May 03

Volt Battery Thermal Management System in the Hot Arizona Sun

 

By George S. Bower

The Volt has a very sophisticated thermal management system. The high voltage battery temperature band is strictly controlled with an active liquid cooling system AND the battery only uses 65 percent of its capacity which should result in a long life.

An excellent discussion of the TMS system written by our own WopOnTour is given here. A schematic of the battery cooling system from that article is presented below in figure 1

Slide1
 

What is the Volt Battery TMS Temperature Band?

 

We have speculated here that the temperature band was 68 F to 72 F which is an ideal range for Lithium batteries. In order to find that temperature band, data was taken using DashDAQ data acquisition device on a hot summer day while charging. Prior to charging, the Volt was parked in full sun for 3 hours and then moved into the garage for charging.

The TMS data taken during charging is presented in figures 2 thru 4.

Slide2
Slide3
Slide4
 

We see from these figures that the Volt’s TMS switches on at 86 F and cools the Volt’s battery via the cars electric A/C compressor to 72 F and then shuts down. This 72 F to 86 F temperature band is somewhat higher than we had speculated.

What Happens if the Volt is Parked all Day in Full Sun?

 

What happens if the Volt is parked in the hot sun with ignition (power) off and NOT plugged in? This would be the scenario for many Arizona workers that park their cars in full sun on a black asphalt parking lot all day. How hot will the Volt’s battery get?

In order to determine, Volt was parked for a day in full sun. Results of this test are presented in figure 5. We see that the Volt’s battery is extremely well insulated. With cabin temperatures soaring to 115 F and ambient air temperatures going to 99 F the Volts battery only reached a maximum temperature of 90 F. Roughly equal to the upper limit during active thermal management during charging shown in figure 2 . We also note that there is NO ACTION taken by the TMS in this case.

Slide5
 

It occurred to me that perhaps there was no action by TMS because the battery was at a 5-percent SOC. Therefore I repeated the test with the battery at 81-percent SOC and the results were unchanged ie there was NO ACTION taken by TMS and battery temp reached 91 F.

How hot would the Volts battery get if ambient air temperature reached 110-120 F as is common at the peak of summer? The answer is that we do not know yet. I do not have data at these extreme temperatures so all we can do at this point is SPECULATE. If the TMS system stays inactive at these high temps, then we could see battery temperatures of 100+ degrees at the peak of summer.

What Happens if we Leave the Ignition (power) on?

 

In the referenced GM-Volt.com thread it was suggested that one might mitigate battery temperatures by leaving the Volt powered on.
Data was taken during a hot soak with power ON (and NOT plugged in) and data was recorded using DashDAQ. The data is presented in figures 6 thru 8.

Slide6
Slide7
Slide8
We see the following from these figures
 

1. Coolant loop pump and cooling fan were on the entire time.
2. A/C chiller cycled on and off maintaining the battery between 73 F and 90 F.
3. This resulted in a substantial loss in battery charge of 30 percent.
4. The flow control valve cycled between radiator (position C in schematic figure 1) and Chiller (see figure 7 and figure 1).

This flow control valve programming is unexplained at this point in time. Since outside air temperature was hotter than battery coolant temperature this actually resulted in heating the battery faster than when the ignition OFF hot soak. Note that during the charging test presented in figures 2 thru 4 the flow control valve cycled between BYPASS and Chill as would be expected. GM must have a reason for this programming but I do know what that reason is.

As a bottom line, leaving the Volt powered on all day in the parking lot DOES NOT seem like a prudent thing to do. I would think that a short power on (remote engine start) would be OK but that to only leave power on long enough to cool the battery via A/C chiller and then turn power off.

What to Do?

 

If the predicted (ambient) high temperature is less than 100 F don’t do anything.
If the predicted high is higher than 100 F, still not to worry. If you were supposed to worry about it GM would have provided a read out of battery temperature to the general public. As said earlier I don’t have battery temperature data above 100 F anyway (stay tuned).

However, if you are a conservative type, it wouldn’t hurt to take some precautionary measures on super hot days.

