Electrical power draw

[JRMichler]

I was curious about how much power it takes to run the electrics on my 06 Canyon, so I borrowed a Fluke 337 AC/DC clamp on multimeter. I put the meter on the battery positive wire and started turning things on and off. All readings are in amps. The results:

Ignition ON W/ DRL’s 10.3 amps
Ign ON - DRL’s OFF 2.7
Ign ON - Park lights ON 9.2
Ign ON W/ headlights 17.3
Ign ON W/ DRL’s 10.3

Park lights alone: 6.5
Headlights alone: 8.1

Ignition OFF Dome ON 3.2
Ign OFF Dome lite OFF 1.4
Ign OFF Park lights ON 7.7
Ign OFF Headlights ON 15.8
Ign OFF Lights OFF 1.4

Park lights alone: 6.3
Headlights alone: 8.1

Ignition ON Lights OFF 2.6
Ign ON Blower 1 5.3
Ign ON Blower 2 8.0
Ign ON Blower 3 12.3
Ign ON Blower 4 15.1
Ign On Blower 1 Headlights ON 19.9

Blower 1 alone: 2.7
Blower 2 alone: 5.4
Blower 3 alone: 9.7
Blower 4 alone: 12.5
Headlights plus running lights: 14.6

All of these were with the engine off. The battery was about 12.4 volts. Power consumption with the engine running will be slightly higher because of the higher voltage.

Since the Reserve Power rating on my battery is well over an hour, I don't have to worry about a few 2 or 3 minute EOC's at night with the heater blower running on low. The Reserve Power rating is the minutes it will last at a 25 amp load.

[Daox]

Nice measurements. A few users have done this over the years, but I don't think anyone with a truck has.

If you have a 20A draw thats about 260W (at 13V which is more where it is when the engine is running). That means the engine has to put out double that (alternators are roughly 50-60% efficient). Thats about 2/3 hp just to have headlights and your fan on low.

[JRMichler]

Just for the fun of it, let's calculate potential savings. First, get the alternator efficiency up to 90%. Second, change all lighting to the latest technology LED. Third, a more efficient (ECM?) blower motor. The total electrical load would drop from 20 amps down to about 6 amps, for a savings of 14 X 13 volts = 180 watts. The engine power needed would drop from 260 / 0.5 = 520 watts down to 6 X 13 / 0.9 = 87 watt, for a savings of 430 watts.

430 watts / 746 = 0.58 hp. Multiply by 0.4 lbs fuel per hp-hour = 0.23 lbs per hour fuel saved = 0.039 gallons per hour. Assuming 40 MPG at an average speed of 40 MPH, the fuel used would drop from 1.00 gallons per hour down to 0.961 gallons per hour. MPG would increase from 40 MPG up to 41.6 MPG. Those getting better mileage would get a larger gain, those getting less mileage would get a smaller gain. Certain practical realities, such as the fact that engine efficiency decreases at lower loads, will make the real world MPG gain less.

If I put in LED bulbs, it will be for reliability, not MPG. I can also get reliability by replacing every single bulb when the first one burns out.

[Longsnowsm]

I like the idea of replacing those DRL's since they are on all the time to both reduce electrical load, improve reliability, and every little bit of fuel savings is nice too. Like you mentioned the other lights can wait until they need to be replaced since they are not on all the time. :-) Thanks for the great analysis on the electrical loads!

[markweatherill]

Originally Posted by JRMichler

All of these were with the engine off. The battery was about 12.4 volts. Power consumption with the engine running will be slightly higher because of the higher voltage.

I was going to point out that at the higher voltage your accessories might just draw less current, but use the same power. But somehow that doesn't seem to work in practice! Headlights always seem to get brighter when the engine is running rather than when it's off. I guess 12V is just not very efficient full stop.
Which might suggest, is there the option to convert to 24V?

[redpoint5]

Originally Posted by markweatherill

I was going to point out that at the higher voltage your accessories might just draw less current, but use the same power. But somehow that doesn't seem to work in practice! Headlights always seem to get brighter when the engine is running rather than when it's off. I guess 12V is just not very efficient full stop.
Which might suggest, is there the option to convert to 24V?

Headlights are a straight resistive load and will always consume more power when given a higher voltage. LEDs behave similarly, and have a bigger problem of drawing more current the hotter the LED gets. This positive feedback can cause LEDs to burn out prematurely which is why they need to be engineered properly for their application. HIDs on the other hand will draw a relatively constant amount of power within a range of voltages.

24v would allow for smaller gauge wire to supply the power, but I don't ever see that being adopted. I'd like to see 240v AC be the standard in US homes for the same reason, but that seems even more improbable.