KeiJidosha
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 2:29 pm

JeremyW wrote: ...Honestly, with the leafs quick charging and getting a staggering 1.5 mi/kWh on the course, these batteries didn't heat up much at all. Tony "lead foot" Williams quick charged after each event, and only got up to 7 temp bars. I can see now why they thought they could get away with out a thermal management system because driving doesn't put much stress on the pack. They must be very low resistance cells. There was a BMW with an overheated battery, and the Volts were mysteriously gone after the first practice run (although I see in the results at least two were in the TT). One of the conversions (with thundersky LiPO4's) apparently was having battery trouble too. There's no doubt that racing puts a lot of stress on the cars, and the leaf handled it with ease. I came away from the event more impressed with the Leaf...
For a vehicle without thermal management, the LEAF's ability to run cool is striking. The MINI E had a temp alarm (>114°) after 3 laps last year and was over 125° in the pits before starting to cool.
- 2009 BMW MINI E > 2013 Honda Fit EV > 2017 Chevy Bolt EV
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TEG
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 3:20 pm

It seems the enemy of the LEAF is prolonged high ambient temps.
Leaving it parked at 100% SOC in the desert in summer seems to be the "bad use case".
With mild climate, it doesn't seem that driving style bothers it much.

tbleakne
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 6:07 pm

KeiJidosha wrote:
JeremyW wrote: ...Honestly, with the leafs quick charging and getting a staggering 1.5 mi/kWh on the course, these batteries didn't heat up much at all. >>>>
For a vehicle without thermal management, the LEAF's ability to run cool is striking. The MINI E had a temp alarm (>114°) after 3 laps last year and was over 125° in the pits before starting to cool.
This is all consistent. As I have reported before, the Gid meter shows that 30 kW power level heats the battery about 1 kW, and 40 kW heats the battery about 1.8 kW. These are relatively low values. An ambient temperature 20 F above the battery temperature probably heats the battery at a higher rate, and what really counts is how long the battery stays at an elevated temperatue. To calculate this, we would need to estimate the thermal resistance between the battery pack and the ambient air. Temperature data from LeafScan will allow us to calculate this.
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surfingslovak
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 6:40 pm

tbleakne wrote:
KeiJidosha wrote:
JeremyW wrote: ...Honestly, with the leafs quick charging and getting a staggering 1.5 mi/kWh on the course, these batteries didn't heat up much at all. >>>>
For a vehicle without thermal management, the LEAF's ability to run cool is striking. The MINI E had a temp alarm (>114°) after 3 laps last year and was over 125° in the pits before starting to cool.
This is all consistent. As I have reported before, the Gid meter shows that 30 kW power level heats the battery about 1 kW, and 40 kW heats the battery about 1.8 kW. These are relatively low values. An ambient temperature 20 F above the battery temperature probably heats the battery at a higher rate, and what really counts is how long the battery stays at an elevated temperatue. To calculate this, we would need to estimate the thermal resistance between the battery pack and the ambient air. Temperature data from LeafScan will allow us to calculate this.
I believe that this is essentially by design: there is no insulation. The battery is heat-sunk in the chassis; it can dissipate heat into the entire body of the vehicle, and then ambient air. If the battery was insulated because of active cooling, the TMS could get overwhelmed on the track, and waste heat might not be dissipated fast enough. Combine this with our collective observation that the Leaf develops very little operational heat, and we get nearly unmatched (save Model S) thermal performance on the track. That said, your heat loss estimates look a bit high: I'm getting about half that using 400V pack voltage and 100 mOhm internal resistance. Image

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TonyWilliams
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 7:34 pm

surfingslovak wrote:The battery is heat-sunk in the chassis; it can dissipate heat into the entire body of the vehicle, and then ambient air.

I disagree that the LEAF battery is heat sunk. There are only six small contact points from the battery to the chassis. It's actually the opposite of a heat sink.

Imagine the car sitting in 122F / 50C Phoenix with the sun heating the sheet metal and interior to 140F / 60C or above. If the battery were heat sunk to the chassis, that scenario would tend to heat the battery, not cool it.

The times when the chassis is cool, the battery seems to only get got from repetitive QC-ing. I've observed the battery COOL DOWN from 136F while driving almost 90 miles. Only one scenario would not provide cooling of the battery, according to the CODA engineer that extensively tested the LEAF; that is, repetitive uphill with stops on the hill and at gross weight.