The following steps would help mitigate battery temperatures on days where the predicted high is above 100F:

1. Park in the shade.
2. Use window shade screens.
3. Plug in if possible.
4. Perhaps do a remote start late in the afternoon. (Caution engine could come on). However, I would only do the remote start long enough to cool the battery and then discontinue remote start for reasons discussed above.

This entry was posted on Friday, May 3rd, 2013 at 5:55 am and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

COMMENTS: 46


  1. 1
    Eric Crowder

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    May 3rd, 2013 (7:18 am)

    Great data analysis. Looking forward to see results from car off unplugged hot soak with hotter ambient temp. I would also like to see TMS behavior with car plugged in AFTER charging is complete, and especially behavior with car hot soaking and plugged in set to delayed charge. I have a suspician that when plugged in and set to delayed charge, TMS does not activate until charging starts. I would like to be proven wrong. Thanks

    -Eric in Texas


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    James McQuaid

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    May 3rd, 2013 (7:21 am)

    George, thank you for a super interesting and informative write up! The selection of your test data, drawn comparing various scenarios, is quite revealing.

    I wonder how much those of us who park in full sun would benefit from a car cover made from highly reflective material (i.e. like a “space blanket”)?


  3. 3
    statik

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    May 3rd, 2013 (8:09 am)

    Next time put a little effort into your writing George!

    …just kidding, that was a great piece, we learned some interesting/new stuff from it. I appreciate the read, and your effort, a lot!


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    Eco_Turbo

     

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    May 3rd, 2013 (8:22 am)

    Great article, George, very interesting to me at least at how complicated that system needs to be. I think the requirement that these batteries last 8 years needs to go though. Imagine how expensive gas car starter batteries would be if they were required to last 8 years. Plus it seems that battery prices are on the way down anyway. It might be cheaper to replace than baby these batteries.


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    joe

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    May 3rd, 2013 (8:29 am)

    Most people who buy the Leaf are not aware about the Volt’s superior battery temperature management system over the Leaf. If they did, they would probably buy a Volt instead, I know I would. The extra cost would be well worth it for peace of mind. Also, I’m sure the resale value will be much better with the Volt.

    Thanks for making us aware of it.


  6. 6
    kdawg

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    May 3rd, 2013 (8:35 am)

    What about the cabin heating system for winter time, and changing it to a heat pump vs. resistive heating?

    OT: Saw my first C-Max Energi in the wild yesterday. It was on a semi-truck trailer, but that still counts! :)


  7. 7
    kdawg

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    May 3rd, 2013 (8:45 am)

    As a bottom line, leaving the Volt powered on all day in the parking lot DOES NOT seem like a prudent thing to do.
    ————–

    Yes, I agree. Even with very hot temps out the Volt’s battery only climbed to 90, with the car off. When it was on, the TMS kept driving the temp back down to 73, then it would take 2hrs to climb back up to 90. However, even in this 8-hour worst case scenario, the battery only loss less than 1/3 of its SOC. Not too bad.


  8. 8
    George S. Bower

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    May 3rd, 2013 (8:51 am)

    James McQuaid:

    I wonder how much those of us who park in full sun would benefit from a car cover made from highly reflective material (i.e. like a “space blanket”)?

    If you use a car cover AND decide to do a remote start (or anything that would activate the TMS), then care must be taken not to cover up the radiator intakes on the front of the car.


  9. 9
    George S. Bower

     

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    May 3rd, 2013 (9:07 am)

    kdawg:
    As a bottom line, leaving the Volt powered on all day in the parking lot DOES NOT seem like a prudent thing to do.
    ————–

    Yes, I agree.Even with very hot temps out the Volt’s battery only climbed to 90, with the car off.When it was on, the TMS kept driving the temp back down to 73, then it would take 2hrs to climb back up to 90.However, even in this 8-hour worst case scenario, the battery only loss less than 1/3 of its SOC.Not too bad.

    yes, 2 hours to go back to 90 versus SIX hours if the car is not powered up. I’m very curious about this flow control valve programing. I can’t explain it. There is no reason to be sending coolant to the radiator if radiator air side temp is HIGHER than coolant temp. Looks like a programming error to me.


