Now, I have been going through all the parameters for the system, learning about the quirks. Some information suggests the battery, under certain circumstances, will only re-charge under braking. Not on the over-run down a long hill. Seems counter intuitive having to brake  going down a long hill, if I am holding the desired speed by lifting off the loud pedal.

Edited 27 May, 20197 yr by gregoir
Punctuation

Try plugging a cheap voltmeter into the cigarette lighter socket. It will show you what the system is doing. I got one combined with a thermometer and USB charger for less that 10 quid on Amazon. The voltage reading agrees with a calibrated meter from work to within 0.1 V.

Usually on over-run the voltage goes up to 14.9 V, but sometimes it only goes up to 14.5 V, which I had assumed was due to extra load on the system. On mine it will run at 14.9 V continuously if it thinks the battery is low, which is quite often for me as I sometimes don't use the car for weeks at a time.

On my Stop / Start mkII Superb I've never fully worked out what it does for regerative charging. One thing I have spotted is under certain circumstances it shuts off the charging - I know this is because when on my travels I  have a coolbox in my boot connected via a PCT VOLTON ZR1220 voltage sensing split relay, which detects when the car isn't charging and shuts off the coolbox to stop draining the battery when parked. However I sometimes notice this after a run driving through a town - my car is very quiet at low speed so you do somewhat notice when the coolbox shutsdown. If I keep my headlights on this doesn't happen.

Edited 28 May, 20197 yr by bigjohn

Thanks. Just ordered a plug-in charger cum volt meter from the longest river in South America.

The 12v battery is so small and low voltage it won't make any difference to your car's speed.

 

If you want this kind of driving, better get an EV, where they can do single pedal driving. My humble first-gen Leaf can harvest up to 40kW of power slowing down, while new Audi E-Tron can harvest 150kW of power slowing down. In both cars, you gain driveable miles going downhill.

 

For my Skoda, I also leave it parked most of the time. I use a smart charger on the 12v battery a few times a year to keep it topped up. The stop/start system puts a lot of strain on the battery, with the "intelligent" charger that sometimes shuts off charging, I don't want to replace it on a 6 year old car when my previous car still had original battery by the time I sold it at 11 years old. Just more money for greedy motor industry if you don't do simple preventative maintenance.

Regenerative charging is just a gimick/marketting tool to make cars seem more "efficient". The difference you will get when braking is negligable.

 

However, the battery monitoring system is not a dumb system, it monitors the state of the battery, electrical load, temperature & should adjust charging according to the current conditions.

There are times where it will allow the battery to discharge, slow charge, fast charge to maintain a good condition of the battery.

A bit like DPF regen, just leave it alone to do its thing, no need to drive differently.

It will tell you if you need to intervene & will disable StopStart automatically if the battery is getting low.

 

My car is 5 years old, with almost 100k miles now, with no signs of the battery going.. (fingers crossed it will last another 5 years)...

Ok, thanks. I get it now.  I can carry on coasting down long hills, in gear, without having to press the brake pedal to keep the battery charged up.

This is really interesting, I didn’t know braking helped charge the battery and contributed to making start/stop kick in. Makes sense now I think about it as to when start/stop does and doesn’t work 👌

23 hours ago, bigjohn said:

On my Stop / Start mkII Superb I've never fully worked out what it does for regerative charging. One thing I have spotted is under certain circumstances it shuts off the charging - I know this is because when on my travels I  have a coolbox in my boot connected via a PCT VOLTON ZR1220 voltage sensing split relay, which detects when the car isn't charging and shuts off the coolbox to stop draining the battery when parked. However I sometimes notice this after a run driving through a town - my car is very quiet at low speed so you do somewhat notice when the coolbox shutsdown. If I keep my headlights on this doesn't happen.

Yes, my voltmeter shows that if the system is happy with the state of charge of the battery, it will drop the voltage down the 13.1 V (as far as I remember). If I use engine braking it will rise to 14.9 V again. I haven't managed to work out what is does in every situation, but headlights causing it to boost the alternator seems plausible.

