Jun 22, 2013
boilerbots I see talks about people wanting to charge as fast as possible all the time just for the hell of it, or because they paid for twin chargers so they feel obligated to use them to the max.
Well, I thought I would throw out some information as to why you might want to slow things down.
Vehicle Losses
I will talk about parts of the system where power is lost and talk about how this can be related to charging current.
The chargers are lossy. They are converting the input voltage into DC and regulating the current that flows into the vehicle. Most DC/DC supplies are most efficient somewhere in the middle of their operating range, I don't think any are most efficient at the upper limit. There are several reasons why this is the case, one simple reason is resistive power loss. The charger circuitry has a fixed resistance in it's circuit that the current must pass. Using the equation to convert current and resistance to power, power=I^2xR you see that as the current increases the power is increased exponentially. Other factors that influence efficiency are losses in the magnetics used by the switching supply, the inductors and chokes. As the loads increase on the circuit, so do the losses.
The battery cells also loose power. The battery stores and releases energy through a chemical process but the battery cell also has a certain resistance internally (also called impedance). This loss can simply be thought of as a fixed resistance and using the power equation P=I^2xR you can determine the power loss due to current and resistance. As battery cells get older their impedance typically increases, so the internal cell resistance will rise over time.
Energy wasted is turned into heat. Maybe you need heat because you live someplace cold, maybe you don't. Let's say you don't need to warm up the battery pack, or worse yet you are parked over hot asphalt. The heat is going to need to be moved away from the critical components, the battery cells, the charger and dissipated to the air. Tesla does this first with a fluid, so a pump is involved, then a radiator and a fan. It takes power to run pumps and fans. If you charge slowly the heat may be able to naturally move through convection and dissipate without extra help. I don't know when active cooling kicks in, wish I could unlock that Tesla diagnostics screen, but you have probably heard fans and pumps running while you observe the Tesla beast sleeping. It isn't purring because it likes your garage.....
Home Losses
When you are charging, the car is part of a bigger system. A system that starts at some generation plant, includes power lines, transformers, your homes electrical, the car. It is big and complex and awesome. Let's focus on the part we care about, the part we directly pay for, and that is the numbers measured by our electric utility meter.
The meter at my house is digital, it shows the voltage, power and kWhr totals on it's display. If I draw enough current to cause a voltage drop between my meter and my car, then that is a sure sign of power loss. That loss is caused again by the fixed resistance in the wire, circuit breakers, and fuses in the network. Multiply the voltage drop by the current and you get the power loss. Another problem that voltage drop can causes is higher current draw. We know the equation for power is voltage times current, we know that a twin charging vehicle is rated for up to 20kW. If the car limited it's charge by power we could have a problem since voltage sag would require an increase in current to keep the total power equal. Lucky for us the fine electrical engineers gave us control over the current limit instead. Current is what trips our breakers and melts our wires, so current is what we need to limit. By the way, a quick calculation shows that since the current limit is 80A, you would actually need 250Vrms to reach 20kW, doable in Europe perhaps. A voltage drop in our home is something we end up paying for, beyond our meter we don't BUT it does reduce the total power being delivered to the car.
To throw out a few numbers:
80A at 240V = 19.2kW
80A at 220V = 17.6kW
80A at 200V = 16.0kW
If your car shows 240V before charging, and 220V during charging then you are loosing 1.6kW continuously due to resistive losses.
Summary
You loose power in your house wiring. You loose power in the chargers. You loose power in the battery cells. You consume power to cool the chargers and the batteries. All of these losses are directly related to the current. If you lower the current you lower your losses.
I would like to see Tesla offer a software option where charging current is minimized based on a deadline. Lets say I leave for work every day at 8AM, I only care that my vehicle is fully charged the second I unplug the charging cable. I schedule a fixed starting time when my rates are lowest, lets say midnight. I set the upper current limit. The vehicle dials back the charging to the minimum required to fully charge by 8AM.
Secondary advantage is lowering your average SOC (State of Charge). The lower the charge level kept in your battery the better for it's life time. This method would optimize the SOC.
The information above is free. Take it, or leave it I don't care.�
Jun 22, 2013
yobigd20 I was talking to a lead tech about this. It's actually harder than you think to do that. That's because the car's charging system is doing a lot more than you think. Everybody's power is "different". One person's power on a NEMA 14-50 is different than another person's power on a NEMA 14-50. (I'm no electrician so I may get some terminology wrong), but things like voltage drop (depending on length of run and many many other factors), spikes, surges, yadda, yadda.
Consider a standard wall socket - you don't know what else is "using power" at any given time on the same circuit - lighting, fans, etc. On top of this, everyone's batteries are different too - different "health" (for lack of a better term). Basically, what may take you 10 hrs to charge may take someone else 5 hrs to charge using the same exact connector and amps. Therefore, I won't go as far to say "impossible", but the tech was more like "nearly impossible" to set a rule on the console to something like "I want 72% charge before 6am" (on the flip side obviously it's *very* easy to set "start charging at this time" but you can't regulate the exact time of completion). So I'm not sure if we're ever going to get that exact functionality even though we all want it. If your circuit is clean one moment and the car waits until a certain time to start charging, if something changes on that circuit then the car won't have enough time to make sure you have what you set by xxx time.
I hope I explained that good enough. Personally, while an algorithmic challenge, I still think they can provide this to us with the caveat that they "can't guarantee it will be right 100% of the time".�
Jun 22, 2013
GSP The Chevy Volt has a "charge based on departure time" feature. I really like it, and it is near the top of my list for desired software upgrades for the Model S.
GSP�
Jun 22, 2013
dtich @op, good points, although I think most on this board are pretty well aware of them already.
I myself do charge at 24A actually, for many of the reasons you state, and because I don't need to charge faster. it works out well for me. heat is the ultimate enemy of batteries and the less we can create most especially when charging, the better the efficiency and the longer the effective life of the battery.
I think some people, like the one you were referring to, know all this but simply want the option to charge at whatever current they want, without hobbling, as they have spent money and time building open evse chargers and want to know and demonstrate that they work up to spec. makes sense to me. I'm sure ultimately they will opt to do what is best for their system.
the option of an actual-power based charging algorithm that estimates charge finish times is doable. it may be difficult as the engineer points out, but the issue of all homes and charging systems being different doesn't really enter into it as the whole point of the algorithm would be to use actual voltage and current readings to make the schedule, so all these variables are de facto taken into account. to my mind anyway... we'll get it from tm eventually, just will take some time. I myself am fine starting charging at 130a and finishing around 6 with a full charge. works for my setup. others have tailored their own systems as well. the more tools the merrier of course.�
Jun 22, 2013
jerry33 The Leaf also has a finish by X setting. An algorithm shouldn't be particularly hard.
1. The driver sets minimum start time (for TOU), stop time, ideal SOC, and ideal amps.
2. The car starts charging at the minimum start time and calculates when the finish will happen based on ideal amps and ideal SOC.
3. If the calculation in #2 is prior to the stop time, ideal amps are reduced (or increased if it appears that it won't finish in time).
