My Leaf Stats : Range vs Temperature

TomT said:

My efficiency has been very consistent. I reset my M/Kwh on the center display every month and is has never varied more than one tenth from 4.5 since I picked up the car on March 1st...

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Do you use heater at all ?

In the last 2 months I've dropped from 4.6 at the peak this summer/fall to 3.8. It kind of snuck up on me because I was away for a bit and my sister in law came to visit while I was gone. She arrived being very skeptical of the car, did a good bit of the driving in it while I was away and left wanting to buy one. Her parting words to me were that she was surprised how fast it was. Between my wife and she I thought the drop was due to driving style but now that I've been the primary driver again for a month I've found no way to get the MPkW back up to what I used to get. Then I pulled up the energy screen and noticed that I could not turn off the heater, that when it gets below 60 outside that climate control has a mind of it's own. At one point I preheated a lot and the whole car turned into a sauna and fogged up. I left the doors open overnight for a couple of nights to dry the car out, and it turns out that has helped reduce the use of defrost, the car had retained quite a bit of moisture over time... something folks might want to keep tabs on if they are constantly having to use defrost. We exhale quite a bit of moisture over time which can soak up in the cushions.

Reading through the posts here and struggling with the heater and driving techniques I am still a bit puzzled as to what is really causing the dip in efficiency.

I really wish I could turn off climate control and still use the circulating fan, isolating out the heating/cooling/defrost tug of war I find myself in. As I've stated in another thread, I'm very surprised to see what looks like a 20% drop in efficiency with what seems like a relatively mild drop in night time temperature. Very curious to see how the colder regions fair.

Curious if folks with heated and or insulated garages are seeing less loss in range/MPkW? Is this really all about density of air and Climate control... hard for me to believe, but what do I know.

this cold whether range issue is a formidable challenge, I'm looking forward to finding out if this ingenious group we have here can come up with a work around.

The only factor for me then would be the denser air since I haven't used heat or pre-heating yet, and I find it hard to believe that denser air (temp in the 60's) is going to cause a .5-.8 m/kW h drop. The last three days have been about 17 degrees below normal and my temp gauge has stayed at 5 bars.

johnr said:

The big question is, is the climate control responsible for most of this? Or is the battery performance alone affected to such an extent by temperature?

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Here's what I came up with from today's rare rainy and cold day here in otherwise sunny San Diego.

I had the worst economy that I've every gotten, on a cold (53F) rainy day. I started with 100% charge, and completed the day with 47 miles driven at 2.9 miles per kilowatt; that's 61 miles of range at normal battery temps using the 21kWh useable battery capacity model. Since I hit "Low Battery" just as I returned home, I only had less than 9 miles remaining, so 56 miles max range for the day (47 driven plus 9 left at 2.9m/kWh).

Factoring backwards, with 21kWh normally available at 70F, at the lower temp, is appears that only about 19.3kWh were available... about 8% less (56 miles / 2.9). That checks good with -1% per 2F degrees less than 70F, or 17 degrees difference (from 53F) diivided by 2F is 8.5% reduced battery useable capacity caused strictly from the ambient temperature on the battery.

Of course, my heater usage is factored into the 2.9m/pKw, where I normally would get close to 4.

NOTE: None of my range predictions are based on the GuessOmeter or CarWings.

dgpcolorado said:

I am surprised that more people don't realize the role that air density plays. There are a number of pilots here at MNL and air density and drag has been discussed before. For driving above about 35 mph and, especially, at highway speeds cold air and drag is a very big deal.

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Also cold tires have higher drag, even when dry and you also have thicker oil/grease in the differential used in the Leaf. The temperature of the transmission oil in a Prius affects the mpg you get, it has to get quite hot for best efficiency. Dry air is also denser.

I'm not sure temps in the 50s are enough to reduce the capacity of the batteries, reduce the power yes but not the capacity. At higher power levels you would have higher losses due to IR but should not be too bad at lower speeds, I hope.

Here is a chart that shows the change in air density with temperature. The first and third columns are the ones that interest us. We pilots are used to expressing this change as density altitude: The effective altitude at which the plane feels like it is flying taking in to account the actual altitude and the prevailing temperature..

Effect of temperature:
Temperature Speed of sound Density of air Acoustic impedance
Temp in C c in m·s-1 p in kg·m-3 Z in N·s·m-3
+35 351.96 1.1455 403.2
+30 349.08 1.1644 406.5
+25 346.18 1.1839 409.4
+20 343.26 1.2041 413.3
+15 340.31 1.2250 416.9
+10 337.33 1.2466 420.5
+5 334.33 1.2690 424.3
±0 331.30 1.2920 428.0
-5 328.24 1.3163 432.1
-10 325.16 1.3413 436.1
-15 322.04 1.3673 440.3
-20 318.89 1.3943 444.6
-25 315.72 1.4224 449.1

I'd suggest a few folks try a long drive, with known higher temperature battery performance, on a cold (dry) day without using heater/defrost, wipers, etc., in order to isolate the temperature effect on the battery charge level. I'm planning this myself on my own 80-something mile max range "single charge" (in summer, anyway) trip. I'm waiting for a clear cold day, and will bundle up for the drive up over the pass to Burney Falls State Park.

