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TomT
Posts: 10611
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Delivery Date: 01 Mar 2011
Leaf Number: 000360
Location: California, now Georgia
Contact: Website

Re: Idea for better highway efficiency

Thu Sep 12, 2013 10:24 am

This is very common on many vehicles due to the aerodynamics involved.

DougWantsALeaf wrote:Also at freeway speeds if back windows are open as wierd and painful wind echoing noise happens.
59,991 miles/12 bars/289 Gids/68.54 AHr/101% SOH/101.64% Hx 7May15 w/ new Lizard (barely made the warranty).
71,770 miles/12 bars/256 Gids/59.04 AHr/88% SOH/87.92% Hx 3Mar16 at lease return.

Now driving a 2016 Volt Premier.

DanCar
Posts: 984
Joined: Sat Apr 24, 2010 12:00 am
Delivery Date: 10 Mar 2013
Location: SF Bay area, 94043

Re: Idea for better highway efficiency

Thu Sep 12, 2013 11:47 am

dm33 wrote:... Thoughts? Any engineer types out there with design knowledge of the Leaf's powertrain?
As others have said, it is mostly due to air drag. https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_velocity . As your speed increases the power needed increases at a squared rate, rather than linearly.
Some solutions:
1. Have a prius or tesla model s look and make the car very aerodynamic
2. Electrify the freeways so vehicle is pushed along by magnets and can recharge the batteries. Similar to how maglev works: https://en.wikipedia.org/wiki/Maglev
3. Larger battery pack.

smkettner
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Location: Orange County, CA

Re: Idea for better highway efficiency

Thu Sep 12, 2013 1:48 pm

I think part of the effect is the battery is too small.
The Peukert effect is hurting the range as LEAF draws 10+ kW continuous.
Probably hurting longevity also.
JMHO.
1 bar lost at 21,451 miles, 16 months.
2 bar lost at 35,339 miles, 25 months.
LEAF traded at 45,400 miles for a RAV4-EV
I-Pace on order for end of 2018 delivery

GRA
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Re: Idea for better highway efficiency

Thu Sep 12, 2013 3:02 pm

smkettner wrote:I think part of the effect is the battery is too small.
The Peukert effect is hurting the range as LEAF draws 10+ kW continuous.
Probably hurting longevity also.
JMHO.

In the case of the LEAF vs. Volt (in CD mode), it's got to be aerodynamics plus gearing. The Voltec powertrain really is kind of trick. IIRR, at around 70 mph clutch 2 is engaged, which brings MG-A into the circuit (MG-B is the main traction motor. MG-A is the motor/generator) and unlocks the ring gear, halving the speeds of both MG-A and B. It's supposed to be good for about a 15% efficiency improvement.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

Yogi62
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Leaf Number: 405771
Location: Boston

Re: Idea for better highway efficiency

Thu Sep 12, 2013 3:25 pm

Is the rate of discharge part of the issue at high speeds?

does draining at 20KW for 30 minutes drain the same amount of energy from the batter as 5KW for 2 hours?

Faster charge (and discharge?) creates heat, which comes from somewhere.

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TomT
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Contact: Website

Re: Idea for better highway efficiency

Thu Sep 12, 2013 3:31 pm

No, due to internal battery resistance and other factors, higher drain for a shorter period depletes the battery faster.

Yogi62 wrote:does draining at 20KW for 30 minutes drain the same amount of energy from the batter as 5KW for 2 hours?
59,991 miles/12 bars/289 Gids/68.54 AHr/101% SOH/101.64% Hx 7May15 w/ new Lizard (barely made the warranty).
71,770 miles/12 bars/256 Gids/59.04 AHr/88% SOH/87.92% Hx 3Mar16 at lease return.

Now driving a 2016 Volt Premier.

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drees
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Re: Idea for better highway efficiency

Thu Sep 12, 2013 11:26 pm

smkettner wrote:The Peukert effect is hurting the range as LEAF draws 10+ kW continuous.
JMHO.

Actual testing data says that round trip efficiency goes up at higher speeds:

http://avt.inel.gov/pdf/fsev/fact2011nissanleaf.pdf

Peukert only applies to lead-acid. At moderate discharge rates lithium does not suffer from similar effects. The LEAF's battery can discharge at over 200 kW until it's nearly empty and it's internal resistance is under 0.15 Ohms.

At 10 kW and 360V, the pack is pushing about 30A. At 0.15 Ohms, you're only losing about 135W (P=I^2 * R) to internal resistance.

Even at 30 kW and 360V, the pack is pushing under 100A. Say it's 100A, that's still only 1500W. Pretty reasonable.
'11 LEAF SL Powered By 3.24 kW Enphase Solar PV

donald
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Re: Idea for better highway efficiency

Fri Sep 13, 2013 6:15 am

I still think field-weakening has something to do with this, as I noted in;

viewtopic.php?f=31&t=13767

Tesla has an induction motor. Renault (Fluence/Zoe) use a coil rotor. Volt has a gear set system that could, in theory, shift the motor's performance so it keeps its perm mag motor to its design for V/Hz.

Leaf flies out of its V/Hz range from some >35 mph, so I am lead to believe from its torque figures.

Tesla and Fluence have a Cd of ~0.25. Volt and Leaf are ~0.29. Real aerodynamics is not as linear as a bald Cd figure might lead you to believe (SCx for all are around the 0.66 m^2 figure), but the lower Cd should mean relatively lower impact from high-speed effects. Leaf might seem to suffer from relatively high aerodynamics, combined with the adverse effects of field weakening above its constant V/Hz range.

donald
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Re: Idea for better highway efficiency

Fri Sep 13, 2013 6:23 am

drees wrote:Actual testing data says that round trip efficiency goes up at higher speeds:

http://avt.inel.gov/pdf/fsev/fact2011nissanleaf.pdf


hmm... interesting.

I can't say that is quite my experience with the Renault battery. Keeping to/below ~15kW seems to be fairly optimal.

I would say you should look suspiciously at anyone saying drawing/charging above 1C is no less efficient than below. I guess if you aim for 1C at 22kW, then inevitably in practice you will be occasionally drawing 10kW and sometimes 30kW. Over that 1C hurts the range/capacity. I guess when I aim for 15kW I still get good mileage because my occasional 'power excursions' stay generally below the 25kW mark. These quoted tests probably benefit from being able to pull a steady 22kW, on some flat test track, without excursions above 1C

edatoakrun
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Leaf Number: 2184
Location: Shasta County, North California

Re: Idea for better highway efficiency

Sat Sep 14, 2013 8:33 am

donald wrote:
drees wrote:Actual testing data says that round trip efficiency goes up at higher speeds:

http://avt.inel.gov/pdf/fsev/fact2011nissanleaf.pdf


hmm... interesting...


See the footnote:

9. The Battery Roundtrip Efficiency is calculated by dividing the DC energy out of the battery (A) by the DC energy from the on-board charger into the battery (D).


If I understand correctly, much or all of the variation reported as "Battery Roundtrip Efficiency" could also be explained by variations in the "100%" charge allowed by the LEAF's BMS/LBC in the post test "100%" recharge session.

This is also, IMO, one of the most likely explanations for the lower recharge capacity shown by the LEAF following the higher-speed tests.

CONSTANT-SPEED RANGE AND CHARGE TESTING


http://avt.inel.gov/pdf/fsev/fact2011nissanleaf.pdf
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