  10. 10
    George S. Bower

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    May 3rd, 2013 (9:16 am)

    statik:
    Next time put a little effort into your writing George!

    …just kidding, that was a great piece, we learned some interesting/new stuff from it. I appreciate the read, and your effort, a lot!

    Thx Jay,
    It was a lot of work. Many days. Also, since DashDAQ sampling rate is 1 data point per millisecond and it is not variable so I could not auto record the data. All data was recorded manually on custom made data sheets. Reminds me of the good old days at AiResearch when all data was taken manually off of such advanced instruments as “water or mercury manometers”.

    Those were the days boy. When men were men and good engineers had horn rimmed glasses, a slide rule on their belt and a pocket protector.


  11. 11
    Nelson

     

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    May 3rd, 2013 (9:22 am)

    Remote start should only keep the car on for ten minutes.
    Chrome vinyl roof wrap may be an option.

    NPNS!
    Volt#671


  12. 12
    KNS

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    May 3rd, 2013 (10:31 am)

    George S. Bower: Those were the days boy. When men were men and good engineers had horn rimmed glasses, a slide rule on their belt and a pocket protector.

    George,

    Your effort is much appreciated.

    OT: I still have my K&E Log Log Duplex Decitrig. :-)

    KNS


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    DrInnovaiton

     

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    May 3rd, 2013 (10:49 am)

    Nice write up george. Curious what happens if fully charged, plugged in but off and it then gets hot outside (e.g. sitting charged at home or the airport for the weekend)

    Finally, some advantage to OBDII over a dashdaq other than cost.. at least I can sample at variable rates :-)


  14. 14
    Jackson

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    May 3rd, 2013 (10:59 am)

    In the early days of this site, when little was actually known about the Volt, there was a great deal of wide-open discussion and speculation, even about EVs in general. One recurring theme involved placing solar cells on the roof of an electric car to recharge it when parked in the sun. There was a lot of back and forth on the subject, the upshot being that you would pay a very great deal for very little benefit. Under what circumstance could you justify the cost? Perhaps this one. Would a battery pack retain more of it’s lifespan if solar cells could power cooling fans and pumps? Would this have enough economic benefit to justify the costs? Or do you think that coming battery types are more likely to achieve greater native heat tolerance?

    Maybe you slide-rule boys could take a SWAG. ;-)


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    BLIND GUY

     

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    May 3rd, 2013 (11:14 am)

    Thanks George for your efforts and all the great info. The Volt was clearly the best EV choice for us in AZ. For people with K9 passengers or if you need to go in a store for 10-15 min. you can leave the car on & keep the AC on eco without burning gas as long as you have the SOC to spare  K9 owners may want to post a sign; letting people know That the AC is on & not to break your window.


  16. 16
    CaptJackSparrow

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    May 3rd, 2013 (11:23 am)

    “3. Plug in if possible.”

    So, if you have a full charge, it’s OK to use/occupy the charge station for just battery thermal purposes?
    :-P

    /just pokin da skunk……


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    vdiv

     

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    May 3rd, 2013 (11:24 am)

    George, this is really good, thank you. I think the GM Tech Center should offer you a position :)

    As others have mentioned it will be interesting to see what the TMS does when the Volt is plugged in, fully charged, and turned off, soaking in the sun. After all there must be a reason why GM recommends keeping the Volt plugged in.


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    vdiv

     

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    May 3rd, 2013 (11:27 am)

    CaptJackSparrow,

    Absolutely, as you know for two possible reasons:

    1. You are paying for the charging spot (for the time or even per kWh).
    2. Preconditioning the car before you take off would preserve the full range.


  19. 19
    Mark Z

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    May 3rd, 2013 (11:36 am)

    Thanks George for a very informative article.

    With afternoon summer sun causing a rise in garage temperature, I am tempted to install a fan at the garage vent to circulate air. One problem is the gas water heater. If I push air out, then exhaust fumes may be pulled into the garage area. At this point it may be better to pull outside air from a lower vent to help remove the super heated air in the garage. A thermostat will start the fan only when necessary.


