Headlights effect on range?

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fasttr

fasttr

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Has anyone ever tested the effects of headlights on overall range? I drove an hour yesterday morning in the dark and it definitely seemed like it had a measurable impact.


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I believe LED headlights have around a 20-30W of power draw each which is pretty minimal. I wouldn’t expect to that to have any appreciable impact on range.

Air is considerably cooler at night, ie more dense, so I would expect this to have a larger impact than the headlights being on.
But, I haven’t done any testing on this. Has anyone else done testing on this?
 
Headlights should be powered by the 12V accessory battery, not the high-voltage battery used to power the drivetrain.

I agree that increased density of the cooler night air is more likely to have an impact.
 
Concur on the LEDs using under 50W of 12V power) that is eventually fed by the traction battery.

If the whole car is otherwise getting 4 miles per kWh, using the lights would mean it is now getting 3.8 miles per kWh (<= 5% reduction), by my SWAG.
 
F14Scott said:
Concur on the LEDs using under 50W of 12V power) that is eventually fed by the traction battery.

If the whole car is otherwise getting 4 miles per kWh, using the lights would mean it is now getting 3.8 miles per kWh (<= 5% reduction), by my SWAG.
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That’s almost exactly what I saw. 3.8M/kWh with the lights on, around 4.1M/kWh on the way back (20 deg F warmer on the way back also).
 
fasttr said:
But the high voltage system is used to keep the 12V system charged, correct?
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Yes but how long will it take the 12 V battery to drain? Does the SE do continuous recharge (like an alternator does when an ICE car is running), or does it recharge the 12 V battery when the SE is recharging? It seems to me the sensible approach would be to recharge the 12 V battery when the SE is plugged in, but could the car know if the 12 V battery is low and do a charge while driving?
 
Educated guess, based on two factors:
1. Car batteries don't like to be deep cycled.
2. Tesla does it this way.
I'm thinking the traction battery is always topping off the 12V, or at least does not let it get very much below full before it feeds a DC to DC converter to charge the little battery.
 
F14Scott said:
1. Car batteries don't like to be deep cycled.
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The SE (all MINIs) use AGM batteries, which actually do tolerate deep cycling. But that has no bearing on how the SE actually does things. Anyone know how the i3 works?

As I mentioned in another thread, I've got a mysterious occasional 12 V battery drain that happens when my SE is parked and not plugged in. It never affects anything, but I guess it means the SE does know the charge state of the 12 V battery. And I don't know if it's getting "topped off" while my car sits.
 
fizzit said:
They won’t have a measurable impact. If you’re getting 4mi/kWh and going 60mph, you’re burning 15kW. At <30W total, headlights are 0.2% of your power consumption. So you’d get 3.99mi/kWh
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Dammit. That math is right. I don't know WTH I was doing.
 
fizzit said:
They won’t have a measurable impact. If you’re getting 4mi/kWh and going 60mph, you’re burning 15kW. At <30W total, headlights are 0.2% of your power consumption. So you’d get 3.99mi/kWh
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I don't know if I agree with the <30W total.

Aftermarket LED retrofits can be 60W each side. Plus the fuse for the headlights is either 40A or 20A (can't tell which from the fuse diagram) and fuses are typically 1.1x to 1.5x the load which would be 14A (or 168W). Assuming that 20A fuse is for both, that would be ~84W each which seems reasonable to me considering how bright they are.
 
fizzit said:
Ok, you made me curious. I just measured the battery draw in mi3. With low beams on and no climate control, the power being consumed ranged from 0.3-0.31kW. With them turned off, it was 0.27-0.28kW.
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I'm guessing that's only measuring the HV battery though so that would be the DC/DC power usage, not necessarily the headlight power usage (if the 12V battery is contributing some).