If you really need a bit more winter range, with the heater defroster, You might consider increasing energy storage by increasing the thermal capacity of your heater system, by increasing the heatant volume. But the rough estimate I came to in the thread below indicates the relatively modest potential benefits.

How about just putting a larger, insulated tank, in line with the stock heatant tank?

That would probably be a cheap mod.

But, as I figure it, you'd only get about 1 KWH worth of heat storage, for 5 gallons of heatant, if heated 80 degrees F above ambient. So, somewhat heavier (but far cheaper) than battery storage. Of course, you'd get 1.5 kWh equivalent storage if you pre-heated by 120 degrees F.

How hot is the LEAFs system set to pre-heat to?


8:30 pst Edit-

Just took a look under the hood. Not as much room there, as I remembered.

Looks to me like the only likely large tank space is at the 12 V battery location.

Whatever happened with those plans some of you had, to replace the 12 V battery, with a smaller unit?

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http://www.mynissanleaf.com/viewtopic.php?f=27&t=6505&start=40" onclick="window.open(this.href);return false;

Interesting thread.

I have a story to relate, and a question. First, the question - does anyone know the SOC for the first low battery warning?

Yesterday I drove to Rosamond From Altadena over the Angeles Crest/Forest Highways before they closed it due to snow. I drove gently, used the heater a bit to clear the windows and for heat for several minutes at a time, so overall I would say ten minutes. I did preheat the cabin before leaving and left with 100% charge. I made it to the FCC (Destination) with one bar and my lowest number yet on the GOM, 4. Temp outside was below 50, much of it 44, lowest 30. Total distance 73.

On the return the fun started. No preheat, 100% charge and confidence since it is an elevation loss to go home. Drove 65 on the freeway into Palmdale, then slowed a bit as the rain started. Got to the turnoff for the Forest Highway and went up, missing a small sign that said road closed. Got to the barriers and had to turn around. No worries for me, not so much for my wife. Returned to the freeway after a short bit of Sierra Crest Highway, and played with the nav system, with it telling us we may not have enough range to get home. With the knowledge a Kohl's had installed a charger right off the freeway, I suggested dinner and a charge and while the downhill run had gained us enough energy the car now said we could make it home, we opted to eat and get a little L2, 30 seconds short of one hour. Temps for this trip were right around 40, but we did hit some hail on a downhill stretch.

Back on the freeway which was dry now, I again did 65 for a bit, lost a bar and reduced speed, realizing the hills ahead were going to take as much hypermiling as I could give them. Traffic was light so could do this with no issues, speeding up where I should to not impede traffic, slowing as much as 45 on one uphill with no traffic nearby. Didn't have to use the heat much, and did not preheat at the L2. Got home after logging 97 miles and a low battery warning as I left the freeway at my normal exit. 6 on the GOM as I entered the garage. We were glad we stopped for dinner, although by being conservtaive I think we might have made it without the charge if I had just kept my speed down and not stopped to charge, although the charger is very close to the freeway. I did thank the Kohl's manager and suggested marking the spaces for EV, since the two closest were ICEd, but the cord stretched easily to the next space which was open. It will reach four spaces so that was a smart install, but too close to the store entrance in my opinion. In a pinch I would have parked in the red on the other side of the island to get the charge, which would have worked too, but might have gotten me a ticket.

Battery had 5 bars on the temp. the whole time, normal is 6.

GaslessInSeattle said:

Then I pulled up the energy screen and noticed that I could not turn off the heater, that when it gets below 60 outside that climate control has a mind of it's own.

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Have you tried simply turning off climate control?

Also, here are a couple of charts that might help to visualize the change in air density in respect to temperature. Apparently it's a rather significant factor. Source: Wikipedia http://en.wikipedia.org/wiki/Density" onclick="window.open(this.href);return false;

johnr said:

air density in respect to temperature. Apparently it's a rather significant factor.

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Got a good chuckle out of this. Yes, apparently it is. :mrgreen:

Your chart doesn't address this, but elevation also is a significant factor.

http://wahiduddin.net/calc/calc_da.htm" onclick="window.open(this.href);return false;

Caracalover said:

Interesting thread.

I have a story to relate, and a question. First, the question - does anyone know the SOC for the first low battery warning?

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Click on the first link in my signature line, "How far can I drive". The info you seek is there.