 

On holiday in Snowdonia recently I've occasionally been getting up to about 5000 rpm down hills in first or second gear. After that the gear change indicator asks me to change up.

16 hours ago, Gabbo said:

Regenerative charging is just a gimick/marketting tool to make cars seem more "efficient". The difference you will get when braking is negligable.

 

However, the battery monitoring system is not a dumb system, it monitors the state of the battery, electrical load, temperature & should adjust charging according to the current conditions.

There are times where it will allow the battery to discharge, slow charge, fast charge to maintain a good condition of the battery.

A bit like DPF regen, just leave it alone to do its thing, no need to drive differently.

It will tell you if you need to intervene & will disable StopStart automatically if the battery is getting low.

 

My car is 5 years old, with almost 100k miles now, with no signs of the battery going.. (fingers crossed it will last another 5 years)...

Totally agree with your marketing/gimmick comment.  I had similar experience to @Rodge but in the mountains of Tasmania, so the regen braking was not discernable, if there at all,.

Like yours, my battery is performing as new even after 5 years and maybe for the same reason, although achieved differently.

Your driving patterns seem to include a lot of open highway and not much stop/start. My base Aussie spec 1.4tsi does not have auto stop/start at all.

 

I drove a brand new loan manual 1.0tsi Fabia recently equipped with stop/start and I found it exceptionally keen to kick in during heavy traffic conditions even with 40+C temperatures with aircon on, and full internal fan.

Now bear in mind that when the engine automatically 'stops' the internal fans continue to operate and I would also expect the radiator fan to be also going full bore in the conditions I describe. So there was maybe 600 watts or more of current draw on the Fabia's tiny battery for the duration. No wonder so many batteries are reported to expire prematurely on stop/start equipped vehicles. Even though it was not mine, I would turn off the stop/start out of mechanical/electrical sympathy.

 

A less intelligent car (16 yo Toyota Echo) can drain its battery overnight by accidently leaving on the internal incandescent courtesy light. The battery is never the same after that event.

Got the voltmeter plugged in today. Interesting changes in indicated voltages from 12.2v minimum after an overnight break up to a maximum 14.7V driving. The voltage when driving goes up and down, all points between, so that's the system doing its thing.

The STOP/START function seems to work across the range of voltages. Thanks for the advice.

Edited 4 June, 20197 yr by gregoir

What's the answer to your original question about charging while descending hills with/without braking?

 

Not been on that long hill as yet-will answer when I can.

Cheers.

 

Drivers that live where it is very flat will never need to think about what happens if they are never going down hills. Or up them.

So far , the brake pedal has no obvious effect on the battery voltage. Indicated voltage varies between 12.2V and 14.6V when I can look safely.

On 04/06/2019 at 16:42, Wino said:

What's the answer to your original question about charging while descending hills with/without braking?

 

No voltage difference between coasting and braking gently down a known long hill. Voltage seems to go up and down as I drive always.  Between 12.2v and 14.6v (when I look down anyway). 12.2v after standing for a couple of days. 

Can I just ask how braking recharges the battery on an Octavia? Is there something apart from an engine driven alternator on these cars?   

 

Or are  we saying that the only charging source is the alternator but the cars ECU only allows the charge to be applied (alternator to be driven?) under braking?  Any advantages would seem extremely marginal.    

 

Using an electric motor "on the overrun" (effectively as a generator) to provide braking and resulting battery charge makes much more sense.  Isn't  that what happens in EVs like the Leaf etc?

Edited 26 June, 20196 yr by juan27

On 30/05/2019 at 02:49, Gerrycan said:

 

 

I drove a brand new loan manual 1.0tsi Fabia recently equipped with stop/start and I found it exceptionally keen to kick in during heavy traffic conditions even with 40+C temperatures with aircon on, and full internal fan.

Now bear in mind that when the engine automatically 'stops' the internal fans continue to operate and I would also expect the radiator fan to be also going full bore in the conditions I describe. So there was maybe 600 watts or more of current draw on the Fabia's tiny battery for the duration.

