Battery Life

[ApertureS]

11 hours ago, J.R. said:

Then the piston would be creating a partial vacuum on every downstroke sucking up air past the piston rings and then compressing it on every upstroke, good for engine braking, not so good for the health of the engine and the pumping losses would no doubt exceed any fuel saved.

 

But indeed that is what I have also read.

Thinking of it this way.

 

if the valves are closed at bottom dead centre the engine uses it’s up stroke to compress the air, the compressed air wants to expand to will use that same power to assist pushing the piston back down.

 

if the valves close at top dead centre as the piston drops and pulls a vacuum it will want to return to its previous state (same as putting your finger over the end of a syringe) it will pull the piston back up.

 

Not sure the science or numbers on it, but both of these processes use power to vacuum or compress, then the air wanting to return to its normal state would negate the losses.

(this is my thinking on the science of things and yes it’s not 100% efficient either)

[J.R.]

I follow your logic but I think it would be very very inefficient due to the pumping losses, if you have ever tried rotating an engine by hand with the valves closed and spark plug in place it would illustrate the forces required better than I can explain, you have heard the gases passing into the crankcase when rotating an engine with working valve gear, the cylinder deactivation with closed valves would have the gases passing back and forth to the crankcase with every revolution.

 

I can theorise a way to minimise the power loss and that would be for the deactivated cylinders to feed into each other and being 360° out of phase which they would be anyway (180° in respect of piston movement, 360° in respect of the combustion cycle), I very much doubt that is what they are doing were it physically possible.

 

I really would like to know what they do to mitigate or overcome the problem, maybe its exactly as you say because the thermal efficiency of a petrol engine is so low anyway that its better to compress and displace gases creating heat than fire up the Otto cycle on more cylinders than are needed for the power output.

Edited 7 October, 2023 by J.R.

[PetrolDave]

This video explains that the valves stay closed when the cylinders are deactivated

 

https://www.youtube.com/watch?v=yoohR8sar5g

[J.R.]

Thanks, I'm not the only one to have reservations judging from the comments:

 

"The problem, however, is what to do with the oil that enters the deactivated cylinders (the piston rings act as an oil pump). The oil inlet is also augmented by the fact that after a few seconds, the air inside the cylinder due to its leakage from the piston rings will cease to act as a spring, as in the cylinder will be vacuum during piston descent. How are these problems handled by Volkswagen, or they are not so important that they do not significantly affect the operation and lifespan?"

 

I don't doubt that it saves a minimal amount of fuel, the large gains have all been made, current and future gains are the sum of lots of tiny incremental ones like this but at what cost?

[Rodge]

On 06/10/2023 at 02:44, Gerrycan said:

I figure that using engine braking uses no fuel and is still turning over the alternator but does this mean that if brakes are applied, however lightly, this will signal the alternator to create a greater output to the battery and more resistive load?

Does that mean that someone who drives like me will not be adequately charging their battery especially if being drained by engine stop/start?

The alternator ramps up whenever I take my foot off the accelerator - pressing the brake pedal is not necessary. I have a voltmeter plugged into the cigarette lighter socket and can clearly see the effect. I use engine braking as much as possible, but the little 1.2 gives a lot less braking than the 1.6 in my 20 year old Focus. The Octavia's battery still seems to be fine after 8 years.

[Micky 32]

Different car ( Passat) but similar 2.0 TDI engine and the same AGM battery. 6 years and 8 months 190k miles. At 5 degrees C the other morning it just about started. Quite disappointing while other cars are getting 10 years plus out of their batteries. Never abused. It actually began showing signs of it beginning to weaken 3 years ago.

[classic]

On 07/10/2023 at 10:42, J.R. said:

 

Edited 22 October, 2023 by classic
Wrong quote

[classic]

7 hours ago, Micky 32 said:

Different car ( Passat) but similar 2.0 TDI engine and the same AGM battery. 6 years and 8 months 190k miles. At 5 degrees C the other morning it just about started. Quite disappointing while other cars are getting 10 years plus out of their batteries. Never abused. It actually began showing signs of it beginning to weaken 3 years ago.

I guess a lot of the difference would be the random differences of use between vehicles. 190k miles in 6 years 8 months is above average, do you use stop start a lot or disable it or don’t do very much urban driving, there’s so many variables. Someone else might get 10 years but somehow their use is easier on the battery, and whilst you have noticed it only just started many drivers wouldn’t.

[classic]

On 07/10/2023 at 07:21, ApertureS said:

Thinking of it this way.

 

if the valves are closed at bottom dead centre the engine uses it’s up stroke to compress the air, the compressed air wants to expand to will use that same power to assist pushing the piston back down.

 

if the valves close at top dead centre as the piston drops and pulls a vacuum it will want to return to its previous state (same as putting your finger over the end of a syringe) it will pull the piston back up.

 

Not sure the science or numbers on it, but both of these processes use power to vacuum or compress, then the air wanting to return to its normal state would negate the losses.

(this is my thinking on the science of things and yes it’s not 100% efficient either)

 

I test drove a Karoq with act about 6 months ago and it got me interested in how it works because it was regularly going into 2 cylinder mode and I really couldn’t feel the change over at all.

Apparently the system closes the valves when the cylinder is in the middle of its exhaust stroke so it is basically half full of exhaust and the piston then pumps up and down easily. It means that the shut down of the 2 middle cylinders is actually in two stages as each one reaches the middle of its exhaust stroke. It “shuts down” one cylinder  before the other. When cylinder 2 is halfway through exhaust and it gets its valves closed, cylinder 3 is halfway through compression and does one more power stroke before it shuts down when it reaches the middle of its exhaust stroke. 

