Big temperature effect on range / efficiency??

[snoltor]

I've read about the Leaf battery degradation in hot climates. My question here concerns not degradation, but if and by how much high temperature impacts range / efficiency in the Rav4 EV. I've driven 1500 miles so far. Most of that is my daily 50 mile round trip commute but I'm also finding all sorts of excuses to drive the car. Lots of short 2 or 3 mile trips into town etc. The short trips are driven on slow 25 mph streets and when I shut the car down after one of those short trips it always reports an efficiency around 4.5 miles/kwh. Bought the car May 9 and the temps have been moderate, 60's to 80's. Temps have been into the 90's on a few occasions and using AC hasn't impacted my daily commute efficiency (as reported by Entunes). Last Saturday it was hot in Davis, 105F, and I had to take three of those same short trips. Each time I shut down the car it reported 2.2 or 2.3 miles per kwh instead of the normal 4+. The next day the temps were back in the 80s and coincidentally or not the efficiency reports were normal for what I've been seeing. So was that an aberration? I don't know how much to trust an efficiency report for a short trip and it was only that one hot day, not a lot of data to go on, clearly we need to gather more data. But maybe 105 is different territory. So I'm wondering if anyone else driving in hot weather can report if their range / efficiency changed or not? Any of the Sacramento area or Central Valley owners have feedback? Do we have owners in Arizona? Toyota just started selling last fall so we don't have a summer's worth of data to pick over yet....

 

[miimura]

If it was me in 100+ weather, I would be blasting the A/C to keep myself comfortable. The car's thermal management system (TMS) will also try to keep the battery in its healthy zone too. All of that obviously takes energy and is incorporated in the net efficiency number presented. It is merely extra energy usage, not battery degradation. The numbers you present are not alarming or unexpected to me.

 

[snoltor]

To be clear I'm not concerned about battery degradation, just performance in hot weather. I'm a glutton for punishment, use eco hi, low fan and just sweat it out! But hadn't considered TMS management of the battery. Good point, thanks.

 

[miimura]

There are many aspects to "Performance". I would expect very cold weather to have a larger impact on RAV4 EV driving range than hot weather. The A/C (cabin and TMS) is much more efficient than the resistance heaters. Also, there is the "Regenerative Braking May Be Limited" message that comes up when the battery is cold. Theoretically, hot weather and high speed prolonged uphill driving could force the inverter to reduce the maximum output of the motor to stay within the thermal envelope. I've not heard how easy it is reach the thermal limit of a Model S on the track. In a Roadster, it's relatively easy.

 

[miimura]

In any case, I would expect terrain and driving style to have a larger effect on range than cooling load. Here's an exercise for you - When the outside temp is over 100F, select the Driving Range display on the right side of the instruments. Set the Vent Mode to ECO LO and the cabin temp to 85F and note the range display. Then set the cabin temp to 70F. Does the range forecast change? We know the Driving Range changes with cabin vent mode Normal/Eco Lo/Eco High/OFF and A/C ON/OFF, but I haven't played with the cabin temp when there is a big difference to the outside temp.

 

[yblaser]

In any case, I would expect terrain and driving style to have a larger effect on range than cooling load. Here's an exercise for you - When the outside temp is over 100F, select the Driving Range display on the right side of the instruments. Set the Vent Mode to ECO LO and the cabin temp to 85F and note the range display. Then set the cabin temp to 70F. Does the range forecast change? We know the Driving Range changes with cabin vent mode Normal/Eco Lo/Eco High/OFF and A/C ON/OFF, but I haven't played with the cabin temp when there is a big difference to the outside temp.

In my experience the effect the AC has on the GOM is a learned behavior. New, the hit was about 10% regardless of fan only or AC. After driving for a month or two it has converged on 4%. I would guess that the above suggestion won't yield any meaningfully data on energy use of the AC system. You could try to use the Aux Power Usage display, but the reading is quite coarse.

 

[miimura]

Also, I obviously mis-spoke about the display on the right, the number there is the "Max Range", ie. what you would see on the GOM if you were to turn the ventilation off. The only change would be on the GOM itself on the left side.

I wonder if the TMS power consumption would show up on the Aux Power display. I've never seen a significant usage on the AUX power even with the A/C On. However, using the resistive heater would probably make that thing skyrocket.

 

[yblaser]

It's hard to tell with the limited resolution of the aux power display. I really wish they had some kind of digital readout on all the gauges. Since the TMS and cabin AC use the same heat pump I would assume both system's energy consumption is displayed. Even with the climate control off, I've seen some power usage when I first turn on the car (on the order of a couple of hundred watts) and when I was actually trying to drive efficiently the first few miles always seemed to give lower than expected efficiency both of which I maybe incorrectly attributed to the TMS.

 

[miimura]

I looked closer at the Aux Power display and was kind of shocked by what I saw. The Orange gradient line is not a bar like I thought, it just floats at the indicated value. So, it is almost impossible to judge the value while driving because you can't see at a glance where the zero line is. Very poor design.