4. At regular intervals the car checks the SOC and remaining time and adjusts the amps as required.
5. Car stops charging at the stop time.
FWIW, I've normally charged at less than the maximum--more to prevent overheating of the UMC than anything else. After the recent discussion about cell equalization, I reduced that to 16 amps. I'll see how it goes.�
Jun 22, 2013
mknox Yes, but it doesn't throttle the charge current... it just delays the start time so that it will finish when you want it to.�
Jun 22, 2013
dhrivnak I am not sure the Leaf and Volt comparisons are valid as they only charge at 15 amps. With a low predictable rate one can more easily calculate the finish time. But that said on my Roadster I charge at half rate (40 amps) for several reasons you may want to consider:
A) Higher rate is not needed as I am always at a full level the next morning.
B) Better on the utility as it is easier for them to balance smaller loads.
C) It saves a little money as when I charge at 70 amps the A/C is frequently on but at the lower rate it rarely comes on. So for the reasons of the intial poster a higher charge rate is more wasted heat that must be gotten rid of.
D) I suspect the batteries will last longer as in most chemical processes and mechanical machines running at half the design rate saves wear and tear. Pushing things at higher rates reduce their life. This is one reason NASCAR will wear our an engine in just 500 miles rather than the 200,000 we are hoping for.�
Jun 24, 2013
boilerbots I am glad to see that some are on board already with these ideas. I assure you that completing a charge at a specific time is not hard to do, a simple slow PI loop will get you there because the system can measure and adjust very quickly.
Also some set their limits at 40, others lower like 20, remember we have virtually 3 size batteries and 2 charging options, so I am on the low end with a software limited 40 plus a 10kW charger and some are on the high end with an 85 and 20kW charging.
Getting done as slow as you feel comfortable is a pretty good choice to make.�
Jun 24, 2013
RodF After reading this thread, I changed my charging level from 40 to 24 on the screen. But the next time I charged, it reverted to 40 amps. Do I need to change the dip switches on the HPWC to retain the setting?�
Jun 25, 2013
Todd Burch Model S remembers your charge setting based on GPS, which means you should make the change when parked at the charging location or it won't stick.�
Jun 25, 2013
jerry33 It took me a couple of times to get it to stick.�
Jun 25, 2013
RodF Thanks for the info, Todd and Jerry. I'll try it again.�
Jun 25, 2013
Benjam I've seen this many times lately - why do people use the word "loose" when it should be "lose"?�
Jun 25, 2013
hvb I'm assuming they don't know any better.�
Jun 25, 2013
David_Cary 2013 Leaf charges at 6 kw on 240V - 25A not 15A. I have a charger that can dial back and I charge at 10A - for heat reasons and because even if I ran to zero, I would still fully charge on my off peak that starts at 9pm and be done by 6am.
I don't know if the Tesla is the same but there is a flat overhead for cooling - about 300W. So if you are charging at 1KW (ie 120V), it winds up being a 30% overhead. Charge at 6 KW and it is only 5%. I would assume that Tesla has a variable overhead based on heat buildup rather than the Leaf's fixed overhead.�
Jun 25, 2013
markwj We did quite a bit of work on this, for the Tesla Roadster:
Charging in High Temperature environments 13A vs 32A vs 70A: cost of air conditioning
And, of course, there was Tom's foundational work:
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
Conclusions start here: Charging in High Temperature environments 13A vs 32A vs 70A: cost of air conditioning - Page 4
Bottom line is that sweet spot for us, in high ambiant temperatures, is around 32Amp.�
Jun 26, 2013
Vger A lot of people above, including the OP have not read Tom's or your work, clearly. The key point is that less and less current is not better, there is an optimum. It is also clear from Tom's work that the sensitivity to current is not as great as one might think. This is why Supercharging still makes sense. Yes, it is less efficient and harder on the batteries, but doing it a few percent of the charge cycles of the car's life is really not that significant.�
Jun 28, 2013
boilerbots The roadster and the Model S do not behave the same.
Also, you can not lump 120V charging in with 240V charging because that is going take a huge hit since the incoming voltage is too low and most likely gets doubled during rectification to DC which is not efficient. I am speculating but this is generally the easy way out since 120V is kind of a desperate situation in the first place.
The data in the thread posted by Markwj says to me, 70A charging 66.7% efficient (80.78/121.2=66.7), 32A is 64.3% (43.01/66.9=64.3%) because you should care about the watts in vs. the watts out of the battery. I don't care how this translates to Wh/km because that is influenced by driving and environment.
The data from tomsax looks a little fishy too. I have never measured my voltage to be exactly 240V when I am drawing 70A out of a receptacle. So how can I believe the numbers posted when it appears the the voltage is always assumed to either be exactly 240V or 120V. A few volts dropped at 70A is a lot of wasted power.
For an accurate and verifiable measurement one would need to measure the power entering their home at the point of their utility meter. Measure the power being drawn out from the battery during non-charging time and calculate the total efficiency under different charging scenarios. All while the vehicle and battery are kept in the exact same environment and driven exactly the same.
If someone did this and I missed it please let me know.�
Jun 28, 2013
markwj I agree the roadster and Model S will most likely be different. However, absent any Model S data, the roadster studies are the best we have. It is, at least, real data rather than speculation.
My measurements were taken (a) at the wall near the utility via a permanently installed meter, (b) in the car displays, and (c) verified by car logs. If you check the thread, you will see I reference kWh and Amps, not volts.
My house gets 200Ax3 from the utility, and that circuit is split via bus bar to a MCB 60Ax3 to the house and another MCB 90Ax3 to the EV charger, with nothing else on the 90A side and a very short cable run. Voltage in Hong Kong is stable around 220V, and I see little difference in voltage when charging at 13A vs 70A, in my environment. I did no testing at 120V.
The efficiency figure I was looking for was charging losses only at 13A, 32A and 70A, in high temperature environments. The result was clearly that little was to be gained beyond 32A.�
Jun 28, 2013
markwj Just noticed this comment. Can you explain how my data looks fishy?
As for Tom - he knows more about Roadster than most anyone here. I think fishy is a strong word to use.
It is real data, with logs to back it up. Not just idle speculation.�
Jun 28, 2013
markwj We've been working on something like this for the roadster, in the OVMS project. Looking at thousands of charging logs, from hundreds of cars, in a wide variety of environments.
The ramp-up and main charging parts of the curve are relatively easy to predict, with the variable being ambient / pack temperature (primarily accounting for cooling losses). The issue is predicting the ramp-down tail at the end of the charge - we are seeing a lot of variance there. The car controls that based on a bunch of factors hard to model (and even harder to predict). Changing charge limit at that point will have zero impact (as the limit is being controlled by the car during ramp-down). But, getting to within 30 minutes seems to be feasible, so that is what we are trying to do.�
Jun 29, 2013
boilerbots I remarked that Tom's data looks fishy. I would like to understand the details about how you and Tom took these measurements.
When I quickly scanned through your thread, I could not see any details of your electrical system, the type of meter you used, the layout of wiring in your home or how you data was collected. All I remember seeing is that you where measuring watts using an external meter and the car's and you logged the data. You also where rightfully concerned about cooling and the ambient air temperature. Your data seemed to stretch many days of collection.
