First little road trip and mileage calculations

[notice]

Just a month into S85 ownership (Gray/Tan/Pano) and took my first family road trip with my wife and kid to my in-law's house in W. Hartford CT from our home in Concord MA. This was only a 200 mile round trip, should be easy but I was nervous about range especially at highway speeds and dropping temperatures. I also only charged the battery to 90% because I want to avoid max range charge as much as possible to preserve long-term battery life, and didn't think it would be needed for this trip. I charged to 233 rated miles (this with v5.0).


Going down was easy. I was neither pushing it nor slouching - kept up with traffic and was often driving around 70mph. Weather was between 62-64F, sunny and dry. I was keeping a close eye on Wh/mi and projected range with a goal of completing the round trip on a single charge and everything was looking great.


On arrival, I figured I would try to plug in anyway to get some extra safety margin. The in-laws, now elderly and living in a home built in the 1950s, had a 110 outlet in the detached garage - but the UMC didn't like it (I'm guessing this was a do-it-yourself wiring job with incorrect grounding). I had purchased a heavy duty 15A 110V outdoor 50' extension cable I had in the car, and ended up using that to connect through a kitchen window into a kitchen outlet. Rain was coming in the evening and didn't want to leave the cable out in the rain, so only charged for about 6 hours on the 110 @ 12A getting about 18mi of extra range. (I also have on order a 50' NEMA 10-30 extension cable found on a site on the Tesla forums - I believe from SteamBrite, and while visiting thought I would check out the logistics of plugging in to their dryer outlet and running the cord out a basement window to the driveway. Much to my surprise, their dryer plugs into a standard 110 outlet and it does not appear they have any 220 service in the house! Good to know! (There are public chargers in West Hartford I noted in case needed but haven't scoped them out).


The return trip was colder and rainy, about 55F, and seems like a lot of up-hill on the CT section of I-84. With the extra range, I felt comfortable in that I could average over 400Wh/mi and make the return trip home, but when I saw 20 miles up I-84 and keeping speeds below 65mph that I was still averaging 450Wh/mi I grew concerned. Reduced speed closer to 60mph and kept watching projected range and the trip meters. Energy consumption was improving by the time we got to I-90 and made it home with 24 miles rated range remaining (so it would have been 5 miles if I had not plugged in to the 110, happy to have the extra safety margin). Success!


Some numbers I found interesting: First the trip itself:


South North Round trip
Actual distance 100.4 100.3 200.7
Rated mi used 105 117 222
kWh used 29.0 32.3 61.3
Actual Wh/mi 289 322 305
Rated Wh/mi 276 276 276


From the above (as of v5.0 firmware), it looks like rated miles are based on a 276 Wh/mi consistently.


Additionally, having experimented with different levels of charge (noting that I have not yet performed a 100% charge but plugged in the 265 EPA rated range number here and it fits the pattern):


Charge to 70% 80% 90% 100%
@85kWh=100% 60 68 77 85
Rated miles 172 202 233 265
kWh@276Wh/mi 47 56 64 73
Reserve 12 12 12 12


Using the 276Wh/mi rated range determined in the first table, there appears to be a constant 12kWh reserve at the "0 mile rated range" point. Other posts suggest on the order of 15-20 miles additional range before the car stops after this point which suggests about half of the reserve (e.g. 12kWh is the 0 mile point and 6kWh is the "anti-bricking" point).


There are other posts here and on the Tesla forum with different numbers, but this is my conclusion which may be different in v5.0.


I'm feeling more prepared for our next road trip for Thanksgiving - trying to go 205 miles one way from Concord MA, picking up the in-law's at Sturbridge parking lot and continuing on to Saratoga Springs NY. I'm very hopeful that there will be a supercharger in either Sturbridge or Albany area before then but not holding my breath - the trip would be a no-brainer with a supercharger. Without, it's going to be tight, especially as the temperature could drop significantly, there could be rain, there's high elevation heading into western Massachusetts. I'll max range for sure, keep an eye on things, and worse case take a detour to a public charging station in Lee. I'll report in again!

 

[Chipper]

Thanks notice! Good report and I am glad it all worked out for you. These kinds of stories keep me encouraged and hopeful.

 

[GlennAlanBerry]

Nice trip report. FlasherZ will probably chide you about the risk you take by using an extension cord to charge.

Really, if you are going to take a road trip, you should range charge. That is what it is there for. Doing a range charge occasionally is not going to hurt your battery longevity.

 

[Cottonwood]

Nice trip report. FlasherZ will probably chide you about the risk you take by using an extension cord to charge.

Really, if you are going to take a road trip, you should range charge. That is what it is there for. Doing a range charge occasionally is not going to hurt your battery longevity.

This what I do about extension cords and rain; make your own safety decisions: Although not recommended by Tesla, using a heavy duty (14, or better yet, 12 gauge) extension cord works fine for 12 Amps at 120 Volts. My experience in the rain is that if you keep connections and the UMC up out of puddles you are in good shape. I have been known to put the UMC and its connection to an extension cord up on a couple of rocks under the back of the car. If you were plugged into any sort of recent kitchen outlet, you were on a GFCI outlet which brings one more level of safety to charging in the rain. Remember that rainwater is pretty pure and not very conductive.

