Fabia April 2016 1.2 TSI 90 

Can anyone give me a detailed description of the how the maintains the correct voltage for the EFB battery. Had the car from new and experienced the usual 12v Battery Low warnings, mainly in winter, and got myself one of the CTEK chargers.

The thing is back in the olden days if a car battery needed topping up the control circuitry would simply activate the alternator and all would be well. Nowadays, even after 40 minutes driving and being left overnight the Battery low warning kicked in.

I'm trying to understand how, when and where from does the battery get topped up during normal driving on my little Fabia? I couldn't give a stuff about the Stop/Start system I just want rid of the damn warnings.

3 hours ago, Flopsy said:

Fabia April 2016 1.2 TSI 90 

Can anyone give me a detailed description of the how the maintains the correct voltage for the EFB battery. Had the car from new and experienced the usual 12v Battery Low warnings, mainly in winter, and got myself one of the CTEK chargers.

The thing is back in the olden days if a car battery needed topping up the control circuitry would simply activate the alternator and all would be well. Nowadays, even after 40 minutes driving and being left overnight the Battery low warning kicked in.

I'm trying to understand how, when and where from does the battery get topped up during normal driving on my little Fabia? I couldn't give a stuff about the Stop/Start system I just want rid of the damn warnings.

 

The battery will charge constantly at a normal rate up to about 75-80%, after that, it only charges on overrun (while the wheels are spinning the engine - i.e decelerating in gear).

 

If you disconnect the monitoring connector on the -ve terminal of the battery, it defaults to the old style standard charge mode, where it'll charge at a steady rate until 100%.

If you still get issues after a good drive like that. Get one of those 12v socket phone chargers with voltage reading. If the battery is dropping a significant voltage overnight then there could be an issue with the car or the battery.

 

There was a software update a couple years back related to power management, might be worth contacting the dealer to see if that's been done. That supposedly helped fix some power drain issues from components not shutting off correctly.

It's a complete nonsense system. Firstly the start/stop puts higher demand on your battery because of all those restarts. Then they limit the battery charge to ~70% or so, as it only charges on overrun. So if you are in a common situation of short journeys in busy traffic, the start/stop is being used but there's virtually no overrun situations to get it charged back up. 

So disconnect the little monitor connector from the negative battery terminal which disables the Battery Control Monitor allowing the battery to fully charge and inhibits start/stop. The only downside is if you have DSG and not manual gears.

8 minutes ago, TerFar said:

It's a complete nonsense system. Firstly the start/stop puts higher demand on your battery because of all those restarts. Then they limit the battery charge to ~70% or so, as it only charges on overrun. So if you are in a common situation of short journeys in busy traffic, the start/stop is being used but there's virtually no overrun situations to get it charged back up. 

So disconnect the little monitor connector from the negative battery terminal which disables the Battery Control Monitor allowing the battery to fully charge and inhibits start/stop. The only downside is if you have DSG and not manual gears.

 

Is there a problem with DSG and having no stop-start?

 

I found that stop-start on the DSG was far more effective, you stop, and so long as you have adequate pressure on the brake pedal, it'll shut off, the moment you start to lift pressure from the brake pedal, the engine starts up. If you only lightly brake as you come to a stop, it won't shut off, presumably as it expects you're about to set off again.

To trigger it on the manual, you have to be stationary, put it in neutral, then release the clutch, handbrake isn't required, but if you're on a hill, it's probably a good idea, you shouldn't be holding the brake pedal anyway. As soon as you press the clutch in to put it in gear, it starts the engine up again.

8 minutes ago, FabiaGonzales said:

 

Is there a problem with DSG and having no stop-start?

 

I found that stop-start on the DSG was far more effective, you stop, and so long as you have adequate pressure on the brake pedal, it'll shut off, the moment you start to lift pressure from the brake pedal, the engine starts up. If you only lightly brake as you come to a stop, it won't shut off, presumably as it expects you're about to set off again.

To trigger it on the manual, you have to be stationary, put it in neutral, then release the clutch, handbrake isn't required, but if you're on a hill, it's probably a good idea, you shouldn't be holding the brake pedal anyway. As soon as you press the clutch in to put it in gear, it starts the engine up again.

Yes. Basically, the small auto-clutch unit (DQ200) with the 7-speed DSG unit can cook if you keep your foot on the brake without start/stop active. So I usually slip the selector into N when I stop and slip it back into D when traffic starts moving again. This doesn't happen with more powerful petrol or diesel VAGs because they use different heavier clutch units. 

1 minute ago, TerFar said:

Yes. Basically, the small auto-clutch unit (DQ200) with the 7-speed DSG unit can cook if you keep your foot on the brake without start/stop active. So I usually slip the selector into N when I stop and slip it back into D when traffic starts moving again. This doesn't happen with more powerful petrol or diesel VAGs because they use different heavier clutch units. 