It only seemed to operate under fairly light engine load, as soon as you demand any real power it went back to 4 cylinders. It seems a lot of extra complexity and I wondered how will these changing loads affect the crankshaft long term ?

 

[Micky 32]

2 hours ago, classic said:

I guess a lot of the difference would be the random differences of use between vehicles. 190k miles in 6 years 8 months is above average, do you use stop start a lot or disable it or don’t do very much urban driving, there’s so many variables. Someone else might get 10 years but somehow their use is easier on the battery, and whilst you have noticed it only just started many drivers wouldn’t.

Thinking of how the car is used you are probably right. Firstly i use my car for work and that entails calling to peoples houses. So after each house visit the starter gets activated which could be a good few times during the day. However the journeys aren’t  short berween house visits. The car gets enough driving to keep the battery at it’s optimum. For the last few months the car is averaging 700 ish miles a week. The car doesn’t get much city or town driving compared to driving out the countryside.

 

I leave the start stop on. When i am in towns/cities i like to think i’m helping to keep the air a little cleaner in those areas.

 

In VCDS you can check how many times the starter has been activated throughout it’s life. I’m not sure what the purpose is. Last time i checked it activated 55,000 times. It’s probably circa 57,000 by now.

 

 

[J.R.]

3 hours ago, classic said:

 

 

I test drove a Karoq with act about 6 months ago and it got me interested in how it works because it was regularly going into 2 cylinder mode and I really couldn’t feel the change over at all.

Apparently the system closes the valves when the cylinder is in the middle of its exhaust stroke so it is basically half full of exhaust and the piston then pumps up and down easily. It means that the shut down of the 2 middle cylinders is actually in two stages as each one reaches the middle of its exhaust stroke. It “shuts down” one cylinder  before the other. When cylinder 2 is halfway through exhaust and it gets its valves closed, cylinder 3 is halfway through compression and does one more power stroke before it shuts down when it reaches the middle of its exhaust stroke. 

It only seemed to operate under fairly light engine load, as soon as you demand any real power it went back to 4 cylinders. It seems a lot of extra complexity and I wondered how will these changing loads affect the crankshaft long term ?

 

That makes sense now as one piston is compressing the other one has an equal and opposite decompression force, a bit like those water powered funicular carriages (or even a passenger lift) where the weight of the one going down counterbalances the one going up

[classic]

I didn’t know that about vcds. I’ll see what mine has done next time I plug it in.

[Micky 32]

41 minutes ago, classic said:

I didn’t know that about vcds. I’ll see what mine has done next time I plug it in.

Yep. Download history data and open with toolbox.

[J.R.]

Do you know the name of the variable so I can search for it amongst the tens of thousands on the list?

 

I can be fairly sure that it will be a term that bares no relation to "Engine starts" or "Starter motor operations/cycles" so pointless me searching without knowing what term the dopeheads decided on that day!

[Micky 32]

3 hours ago, J.R. said:

Do you know the name of the variable so I can search for it amongst the tens of thousands on the list?

 

I can be fairly sure that it will be a term that bares no relation to "Engine starts" or "Starter motor operations/cycles" so pointless me searching without knowing what term the dopeheads decided on that day!

 I can’t remember exactly but i’ll have a route tomorrow and will find it and i’ll  post it here exactly how to find it tomorrow.

[Micky 32]

20 hours ago, J.R. said:

Do you know the name of the variable so I can search for it amongst the tens of thousands on the list?

 

I can be fairly sure that it will be a term that bares no relation to "Engine starts" or "Starter motor operations/cycles" so pointless me searching without knowing what term the dopeheads decided on that day!

Right here’s what to do.

1. Connect car to VCDS

2.Go into applications 

3. Click on History Data

4. Choose address ‘19’ and start. It will go through a download. Save when finished

5. Go out of that and select VCDS Toolbox. Click on B.history and should open a box with the history file. Click on it and the toolbox screen should fill with data.

6. Click on the drop down box and select 16. Vehicle energy balance

7. There’s a smaller dropdown box to the right, click on that and select one of the numbers. My starter info was number 3 on the list. Look for “ engine start counter” My car has now 59994 starts!

 

There’s another dropdown box “ Battery aging”. My readings are:

 

Age in relation to charging = 70%
Age in relation to performance = 53%

Edited 23 October, 2023 by Micky 32

[J.R.]

Thanks for that, I must download VCDS to my new computer and have a play.

 

I don't think I have seen "Applications" as a menu item, I have certainly never seen "VCDS Toolbox" also on my old computer whenever I saved any data I could never find it again, Mike The Thinker set up a file for all the saved scans but after a while they either went somewhere unfindable or dissapeared into the ether.

 

Time for me to get is sorted before I need it.

 

I have some dim recollection of seeing a data field called engine starts but dismissed it because the number had too many zeros, do you really think your car will have done 60K engine starts? Only you will know how many miles its done and your journey profile and if there were previous owners, I know my figure was implausible.

 

Battery aging sounds very useful.

[Micky 32]

47 minutes ago, J.R. said:

Thanks for that, I must download VCDS to my new computer and have a play.

 

I don't think I have seen "Applications" as a menu item, I have certainly never seen "VCDS Toolbox" also on my old computer whenever I saved any data I could never find it again, Mike The Thinker set up a file for all the saved scans but after a while they either went somewhere unfindable or dissapeared into the ether.

 

Time for me to get is sorted before I need it.

 

I have some dim recollection of seeing a data field called engine starts but dismissed it because the number had too many zeros, do you really think your car will have done 60K engine starts? Only you will know how many miles its done and your journey profile and if there were previous owners, I know my figure was implausible.

 

Battery aging sounds very useful.

It’s quite possible it has done 60k starts, given the mileage, unfortunate battery condition and i don’t turn off the start stop. Whether it’s accurate i can’t say for sure.