Can you give me the make and model of your power meter.
You said that you have a dedicated feed for your charging. If this is after your service meter, how long do you estimate the wire run and what is the gauge and type of wire?
According to Wikipedia, the roadster has 53kWh of capacity and can charge at up to 70A @ 240V equivalent to 16.8kW.
Also, in Hong Kong you have 50Hz power, we have 60Hz.
Can I see your daily logs vs. the summarized data? Perhaps during the short 32A chargers there was something strange happening, for example what if cell balancing kicked in and wasted a ton of power on one of those few days and never happend during the 70A charge. If the daily logs are available I would like to compare day by day efficiencies vs a lump sum.
To put some numbers up I would at least need a logging true power meter (that logs voltage, current and watts) and a logging volt meter. I would place the logging volt meter at my service entrance and the logging power meter as close to the car as I can get it. Then I would need a dual charger Model S for a complete study, I only have a single charger. It would also help to record the ambient air temperature and what the vehicle's cooling/heating system is doing.
Since the Model S will pull power from the wall when connected to prevent battery drain, you would need to analyze the data logs and extract the power consumed only when charging is active. During those times the climate control should not be activated.
Once everything is in place, drive a lot, log a lot and analyze the results. Repeat with different current limits.
This would be a lot of effort and some expense to put this together. I have better things to do with my time, I can't even believe I started this thread in the first place. Like I said in my first post, "The information above is free. Take it, or leave it I don't care." I can also stick to the general principals of physics and say that power=current^2 x resistance. The resistance in the "system" is basically a constant. So, your power losses due to resistance increase exponentially with current.
�
Jun 29, 2013
markwj The actual quote was 'too' - ie; both our data.
That is essentially what I did, and yes it was a lot of work and discipline over several months. I am glad I did it, as it gave us a lot of insight into real-world behavior. It would be great to see this done with the Model S.
Note that while I see more voltage drop on 70A charges than on 13A charges (dialing the current down on a 70A circuit), I see even more voltage drop at 13A on a standard household 13A circuit. The reason is that the 70A circuit has less other equipment on it and better wiring. My 70A wiring run is with wires rated to 100A and only about 12' from the utility feed.
My conclusions were that it is not as simple as charge slower. If it was, then a 1A charge would be more efficient than a 80A charge - which it is not. While I agree that the charge system electrical losses are in general greater the higher the current, what you are missing is that there are also fixed losses during charging that depend on the duration of the charge (primarily pumps, computer systems and HVACs) - the longer the charge the greater those losses. In my experience, such resistive losses are less than battery conditioning system losses, but beyond 32A the benefit tails off.
As you say, take it or leave it - but that is the result of the biggest study into this.�
Jun 29, 2013
stopcrazypp You have to take into account the powered delivered is linear with the current. That means percentage loss = (I^2 * R)/(I*V) = I * R / V, which means as a percentage it only goes up linearly. Plus there are also fixed losses that make transformers have higher losses at low loads, although the I^2*R losses you mention contribute to more losses at higher loads.
The fixed loss from air conditioning is going to be extremely important to determine overall charging losses. Air conditioning load is going matter more at lower charging rates than at higher ones.
For both cases there will be a "sweet spot" for efficiency because of those fixed losses, so I don't think you can say for certain lower power definitely is more efficient.�
Jun 30, 2013
Dien Kim Nguyen There is one very important fact that everyone seems to forget: higher current means more stress on the battery. Over time this stress leads to fracture of the graphite particles which hold the lithium -- hence, battery degradation. This is the same reason that when one uses SC -- the current slows down dramatically to prevent this kind of stress when about to reach capacity. When there isn't a good reason to charge fast, one shouldn't do it.�
Jun 30, 2013
markwj Looking at charge profiles, this impacts most at high levels of SOC - which is why the car tapers off the current towards the end of the charge. Tom's work on the roadster showed the ramping down of charge currents towards the end of the charge means that no matter the current limit selected, all are the same towards the end (for example, a 70A charge would ramp down and pass the 40A level at around the same point that a 40A charge starts to taper off).
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
A dual charger, maximum 80A @240V is around 20kW. About 1/5th the rate of a supercharger (and they are proposing to increase the supercharging rate even higher - figures I hear are 90kW to 100kW today, with 120kW coming). So, how conservative should we be? 80A is five times as conservative a rate as the superchargers. 40A is ten times as conservative, and 20A is twenty times as conservative.�
Jun 30, 2013
boilerbots I am not missing anything. My post clearly talks about this under vehicle losses, cooling pumps, fans all add up. Can you charge without active cooling, seems possible, do I sleep in my garage every night to verify what is happening, nope.
When I charge at 40A I noticed the fans where running in the radiator and the charging cable was very warm.
Since I dialed back to 20A I haven't heard the fan running but I hear a noise that sounds like a very small circulation pump. It might run at some point.
Randomly when I check the vehicle the computer screen is on and I hear the pump noise but this is outside of charging, seems the car sometimes just wakes up and then goes back to sleep around 5 minutes later. This has nothing to do with charging.
My feed is more than 280 feet. First I have about 220 feet of 2/0 aluminum wire from my 200A service entrance meter to my main panel. Then I have another 60 feet of 2/0 aluminum to a sub panel, then a few feet drop to the 14-50 outlet. Unfortunately my house was built when 2/0 was allowed for 200A service, now they require 4/0 aluminum. Anyway this is acceptable for 150A service. What matters is the resistance per foot. If I take Southwire's value of 0.176 ohms per 1000 feet, and take my approximate length doubled, since their are two conductors I get 0.09856 ohms total. If I could charge at 80A, that would be 631W lost to wire resistance. If I charge at 20A, that is 39W. Multiply by charging times, lets say I need 20kWh every night to recharge (power delivered to the car). That equates to 20000/(240*80)=1.042 * 630.784 = 657.1Wh vs 20000/(240*20)=4.167*3.424= 164.3Wh every charge cycle. For me this is a delta of 492.8Wh every day, times 30 days is 14.8kWh lost every month to resistance in my electrical wiring if I where to charge at 80A vs. 20A.
In your data summary I saw 66.7% vs. 64.3% efficiency difference, so 2.4%. In my above example 2.4% x 20kWh is 480Wh saved however my wiring would have wasted 493Wh because of the increased power dissipation. Theoretically this is a wash if these efficiency numbers hold up for the Model S, also I am mixing 70A, 32A vs 80A and 20A in my example.
The big unknown is what is the charging efficiency of the Model S under every possible scenario?�
Jul 3, 2013
jaanton I look at voltage drops together with current. With my utility smart meter, it shows voltage and current. My Roadster shows voltage and current. I have The Energy Detective (TED) installed so I get detailed graphs of voltage and power.