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surfingslovak
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 8:12 pm

TonyWilliams wrote:Imagine the car sitting in 122F / 50C Phoenix with the sun heating the sheet metal and interior to 140F / 60C or above. If the battery were heat sunk to the chassis, that scenario would tend to heat the battery, not cool it.
I think we might be going off on a tangent, but perhaps it's an interesting one. Yes, you are right, that would be a distinct implied disadvantage of this design. To be honest, I don't know how well the body acts as a heat sink. It would appear logical, and it's been repeated here a few times. I will try to dig up a few other sources, if they existed.

Aside from Luke's recent data, we don't know much about solar loading in Phoenix. His battery seemed to stay relatively cool. Unfortunately, he did not record ambient temps and only had the max daily temp for Phoenix available.

Image
TonyWilliams wrote: The times when the chassis is cool, the battery seems to only get got from repetitive QC-ing. I've observed the battery COOL DOWN from 136F while driving almost 90 miles. Only one scenario would not provide cooling of the battery, according to the CODA engineer that extensively tested the LEAF; that is, repetitive uphill with stops on the hill and at gross weight.
Interesting! Would you know if CODA instrumented the car better? One would hope so. Any other observations they shared?

I remember reading something from Nissan implying that more heat was developed during charging than driving. There was another debate about how the charging proces was endothermic. I don't believe that it is. I'm pretty sure that discharge is not endothermic either, although very little heat is developed under normal circumstances. With that I aree.

At what rate did heat develop in the battery when racing on the track? If it was around 1 kW, perhaps it was simply absorbed by the battery mass? If Leaf's battery pack was not heat sunk, the only explanation would be vastly superior battery chemistry. While that's a possibility, I would have hard time believing that.

For what it's worth, although my instrumentation is non-existent, I believe that the battery pack in the ActiveE heats up faster. Perhaps twice as fast as in the Leaf. It could be my location, but with the exception of cooler temps after level 2 charging, I have never once perceived the benefit of active cooling in that car.Image

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DaveEV
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 9:43 pm

surfingslovak wrote:Aside from Luke's recent data, we don't know much about solar loading in Phoenix. His battery seemed to stay relatively cool. Unfortunately, he did not record ambient temps and only had the max daily temp for Phoenix available.
Looking at the weather data for that day at Wunderground, it appears that it was around 109F between 5-6pm at the Phoenix airport.

http://www.wunderground.com/history/air ... atename=NA" onclick="window.open(this.href);return false;

I checked a few other stations and they reported similar temps - no more than a degree or two different.

nader
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 9:54 pm

A few pics from Sunday.

Image

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DaveEV
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 10:14 pm

Car looks awesome, nader - you've got to spill the beans on your setup and how it handled on the track. Only a few seconds off the times the fastest Roadsters were setting...

nader
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Re: Event - REFUEL at Mazda Raceway Laguna Seca 07/01/12

Tue Jul 03, 2012 10:41 pm

The goal of the day for me was preservation of speed. Last year I ran a 2:10.xx. I was hoping for a 5 second gain and was pretty happy when I heard the 2.02.883 time. Of course the Leaf is way under powered for a track like Laguna Seca so the strategy this year was to put on a sticky tire, in this case it was a set of 225/40/18 Falken Azenis RT615 mounted to 18x9 Enkei RPF1 (35mm offset) with a 3mm spacer up front to clear the caliper. This combo is one pound heavier than stock.

The suspension is a prototype setup by KW with a 13mm rear sway bar. Alignment was set to -1.8 degrees camber with factory toe settings. The rear is not easily adjustable, but was within spec. The rear bar is pretty benign, but you can get off throttle oversteer. The only problem is that the stability control is set so conservative that the once the car starts to rotate the ABS kicks in to stop the fun. I was able get pretty good trail brake oversteer in turn 10 until the ESP kicked in. I did try removing a relay awhile back which I assumed disabled the ESP and ABS. All sorts of dash lights came on as a result. I was unsure about testing it since it would require pushing the car beyond the the limit on public streets so I left well enough alone.

I bled the brakes the day before which made a huge difference in pedal feel. This was after having a few autocrosses and last years ReFuel event. I should have done this sooner. The stock brakes did well with only a touch of fade at the end of a 15 minute session. Remember that the car isn't fast so I'm not trying to scrub a whole lot of speed before the turns.

Wish list for Nissan: disable ESP or offer detuned modes to allow some fun, but keep ABS functioning. Reduce steering power assist to increase road feel. It is pretty numb. I can drive one handed on the track if I wanted too.

Does the car have a sub 2 minute lap time in it with race rubber? We'll have to see about that next year...

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