 

[snoltor]

I'm happy to report that this whole thing is an Entunes issue. Yes I know, shocking (sarcasm). Originally I was checking the "Last Drive" data in Entunes on my phone. Turns out that data can vary significantly from the data you get on the dashboard when you shut down the car. For the past 2 weeks I've been logging the dashboard data you get when you shut off the car, and comparing it with the Entunes "Last Drive" data on my phone. The dashboard data is very consistent. The Entunes data is usually consistent but every now and then is way off. It's as if occasionally the Entunes "Last Drive" data reports an instantaneous EV efficiency and Eco score at the moment of shutdown. At any rate today it was 104 on the drive home and I still got 4.0 mpk for the 19 mile drive along route 80 from my office to my kids daycare, and then 4.6 mpk for the 4 mile drive on city streets to home. Just like other days when it was much much cooler.

 

[jspearman]

This is anecdotal, not scientific, but my range in PHX with A/C on Eco Lo at the start of an 80% charge reads 103 mi in >110 degree temps. It's basing that number on our not-so-efficient driving style, although we are neither leadfoots or hypermilers. I've found the GOM to be pretty accurate for us. In the spring when we didn't run AC, the GOM would read around 116 mi, so for us a 40 degree rise in temps knocked off around 10%. After suffering through the Leaf's limited range at even 100%, we can definitely live with these numbers.

 

[n3ckf]

i've kept a log of the GOM and the "real" odometer every time i start/stop the Rav4EV since i got it (about 1800 miles now).
I find that my actual miles "beats" the GOM by a small percentage (usually 5% or so) in "around town" traffic. however i just did my first long trip and i found that it went up to 14% in the uphill direction and almost 30% in the "downhill" direction. This might be because i was really paying attention to not speeding up/slowing down, using cruise a lot and using "B" whenever heading downhill.

 

[TonyWilliams]

I've been driving exclusively steady freeway driving at 50-65mph for the past 10 days, so the GOM should be the "best it can be" at future freeway driving.

When the 12 volt is disconnected, the default GOM is about 146 miles (3.5miles/kWh). My full charges typically show 120-130 miles on the GOM. Yesterday, I drove 151.9 at 50mph with the climate control off, with 12 GOM remaining on the GOM.

At face value, I "could have" driven 151.9 + 12 = 163.9 miles, versus 125 on the GOM. Error rate in near ideal conditions; 24%

 

[priuspete]

Just a general note, since it's possible some are unaware: ECO Hi is the most-efficient operational mode for the climate control. Yes, counter-intuitive for most casual observers, but in this vernacular apparently 'Hi' refers to "highest efficiency".
Here in the warm flatlands of southwest Florida, it's providing very satisfactory performance.
As a datapoint, and apparently in the 'average user' category, 3.5 mi/Kwh is about what I'm managing at this time. AC operating full time, of course, and really enjoying the programmable pre-cooling (and also the remote operation of that feature as needed).
My employer has been kind enough to provide a Level 1 connection, so the programmed pre-cool doesn't compromise range.
Pete

 

[snoltor]

More potential good news on the question of whether hot climate affects battery performance / longevity. A Plug in America study reports that the Tesla Roadster 53kWh battery retains 80 - 85% of initial capacity after an average of 100,000 miles, and they found "no discernible effect of climate on battery-pack longevity. Roadster owners in hot climates are not seeing noticeably different battery capacity profiles than owners in moderate climates."

Hope this applies to us.

http://green.autoblog.com/2013/07/1...likely-to-perform-better-than-tesla-predicts/

 

[ground_gainer]

Just remember the Roadster has the climate control system for the battery running all the time (even when it is just parked). My brother-in-law's brother has one and I can confirm it runs when it is idle and no one is driving and it is not plugged in.

Our RAV4 EV's only run the climate control when in "READY" mode or when plugged in. I saw the article said it was researching the affect on the Rav4 EV so maybe they'll have some results soon?

 

[miimura]

I saw the article said it was researching the affect on the Rav4 EV so maybe they'll have some results soon?

GreenCarCongress.com says:

Plug In America has also launched battery-pack performance surveys of the 1997-2003 Toyota RAV4-EV and the new Tesla Model S. The RAV4-EV survey will document the 10-year experience of owners of these early electric vehicles.

This is a long term study of the old first generation vehicles. Totally non-applicable to our 2012+ RAV4 EVs since the first gen had NiMH batteries, among other differences.

 

[snoltor]

The article says the study is on first gen Rav4 EVs. Maybe we should contact Plug In America and suggest they start a survey on the second gen Rav4 EV.

http://www.pluginamerica.org/contact

 

[miimura]

The article says the study is on first gen Rav4 EVs. Maybe we should contact Plug In America and suggest they start a survey on the second gen Rav4 EV.

The question is, what meaningful data can we give them that they could track? I don't know of a way to get the car to report the amount of energy stored in the battery. We have no "Rated Range" or equivalent that is always proportional to the stored energy by a fixed constant. Please prove me wrong. I would like to follow that for myself.

 

[snoltor]

The question is, what meaningful data can we give them that they could track?

The only data we can provide is the range estimate after a standard or extended charge.

Here's the instructions from the PIA website for participating Roadster drivers:

"Before you start, you may want to go collect several bits of information from your car:

Current odometer reading
VIN sequence number
Assembly date
Ideal Miles/Km after a Standard and/or Range mode charge
Measuring Battery Capacity

To get a good reading of you battery capacity, you need to read the "Ideal Range" (not Estimated Range) from the charge state screen after waiting at least 10 minutes after the charge has completed. The reason for this is because often the value shown immediately after charging has completed is inaccurate. In the 10 minutes following the end of a charge (or drive) the Roadster takes additional measurements from the battery pack to calculate a more accurate estimate of the pack's stored energy."