Electrics and MPG

[Jit C240]

Hi All,

Can someone explain to me how turning off in car electrics such as the radio, heater etc, can improve MPG?

I understand that using these items places more stress on the cars electrical system, however how does this effect the cars MPG?

Thanks

 

[seymansey]

More load on the alternator - great effort required to turn the alternator round = more effort on the engine, thus increased fuel consumption.

 

[tali]

Ususally A/C takes the biggest hit on MPG - but in nearly 20 years of driving it has only had affect on one car i have owned - so imho car electrics will do sweet FA
If car electrics -improve MPG - then it must be a sub atomically small level it would not be worth bothering about -that's from my experience anyway

 

[Colin_b]

Ususally A/C takes the biggest hit on MPG - but in nearly 20 years of driving it has only had affect on one car i have owned - so imho car electrics will do sweet FA
If car electrics -improve MPG - then it must be a sub atomically small level it would not be worth bothering about -that's from my experience anyway

I understand that aircon uses less fuel than driving with a window open one you are doing more than 40 or 50mph as the aerodynamics are not good.

My SLK is about 3mpg down with the roof down at 70.

 

[Stratman]

Head and sidelights, say 150W
HRW, 100W
Radio, 10W
Heated seats no idea, say 50W.

Let's say with a few other consumers going there's a 500W load, that's about two thirds of one horsepower. With the mechanical losses of the belt and alternator call it one horsepower required to drive the electrics.

T'aint much in the real world.

 

[steve333]

Ususally A/C takes the biggest hit on MPG - but in nearly 20 years of driving it has only had affect on one car i have owned - so imho car electrics will do sweet FA
If car electrics -improve MPG - then it must be a sub atomically small level it would not be worth bothering about -that's from my experience anyway

Never noticed any difference in mpg the few times i've experimented in varios mb's

 

[Dryce]

Head and sidelights, say 150W
HRW, 100W
Radio, 10W
Heated seats no idea, say 50W.

Let's say with a few other consumers going there's a 500W load, that's about two thirds of one horsepower. With the mechanical losses of the belt and alternator call it one horsepower required to drive the electrics.

T'aint much in the real world.

Depends on how many HP your vehicle uses as opposed to the rating of the engine.

ISTR a previous discussion about the BMW energy saving system that charges the battery and that these loads actually do become more measurably significant when cruising.

 

[tali]

I understand that aircon uses less fuel than driving with a window open one you are doing more than 40 or 50mph as the aerodynamics are not good.

My SLK is about 3mpg down with the roof down at 70.

That is possible as open window causes drag

Never noticed any difference in mpg the few times i've experimented in varios mb's

Supposed to be a 8% hit on MPG- but only my Mondeo was only car affected that i owned
There is all this hypermiling nonsense- why not just bin radio and save weight? It won't be too long before some MPG hypermiler fetshist will be driving around just in his underpants!

 

[mbenz76]

I wondered this myself, and how much cold and weight impacts on it.

During summer I was getting 25 around town (full blown rush hour) in my E350. However in the thick of winter with the temperature not getting above freezing for days I was lucky to get 15 in the same conditions.

During the freezing conditions I also kept the fuel tank full (80 litres of diesel) and kept 100kg of rock salt in the boot, so increased mt weight as if carrying a very overweight person in the boot I guess.

Had the heated rear window, heated seats and heated steering wheel on (though was conscious of not keeping them on too long).

Can that really account for a drop of 10?

 

[tali]

Those E350 figures are pretty poor V8 levels-sort of rubbish figures i only manage -however my rubbish MPG has always been consistent regardless of any variable or factors

 

[biturbo]

My S600 makes absolutely no difference in mpg with all gismos on / off

Heated seats on both front and massage.
heated rears and massage both on.
fridge,
stereo on full wack
ac on
lights on
headed rear window.

Still doing exactly the same mpg.

I think the smaller the car engine the more elecs make a difference, 50mpg and lose 2-3 mpg for AC etc.

anything above 3ltr i would think it does absolutely nothing.

 

[tagnut]

I think the smaller the car engine the more elecs make a difference, 50mpg and lose 2-3 mpg for AC etc.

This reflects my experience too. I'm sure it's to do with the percentage of power being generated that is taken for the electronic features

 

[Dryce]

I think the smaller the car engine the more elecs make a difference, 50mpg and lose 2-3 mpg for AC etc.

anything above 3ltr i would think it does absolutely nothing.

I suspect the effect is down to the impact of the electrics and A/C as a proportion of the cruising HP on the car.

Also small cars typically have A/C without controls. So people switch them on and leave them on continuously. Meanwhile climate control in a larger car will turn the A/C down to minimum and mix the ambient air once it reaches temperature.

 

[JamesCB]

My S600 makes absolutely no difference in mpg with all gismos on / off

Heated seats on both front and massage.
heated rears and massage both on.
fridge,
stereo on full wack
ac on
lights on
headed rear window.

Still doing exactly the same mpg.

Lol - You'd have thought that would be placing quite a strain on it!