Technical Stop Start Story

[jrkitching]

But its not necessarily only a 'tiny' amount of fuel being saved.

It's worse than that.

What UFI's linked report is saying is that, after as little as two weeks use, a car with S/S actually uses more fuel than the same car without it. The energy losses in recharging the battery mean you use more extra fuel after the engine restarts than you saved whilst it was switched off.

I've seen this story before, and I believe it.

As Mick says, the environmental benefit of S/S in an urban environment is a much better justification for having it.

 

[Mick F]

I suppose over the life of the vehicle, the fuel savings could be substantial especially if the vehicle is used in traffic most of its life.

How much fuel per minute does a car consume at tickover?
Are there any figures?

Regards,
Mick.

 

[jrkitching]

I suppose over the life of the vehicle, the fuel savings could be substantial especially if the vehicle is used in traffic most of its life.

No, read that linked report again.

For the majority of the vehicle's life, you will use more fuel replacing the energy taken from the battery whilst the engine was stopped than you would have used if you'd just left it running.

The question you should be asking is how much fuel is consumed recharging a battery that's been left standing overnight, and how this figure changes as the battery ages.

 

[Mick F]

I don't agree, though I have no real knowledge here, just a guess.

If the car is stopped engine off for three minutes at traffic lights before being restarted and the battery replenished, how much fuel is used to restart and replenish?

Same car, ticking over for three minutes at the same traffic lights, then drives away. How much fuel is consumed ticking over?

If you can answer those, I'd bow down and agree.

Regards,
Mick.

 

[jrkitching]

If the car is stopped engine off for three minutes at traffic lights before being restarted and the battery replenished, how much fuel is used to restart and replenish?

Same car, ticking over for three minutes at the same traffic lights, then drives away. How much fuel is consumed ticking over?

If you can answer those, I'd bow down and agree.

Regards,
Mick.

It's not that simple.

What you also need to calculate is how much extra energy is lost by the heavier-duty battery over the lifetime of the car. An older S/S battery will likely have a greater overnight charge depletion than a non-S/S one, and unless you connect a charger every night, that greater charge depletion must be paid for in fuel the next time you use the car.

UFI has done some real-world experimentation on the 500 and seems to have a pretty good handle on the whole battery issue.

Sometimes you make an apparent saving in one area, only to pay it back with interest somewhere else.

 

[Mick F]

Again, it's not that simple.

If you consider "the lifetime of the vehicle" you're entering into the realms of all sorts of imponderables. Over a lifetime many things come into play and we cannot take them all into account.

My question still stands.
How much fuel is consumed per minute at tickover?
How does this compare to starting the car and replenishing the battery?

Thanks,
Mick.

 

[jrkitching]

Over a lifetime many things come into play and we cannot take them all into account.

Unless you take them all into account, any calculations you make about the economics of S/S fitment could be misleading.

How much fuel is consumed per minute at tickover?

It depends on the electrical load on the car.

How does this compare to starting the car and replenishing the battery?

It depends on the electrical load whilst the vehicle was stationary, the age and condition of the battery, the speed with which the engine restarts, and probably some other stuff as well.

But as I've said before, if you only take those two factors into account, you'll come to the wrong conclusions about the economic benefit of S/S anyway. The greatest battery losses likely occur when the car is parked.

How about looking at this another way. Below are the average mpg figures taken from fuelly for the 500 by year of manufacture:

2008: 47.2 mpg
2009: 48.6 mpg
2010: 46.9 mpg
2011: 44.3 mpg
2012: 41.4 mpg
2013: 40.2 mpg

S/S was introduced as standard for the 2010 model year. All the average mpg values for cars built since it was introduced are worse than for the two years when it didn't have it.

Now I'll be the first to agree this isn't a rigourous analysis - but if implementing S/S across the fleet was supposed to save fuel, there's no indication of it in those numbers.

 

[Mercky]

It really should be all about emissions and not fuel savings although they are obviously directly linked, and also more about the collective effect rather then the individual. Imagine if the millions of cars currently in the world right now this second that are sitting in traffic chucking out fug were to stop for a few mins - it has to be beneficial to the environment / global warming or whatever over a period of time. I use the analogy of going down to your local recycling centre and throwing 5 or 6 plastic bottles in to the big container, that alone has little environmental impact but when you look in and see a couple of hundred other bottles that would have otherwise gone to landfill you realise it has to be a good thing. And yes, I know cows fart a lot!

 

[306maxi]

Unless you take them all into account, any calculations you make about the economics of S/S fitment could be misleading.



It depends on the electrical load on the car.



It depends on the electrical load whilst the vehicle was stationary, the age and condition of the battery, the speed with which the engine restarts, and probably some other stuff as well.