Typically, my house voltage idle is around 248 v. With the car plugged in but not charging it reports the same. If I charge at 40 A my voltage at the car drops to about 244 v and at my meter is about 246 v. So I figure those 40 A cost me 2 v each before the meter and after. 2 * 2v * 40A is 160W of power lost to wiring, breakers, outlet connections and not going into the car. (Although the before meter loss isn't something I'm paying for! Shortly after I got the car, my utility replaced my power drop and that improved my voltage. The utility wasn't dumb. They knew my old drop was going to cost them when I start using serious power. A few months later they even added another transformer on my street. Definitely tell your utility you have a Tesla!)
When these detailed measurements are taken, ambient temperature should also be logged. When I do daytime charging in summer, the car cooling system comes on several times but that cooling system runs off the power into the car which is power not going into the battery. At night with the much cooler environment less active cooling is needed. The need for active cooling will probably sap a few percent and will be environmental so where you are in the world will make a difference.
Copper resistance is also temperature related. If you run your current at your wires capacity, it may get warm and probably have more resistance then when cold. You can see this with a meter on a toaster oven, initially maximum current flows and as the oven filament heats the current will drop a bit. I like to back off of full current just on the principle of not pushing the wiring to its limit.�
Jul 4, 2013
Merrill This seems like a silly question but I would like to know if my thinking is correct. The question is that if you charge at a slower amperage and it takes longer are you using the same amount of electricity as if you charged at a higher amperage and finished In less time. I assume that either scenario uses the same amount of kWh.�
Jul 4, 2013
pilotSteve I thought the 'range increased by slow charging' was kind of bogus, but I gave it a try. The last two 12 hour charges (240V@5A) resulted in my rated range increasing from 209 (where my slider ended up and its not been touched since then) to 212 and 214 today.
Maybe not such a crazy idea after all, thanks! Does make sense to me that slow charging will allow various banks of cell to stop charging before others hence leveling out all cells to a full charge due to long charge time.
Or maybe its just PFM (pretty fine magic) at work.�
Jul 24, 2013
boilerbots I bought a power meter to make some efficiency measurements and after only a few days I ran into a problem. I want to try and record the power used during charging and not just drawn from the wall when the car is sitting idle. To do this I unplug the car in the morning after charging is complete regardless of driving the car. I unplug the car on Saturday morning after charging from my Friday commute and the car sits the whole weekend. Monday morning the computer reports zero power used but the car is down 13 miles. I drove to work and home and then charged, Tuesday morning the car took an additional 4kW-hr of power to replenish those lost 13 additional miles but the computer trip meter does not report this in the totals.
So now it is nearly impossible to know how much power is drawn out from the battery to compare with the power that I measure going into the car unless Tesla makes a software change to fix this problem.�
Jul 24, 2013
markwj Boilerbots: nasty. On the roadster, we found the car display buggy and useless as well.
If you measure change in indicated miles (ideal miles?), you could at least get a comparison. For example, to add X miles uses Y kWh from the wall, repeat in different conditions.�
Sep 28, 2013
Cal1 I just took possession of my car. We're retired and live in a pretty rural area. I anticipate many of our trips to our local town will be very short. On a given day I might put 30-40 miles and on others nothing. I wondered if it would be better to wait until the range has gone down to say 80 or 90 miles or still recharge every night regardless of how much range is left.
I realize we could be SOL if we suddenly wanted to go far but we typically plan our longer trips to bigger cities well in advance. (Still got ICE vehicles as a backup).
God I love this "wake up every morning with a full tank" thing! I really don't think anyone can really get it until they live with a EV. Doesn't take long but no amount of test drives or research will really bring it home.�
Sep 28, 2013
djp The charging screen has a slider that you can use to set a maximum charge level. If you're only driving 30-40 miles per day you could get away with dropping it to 50% and still charging every night, and bring it back up before you do a longer trip.
The battery will last longer by keeping it at a low state of charge and cool temperature, and doing shallow charging cycles.�
Sep 28, 2013
yobigd20 Read this How to Prolong Lithium-based Batteries - Battery University
Your going to want to charge every possible chance to keep the charge cycle as shallow as possible to extend the life of the battery. The two worst things you could do are 1) discharge completely before recharging (thus making this a full charge cycle) instead of many small shallow discharge/charge cycles) and 2) Range charge to max and leave it sit there, especially in hot climates. Avoid those 2 things like the plague, and your battery will last a very very long time. Also, only really charge to what you need on a daily basis to keep your car around that 50% state of charge.
For example, if you only drive 50 miles daily, you could do something like set the charge limit to 60%. That should have you at about 159 miles range every day. Driving 50 miles would put you at 109 before charging again. That's about 41% battery (assuming 95kWh battery). So in this case you're always staying between 41-60%. AFAIK that's best case scenario. Try to always stay between 30-80% if you can. It's not bad if you need more or you drain more on long trips, but the shallowest you can keep your charge cycles on a daily basis would be the best you could possibly do on a daily basis to really make this battery last decades.
This is of course my opinion based on my own research and from talking to Tesla folks and other owners. There is no "official" guideline from Tesla afaik except for 1) plug it in every night and during long term storage and 2) don't range charge unless you really need it.�
Sep 28, 2013
wycolo > 2) don't range charge unless you really need it. [yobigd20]
Aren't you forgetting that the battery needs to be balanced on a regular, let's say monthly, basis? The phobia against Range Charging, like all phobias, can get overblown into a PROHIBITION such that it never is attempted. Might be better to adopt MicroSoft's old motto: "Where have you gone THIS MONTH (with your Tesla)?" and do a breakout of the tether, long range trip. [This is me talking to self here].
--�
Sep 28, 2013
AmpedRealtor I disagree. I've spoken with multiple people at Tesla Ownership who have indicated that the "ideal" charge level for maximum battery life is 50%-62%. Ownership qualified the recommendation by saying gains would be "negligible", but that technically that is where the battery needs to be for maximum long term life. Of course those who think they know better than Tesla will quickly debate this and question the source, that unless it comes from an engineer the information is useless, blah blah. Yet nobody here is a battery engineer either, and many think they know better than what Tesla says or simply rely on the written marketing recommendation.
To each his own. We can come back and compare notes in a few years. This is a major capital investment, I'm going to do everything I can to take care of this battery. It's better to err on the more conservative side. One day when we go to resell our Model S vehicles, the battery capacity will end up being a critical factor in someone's purchase decision. If my car gets 25 miles extra range over another vehicle after 5 years, I consider that significant and more resale money in my pocket.
This is just what I have chosen to do for myself based on recommendations from those at Tesla who know much more about this car and its technology than I.�
Sep 28, 2013
liuping Is balancing only done when you range charge?�
Sep 28, 2013
RodF Well said. Exactly what I am doing based on the low miles I need on a daily basis. Charging at 60%, using to 40% and plugging in at the end of the day. No hassle, and if happens to prolong the life of my battery, what the heck.�
Sep 28, 2013
wycolo > Is balancing only done when you range charge? [liuping]
Yes, I believe that has always been the assumption. And that means a 'full' range charge which means going ON for a few minutes then OFF, over and over until finally all segments of the pack are equal. Quite a ruckus just before a long trip if the contactor is clunking away under your bedroom while you are still trying to sleep. :frown:
I don't think TM Ownership is going to sway R & MS owners *not* to range charge on some kind of regular basis; this would be for Engineering to do. Keeping a balanced battery is rather basic. My R gets charged only every few weeks and I finally did a full range charge. Might have been the only one it ever got (over 7k miles on clock). Result was 235 miles, whew, which is very good. I plan to do full range charges every 60 days on the MS if long trips don't require this beforehand. Staying around 50% SOC is fine, but doing balancing is a separate requirement.