 

Does the stop/start Fabia have a "tiny battery"? I know my stop/start Octavia 3 has a much bigger battery than my Mk2 had. 

 

That being said when I looked out of interest when buying my current car the £250+ aftermarket batteries only had a 3 year warranty, which suggests even "big" stop/start batteries have a shortened life.

 

      

47 minutes ago, juan27 said:

Or are  we saying that the only charging source is the alternator but the cars ECU only allows the charge to be applied (alternator to be driven?) under braking?

Almost this - but the ECU doesn't only charge the battery under braking, it doesn't fully charge the battery under normal driving leaving some "headroom" in the battery to fill when under braking (and deceleration?).

2 hours ago, PetrolDave said:

Almost this - but the ECU doesn't only charge the battery under braking, it doesn't fully charge the battery under normal driving leaving some "headroom" in the battery to fill when under braking (and deceleration?).

Ah so that only really makes sense if the extra charging load is taken when the engine is "braking" or being turned over by residual energy remaining in the car when the engine is still turned by the wheels. So it doesn't matter if you are actually using the brakes. So you'd have to measure the voltage when the engine is under load and off load to see if it's happening.

 

So I guess what we are saying is the ECU switches the charging connection to the battery depending on engine load to try and charge from "free" energy when the cars residual energy is turning the engine rather than petrol.

12 hours ago, juan27 said:

So I guess what we are saying is the ECU switches the charging connection to the battery depending on engine load to try and charge from "free" energy when the cars residual energy is turning the engine rather than petrol.

Correct. I expect the battery also get some charge if there's excess energy being generated by the engine during your normal drive.

 

This is how Prius work, albeit with much better battery and beefier motors. The ICEngine is considered as an energy generator, it is kept at most optimised conditions (rpm, load, etc) by altering the eCTV and battery charging. Unfortunately these Skoda have such a small battery, tiny motor and so few gear ratio in the DSG, it hardly matters.

 

I believe VW are developing/developed a 48v very mild-hybrid system to make better use of the free energy. As I said, the 12v system is too small to make any significant impact to economy.

 

 

2 hours ago, wyx087 said:

Correct. I expect the battery also get some charge if there's excess energy being generated by the engine during your normal drive.

 

This is how Prius work, albeit with much better battery and beefier motors. The ICEngine is considered as an energy generator, it is kept at most optimised conditions (rpm, load, etc) by altering the eCTV and battery charging. Unfortunately these Skoda have such a small battery, tiny motor and so few gear ratio in the DSG, it hardly matters.

 

I believe VW are developing/developed a 48v very mild-hybrid system to make better use of the free energy. As I said, the 12v system is too small to make any significant impact to economy.

 

 

 

Hmmm. 

 

Pretty sure the only excess energy available is when the engine is being turned by the road wheels through the cars residual momentum and/or gravity as previously discussed.  (Well there is generally excess heat produced but that pretty much goes to waste) 

 

What is different from old school cars is that the ECU decides when it can afford to switch off charging the battery to save a very small amount of fuel.     

 

What is the tiny motor you are talking about?  There is no electric motor involved in the Octavia drive train other than the starter?  The battery is not in any way directly part of the drive train.     

 

It is fundamentally not a hybrid. 

There is also excess energy produced by the engine during gear change, but yes, vast majority of it comes from the wheels.

 

The tiny motor I was talking about is the starter/alternator. It is matched to the 12v power system, but ultimately it is too small to make any real difference in economy. I agree it's not a hybrid. I personally don't even consider 48v systems in new cars today as hybrid.

As usual with these 'developments', the key is usually to look at how the emissions test cycle results might be improved by their presence, and not necessarily any real benefit to the end user. Alternator not charging = less load on engine = better CO2 and emissions performance in the test cycle.

 

Real-world benefits to the environment or the owner, and battery longevity will not be given anything like the same level of consideration. There seem to be quite a few threads around at the moment about stop/start systems being inhibited due to lack of charge in the battery; this charge governance system seems to lend itself to creating this situation. Irony, anyone?

 

Do VW group actually own any battery manufacturers, does anyone know?