I looked at the headlights themselves and found this marked on the back and on the side:
  • DRL 18W: Daytime running lights. 18W is surprisingly high but I guess they are pretty bright, just unfocused.
  • TI 24W: I don't know what TI stands for but this is the headlight power for each side. Less than I expected (the fuse may have other lights on it) but still more than 30W combined.
  • PL 2W: Probably stands for parking light aka the bad weather/cornering lights
20211102_075058.webp

I also just want to note that with projector style headlights, there is no separate low beam and high beam. The LEDs are using the same amount of power all the time and there is a little "cutoff shield" that moves to block part of the beam: how-projector-headlights-work-1024x844.webp

To the original point of this thread, headlight use is still negligible regardless of what the actual power consumption is. With the values above, using the headlights and DRLs and cornering lights for an hour would use an additional 0.088kWh or 0.3% of your battery.
 
It doesn’t seem that our headlights use that shutter mechanism. The power draw goes up by another 40-50W when high beams are turned on, indicating that they’re separate diodes. And the high beams are noticeably brighter and a different color temperature.

I feel pretty confident that the power draw in mi3 corresponds to the full power being used by the car, because it seems unlikely that just turning on the low beams is enough to max out the DC/DC and start draining the 12V battery.
 
fizzit said:
It doesn’t seem that our headlights use that shutter mechanism. The power draw goes up by another 40-50W when high beams are turned on, indicating that they’re separate diodes. And the high beams are noticeably brighter and a different color temperature.

I feel pretty confident that the power draw in mi3 corresponds to the full power being used by the car, because it seems unlikely that just turning on the low beams is enough to max out the DC/DC and start draining the 12V battery.
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I agree the DC/DC wasn't maxed out but my thought was that if the 12V battery was full, it would be at approximately the same voltage as the DC/DC so they would be acting as parallel power sources and current would be supplied by both. My electrical circuit knowledge is rather basic though so I could be wrong.

The sharp stepped beam cutoff is a signature of the cutoff shield (the shield itself is stepped). It would be very difficult if not impossible to get that beam shape from just optics. It's entirely possible though that more LEDs turn on when the shield flips down which could explain the higher power use.
projectors-10.gif.pagespeed.ce.q8RQvEahkR.gif
 
Carsten Haase said:
The sharp stepped beam cutoff is a signature of the cutoff shield (the shield itself is stepped).
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The bump in the top of that shield explains the pattern I see on a wall! It was driving me crazy that it's left-right asymmetric, but at least now I know why. I'll have to post a photo of the pattern to show what I mean.
 
Puppethead said:
The bump in the top of that shield explains the pattern I see on a wall! It was driving me crazy that it's left-right asymmetric, but at least now I know why. I'll have to post a photo of the pattern to show what I mean.
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I noticed that same thing a while ago and took a picture so I could ask on this forum. Now I know!
IMG_2416.webp
 
Than
Carsten Haase said:
I agree the DC/DC wasn't maxed out but my thought was that if the 12V battery was full, it would be at approximately the same voltage as the DC/DC so they would be acting as parallel power sources and current would be supplied by both. My electrical circuit knowledge is rather basic though so I could be wrong.

The sharp stepped beam cutoff is a signature of the cutoff shield (the shield itself is stepped). It would be very difficult if not impossible to get that beam shape from just optics. It's entirely possible though that more LEDs turn on when the shield flips down which could explain the higher power use.
View attachment 13928
Click to expand...

Thanks for posting this. I noticed when I switched from low to high beam I could almost see a shadow where the low beams are separate from the high beams.
 
Carsten Haase said:
I agree the DC/DC wasn't maxed out but my thought was that if the 12V battery was full, it would be at approximately the same voltage as the DC/DC so they would be acting as parallel power sources and current would be supplied by both. My electrical circuit knowledge is rather basic though so I could be wrong.

The sharp stepped beam cutoff is a signature of the cutoff shield (the shield itself is stepped). It would be very difficult if not impossible to get that beam shape from just optics. It's entirely possible though that more LEDs turn on when the shield flips down which could explain the higher power use.
View attachment 13928
Click to expand...

Holy crap! I've wondered about the uneven shadow. Thanks! Why does it need that uneven shape??

EDIT: And this now explains why, when you turn on high beams, the 'extra' light is appearing directly above the existing low beams rather than flooding the low beam area with more light.
 
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