electrical contracting work for 6-7 years of discounted electricity - and that EV was a 36-month lease. 

These same principles generally apply to portable consumer products - their internal charging mechanisms attempt to shield the battery from deep discharge and overcharge. It is still true that consumers can benefit from charging their phones or laptops as much as possible. And unlike cars, it's very easy to leave a phone or laptop in the sun in a window or car and irreparably damage or severely cripple the battery in one event.

Sunday, September 10, 2017

A Solar-Powered Electric Motorhome? Not Exactly

This recent article reported about the “e.home” concept motorhome being displayed by German leisure vehicle manufacturer Dethleffs.

Many casual readers might interpret this story (which is NOT in fact an actual product announcement, but only the debut of a “concept vehicle”) as suggesting that it is a “solar powered RV.” I hope to communicate here the reality of what is and is not possible regarding solar power and an electrically-propelled RV.

As an owner of a small diesel-powered motorhome and having exclusively driven electrically-powered vehicles as a “daily driver” for the past four years, I’ve frequently done hobby number-crunching to understand the realities of living with a motor vehicle which carries less stored energy than a single gallon of gasoline. I’ve also had to calculate our energy requirements when “dry camping” - going for days “off the grid” depending entirely upon the power stored in what amount to a couple of large automotive-style batteries.

The "home" part of a motor home has very modest power requirements - a couple of hundred watts worth of PVs (photovoltaic panels) can indefinitely maintain "house batteries" to allow frugal power use for lighting and modest ventilation, water pumping and communications/computing requirements. Heating and cooling the cabin beyond 20F differentials between ambient conditions and target interior temperatures requires thousands of watts of power. The Dethleffs e.home features a couple of nice ideas to address cooler climates (like Germany): a way of storing daytime solar warmth in the form of phase-change materials (like the resuable medical heat packs that can be activated on demand, and “reset” by melting their crystallized contents in a microwave oven) for release during cool evenings; and electrically-generated heat delivered to the users via radiant heat - as through warmed floors - which provides comfort in cool climates without attempting to directly heat the cabin air.

Our “small” 11,000 pound diesel-powered Class-C motor home is capable of 20mpg at 60mph - quite good in a category where similar RVs can get single-digit mileage. Driving electric cars around the streets of Los Angeles, we’ve averaged 4.5 miles/kilowatt-hour - this fuel efficiency can be represented as “151 MPGe.” “MPGe” is the U.S. Environmental Protection Agency’s unit of measurement to allow consumers to compare the efficiencies of gasoline-powered internal combustion engines with those of alternatively-fueled vehicles. So the suggestion here is that our BMW i3 has been using stored electrical energy as efficiently as a gasoline-powered vehicle that could go 151 similarly-driven miles on a single gallon of gas.

The article mentions that the 3,000 watts of solar panels “help provide power to its electric drivetrain.” That’s a generous allowance, if potentially misleading. Pushing a small Class-C motorhome through the air at cross-country travel velocities using electochemical batteries is an ugly energy use proposition. The claimed battery capacity for the e.home is 228 amp-hours - about 4 times the capacity of today's typical 80-100 mile EVs, and about the same as a mid-sized Tesla Model S or X battery. Such a battery pack would likely weigh and cost 4 times as much (3K-5K pounds, and $25K-$40K) as typical EV battery arrays.

I estimate that pushing the e.home through the air on level ground at 60mph requires about 40kW (54bhp), which is using stored power over 40 times the rate at which it can charge from sunlight. (Aerodynamic loading is exponential, meaning that the power requirements square with the speed. So if it takes 10 horsepower to push the shape through the air at 30mph, it takes 40 hp to push it at 60mph.)

Three kilowatts (3kW) of photovoltaic panels aren't really going to have much charging impact upon an estimated 72 kW/hours of propulsion battery storage. Even if the e.home were parked in the sun, in the summer, close to the equator, in front of a mirrored wall to expose all the panels at once, it would take at least two days (72kWh/3kW = 24 hours) to restore a fully depleted battery. In real life, days are partly-cloudy, one lives in an arbitrary region below the Arctic Circle and less than half the panels are exposed to the sun at any given time, and then at inefficient, oblique angles. During a 12 hour day, the average yield of 3 kilowatt array would be little more than 1kW. For every hour driven at 60mph, the e.home would require 40 hours of sunlight to replenish in those conditions. That would result in a very leisurely travel schedule. If the e.home were driven to full depletion (all modern battery systems actually preserve a significant proportion of the cells' actual charge to prevent damage), then stopped somewhere in the German countryside to allow the PV panels to top off the propulsion batteries in "mostly sunny" conditions, I guess that the the propulsion pack would achieve 100% charge about Day 8 (maybe Day 11 or 12 if it were short winter days , and maybe 14-16 if you were trying to heat the cabin very slightly with electricity).

