Efficiency dropped recently

[rkshack]

I have a 2012 leaf. I have owned it since May of this year. Up until about a month ago I was getting about 3.9 mimes/kw. Over the lat month or so I have been getting around 3.5. The temp is in the mid 50s. In the summer I was getting better mileage. Is there a reason for this change? Is it due to weather or a problem with the battery?

Rkshack

 

[TomT]

There is nothing that can happen with the battery that will affect efficiency, just range. Thus, it is other considerations.

Is it due to weather or a problem with the battery?

 

[surfingslovak]

We observed this last winter as well. It's most likely due to denser air and higher aerodynamic drag. Another thing worth noting is that rolling resistance increases on wet roads, and will lower the overall energy efficiency. Running the resistive cabin heater, even on a low setting, will burn significant amount of energy, and have an appreciable effect. Your energy economy should recover next spring and summer. It will be better on warm and dry winter days as well.

 

[FalconFour]

+1 on the dense air and heater usage thing. Heater uses enough power to kill about a bar of battery power an hour if you push it (I was testing that a few nights ago while, well... using my LEAF as a clothes dryer! Physics experiment, I swear!). The heater is a huge drag on the battery. If range is a concern - which it really isn't for me in Fresno where I could make it home from anywhere in town on "VLB" power - then you've got to keep an eye on the heater usage.

Most importantly, ALL functions of the car are taken into account when you get your efficiency rating. So if you sit in a garage with a 4.0 miles/kWh reading from your last trip, then run the heater an hour, that number might drop down to 3.0 while you sit there.

Also, cold air, from what I understand, is more dense than warm air and harder to cut through as you drive. I got a good lesson in that not too long ago, expected to make a slow 100-mile trip back home but only made it 80 miles due to the freezing temperature (34-38 F that night). :/

 

[surfingslovak]

Also, cold air, from what I understand, is more dense than warm air and harder to cut through as you drive. I got a good lesson in that not too long ago, expected to make a slow 100-mile trip back home but only made it 80 miles due to the freezing temperature (34-38 F that night). :/

Hats off to you for that trip. About 380 miles, 4,000 feet of climbing over Mt. Hamilton both ways, without heating, and with a battery that's a bit down from new performance. Incredible. About the effects of temperature: we discussed this last winter, and I believe that Tony and others measured ~5% less capacity around the freezing point. It's a double whammy, the economy is lower, and the battery will hold less energy. I once ran out returning from a trip to the city. Ambient temps were dropping precipitously, and I came up a mile short, despite best efforts.

 

[GRA]

Also, cold air, from what I understand, is more dense than warm air and harder to cut through as you drive. I got a good lesson in that not too long ago, expected to make a slow 100-mile trip back home but only made it 80 miles due to the freezing temperature (34-38 F that night). :/

Hats off to you for that trip. About 380 miles, 4,000 feet of climbing over Mt. Hamilton both ways, without heating, and with a battery that's a bit down from new performance. Incredible. About the effects of temperature: we discussed this last winter, and I believe that Tony and others measured ~5% less capacity around the freezing point. It's a double whammy, the economy is lower, and the battery will hold less energy.

Tony's chart assumes 10% less around freezing: 1% per 4 deg. F. below 70 deg. F, so 70-32 = 38 degrees / 4 = 9.5% (temporary) capacity decrease. Add to that thicker air so more drag, plus heat/defroster use, plus increased rolling resistance on wet or snowy pavement, and winter hits the range with a double, triple or quadruple whammy.