--�
Sep 28, 2013
dennis 1) What do you mean by a 'full' range charge? Is it as simple as setting the charge limit all the way to the right and then plugging in? Or does the last part of the charge need to be done at low amps in order to balance the pack?
2) Is a single 'full' range charge once per 30 or 60 days good enough to keep the pack balanced? Or do you need multiple range charges on successive days for a week or so to fully restore the pack to its maximum capacity as I read elsewhere on TMC?�
Sep 28, 2013
Puyallup Bill I doubt it. The following is a lift from a Tesla engineer(?) discussing the Roadster battery, and it would seem to me to be applicable to the MS as well.
Just remember that the car does benefit from being allowed to sit fully charged in Standard mode, and should be allowed to do so frequently, especially if being used on a daily basis. Leaving the car plugged in in Standard mode after it is done charging will initiate this balancing program automatically. This doesn�t take much time, 30 minutes or so should do. It may take several of these balancing cycles to bring the car back to a balanced state if it has become imbalanced, which is something that a lack of regular Standard mode top ups and subsequent balancing cycles can induce.
The full text is at: http://www.teslamotorsclub.com/showthread.php/3848-Tesla-Roadster-Battery-Care�
Sep 28, 2013
liuping I'm not really sure what they mean by "a lack of regular Standard mode top ups and subsequent balancing cycles can induce."
Does that mean if I only charge to 70% daily it will not run the balancing program regularly?�
Sep 28, 2013
jerry33 Hard to say. There is, unfortunately, no indication of when balancing is taking place.
Bear in mind that there is driving as well as charging. My understanding is that it's better for the battery to drive between 90% and 50%. So it's possible that charging to 50% and driving may be worse than charging to 90% and driving.�
Sep 28, 2013
montgom626
Chevy did some great work on the Volt.�
Sep 28, 2013
djp IMO, balancing is overrated. A properly balanced battery will give you a slightly higher range on a full charge, which might make people feel better by seeing a high number on their screen, but doing regular max charges for the sole purpose of balancing does real damage to the battery for a purely optical benefit.
For example, the 40kWh models never get top end balanced since they're limited to 66% of a 60kWh battery. The balancing doesn't matter since the top 33% never gets used.
A battery that is out of balance isn't permanently degraded, a couple of 90% or 100% charges will bring it back to its full potential. I'd avoid doing max charges just for the sake of balancing and let the battery balance on its own whenever you do a full charge for a longer trip.�
Sep 28, 2013
liuping I plan on charging to 70% during the week, which would put me just below 50% at the end of the day most days and rarely below 40% even if I have to run errands, etc.
There is a lot of conflicting info on what is really best for the batteries, but staying as close to middle as possible seems to be one of the consistent bits as far as I can tell.�
Sep 28, 2013
AmpedRealtor Your advice is dangerous and contrary to Tesla's recommendations. Max charging reduces the long term life of your battery. Tesla has never said that the battery requires "balancing" and that max charging accomplishes that. Can you please cite a source for this information?
You just spent around $100,000 on a car with brand new technology. The most expensive item in your car is the battery. Why in heavens name would you base your charging habits on assumption rather than facts and recommendations provided by Tesla? Nothing that you say about "balancing" the battery is supported by facts or anything that was actually stated by Tesla.
When you make a recommendation to someone here, shouldn't it be based on facts rather than assumption?�
Sep 28, 2013
MarkR I am, perhaps, na�vet�. I gotta think that the Tesla engineers want to do everything they can to extend the life of the battery and maximize the number of miles that we can drive on a charge. I REALLY like the idea of having a "charge by xx:00" option that enhances the functionality and life of the battery. I have faith that we'll get the software options we want in due time because its in everyone's best interests.�
Sep 28, 2013
ModelS1079 Okay Jerry33, I have been relying on you for tech advice for over a year, and I give you the final word- what is the best way to charge our batteries. Full standard charge or mid range somewhere? Full speed at 40A etc, or more slowly? Rebalance yes no hogwash absolutely? Marianne, or Ginger?�
Sep 28, 2013
jerry33 I don't pretend to be an expert on batteries. However, hcsharp is, and he's written the best explanation I've seen. Post #16.
I charge at 32 amps normally. This has more to do with being easy on the grid, UMC, and house wiring than it does with the car.
I don't believe rebalancing needs to be done very often. My opinion is that most of the variations seen to date are due to software changes, not battery degradation (other than perhaps a few outlier cases). Measuring SOC is not an exact science--there is a lot of estimation done. What's known about rebalancing and reduced amp charging comes from the Roadster. We're making assumptions that the Model S will work like the Roadster in this regard. It probably does, but we just don't know and won't know for awhile.
Marianne. I think Ginger would get on your nerves after a short time. However, as Bad Billy Pratt says, "I wouldn't mind eating a whole chocolate cake once in a while."�
Sep 28, 2013
stopcrazypp The evidence so far seems to show that the MS does not do the same kind of balancing the Roadster does in Standard mode. The only way that reliably forces the Model S to do balancing is extremely slow charging in Range mode (or 100% equivalent). Here's how you know balancing is happening (adjust range number as appropriate to match you pack):
I agree with djp though. The battery does not have to be balanced regularly. The only benefit that carries is the psychological one of seeing slightly higher numbers on the screen. I have only recommended it when people are wringing their hands over "losing" a couple miles of range recently (it gives them the peace of mind they needed).�
Sep 28, 2013
Dreamin Jerry, what thread were you referring to here?�
Sep 29, 2013
yobigd20 THIS.
very good point.
I second this.�
Sep 29, 2013
bob_p Tesla's official position is that charging to 100% (maximum range) infrequently or other charging habits (as long the battery doesn't become discharged) should have little long-term impact on the battery life and capacity. Their recommendation continues to be to have the car plugged in, when possible.
They have yet to officially indicate why the variable charging feature was added - and how they recommend it should be used.
For the vast majority of Tesla owners, following Tesla's simple instructions is probably the best strategy - and if Tesla determines that a change in charging practice should be adopted for owners, they'll provide us something in writing and/or make a change to the car's onboard software to help owners implement a different charging practice.
That doesn't mean that the strategy recommended by some owners to charge to 50% or to use lower charging rates may not help - but only Tesla really knows the real impact of those practices on the battery pack - and hopefully by tracking how we are all charging our cars, they'll learn what practices work best.