Air density is perhaps not as significant in the overall scheme of things as it might appear at first... The difference in density between 20C and 10C is only slightly more than 3 percent (96.55)... For 20C versus 0C, about 7 percent (93.12). Add in all the other losses (parasitic, tires, friction, etc.) and the percentage affect is even less pronounced.

johnr said:

Also, here are a couple of charts that might help to visualize the change in air density in respect to temperature. Apparently it's a rather significant factor. Source: Wikipedia http://en.wikipedia.org/wiki/Density" onclick="window.open(this.href);return false;

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TomT said:

Air density is perhaps not as significant in the overall scheme of things as it might appear at first... The difference in density between 20C and 10C is only slightly more than 3 percent (96.55)... For 20C versus 0C, about 7 percent (93.12). Add in all the other losses (parasitic, tires, friction, etc.) and the affect is even less pronounced.

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Then, we are back to the question of - why does m/kwh go down even when not using CC.

TomT said:

...Add in all the other losses (parasitic, tires, friction, etc.) and the affect is even less pronounced.

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This I don't get. Those effects are additive, they don't cancel out. A bunch of small losses can add up.

For me, I'm looking at something in the range of 25º to 30º (summer) and -10º to 5º (winter). That's a hit of as much as 15% just from temperature density alone. And, around here, cold winter air tends to be much lower in humidity (more dense) than summer air (more humidity = less dense), although I would expect those effects to smaller.

What I meant is that the percentage affect of air density is reduced by the cumulative affect of all the other losses. For example, let us say that, hypothetically, air density accounts for half the energy required at a given speed. If the air density increases by 10 percent, the actual overall affect on range would be half of that or 5 percent since drag only accounts for half of the energy required.

dgpcolorado said:

TomT said:

...Add in all the other losses (parasitic, tires, friction, etc.) and the affect is even less pronounced.

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This I don't get. Those effects are additive, they don't cancel out. A bunch of small losses can add up.

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Perhaps the other losses go up more than we realize or the car is using heat more than they realize...

evnow said:

TomT said:

Air density is perhaps not as significant in the overall scheme of things as it might appear at first... The difference in density between 20C and 10C is only slightly more than 3 percent (96.55)... For 20C versus 0C, about 7 percent (93.12). Add in all the other losses (parasitic, tires, friction, etc.) and the percentage affect is even less pronounced.

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Then, we are back to the question of - why does m/kwh go down even when not using CC.

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Li-Ion battery internal resistance rises as the temperature falls. This is very significant and is the primary reason for the reduced efficiency, although heater use can also be very significant. There are a few related phenomena besides reduced range.

- Charging time increases. Not so noticeable unless you are doing DC quick charging at very low temperatures.
- The battery freezes at about -25°C (-13°F). No power at that temperature. Hence the cold weather package with the battery heater that prevents this from ever occurring so long as you are plugged in. LEAFers up North please keep your cars plugged in!!! Especially overnight.
- As current passes through the battery pack the resistance converts a portion of the electric current to heat. The colder the pack and the greater the power, the more heat is generated. This tends to stabilize the situation when driving in very cold conditions. When I say very cold I mean not you folks in California.
- Increased internal resistance means less power can get through the pack. Usually not noticeable, but when very cold it can be. Again, does not pertain to you folks in California. I mean hats and gloves and seeing your breath while your teeth chatter weather.

The good news though is that the cold is good for battery life.

Li-Ion batteries are a lot like us. They complain when it gets too warm (increases deterioration rate) or too cold (reduces efficiency and power). We bundle up when it gets cold outside and try to stay indoors next to a warm fireplace with a hot chocolate. Li-Ion batteries like to be inside and plugged in. I have never asked their opinion about hot chocolate however? :lol:

johnr said:

GaslessInSeattle said:

Then I pulled up the energy screen and noticed that I could not turn off the heater, that when it gets below 60 outside that climate control has a mind of it's own.

Click to expand...

Have you tried simply turning off climate control?

Click to expand...

You can't turn climate control off without also turning off the circulating fan which causes the windshield to fog badly.

Caracalover said:

First, the question - does anyone know the SOC for the first low battery warning?

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On my gauge, it showed 20% SOC with LBW (11miles/1 bar) today. CarWings will show you 8%. I QCd @ the 90% Blink setting (Blink charged to 89%) and it charged to 79% (SOC gauge/9 bars) in about 25 minutes. Temp bars rose to 6 from 5.

johnr said:

Also, here are a couple of charts that might help to visualize the change in air density in respect to temperature. Apparently it's a rather significant factor.

Click to expand...

Contrary to what other people may believe, you are absolutely correct. I didn't want to believe that the colder, denser air would have much of an effect on my m/kW h by as much as .5-.8, but it does! When I was QCing today, one of the ECOtality techs verified exactly that. He said it IS a significant factor. He also said, as some on here have posted, that a colder battery pack will NOT have any effect on your efficiency (m/kW h).