But as I've said before, if you only take those two factors into account, you'll come to the wrong conclusions about the economic benefit of S/S anyway. The greatest battery losses likely occur when the car is parked.

How about looking at this another way. Below are the average mpg figures taken from fuelly for the 500 by year of manufacture:

2008: 47.2 mpg
2009: 48.6 mpg
2010: 46.9 mpg
2011: 44.3 mpg
2012: 41.4 mpg
2013: 40.2 mpg

S/S was introduced as standard for the 2010 model year. All the average mpg values for cars built since it was introduced are worse than for the two years when it didn't have it.

Now I'll be the first to agree this isn't a rigourous analysis - but if implementing S/S across the fleet was supposed to save fuel, there's no indication of it in those numbers.

Firstly as time has gone on, more and more less fuel efficient 500's have appeared non? Plus as cars get more miles on them they get more economical.

 

[jrkitching]

Firstly as time has gone on, more and more less fuel efficient 500's have appeared non? Plus as cars get more miles on them they get more economical.

That example was a bit tongue in cheek . You'd need to do a much more rigorous analysis to form any statistically valid conclusion.

But it's also interesting that as the number of TA's has increased, the average mpg of the fleet has worsened. It certainly reflects the widening gap between 'official economy/emissions figures' and real-world experience.

If you take my 500 out of the dataset, the results for the 2010 cars would look even worse .

My real point is that there's a lot of misinformation and misunderstanding out there about the real value of a whole host of supposed eco-benefits - there are some powerful vested interests at stake and things are not always what they seem to be.

If you want an interesting example of this, look at what Nissan have done in the US recently to fudge up the range figures for the Leaf.

 

[306maxi]

Is it though? The problem with turbocharged engines is that they can be economical, but if you put your foot down. Our Legacy turbo has done 40mpg on a run and can get into the teens, the estate we have with a normally aspirated engine is more consistent in its mpg's even if thrashed.

 

[jrkitching]

Is it though? The problem with turbocharged engines is that they can be economical, but if you put your foot down. Our Legacy turbo has done 40mpg on a run and can get into the teens, the estate we have with a normally aspirated engine is more consistent in its mpg's even if thrashed.

Whichever way you cut it, the figures show that real-world economy is out of step with the fiscal advantages conferred on the latest cars.

Have Fiat been clever, or is the system broken?

 

[306maxi]

Or are the changes resulting in cars which people end up driving differently?

 

[Mick F]

How much fuel is consumed per minute at tickover?
It's a simple question.

If it needs to be said:
Fully charged battery.
Zero electrical drain.

How many millilitres per minute?
10?
20?
30?
100?

Sorry for being grumpy,
Mick.

 

[jrkitching]

How much fuel is consumed per minute at tickover?
It's a simple question.

If it needs to be said:
Fully charged battery.
Zero electrical drain.

How many millilitres per minute?
10?
20?
30?
100?

Sorry for being grumpy,
Mick.

You're not being grumpy - it's a good question & I'd like to see these figures too.

I'd also like to see how they change as various electrical devices are switched on & off, and how they change according to the state of charge of the battery.

Unfortunately those figures are not to my knowledge published anywhere, and obtaining them to a meaningful level of accuracy would take quite a bit of time and also need some reasonably sophisticated equipment.

I've no doubt Fiat have a whole bunch of relevant data; I've also no doubt they're not going to be releasing any of it anytime soon.

 

[UFI]

My question still stands.
How much fuel is consumed per minute at tickover?
How does this compare to starting the car and replenishing the battery?

See my data here:

https://www.fiatforum.com/500/342685-some-interesting-data-collected.html?p=3407737

A LOT of fuel is wasted idling. 4.52l per 450km or 1l/100km in the case of the Merc, or about 0.5l/100km if adjusted for a 500 on the same routes.

Restarting a healthy car (in the case of a TA at least) uses no extra fuel at all. Ford and BMW claim it's better to use S/S even if only stopped for 3-5 seconds.

Older ECU''s may go open loop for a few seconds on restart, but no S/S car would do that.

As for the extra fuel used to replenish the battery, no one really knows. I stop/start my new Renault all the time (manually), I've added a Supercap to boost battery life, unfortunately, I'm 99% sure adding a battery saving supercap to UFI will render the factory S/S inoperable :bang:

 

[UFI]

How much fuel is consumed per minute at tickover?
It's a simple question.

If it needs to be said:
Fully charged battery.
Zero electrical drain.

UFI takes about 0.6l/hr with no accesories and a good charge. The ventilation fan on full can take about 0.2l/hr and the A/C compresor takes about 0.3.

Idle is very efficient on the TA which makes the S/S argument more of a 50/50 debate than it is on many other cars.