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    Sam Jaffe

     

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    May 3rd, 2013 (11:41 am)

    Jackson,

    Completely covering the roof and hood with solar panels would, at best, provide only 15% of the power needed to keep the cabin temperature controlled. I would assume that the battery TMS would require even more power. Now add to that the extra efficiency cost of the extra weight and aerodynamic drag of the panels and you’re in deep negative territory. Solar panels on vehicles might one day make sense for long haul trucks and Fed-ex type delivery vans (for auxilliary power only–never for motive power), but I don’t see them ever becoming practical on passenger vehicles.


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    Larry4pyro

     

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    May 3rd, 2013 (11:41 am)

    Once again thanks George, great study. Your articles should be combined into a reference book for Gen 1 Volt owners.


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    Jim I

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    May 3rd, 2013 (11:54 am)

    Usually the “tech” posts leave me with glazed over eyes, but this one was very interesting!

    Good job.

    And what is wrong with pocket protectors?????

    :)

    C-5277


  23. 23
    Fredo

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    May 3rd, 2013 (12:01 pm)

    Very nice write up.

    To help mitigate battery temperatures on days where the predicted high is above 100F I would add to your 4 bullets:
    - Do not leave the car with high SoC if not plugged in. Below 70% may be a good compromise.
    - Crack open the 4 windows (an inch), this will drop cabin temperature significantly.

    I too monitored SoC (using a script on this forum) during L2 charging and noticed the same inflection point as you seen on fig.2B between 13:00 and 13:15. It seems to match when the chiller starts for the 1st time and draws maximum power from the wall leaving less power for the battery.
    However, the weird thing I noticed is that even during the winter when the car was left in freezing temperatures, charging the car after a 20 minute trip shows the same notch in the charging curve. It might be because this time the heater is turned on for some time.


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    Kent

     

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    May 3rd, 2013 (12:02 pm)

    Jim I:

    And what is wrong with pocket protectors?????

    They cover the logo of my Polo shirts. When I’m wearing a $100 shirt I want people to know I’m wearing a $100 shirt!


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    Evan

     

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    May 3rd, 2013 (12:21 pm)

    Now what happens during a cold soak? That would be a lot more interesting to be, being in NH.


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    kdawg

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    May 3rd, 2013 (12:38 pm)

    Evan: Now what happens during a cold soak? That would be a lot more interesting to be, being in NH

    To me too. It’s finally in the 70s here in Michigan. Was nice to get in my Volt this morning with an actual “40″ miles of range showing! I’m using less than 250wH/mile now.


  27. 27
    kdawg

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    May 3rd, 2013 (12:40 pm)

    OT: but might be a good read for the weekend.

    MAY 2013
    What If We Never Run Out of Oil?
    New technology and a little-known energy source suggest that fossil fuels may not be finite. This would be a miracle—and a nightmare.
    CHARLES C. MANN APR 24 2013, 9:58 PM ET

    http://www.theatlantic.com/magazine/archive/2013/05/what-if-we-never-run-out-of-oil/309294/?single_page=true


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    Raymondjram

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    May 3rd, 2013 (1:15 pm)

    George S. Bower

    Those were the days boy. When men were men and good engineers had horn rimmed glasses, a slide rule on their belt and a pocket protector.

    I was one of those (except for the glasses – mine were black plastic)!

    Raymond


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    WVhybrid

     

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    May 3rd, 2013 (2:20 pm)

    Thank you, George. That was very informative. Good job!


  30. 30
    Streetlight

     

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    May 3rd, 2013 (3:24 pm)

    George S. Bower: Those were the days boy. When men were men and good engineers had horn rimmed glasses, a slide rule on their belt and a pocket protector.

    George: A well done analysis.

    To us in the 60′s-70′s design engineering world, AiResearch’ name was magic. Then just the mention of AiResearch — heads all nodded.