I've already got 16K miles on my Model S - and if I continue driving at this rate - I'll have a much better idea in the next year of how charging to 90% and leaving the car plugged most of the time - impacts range.�
Sep 29, 2013
yobigd20 I believe they said that it was "because owners requested it", and that they recommended to "charge to only what you need". If I recall that was purely from statements by Elon and their other V.P., and I don't think its "officially" written on any documentation anywhere.�
Sep 29, 2013
Sacrament055 Actually the 40KWh pack is limited to 72% of 60KWh battery and although I expected to never see losses because I reasoned that I'd have to see 28% loss before I noticed any degradation, that has proven incorrect. Apparently the car is taking into account that the top end has reduced and there for 72% of that has also reduced. When I got the car (admittedly on older firmware) it used to show 145 rated miles on full charge. Lately I'm seeing 139 (it's been 4.5 months) I know how to drive for max range and feel like I could still go close to 150 miles on a single charge if needed but I'm a bit surprised to see the rated range drop so quickly. I'm taking it in next week to get the fog lights added and will ask about the range loss and see what they say.�
Sep 29, 2013
djp I think the 72% accounts for the fact that some of the charge range at top and bottom is hidden, so the 40kWh uses 66% of the total 60kWh but 72% of the available capacity.
I'm surprised you're seeing a drop too. Let us know what the techs say, it could be changes in the firmware.�
Sep 30, 2013
bob_p I've only connected to a public (pay) charger several times - and using the slider to limit the charging would be a useful feature to limit the cost of charging the car only to the level needed.�
Sep 30, 2013
wycolo Re Battery Pack in MS:
1. If it balances it does so internally; it is the Roadster that balances by turning EVSE on & off repeatedly at the very end of charge cycle. My bad.
2. Why obsess over this issue? The battery you try so hard to 'save' may not be yours for long. Mine was replaced @8000 miles due to circuitry issues.
3. If you can plan a long max range trip, do it! Don't take the ICE due to fear of doing a range charge.
4. 'Regular Basis' - I read this as either monthly or every other month.
5. I've just recently gotten 4.5 and with 5.0 being released, things are in flux, at least the GUI. Actual battery management being in Firmware may continue unchanged(?).
6. I occasionally arrive home with 20 miles showing, at which point the 'battery limited' warning pops up. So this would border on stressing the battery. Thus my interest on being sure the battery is not out of balance or otherwise limited. Oddly, up at the Pass the miles is down to 16 but perhaps since the car doesn't stop, the warning does not appear.
--�
Sep 30, 2013
scaesare Clearly there is much debate about balancing, charge/discharge activity suggestions, etc...
One thing that seems to be universally agreed upon however, is that the two thing Lithium ION cells like are:
-Being at a SOC that's not at one extreme or the other (especially for extended periods)
-Staying cool
My question is: what's "cool"? My garage can get to be 100-110+ in the summer during the day... and even at night when I'm charging can stay 100+. What's the range for a LiON cell to be happiest?�
Sep 30, 2013
AmpedRealtor This is why you are supposed to keep the Model S plugged-in whenever possible. When the car is plugged-in, the battery's temperature is properly maintained regardless of ambient air temperatures. The same happens when you pre-condition the car using the remote app.�
Sep 30, 2013
scaesare I've also seen some discussion that simply being connected to shore power doesn't necessarily enable the pack temp management systems... or it may be that there's not solid evidence it's been triggered that anybody has posted.
I know I haven't ever heard my my car automatically spin up the systems to start managing temp even in an awfully hot garage when plugged in. It's ostensibly the same compressor as used for cabin HVAC, so it should certainly be audible...
In any case... I'd be interested in what the "happy" temp range is is surmised to be...�
Sep 30, 2013
mknox I've left mine plugged in for extended periods and have a dedicated meter on my EV circuit. I've only ever seen power drawn to top up vampire losses (5 kWh every other day). Never any evidence of anything other than that.�
Sep 30, 2013
wraithnot
This paper has some relevant info: http://www.nrel.gov/docs/fy12osti/53817.pdf
Check out the bottom panel of figure 1�
Sep 30, 2013
montgom626 Batteries are like people
Batteries are like people. If you are comfortable, the battery is comfortable. Best temp is around 70 degrees. Too cold or too hot and the battery, just like you, is not comfortable.�
Sep 30, 2013
jerry33 So far there is no evidence that this happens except when charging. I'd be thrilled to learn otherwise.�
Sep 30, 2013
djp Four reasons:
1. Battery degradation isn't covered by the warranty.
2. Battery packs cost $40,000 to replace.
3. It's not hard to dial down the charge slider to a level that covers what you normally do in a day, and dial it back up for long trips.
4. The first question asked when a used Roadster comes up for sale in this forum is "What's the condition of the battery pack?"
In a case like this, balancing might actually hurt you. Battery packs can be either top-end balanced or bottom-end balanced. Think of it like lining up a bundle of sticks all with different lengths. Tesla does top-end balancing, which guarantees the bottom end will be out of balance. Running your battery down to a low SOC will put greater stress on those cells which are already lower than others at the bottom end.�
Sep 30, 2013
AmpedRealtor The evidence is on the card that was provided at purchase and which is attached to every service receipt. You have at least one of these as well. My source is Tesla itself. Good enough for me.
�
Sep 30, 2013
yobigd20 Agreed, however *unlike* the Nissan Leaf which clearly shows degradation problems in hot climates
Tesla cooling and battery management system is far superior in the roadster.
And that was first gen. The Model S is 2nd gen tech, leaps ahead of everyone else in the game (if you even consider anyone else in the ballpark, lol) and being 2nd gen tech I would expect it to be even more sophisticated and refined.
My take on that roadster study is that Tesla's perfected the battery thermal management system to keep battery temps in an ideal range in all climates such that it doesn't matter if you live in Alaska or Texas, outside temperature really has no effect on battery life in a Tesla. Great for us.�
Sep 30, 2013
TommyBoy I picture the real Tesla battery engineers reading these threads and laughing. I know because I work in the high-tech industry and there are many forums about one of our products and the engineers make a point of having beers in the office on Friday night and reading the thoughts of "experts". It's all over my head as a sales guy but they seem to get quite a kick out of it.�
Sep 30, 2013
yobigd20 I actually spent a lot of time today reading a lot of their patents and learn more on a detailed technical level so I can speak more accurately about the subject. I'm quite impressed. They're systems and methods are very sophisticated. They've got to be leap years ahead of competition. Even when (if?) the competition "catches up", Tesla's got quite the collection of patented IP regarding charging and battery management. That puts everyone else at a major disadvantage unless they can somehow "out-think" Tesla's engineers. Even while they (competition) keeps trying to catch up, Tesla's already filing patents for the next-gen technology (their metal air + lithium ion hybrid battery systems sound very cool, I'm guessing that's for Gen III).