The article does refer to a “plug-in motor home,” but again, this may be misleading. In the EV community, “plug-in” refers to motor vehicles which can be fueled by connecting them to the electric utiltiy. However, even this paradigm has its limiations. If a commuter drives 40 miles round-trip to work and home in a typical EV, the vehicle can be charged from any household outlet (so-called “Level 1” charging) in about 10 hours with no special equipment. Installing a “Level 2” EVSE (Electric Vehicle Supply Equipment) at one’s home or office allows charging at an increased rate so that the same 40 miles of battery use can be replenished in just two hours. Even at the higher Level 2 rate which is the most widely available public charging infrastructure, the e.home RV’s large 228Ah battery pack - similarly sized to the mid-sized batteries available in Tesla Model S and X cars - would take most of a day to fully replenish (~14-15 hours from depleted to full). (Most campgrounds have 30-50A power service at each RV site, allowing for similar or shorter EV charging times.) So even with plug-in charging rates 6-7 times higher than its solar panels can achieve, the e.home must plug in for at least 14 hours every 100 miles. (There is a faster commercial-only Level 3 charging infrastructure, but it is not widely distributed, and would almost certainly NOT exist along travel corridors conducive to camping.) If the e.home was plugged into a typical 6-7kW L2 charging station during a long summer day in the sunshine, the ~1kW contribution from its solar panels could shorten the charging time from depleted to full by an hour or so.

So this concept RV shouldn't be interpreted as a "solar powered vehicle" (the title of this article appropriately calls this a "solar-assisted" concept vehicle). Unfortunately, many casual readers won’t perceive that. There's a reason that those cockroach-shaped solar-powered vehicles you see college engineering students "racing" (at 50-60mph) across the Australian outback ride on bicycle tires, can be picked up (gently) by two people and cost hundreds of thousands of dollars. We reached a technological threshold some years ago beyond which it's been possible to build a vehicle which can propel a human at 60mph on level terrain using the sunlight that falls upon the approximate surface area of a conventional motor vehicle. That said, accomplishing this feat requires that such a machine be made of exotic, expensive materials to manage weight and reduce aerodynamic drag, and utilizes the most efficient photovoltaic panels and electric motors, with impracical cost implications for consumer products. The World Solar Challenge takes place across thousands of miles of sunless, hot Australia, and also exposes the drivers to vicious and even dangerous interior temperatures, yet no competitor risks adding performance-robbing weight with refrigeration systems. These vehicles also provide no specific protection in a collision with a conventional vehicle, which weighs 10 to 20 times as much.

So can an RV be propelled by sunlight generated by its own photovoltaic panels?

Photovoltaic panels for residential use currently cost ~$3/watt and achieve efficiencies of 8-10 watts per square foot. So a fantasy solar-PROPELLED RV equipped with 100kW of PVs (so that the 80kW motor can operate in overcast conditions, and can have some reserve power to accelerate and climb hills, in addition to a 40kW cruise demand) would cost at least $300K for the PV panels alone (not including physical support infrastructure, plus interconnecting wiring and control circuitry, or batteries for load surges). The PVs would take 10,000 square feet of surface area. Figure 20% loss in area to framing, so that 12,000 sq ft of area is necessary to mount the solar panels. The surface area of a 53-foot semi-trailer is 450 square feet, so 26.6 trailers - we’ll round that up to 27 semi-trailers worth of PVs would be required to support the 100 kilowatt array. Unfortunately, the mass added by those 27 trailers exceeds the power produced by the 80 kilowatt motor in the RV, which can no longer move the $2M, 1/4 mile long solar road train. Point is, a self-contained solar-powered RV isn't in our future. For that matter, we won't likely be driving cars that are directly powered by the sun. Electrical energy storage will always be a part of the EV model, whether chemical, mechanical or otherwise.
It's certainly possible to travel entirely on _stored_ energy generated by sunlight - we do that when we use gasoline and diesel fuels, which store years of sunlight collected by living plants and allow us to release that energy in a fraction of the time. In fact, wind and hydroelectric energy production are ultimately driven by our Earth's solar-powered weather system. Only nuclear power (which uses radioactive material produced billions of years ago) is a non-solar power source we currently utilize to propel our motor vehicles (in some municipalities, including ours).
So, like many such announcements in our our current age, and appropriate to “concept vehicles,” the Deffleths e.home concept RV is more of a promotional idea than a product. All RVs could benefit from many of the efficiency features touted in the showcase vehicle. But the dream of an electrically-propelled RV that can recharge from sunlight on a self-contained system will remain a fantasy.
I welcome the future in which a electrically-powered RV might exist. I've explored the idea as a Thought Experiment many times, and have commented that it will be a real landmark in EV battery, propulsion and charging infrastructure technology when and if it becomes economically viable to perform long distance leisure travel with the weight loads of an RV (in current practice, RV design goals of utility and comfort increase vehicle weight from 3 to 10 times as much as a passenger vehicle).

I hope to see that.

Sunday, February 5, 2017

How Cabin _and_ Battery Preconditioning Work on the BMW i3

Blogger Tom Moloughney wrote this nice post describing the behavior and functionality of the BMW i3's "preconditioning" features.

Importantly, the i3 has preconditioning functionality for both its cabin climate system - whereby making the cabin comfortable for occupants regardless of ambient temperatures outside the vehicle - and also preconditioning for the high-voltage (propulsion) battery - which can significantly improve battery performance in extreme operating temperatures. BMW has not been particularly helpful in describing these two separate systems to i3 owners, and it's far from obvious how to use them to best advantage.

Tom Moloughney's BMW i3: Understanding How Preconditioning Works