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Headlights effect on range???

daniel

Well-Known Member
May 7, 2009
5,467
4,997
Kihei, HI
So as I've posted elsewhere, I'm going to be taking a long road trip up to Canada soon. In Canada, it's highly recommended, if not actually required, to have your headlights on during the day.

Can anybody tell me how much this will affect my range? I presume not a lot, since they are LEDs, but it would be nice to have an idea.

Also, since this will be my first road trip in this car, and it will be summer, how much does A/C affect range? Should I use it sparingly, or is the effect minimal?
 

smartypnz

Active Member
Supporting Member
Jan 23, 2013
2,362
2,567
Monterey Peninsula
No idea what the wattage is for the headlights, but you have approximately 80,000 watts of battery. So, if headlights were 400 watts (not likely since they are LED's) that would take 200 hours if just headlight usage.

In Spain, some taxi drivers run without lights or wipers to save gas. Ever have any concern about that?
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
20,678
28,615
Texas
HID headlights are 70 W per pair. LEDs are far lower. This amount won't even register. Aerodynamic losses are the biggest followed by tire rolling resistance and drivetrain losses (especially when cold as the lubricant needs to be warm).
 
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I'm not sure what the power draw is on the LED headlights, but it's certainly going to be less than a comparable HID headlight. Lets assume for a moment that the entire lighting system will be 50 watts.

Now, let's assume that your average speed will be 60 mph (sure you may drive faster on parts of the expressway, but you'll also encounter some slower traffic, and drive much slower while you're off the expressway).

Finally, lets assume that your average efficiency is 230 Wh/mile.

At an average speed of 60 mph, it will take you 0.01666 hours to drive 1 mile.

50 watts * 0.01666 hours = 0.83 Wh/mile. So your trip will increase to 230.83 Wh/mile

Assuming that you use 63.75 kilowatt hours per day on your road trip, your range for those 63.75 Watt hours will be reduced from:

63,750 watt hours / 230 watt hours per mile = 277.174 miles

to

63,750 watt hours / 230.83 watt hours per mile = 276.177 miles

Looks like (if my assumptions about speed, your personal efficiency, and the power draw of the lighting system are reasonable) those headlights could reduce your daily range by nearly a mile!
 

daniel

Well-Known Member
May 7, 2009
5,467
4,997
Kihei, HI
Thanks for all the comments and numbers about headlights. Nobody mentioned A/C. Is that not a concern either? As for speed, I do know that's the biggest thing. There are no freeways on my route, other than Revelstoke to Golden, which is only 92 miles with superchargers at both ends. But the rest of my trip is on secondary roads where most of the time I could drive 70 mph if I wanted to risk the speeding tickets. (I won't do that. But much of the trip is pretty wide open.) I will be using TACC. The great thing about TACC is that it prevents inadvertent speed creep. CC does also, but TACC does not have to be disengaged every time there's a slower car ahead.

Has anybody published numbers for wh/mile at, say, 55 mph and 65 mph?

FWIW I have the standard wheels and the aero covers.
 

efusco

Moderator - Model S & X forums
Moderator
Thanks for all the comments and numbers about headlights. Nobody mentioned A/C. Is that not a concern either? As for speed, I do know that's the biggest thing. There are no freeways on my route, other than Revelstoke to Golden, which is only 92 miles with superchargers at both ends. But the rest of my trip is on secondary roads where most of the time I could drive 70 mph if I wanted to risk the speeding tickets. (I won't do that. But much of the trip is pretty wide open.) I will be using TACC. The great thing about TACC is that it prevents inadvertent speed creep. CC does also, but TACC does not have to be disengaged every time there's a slower car ahead.

Has anybody published numbers for wh/mile at, say, 55 mph and 65 mph?

FWIW I have the standard wheels and the aero covers.
A/C's impact will be more noticeable for sure, but it still is not dramatic, in my experience, compared to using the heater. It also depends a lot on what temperature you have the AC set to and what the outside air temp is and how much direct sunlight you're getting (heating the cabin via greenhouse effect). I'd estimate that it increases the Wh/mi by 10-20 in my Model S and X roughly.
 
I don't think you need headlights on during the day in Canada. You just need daytime running light which Tesla already has. Now if you car doesn't have daytime running light, then you should turn headlights on.