    Couple things. I took cabin temps to understand temp needs for a car-installed product in 1982. In Sunnyvale (Calif) it gets pretty warm. My dash temp recorder, a 24-hour rotary hand-held pen deal (You’ve seen these, very low cost devices then) recorded typically over week or so temps exceeding 140 degrees F. That is, between the windshield and top of dash. Later I subscribed to SAE’s then set of car specs and decided it had to meet -40 degrees C to +80 degrees C temp range. (And later I called this out to folks concerned with out-gassing (which my product inadvertently detected) of imported plastic material.)

    One other note: Isn’t there concern about reflected pavement temp under the battery location?


  31. 31
    Loboc

     

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    May 3rd, 2013 (4:32 pm)

    Having covered parking should be a must when the temps soar over 110. Even normal cars would benefit since cooking the lead-acid battery is pretty expensive any more. (last one I bought was $180 bucks!).

    What I don’t get is that you can’t remote-start more than twice before needing to do a ‘real’ start. What is the thinking around that design feature? Heck, when I’m on grid power, let the car keep itself cool/heated as needed.


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    Loboc

     

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    May 3rd, 2013 (4:40 pm)

    Streetlight: temps exceeding 140 degrees F.

    When I first moved to Texas, I put a meat thermometer on the blacktop in front of my house and hit 134ºF in the open air!


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    James

     

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    May 3rd, 2013 (4:49 pm)

    George, you’re great.

    Nice to have technical information like this which makes GM-Volt a better
    site than say – PriusChat.com which seems more like guys talking about
    the latest wheels they bought for their Prii, than real technical info people
    can use.

    I’d like a sunroof/solar roof option to keep the interior cooler. Such options
    on the current Prius don’t totally cool the interior, but do make a difference
    which would appropriate for hot climates like Phoenix.

    RECHARGE! ,

    James


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    Mike

     

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    May 3rd, 2013 (6:45 pm)

    I see the cabin air temperature going far above the ambient air temperature in the graphs.

    We have very hot summers where I live. Before I had a charger at work, I used the Volt car cover as recommended in the owner’s manual. The cabin air temperature stayed below the outside air temperature and I’m sure the HV battery benefited as well.


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    TedinFortMyers

     

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    May 3rd, 2013 (7:59 pm)

    Thanks George,
    We are moving to Arizona in the next couple of years. I really learned alot and it will help us to get the most out of our Volt/Volts when we move to Havasu. We seldom reach the temperatures in Fort Myers Florida which will have the adverse effects you mentioned. I will make certain if seeking employment in Havasu that we have a charge station and can remained plugged in during the heat of the day.
    Take Care, TED


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    George S. Bower

     

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    May 3rd, 2013 (8:30 pm)

    James:

    Nice to have technical information like this which makes GM-Volt a better
    site than say – PriusChat.com which seems more like guys talking about
    the latest wheels they bought for their Prii,

    RECHARGE! ,

    James

    Yeh I know , the Prius is so boring. I’m thinking some moonies might spice it up , but it really isn’t worth the effort.


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    George S. Bower

     

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    May 3rd, 2013 (8:34 pm)

    TedinFortMyers:
    Thanks George,
    We are moving to Arizona in the next couple of years.
    Take Care, TED

    Welcome Ted!!


  38. 38
    George S. Bower

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    May 3rd, 2013 (8:36 pm)

    Raymondjram: I was one of those (except for the glasses – mine were black plastic)!

    Raymond

    Yes Raymond.
    That is why I always read every one of your posts!


  39. 39
    George S. Bower

     

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    May 3rd, 2013 (8:50 pm)

    Eco_Turbo:

    It might be cheaper to replace than baby these batteries.

    Your point has some validity in light of the fact that the upper limit of GM’s system up to 90F.

    However, as of right now, battery prices have the strongest influence coefficient. So one is better off gambling on the conservative side.

    Nissan has taken the opposite approach you are talking about……and we see a Leaf that is 10K LESS than the Volt……but having problems in AZ.

    Which approach will win??

    Right now from a consumer POV (at least an AZ consumer). I’d take GM’s approach.