 

[PuntoHowTo]

There is one inherent floor in the stop,start system, which is car batteries don't like to deep cycle, delivering huge jolts of power then being allowed to replenish, is what keeps them happy, in this respect they differ in design from something like a leisure battery which looks the same externally but is designed to deliver low currents for long periods of time essentially the internal structure is the same lead and acid but the design of the lead plates differed greatly to allow long deep cycling then charging repeatedly without loss of the plates surface to sulfation.

With stop start you need a regular car battery to deliver the jolt to start the car then when the car is in its stopped mode the battery is being used like a leisure battery to run fans ecus screen/mirror heaters radios etc etc, effectively deep cycling the battery.

Car batteries will charge quickly because of there internal design just as they can deliver power quickly, a leisure battery delivers the power slowly and as such will charge slower even if charged at the same current and voltage.

Stop start batteries fall somewhere in between but err more towards a regular car battery which means when stopped the battery really isn't happy.

Car alternators are designed to run the electronics on car and top up the battery but they are not battery chargers so they are not designed to deliver constant high levels of driven current to a battery, so to charge a battery you need to overcome its internal resistance and then push more current in, a bench battery charger will do this with ease as its designed to take your mains 240v 13A supply and push energy into the battery at 4+ amps continuously for long periods.
An alternator is pushing out current at 14ish volts but the current can be going up and down dependent on what is using that power and only a small amount is trickling into the battery. The steering on these cars can uses in excess of 90Amps so when this happens it drains everything the alternator can deliver and the battery gets abused as well.
So you have a battery which charges slower yet is getting used more to keep starting the car. When it's stopped the battery is being deep cycled in a way it doesn't like.

This is why it never hurts to give a battery a proper charge every now and again off the car. And why they don't last as long in stop start use.

Fiat basically bolted the stop start system into existing technology so the cars use a regular starter motor and a regular alternator.
Better systems use a combined uprated generator/alternator which is also used as a motor to spin the engine up. This system uses less fuel to start the car because it doesn't need to pour fuel in to get ignition it can slowly drip the fuel in till it fires as the motor is more than powerful enough to turn the engine at full speed. This type of starter is also better suited to a deep cycling battery so the battery can be more designed like a leisure battery for longevity and long power delivery, better for when the car is stopped, and the alternator/generator is designed to deliver much higher currents to properly charge the battery when the car is running.

If you are still with me, In answer to an earlier question fiat batteries are not 'crap' fiat stop start systems are crap.

I've seen it in the past but can't for the life me remember, there used to be a car that when stationary in traffic would change Mpg to Litre per hour, so you could see in realtime what the engine was doing, my old mondeo used to have a hidden test function that would also bring up this figure. I'm sure MultiEcuScan would bring up this data if you wanted it to, it would be fairly simple to try it with a normal battery that's been used every day, then give it a good charge before trying again and seeing if there was much difference in consumption at idle, I would think that only if the battery is really depleted would you see the engine needing to use more fuel at idle otherwise it might not be normally measurable.
Just changing the temperature of the battery will change how well it charges.

So essentially stop start was designed to reduce co2 at the tail pipe, as pointed out once in regular use the benefits of the system become outweighed by the constant need to inefficiently charge the battery. But at least it looked good on the MPG tests and makes for a sales point 'this stop start thing will save you fuel'
I remember seeing it on a VW golf about 20 years ago on BBC's tomorrow's world so it's not new technology just with ever more stringent regulations on emissions it's working in the favour of the manufactures now.

As maxi pointed out though and I completely agree an older car 3-4 years old will be more efficient than a brand new car as the engine will have loosened up and worn in on the older car. So figures from fuelly don't really prove anything.

 

[logger]

..I've seen it in the past but can't for the life me remember, there used to be a car that when stationary in traffic would change Mpg to Litre per hour, so you could see in realtime what the engine was doing, ... I'm sure MultiEcuScan would bring up this data if you wanted it to...

My 5 year old Golf 6 does this. Switches to litres per hour when stationary. Fuel flow is also available in VCDS which is the VW equivalent of multi scan.

 

[larslarsen]

.......

Fiat basically bolted the stop start system into existing technology so the cars use a regular starter motor and a regular alternator.

.......

Thank you for your helpful explanations, but for the above sentence I cant agree since I have read the opposite.

Without adapted alternator, starter motor and battery sensor S&S could not work at all.

In my TA it works, but not if cold outside, quite good (not below 0 Celsius).

Possibly ist related to Italien climate test eviroment ....

At the time BMW released first version of EfficientDynamics, S&S was Off below 3 (?) Celsius (in between its no more the case).

Unfortunately FIAT did not take this into account.

FIAT made it worse, with an Update (it allows also to switch Off S&S permanently - this is good), from now S&S also kicks in case rear window heater is on and/ or wiper is active on high speed, what was not the case before the Update, resulting in high battery drain, if engine stopped.