Anywho, after reading a lot of these patents, it's quite clear to me that they have completely control over charging and the battery pack systems. I don't think that charging at 110v wall outlet vs NEMA 14-50 vs HPWC vs supercharging makes much of any difference as long as you're keeping the SOC between 10-90%. Their thermal heating/cooling system keeps the battery temps at an ideal temp pretty much at all times so I can't see how any of us can really do our battery much harm unless you range charge it to max and keep it like that for an extended period of time or vise versa - deplete the battery and keep it like that. Their advice to just "keep it plugged in" couldn't really be more true and any simpler. They have a method of calculated an estimated "rated range", but really that's it in a nutshell - it's an algorithmic estimate that tries to be as accurate as possible but in fact it is technically impossible to do so. The only way to accurately calculate a lithium-ion batteries capacity has to be to deplete it fully (bad for battery) and then to range charge it fully (also bad for battery). So basically they are left to do some mathematical tricks to "best guess" rated range based on a number of factors. It seems to be "more or less accurate". So when I read posts of people saying "hey my rated range is down 5 miles, down 8 miles, and then say *oh no I have battery range loss* , I chuckle. It's not really range loss at all. It's the weighted estimated guess. And then they come out after doing a long trip and now they see higher rated range. These estimate is going to fluctuate a good 5,10,15 miles. I wouldn't worry about any of this. Everyone should just plug their cars in at night and go to bed and sleep well knowing that Tesla knows what the hell they are doing & they are damn good at it. Make's me feel kind bad for the "other guys" trying to catch up to them lol I particularly liked how Toyota said today "there's no place in hte market for EVs" and then Tesla's stock shot straight up again! LOL! Toyota has no clue really and has to buy the tech from Tesla for the Rav4 EV bc Toyota doesn't have the in-house tech or the know how to do it themselves haha
You can read these patents yourselves. They are all published publicly.�
Oct 1, 2013
brianman Not every purchase included this card. Mine didn't, for example. I picked up one while I was at Fremont service (not for my car, they didn't have any room for appointments) during my Teslive trip.
Don't always believe everything Tesla prints as "fact" though. For example, the red HPWC on the back of that card was never made available to customers -- though it does exist, as there is one of them at the Fremont service center.
Somewhat random tangent, perhaps.
�
Oct 1, 2013
brianman Warning: Keep an eye on your vehicle when trying out low charging rates
I lost track of which thread was covering the "charge at 240/6A for a few days to allow rebalancing" so if this is the wrong one, feel free to move this post.
My fuzzy recollection of my new data point is this...
A few weeks ago I had my 12V battery replaced as part of what seemed to be a general push to replace the "original" or "early" 12V batteries with the new "red" ones. My original 12V never exhibited problems. My new 12V hadn't exhibited problems -- until today.
I planned on a "hibernate at home" weekend with little driving activity, so it made for a good break from "daily driver" role to try out the slower charging rate balancing theory a bit. On Friday night, I dropped the max amperage (in car) to 5A. The car didn't seem to want to settle on a duration for a few minutes so I bumped it up to 20A and it quickly converged on a reasonable ETA. A few hours later I dropped it to 10A, and then a bit after that I dropped it to 5A and went to bed. All seemed well. I left it at 5A for all of Saturday and Sunday. No surprises, no drama.
Tonite (Monday) when I got home I plugged in with 170+mi. (maybe 180+, I forget) rated remaining. I didn't do anything special. Something reminded me to check my logs (instinct anytime I "change something in the matrix") and I noticed that charging_state wasn't "Completed" but instead read "Stopped" and that battery_level was 80. (I have the default limit of 90 set.) Well that's curious.
So I load my test app and invoke charge_start. Nothing happens. It stays at charging_state = Stopped.
I walk outside and notice my instrument cluster is lit up. Note that this is before I'm in range with the key fob so the car hasn't "been alerted to my presence" yet. Even more curious.
The instrument cluster reads "Car Needs Service" and as I get closer I see it's complaining about the 12V being low. Lovely.
Assuming it's related to the low amperage max setting, I tap the button the HPWC cable so that it goes into "plug unplugged, and replugged -- let's renegotiate" mode. Immediately I bump the amperage up to 20A. After a bit, the car is now at 83 battery_level and remains in charging_state Charging.
So it seems like -- from a charging perspective -- it's underway.
But I now have a new reason to be nervous about the 12V. With the main battery at SOC of 80% why would the 12V trickle-charging be impacted by the wall charging rate? Very odd. Makes me suspicious that something is "troubled" regarding the 12V generally.
I already had a reason to chat with the service center in the near future (second set of TPMS, for the 19s) but now I have a another topic to discuss.
Moral of the story: Keep an eye on things if you drop your charging rate to "very low" (240V/5A), just in case.
car_version = 1.33.61�
Oct 1, 2013
scaesare Indeed... your comment here seems to agree with mine that we've not seen any evidence (at least that I can recall) that the temp mgm't systems have kicked in when the car is at rest and not actively charging (plugged in or not).
Now maybe we could argue that the batteries really aren't affected much by "typical ambient temps" in the areas we live in, but the PDF that wraithnot proved a URL to (thanks!) indicates that there some noticeable effect on LiON cells with just a 10 degree spread between 20 and 30 degrees. My garage can easily exceed 45 deg. C... thus my earlier questions.�
Oct 1, 2013
Merrill Keeping the car plugged in at all times does not work if it does draw shore power even if not charging and you are on a TOU electric rate. I do not want to pay the electric company the higher rate, so start charging after midnight. Can someone verify that you would be using power even if you are not actually charging. There has been lots of posts on this but they all leave me confused.�
Oct 1, 2013
ZBB My experience is that the car will not draw power after charging completes. There are 2 exceptions to this:
1) If its left parked and plugged in -- at which point it will start charging every 2 days to top off. I believe it uses the scheduled charging start time to do so (this will top off for vampire loss).
2) If you remotely start cooling/heating the car, or open a door while its still plugged in. It will then draw shore power for the AC use.
When we were on vacation this summer, #1 is the behavior I noticed -- and all top-off charges happened over night (I have my scheduled charging set for 2am, so I didn't stay up to check to see if it started charging at 2am every other day...).�
Oct 1, 2013
Merrill Thanks ZZB, I normally charge when needed. I plug in normally when I get down to 60 to 80, otherwise it is not plugged in. I still get confused with all the different options that this forum talks about. I hear that keeping the car at a high SOC all the time is not good, so does this not happen if you keep it plugged in and it charges everyday based on your charge schedule. If you do not drive the car, then it stays at the top end of the SOC.�
Oct 1, 2013
montgom626 No need to worry. I ran 120v at 15 amps x 4 months until I got my 240v 50 amp NEMA 14-50 installed. I run the 14-50 at 5 amp x 240v when I only need 10 kW. Never had any problems with either setup.�
Oct 1, 2013
mknox Consider it verified. I set the charge timer to 10:00 PM and left it for two weeks on vacation. I have a sub-meter on my EV outlet. The car charged every other day to the tune of exactly 5 kWh starting at 10:00 PM. It did not draw power at any other time.
Now this was summer. I'll be doing the same in mid-December so I'll be watching to see how it fares in the colder weather.�
Oct 1, 2013
wraithnot If I'm parsing the battery diagnostic here correctly: Please Enter Access Code - Page 11
active cooling only kicks on when the battery hits 55C (a toasty 131F). Of course I don't know if this screen only applies to a moving car, a parked car on shore power, or at all times. And I don't really want to try and heat my garage to 55C to find out . . .�
Oct 1, 2013
djp Yes, you're parsing that right, the Model S battery seems to operate about 10-15C hotter than the Roadster battery. This explains why the pack heater draws so much power in the winter (the 10C target is toasty in Canadian terms) and why active cooling rarely kicks in, except on a track. I had my Roadster at a track yesterday along with three P85s. The Roadster cooling system was a jet engine for most of the day while only one Model S had the HVAC spin up, and that was only for a few minutes after a professional driver did some exceptionally hot laps.