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    ItsNotAboutTheMoney

     

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    May 3rd, 2013 (11:11 pm)

    joe:
    Most people who buy the Leaf are not aware about the Volt’s superior battery temperaturemanagement system over the Leaf. If they did, they would probably buy a Volt instead, I know I would.The extra cost would be well worth it for peace of mind. Also, I’m sure the resale value will be much better with the Volt.

    Thanks for making us aware of it.

    Reasons to buy a Leaf instead of a Volt:
    1) You don’t live in the middle of a blisteringly hot desert so you won’t suffer rapid degradation.
    PLUS
    2) It’s cheaper, even compared to good deals on the Volt AND/OR
    3) You commute beyond the Volt range and want to minimize gas consumption AND/OR
    4) You already have a Volt and don’t need another one


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    kdawg

     

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    May 3rd, 2013 (11:24 pm)

    TedinFortMyers: We are moving to Arizona in the next couple of years.

    You’ll have to change your handle to TedinArizona
    :)


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    Shaft

     

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    May 4th, 2013 (12:00 pm)

    If the car is plugged in, charging and on, then will the temperature be controlled? I’m guessing yes, but the scenarios above do not nail the answer.

    If the car is plugged in, fully charged and on, then will the temperature be controlled? I’m guessing yes, but the scenarios above do not nail the answer.

    If the car is plugged in, fully charged and off, then will the temperature be controlled? Figure 2 indicates that the answer is yes.

    I wore horned rim glasses, and certainly sported a slide rule and pocket protector during my engineering years. But my university son’s engineering friends think my Volt is pretty cool. So, I guess I’ve become pretty cool!


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    engineer

     

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    May 4th, 2013 (2:14 pm)

    From an older engineering powertrain seminar (~2010) the RANGE the pack can be is 0-32C.

    ( http://gm-volt.com/forum/showthread.php?5529-Saw-my-first-Volt-I-like. )


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    kdawg

     

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    May 5th, 2013 (4:46 pm)

    Argh, haven’t used gas in a couple months and “Engine needs to run for maintenance” alert came on today :(


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    George S. Bower

     

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    May 5th, 2013 (5:33 pm)

    I just ran thru a little calc on how much juice was used to keep the battery cool during the charge from the graphs above. The compressor’s kw is shown in the plots. I didn’t have the power for the coolant pump and the cooling fan so I just assumed it would be 10% of the total compressor kwh.

    The number I came up with was 1 kwh. Since we are putting in 10 kwh INTO the battery this 1 kwh amounts to a 10% loss in charging efficiency.

    The EPA sticker numbers imply an 80% charging efficiency. I wonder how much of the 10% loss I calculated here is included in the EPA numbers……ie if I had had a kill a watt meter at the wall when I charged I wonder what the number at the wall would have been.

    any ideas?


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    Joule Thief

     

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    May 5th, 2013 (5:46 pm)

    George, thanks for the data. I’ve been doing some research on Mitsubishi’s TMS for the upcoming Outlander PHEV. What’s interesting is, according to reports from Mitsubishi, they only use the chiller during DC fast charging. During L2 charging they only circulate ambient air. And of course they use an air medium rather than liquid. It makes me wonder how well it will hold up here in Phoenix. So far the i-MiEVs seem to be holding up well here in AZ compared to the Leafs. So if GM’s TMS is top-of-the-line and Nissan’s is at the bottom then I suppose Mitsubishi (and Toyota) are in between.

    Something else I’ve been thinking about is, given Li-ion batteries are more sensitive to temperatures at higher SOCs, for battery longevity I wonder if it’s better to leave a car on an empty battery (20% SOC in the Volt’s case) and unplugged in the hot sun or is it better to keep it plugged in and charging where yes the TMS is on but then you’re also increasing the SOC as you charge (which is flowing current and generating heat). In other words would you rather have a battery at 90-100 degrees with a 20% SOC or a battery at 72-86 degrees with an 85% SOC. Maybe it would be good to have a “TMS Only” option when you plug in that doesn’t charge the battery.

    Maybe we can meet up sometime, I think we’re overdue for an AZ Volt owners gathering :)