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How much power do the headlights draw?

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Transformer

Do the math. Save the world. — Mark Leon
Dec 26, 2019
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Silicon Valley
How much power (watts) do the headlights draw on low beam?

I'm curious how fast they'd drain the battery if the lights were left "on" in the manual setting, and didn't find anything in the Energy app.

Ideally, info for both matrix or pre-matrix headlights.
 
I don’t know how one would measure that. But it would be in the magnitude of days with a full battery.
Best case and cleanest scenario would be to find out what connector is used to attach the headlight(s) to the associated wiring harness and build a short extension cable (male and female ends) and put an ammeter inline on one of the leads. That way you could get the current/power measurement needed and there would be no evidence after the fact, like a spliced wire.
 
Web sources:
Even 2 x 72W x 10 hours is only 1440 Wh, which is < 2% of a 75 kWh battery pack. A full charge would last > 3 weeks.

Exiting the car with the headlights on manual gives a warning beep and a warning message. If they'll eventually time out, it takes longer than they were on for my neighbor's car before I noticed.

Interesting idea to measure the current. Replacing one requires a firmware reinstall (Tesla Model 3 (2020) DIY headlight replacement write-up), which means you'd have to figure out which leads have power.
 
find out what connector is used to attach the headlight(s) to the associated wiring harness and build a short extension cable (male and female ends) and put an ammeter inline on one of the leads
Or, if you can isolate the wire supplying the power, use a clamp on DC current meter. Then, there's no need to insert a conventional ammeter inline.


Actually, you could probably just clamp the meter around the positive wire from the low voltage battery and measure the difference between the lights on and off, provided that the base draw without the lights on wasn't too high. Inserting an ammeter inline with the positive battery wire, and using this technique, probably wouldn't be too difficult, either.
 
Or, if you can isolate the wire supplying the power, use a clamp on DC current meter. Then, there's no need to insert a conventional ammeter inline.


Actually, you could probably just clamp the meter around the positive wire from the low voltage battery and measure the difference between the lights on and off, provided that the base draw without the lights on wasn't too high. Inserting an ammeter inline with the positive battery wire, and using this technique, probably wouldn't be too difficult, either.
While that clamp-on method can measure current, I believe it's best used on AC current measurements, rather than DC. In order to get the most accurate reading, at a reasonable cost, an inline ammeter is the best.
 
I believe it's best used on AC current measurements, rather than DC. In order to get the most accurate reading, at a reasonable cost, an inline ammeter is the best.
Just how accurate does it need to be for this situation, where the goal is to get and idea of how fast the battery would be drained with the headlights on?

I have a UNI-T UT210E clamp style meter. This is a relatively inexpensive mid-quality brand. On the 20A and 100A DC ranges, the accuracy is ±(2% + 3 counts). For AC current, the accuracy is actually worse, at ±(2.5% + 8 counts) on the 20A range and ±(2.5% + 5 counts) on the 100A range.

 
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Just how accurate does it need to be for this situation, where the goal is to get and idea of how fast the battery would be drained with the headlights on?

I have a UNI-T UT210E clamp style meter. This is a relatively inexpensive mid-quality brand. On the 20A and 100A DC ranges, the accuracy is ±(2% + 3 counts). For AC current, the accuracy is actually worse, at ±(2.5% + 8 counts) on the 20A range and ±(2.5% + 5 counts) on the 100A range.

Okay, I'll admit that DC current clamp-on meters exist and some are more accurate than my Craftsman True RMS Multimeter (81079); accuracy of +/-2.5% + 5 digits in the 4A and 20A ranges, but maybe not as accurate as my HP E2373A (+/-1.5% + 2 digits in 10A range).

However, I still like my inline adapter method...