What is odd is 55C is extremely hot for standard Li-Ion NCA batteries. Either Tesla is using a very unique chemistry, or they've decided that the Roadster BMS settings were overkill and they can still get a decent life out of the battery while spending less energy on cooling (or a combination of both).
- - - Updated - - -
There's a slider on the charging screen that lets you set the maximum %SOC level, so you can plug in every night and not stay at the top end of the SOC.�
Oct 1, 2013
SFOTurtle Have you noticed any difference in the displayed rated miles one way or the other?�
Oct 2, 2013
brianman Update
I gave Tesla Service a call Tuesday morning and gave all the details I could remember, and requested that they pull whatever logs they can to research and get back to me with their thoughts.
What follows is a loose retelling from memory of a phone conversation so don't freak out if anything sounds troubling as it may be just poor memory or phrasing on my part....
- We had at least one brownout on Monday night, and that is likely to blame for the HPWC triggering a fault and telling the car about it. This is what stopped the charging.
- Either in reaction to the fault from the HPWC or for loosely related but not causal reasons, the vehicle registered a fault of its own.
- The vehicle's registration of a fault put the systems into a "protection mode" of sorts that halted trickle charging of the 12V, despite the main battery having plenty of charge available.
- In part because I don't have 5.0 yet, the normal vampire load accumulated enough that the 12V started reporting in as "below appropriate levels".
- Unplugging and replugging the cable (to trigger negotiation of a new charging session) seems to have bypassed the fault in the HPWC which woke up charging.
- The bump to (240V/)20A limit from (240V/)5A limit appears to have been an unnecessary step and not critical in getting everything "back on track".
- Tesla-fetched telemetry from the car suggests the 12V is fine. It didn't go into "troubled territory" as relatively quick observation of my telemetry logs and response with subsequent actions addressed the low 12V situation promptly.
TLDR: When there's a brownout, interesting things can happen with the HPWC and the car but so far nothing permanent/harmful has been identified in my case.�
Oct 2, 2013
wycolo Shouldn't you 'invest' in a plug-in voltmeter?
--�
Oct 2, 2013
djp Interesting - that's a good argument AGAINST charging every night at low amperage, it increases the probability that you'll be hit with a brown out (or a voltage surge during a thunderstorm). If either are a risk in your area, you should consider charging once a week, and charging faster! :smile:�
Oct 2, 2013
montgom626 None.
Given how "crude" the dash is as a measuring instrument, that is to be expected. For example, if I see 197 miles one day and 199 miles the next, that is a 1% difference. As much as I love my P85, the 1% is within the margin of error for the dash gauges. Some folks see the gauges as precise, reproducible and highly accurate. Nothing could be farther from the truth. So, assume a +/-1% variability, 197 is the same as 195 to 199.
I hope I did not confuse anyone.
- - - Updated - - -
It is a reason not to get a HPWC.�
Oct 2, 2013
mknox Wow. 55C is quite warm and would explain why I never saw any battery conditioning draw from my outlet when I was away in July. The car would get nowhere near that hot in my garage unless the house was on fire.
I do see the pack heater on when driving and the weather falls below about 60 degrees F (based on the dash power gauge) but I've never seen it come on (based on my wall outlet meter) when the car is just parked and sitting. I'll be going away in mid-December for a few days, so we'll see if any battery heating draw is present. My guess is that I won't. I've read that Tesla lets the battery get pretty cold and only starts to warm it when the car is turned on or when you actively turn on cabin heat via the mobile app.�
Oct 2, 2013
AmpedRealtor The Model S battery seems to like higher temperatures. If you look at the range calculator over at Teslamotors.com, range is highest at 90 degrees ambient. As the temps go down, so does the range. Usually higher temperatures are a battery's enemy, so Tesla definitely has some unique chemistry.�
Oct 2, 2013
drees All lithium batteries perform better (lower internal resistance, can handle more power) when hot - nothing specific to Tesla's. It allows electrons to "flow" more easily. That is why a cold lithium battery appears to have less capacity - more energy is lost to internal resistance.
The problem with high temperatures is that the battery degrades faster thanks to Arrhenius' equation. It seems that Tesla is confident enough in the durability of the cells that they don't feel the need to cool the pack much. It would be very interesting to see what operating parameters do trigger pack cooling.�
Oct 2, 2013
djp They're on the screenshot in the other thread. Passive cooling is triggered at 40C and active cooling at 55C. The pack heater target is 10C.
Agreed all Li-Ion batteries perform better but degrade faster in warm temperatures. The Roadster even has a Performance mode that pre-heats the battery, but the manual advises not to use it to often since it'll shorten the life of the battery.�
Oct 2, 2013
jerry33 Bear in mind that range increases in hot weather because the air is less dense than it is in cold weather.�
Oct 2, 2013
montgom626 What? Not a measurable increase by any mortal I know of.�
Oct 2, 2013
stopcrazypp The density of dry air at -13F(-25C) is 1.418 kg/m3 and at 90F(32C) is 1.153 kg/m3. This is a 23% difference.
The impact on drag is directly proportional, so I would say that is noticeable. The impact would be the same as if the Model S's Cd went from 0.24 (one of the best in the industry) to 0.29 (same as many decades old sedans).
http://en.wikipedia.org/wiki/Drag_(physics)�
Oct 2, 2013
David_Cary Air density is totally noticeable and measurable. Aerodynamic resistance is the vast majority of energy use at cruising.�
Oct 2, 2013
jerry33 Just ask any pilot if it's easier to take off on a cold winter day or a warm summer day. The difference is very measurable.�
Oct 3, 2013
wycolo Air density - the joker here is water vapor. Makes computation complicated. High moisture content reduces air density since water vapor takes up more space than most other air components do. Florida actually a good place to view stars since it is generally warm & moist.
--�
Oct 8, 2013
wycolo > I'll be watching to see how it fares in the colder weather. [mknox]
Cold morning: NO regen available - dotted orange line @1 o'clock (power limited). MS always plugged in so conclude: MS does NOT maintain min temp of battery yet. Maybe in a few months it will when it gets *really* cold.
New software finally nagged me: "Do you *really* want to keep slider @235?" So I reduced it to 200. Conclude: MS *now* prefers lower SOC. Noted.
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Oct 8, 2013
mknox I had limited regen last March when I got the car and we still had some cold weather, but never saw zero regen. The only time I had zero regen was right after a Range Charge, and it sure threw me for a loop when I let off the "gas", even though the power meter clearly showed it.
Now with the mobile app and "shore power" support, I'll be pre-conditioning the car in the morning once it gets cold, and I'm given to understand that when you turn on the heat, pack heating also starts. One thing I have to figure out is how far in advance of setting out should I turn on the heat.�
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