Does this steal MPG?

[MazdaMatt]

A buddy of mine had a HUGE subwoofer in his car and matching amp. Even running that thing at "listening" volume (rather than competition volume) he took a 30% hit to MPG.

[jamesqf]

Originally Posted by HypermilingNoob

Now how about the heater? It uses electricity obvious but is it a large amount?

No, the heat is coming from waste engine heat, that would otherwise go to the radiator. That's why, if you have a radiator block and your coolant temp starts getting too high, you can bring it down by turning on the heater.

The only extra energy it uses is the little bit of electricity needed to run the fan.

[theunchosen]

right James,

If you just flip the deal to heat and let the ambient pressure at your intake vents push the air(usually its at the windshield hood intersection) it will not consume any energy because the heat comes off the engine.

If you run the fan on low I think that table was like 30 watts. . . or .03 Kilowatts so .04 hp. . . really negligible FE improvement considering being cold is likely to slow your response time and ability to effectively hypermile.

[some_other_dave]

I feel (without a lot of data to back it up) that the pulley, belt, bearings, and such of the alternator always put a noticeable load on the engine. In fact, I believe that makes up a substantial part of the ~10% MPG improvement that some people have seen by pulling their alternator belt all together. As a result, I don't think the electrical loads are going to make a huge impact on fuel economy.

The heater does take some electricity to run. Not only that, but it also cools off the coolant of the car a bit. (My dad's old car's cooling system was marginal, and on hot days he would have to run the heater to keep the car from overheating!!) A colder engine is a less efficient engine, up to a point. By running the heater, you will be cooling the engine slightly more than without running it.

Now, if your engine is fully warmed up and runing on the heater doesn't cause a noticeable drop in coolant temp, then the energy lost to the "extra" heat needed by the coolant is negligible. But running the heater during warm-up will make the warm-up phase last longer, which burns noticeably more fuel.

Not all consumption is related to work being done by the engine...

-soD

[theunchosen]

The alternator proper is not drawing power away from the engine unless you use it.

So 60 watts from fans on 2 settings, 200 watts for ignition. . .those aren't big numbers but the alt is having to convert from AC to DC and its only going to keep about 75-80% there. So that 60 watts of sound or air becomes 80 watts. The real savings are to elimintate he big boys like 200-300 watts of engine draw(.5 hp).

[some_other_dave]

How's this for a test: Unplug all of the wires to the alternator. Check fuel economy. Then unhook the belt. Re-check economy. My belief is that you'll see a noticeable difference, which means that even when it isn't giving you any "juice", the alternator is still taking noticeable amounts of power to run.

-soD

[Concrete]

Dear Mr. Noob

determining ball park parasitic loads is not too hard with instrumentation
I just pulled the serpentine and watched the scan gauge

~.1 GPH difference without any belt (from 900-3000 RPM pretty flat)
~.1 GPH difference A/C on and off (idle)
~.12 GPH difference steering wheel still vs. loaded against the stops (idle)
~.01 GPH difference head lights on and off (maybe)

Note: I could barely tell the head lights were on or off
- thus most electrical loads would be smaller and even more insignificant

during the test my unloaded consumption was ~.46 GPH
parasitic load can be 70% of my idle load and 10-20% of my cruise load

Hope this is helpful,

[Ernie Rogers]

Hello, Noob,

Are you still around? Let's try answering your questions. In order to figure out the impact of various loads, we need some rules. So, I will make some up. First, we need a baseline car to look at. We are all hypermilers here, so the baseline will be an "ecomod special" that gets pretty good mileage. Here are the numbers I chose--

For the condition of interest, it takes 6 kW of power to move the car down the road. This is the actual "load," the power delivered to the tires:

Driving load..........6 kW (Energy delivered to the wheels)

Which translates to---
Gasser at 27%.....58 mpg (With 15% other losses)
EV at 70%.........227 Wh per mile = 150 mpge (at 34 kW /gal)

So, what if we just assume that all other loads have a 15% waste factored in? Then we can compare them directly to the 6 kW.

Running lights, about 250 watts?..............4% mileage penalty with lights
How much for power steering?

Okay, let's look at the list of questions--

1) The Heater (Does low or high make a difference?)
ANS: Maybe 50 watts max. for the fan.........1%
2) The Defrost (I think I heard it does steal some MPG)
ANS: If the AC runs, maybe 250 watts?........4%
3) Small things in the power outlet (like a GPS or L.E.D. or something)
ANS: Maybe 20 watts?..............................0.3%
4) Big things in the power outlet (like a 100 or 200 Watt converter thingy)
ANS: 200 watts to something.....................3.3%
5) The Radio (Does low or high volume make a difference?)
ANS: 100 watts radio + 3 watts for loud.......1.7% + .05% for loud
6) Electricity of running the wind shield wipers
ANS: Oops, sorry, I don't know. 100 watts?..1.7%

Leadfoot driving.......................................20%

So, there you are.

Ernie Rogers

Originally Posted by HypermilingNoob

Ok so it is very obvious that the a/c is always talked about as stealing MPG. But what about these other things? And how much? Remember to be as specific as possible because if you say "it hurts a little" that could mean to me 0.001 MPG difference or 0.5 MPG difference...
1) The Heater (Does low or high make a difference?)
2) The Defrost (I think I heard it does steal some MPG)
3) Small things in the power outlet (like a GPS or L.E.D. or something)
4) Big things in the power outlet (like a 100 or 200 Watt converter thingy)
5) The Radio (Does low or high volume make a difference?)
6) Electricity of running the wind shield wipers
And don't side track and try telling me about how dangerous it would be to go without the wind shield wipers or something because that is obvious and I wouldn't anyways. I figured these things might use up MPG from running the alternator harder or something?

[RandomFact314]

So your saying that daytime running lights use as much energy as having the a/c or defrost on? If that is true, Holy crap! well according to these calculations of his and mine my mpg should go something like this:

at 31.5 mpg originally so 378 miles per tank (assuming I run out all 12 gallons)

lead foot (@20% loss): 302.40 mpt (25.2mpg) (haha)
daytime running lights: 362.88 mpt (30.2mpg)
The Defrost (a/c): 362.88 mpt (30.2mpg)
big things (200w): 365.64 mpt (30.4mpg)
the radio (100w): 371.64 mpt (30.9mpg)
windshield wipers (100w): 371.64 mpt (30.9mpg)
The heater: 374.28 mpt (31.1mpg)
Small things: 376.92 mpt (31.4mpg)

[theunchosen]

I forget the OP topic but the engine is stealing some power for ingition and other functions.

These don't look like very major differences with them on but something Ernie accidently dropped is your alt is nowhere near 100% efficient. On a good day its 60-75%. So it takes anywhere from 30-50% more power from the engine to make those watts. The more you draw the bigger the problem. Like I said that 200w in your cigarette lighter is going to be more like 300-350 watts(.4-.5 hp).

Also adding a few of those functions together and its serious gas mileage(for quick and easy just add 1/3 more than what it cost originally to account for ALT inefficiencies).