Heated seats and heat take a lot of juice to run. I had to tell my wife to turn off the heated seats one time... we got home with 17 miles left on the screen.
 

TexasEV

Well-Known Member
Jun 5, 2013
7,656
8,935
Austin, TX
Heated seats and heat take a lot of juice to run. I had to tell my wife to turn off the heated seats one time... we got home with 17 miles left on the screen.
You’ve got that backwards. Heated seats use much less energy than the heat. That’s why you should use the heated seats in winter, so you can set the temperature way down on the heater.
 

daniel

Well-Known Member
May 7, 2009
5,467
4,997
Kihei, HI
I don't think you need headlights on during the day in Canada. You just need daytime running light which Tesla already has.

I don't know if the lights are required by law, but they definitely want you to have your headlights on, not just running lights. Headlights make the car more visible to other drivers. Running lights in the daytime have minimal effect on the visibility of the car.
 
You’ve got that backwards. Heated seats use much less energy than the heat. That’s why you should use the heated seats in winter, so you can set the temperature way down on the heater.

Really? Oh.... good thing my wife doesn't read these forums.. :p Or I will never hear the end of it.."You made me turn off the heated seat for nothing???"
 
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You’ve got that backwards. Heated seats use much less energy than the heat. That’s why you should use the heated seats in winter, so you can set the temperature way down on the heater.
Sure, but they still use a lot more energy than not having any heat at all.

I assumed that he meant that he had already turned off the cabin heat, but was concerned that there still wasn't enough energy left in the battery to BOTH get home AND run the seat heater. Therefore he had her also turn off the seat heater (and suffer in the cold). Leaving the seat heater turned on certainly wasn't going to INCREASE his range.
 
Sure, but they still use a lot more energy than not having any heat at all.

I assumed that he meant that he had already turned off the cabin heat, but was concerned that there still wasn't enough energy left in the battery to BOTH get home AND run the seat heater. Therefore he had her also turn off the seat heater (and suffer in the cold). Leaving the seat heater turned on certainly wasn't going to INCREASE his range.

Hmm... about that.. nope. I thought it was the heated seats using most of the juice. But I did have the car in Range Mode. Not sure if that limit heat AND heated seat? It kind of sucks when your family decided to go out 20 miles (40 miles round trip) for dinner and you realized that you only about about 70 miles left from day use :p
 

daniel

Well-Known Member
May 7, 2009
5,467
4,997
Kihei, HI
A/C's impact will be more noticeable for sure, but it still is not dramatic, in my experience, compared to using the heater. It also depends a lot on what temperature you have the AC set to and what the outside air temp is and how much direct sunlight you're getting (heating the cabin via greenhouse effect). I'd estimate that it increases the Wh/mi by 10-20 in my Model S and X roughly.

Hi, Evan. I'd kind of forgotten you were on here. Yeah, I know that A/C is less of an issue than heat. But I'd heard that A/C decreases the gas mileage on stinkers, so I figured it would have an effect on this car as well. Most of my trip is well within my range, but the Spokane to Kelowna leg is 243 miles, and I don't know what the terrain is like. I'll be driving up in early July, so it could get hot. I'll be wearing shorts and using as little A/C as I can without getting too uncomfortable.
 
Hmm... about that.. nope. I thought it was the heated seats using most of the juice.

Oh my! My sympathies to your wife. :(

The seat heater heats the seat cushion, which in turn heats your body directly. Not a lot of losses there. The vast majority of the heat created goes directly into heating either you or your seat.

The cabin heater heats air, which then spreads throughout the entire cabin heating the windows, the roof, the dashboard, the floor, the unoccupied seats, the doors, the center console, you, your passengers, etc. Much of the heat energy that was put into the floor, roof, windows, and doors then escapes to the outside. Only a very small percentage of all that heat actually makes it directly to your body. Therefore, a LOT more heat needs to be added to the air escaping the air vents for you to feel the same amount of heat directly to your body as you would from seat heaters.

In terms of efficiency, if it's cold enough that you would like to be warmed up a bit, you should always start with the seat heater. Then if you still need a bit more warming, you can boost the cabin temperature until you feel comfortable. You should feel comfortable with a MUCH cooler cabin if your seat heaters are on than if they are off.
 
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