Is using auto start-stop bad?

Zandoni

WellKnownSid wrote: »

But that's my point you're not, when the car isn't moving you're NOT using extra fuel because the engine's already been turned off. It's only when you start moving.

Think of it another way. If it takes you 60 minutes travel up a motorway - and for 15 minutes of that the engine was not running - which was what happened to me on Friday night - you've avoided idling your engine for 15 minutes. Now, the electrical drain during that time was, what, 20 amps - so 5Ah lost from the battery. There might have been ten restarts during that time - if you ignore the capacitor and assume 5 seconds total at 900A that's 1.25Ah.
Your charging system is only 80% efficient so you need to put back 6.25/0.8 = 7.8Ah call it 8Ah.
It's a 12V system - so 96Wh. As a side check we want to put that ALL back in the last six minutes of the journey when I pull off at the junction. That's a load of 96/0.1 = 960 watts. 80A - about right for a big alternator.

My car uses 0.2 gallons / hour idling - so I've saved 0.05 gallons = 0.22 litres of fuel.

Energy density of diesel is 10kWh/litre - my 96Wh would take 0.0096 litres at 100% thermal efficiency or 0.024 litres of fuel at 40% thermal efficiency.

So I saved 0.196 litres or 21p of fuel on Friday.

How about the extra car weight from the big battery, alternator and starter motor that you carry around all the time. Plus the extra price you pay for the system of course.

prowla

peter_the_piper wrote: »

Picanto. I use stop start Stop/start when the lights have just turned red, if not I keep the foot on the clutch. If the level crossing is down then its used also, normal s/s in traffic I will not use it. Its turned off by turning the air vent knob(if that's the right word) S/S won't work if air con on.
Don't know if it makes any difference to mpg as I don't keep such a close watch on things. I do find leaving the MPG setting on the dashboard shows what my full tank would do and has a great effect on the weight put on the accelerator pedal.

Keeping your foot on the clutch is bad for the clutch.

DUTR

Zandoni wrote: »

How about the extra car weight from the big battery, alternator and starter motor that you carry around all the time. Plus the extra price you pay for the system of course.

I think you are missing an obvious point.
If the engine is not running then it is not consuming fuel or emitting exhaust.
Even with the weight of the battery the car over all is lighter than the previous generation, (in my model at least) , SS is not an optional extra, so much as you may not like it or be sceptical about it, 4 for sure, your future car will have it at some point.

Zandoni

DUTR wrote: »

I think you are missing an obvious point.
If the engine is not running then it is not consuming fuel or emitting exhaust.
Even with the weight of the battery the car over all is lighter than the previous generation, (in my model at least) , SS is not an optional extra, so much as you may not like it or be sceptical about it, 4 for sure, your future car will have it at some point.

But it would be lighter still if these heavier components weren't fitted. Although it's not an optional extra, the price of it is added to the overall cost and I just wonder if all the factors added together really make any savings.

DUTR

Zandoni wrote: »

But it would be lighter still if these heavier components weren't fitted. Although it's not an optional extra, the price of it is added to the overall cost and I just wonder if all the factors added together really make any savings.

Keep wondering, but you will have to accept it.
There is an overide button, so you don't have to have it active (personally I cannot see the need to disable the system) .
As said there is no need to have the engine idling for a couple of minutes every stop and those stops soon add up, there are 7 sets of traffic lights on the way to work, that excludes pelican crossing, if they all changed to red as I approached then that's 14 mins of idling time for an 18-20 minute commute.

I'd say if you have it so right and the MFRS have it so wrong, then perhaps an application for a position within the industry maybe wise, I hear VW are hiring, something to do with DERV Nox emissions :A

Zandoni

DUTR wrote: »

Keep wondering, but you will have to accept it.
There is an overide button, so you don't have to have it active (personally I cannot see the need to disable the system) .
As said there is no need to have the engine idling for a couple of minutes every stop and those stops soon add up, there are 7 sets of traffic lights on the way to work, that excludes pelican crossing, if they all changed to red as I approached then that's 14 mins of idling time for an 18-20 minute commute.

I'd say if you have it so right and the MFRS have it so wrong, then perhaps an application for a position within the industry maybe wise, I hear VW are hiring, something to do with DERV Nox emissions :A

Wow, I wonder if something is a marketing gimmick and not worth the extra price and I get insulted.

I'm not convinced that if all cars are fitted with this technology there will be any savings across the board. It's all these so called green policies that has got us into the problems like Volkswagen and the others that could soon be following.

Retrogamer

Save money on fuel over the vehicles life time so you can spend the savings on new starter motors and batteries.

reeac

It's possible to postulate thousands of different traffic scenarios but my feeling is that as far as economics is concerned the effects of SS are marginal. There can be no doubt though that air pollution in traffic jams is a problem and perhaps SS can reduce it since it would operate more often than the average driver would switch off.

DUTR

Zandoni wrote: »

Wow, I wonder if something is a marketing gimmick and not worth the extra price and I get insulted.

I'm not convinced that if all cars are fitted with this technology there will be any savings across the board. It's all these so called green policies that has got us into the problems like Volkswagen and the others that could soon be following.

I'm sure there maybe extra costing, when I purchased my car I wasn't woo'd by the CO2 or fuel features, however I do note that I have increased 30ps with engine power yet my VED has reduced from £265 to £145 , now there is the AEB system too, that will add weight and price again this was not a selling feature of the vehicle, my insurance renewal was just over 50% of the previous car. Ok, I splashed out thousands to buy the car (and without regrets) as there is no point saving without any intent to spend it, I worked for it so I'm going to spend it on myself, not leave it for everyone else to fight over.
In fact I don't recall SS being marketed, it maybe a Euro thing, just like daytime running lights, airbags etc.

DUTR

Retrogamer wrote: »

Save money on fuel over the vehicles life time so you can spend the savings on new starter motors and batteries.

How many reports have you seen regarding replacement starter motors?
Last starter motor I replaced or had to have replaced was on a 1973 Vauxhall Viva HC, not saying cars don't require component replacements, but it's not common place like back in the day.