As for the fear of range charging, it is time at high charge state that works on the battery the most. If you want to be obsessive and still do a range charge, here is a little trick that I use. The evening before your trip, charge to 90%. Figure out the time that you will be leaving, and calculate the time that will be needed to start your range charge. Then set the charge start time to departure time minus charge time needed minus one more hour for margin. For example, on a UMC with a 14-50, 40-Amp service, it takes about 1.5 hours to do a 90% to range charge. If I want to leave at 8am, I then subtract the 1.5 hour charging time and the 1 extra hour for margin, giving me a charge start time of 5:30am. Before I go to bed, I verify the 90% charge state, and then set the charge start time to 5:30 and the charge target to 100%.

With this method, you are at a Range level of charge for only 1-2 hours, a minimal time for battery degradation. VERY IMPORTANT: Don't forget to turn off time charging at your next stop, or the car will not charge until that wee hour of the morning!

 

[notice]

On extension cords - I was sure to get one rated for 15 amps and outdoor use, and still avoided getting it wet. It's massive (as thick as the UMC cable). And it stayed cold to the touch.

On Range Charging - I hear you but disagree. I've seen on these forums the statement that max range does not harm the battery if full charge state is only done a moment before heading off on the trip. This is partly true in that a fully charged battery if exposed to an increase in temperature stresses the cells (more energy and nowhere to go) - so burning this off right away by driving is helpful. However, that's not the whole story. Li-ion chemistry (as I've posted about on the Tesla Model S forum) degrades as a function of "cycles", usually measured in some percentage loss of capacity after some number of "cycles". When cycles are "full" e.g. from full charge to empty, you might expect to see 10-20% loss of capacity over several hundred cycles. However, this improves by an order of magnitude by decreasing the charge level even to 90% (and also improves with lower depth of discharge). So, the way I understand the chemistry (which by the way is consistent with what little Tesla says publicly in their manuals/documentation and is in conflict with much of what is posted on the Forums), the number of Max Range charges is what will relate most to the long term loss of battery capacity. I could be wrong, but I believe this to be true from my research on Li-ion technology and am not swayed by opinions to the contrary that aren't backed up by scientific data (though I remain open to being convinced differently). I suppose it would be most interesting to learn from owners with many more miles than I have how many times they have used max range and what kind of capacity loss they've seen to see if there is indeed a correlation (I predict a correlation but could be proven wrong).

Of course I would also point out that (assuming I'm right) if you only range charge a few times a year, you could go 100 years before seeing 10-20% loss of capacity! If you range charge every week, it might take 5 years. So used sparingly, makes no difference. I just want to try to avoid it if I don't really need it.

So, for my short trip above, if I was concerned about range, I would still 90% charge the car and then just add some more miles at a public charger at the destination. It's too bad I can't charge efficiently at the in-laws house, but that's not so bad is it? "Hi guys, would love to stay and chat, and argue about our different political views until we start yelling at each other, really, but I've got to go charge the car, be back in a few hours just in time for that home cooked meal!"

But for the 200+ mile one-way trip planned around Thanksgiving, I'll use max range for that for sure.

 

[GlennAlanBerry]

I guess everyone has to make their own decision about the risk of an occasional range charge vs. the stress of worrying about not making it to your destination on a road trip because you decided not to range charge. Personally, I would feel pretty silly if I ran out of charge a few miles short of my destination and had to take a ride on flat bed because I decided not to range charge. But as long as you plan your trip and pay attention as you are driving, that should not happen to you.

I am more concerned about negative stories from people "Brodering" their Model S (running out of charge because they did not charge to a high enough state before leaving on a long leg of a trip), and then loudly complaining that it was the car's fault that they ran out of energy. Most of the early-adopter Model S owners seem to have enough intelligence and common sense to avoid this scenario, but I worry about happens in the future as more typical customers (who don't pay as much attention to technology or details) start taking road trips, and inevitably someone does not make it to where they were going. I think it was George Carlin who said something along the lines of "Think about how dumb the average person is, and then think about the fact that half of the people are dumber than that".

 

[liuping]

On Range Charging - I hear you but disagree.

You are most like doing far more damage to the pack running below 10% than range charging. Something to take into account...

 

[notice]

@liuping - I agree that <10% is bad too - but "0 miles" range looks like 14%, and with the extra buffer I had on the 110, I was really only down to about 22% charge, no worries there.

 

[texex91]

Lot's of great info.

Remember the battery has a warranty, and was made to be maxed out for trips--so don't hesitate to do so!

I have a great extension cord made for 14-50 heavy duty--it's in the S at all times. Never used, but I'm ready: http://www.amazon.com/gp/product/B002XL2IG8/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1

 

[gregincal]

@liuping - I agree that <10% is bad too - but "0 miles" range looks like 14%, and with the extra buffer I had on the 110, I was really only down to about 22% charge, no worries there.

There is really no degradation if you range charge just before setting out of a trip. Not range charging when you are going to take a 200 mile trip is really silly in my opinion. The whole reason there is a separate range charge setting is that it is bad for the car to sit at range charge doing nothing.