 

The clutch should completely disengage when stationary. When you lift the pedal there's a split second before it starts to engage, you can feel it. You can cook it though by pulling the handbrake and releasing the brakes while keeping it in D, it tries to pull away, and if it doesn't stall out, it'll cook the clutch.

If I am not using the car I put the battery on charge, using the excellent C Tek charger.

After the lockdown I gave it the refresh cycle, it is a "new" battery but it certainly

perked it up, the cars system cannot be doing it any good.

On 09/07/2020 at 16:43, TerFar said:

It's a complete nonsense system. Firstly the start/stop puts higher demand on your battery because of all those restarts. Then they limit the battery charge to ~70% or so, as it only charges on overrun. So if you are in a common situation of short journeys in busy traffic, the start/stop is being used but there's virtually no overrun situations to get it charged back up. 

So disconnect the little monitor connector from the negative battery terminal which disables the Battery Control Monitor allowing the battery to fully charge and inhibits start/stop. The only downside is if you have DSG and not manual gears.

The stop start batteries are specifically built to handle the extra demands of repeated engine starts and are specc’ed according to the vehicle electrical system. That’s why amongst other things you can’t just shove any old battery in and not tell the car it’s been changed. The programmed charging strategies in the car systems target 80% SOC as 100% is just not necessary, the alternator is turned down when not needed above this. Each type of battery takes a different charging profile. EFB takes a much more gentle charge rate than AGM which take all sorts of abuse way better. Stop start operation can take a while on EFB equipped cars vs AGM as a result. 

 

Overrun charging is free energy that the battery can hold so there is less time needed taking energy from the fuel and the alternator turns down until the battery is back down to 80% SOC again. The alternator is still used when necessary. 

 

What you don’t want to do is send the charging system blind by disconnecting the fly lead off the battery monitor. It inhibits stop start but it also creates an overcharging situation pushing the battery outside the specific window of operation. This slowly overworks the batteries eventually drying them out and turning the materials inside to sludge due to increasing acid density particularly in EFB types. The minder also controls temperature compensation strategy turning the charge rates down the hotter the battery gets further preventing water loss. 

 

Three prime methods to kill car batteries are underuse of the vehicle, repeat deep discharge cycling from constant background energy drains, and overcharging. The latter is the worst situation as the battery materials decay quicker leading to loss of capacity, overheating and drying out as they can’t handle the extra energy, in some extreme instances they have been known to pop!

7 minutes ago, BigEjit said:

The stop start batteries are specifically built to handle the extra demands of repeated engine starts and are specc’ed according to the vehicle electrical system. That’s why amongst other things you can’t just shove any old battery in and not tell the car it’s been changed. The programmed charging strategies in the car systems target 80% SOC as 100% is just not necessary, the alternator is turned down when not needed above this. Each type of battery takes a different charging profile. EFB takes a much more gentle charge rate than AGM which take all sorts of abuse way better. Stop start operation can take a while on EFB equipped cars vs AGM as a result. 

 

Overrun charging is free energy that the battery can hold so there is less time needed taking energy from the fuel and the alternator turns down until the battery is back down to 80% SOC again. The alternator is still used when necessary. 

 

What you don’t want to do is send the charging system blind by disconnecting the fly lead off the battery monitor. It inhibits stop start but it also creates an overcharging situation pushing the battery outside the specific window of operation. This slowly overworks the batteries eventually drying them out and turning the materials inside to sludge due to increasing acid density particularly in EFB types. The minder also controls temperature compensation strategy turning the charge rates down the hotter the battery gets further preventing water loss. 

 

Three prime methods to kill car batteries are underuse of the vehicle, repeat deep discharge cycling from constant background energy drains, and overcharging. The latter is the worst situation as the battery materials decay quicker leading to loss of capacity, overheating and drying out as they can’t handle the extra energy, in some extreme instances they have been known to pop!

 

No it doesn't. Disconnection the BCM sensor hands over control of the battery charging to the alternator. It works fine. It doesn't cook the battery.

And if you look at the statistics for small car owners, they tend to do most of their mileage on short local journeys anyway.

 

Edited 14 July, 20205 yr by TerFar
add detail

Sure it’ll be ok for some folks and short term there will be no noticeable effects, if you regularly bin the car off after a year or so or are prepared to just bung a battery in when it fails.

 

But then you get those who are long term owners on a tight budget wondering why the battery is done after a few years normal use and they are stranded somewhere spending hard earned on the car, recovery and garage services, (supplier quality issues aside).

 

10 years/100k miles is the achievable lifetime target for the battery set by the OEM for 95 percentile customer usage pattern. Changing the optimised charging strategy reduces that expectation.

1 minute ago, BigEjit said:

Sure it’ll be ok for some folks and short term there will be no noticeable effects, if you regularly bin the car off after a year or so or are prepared to just bung a battery in when it fails.

 

But then you get those who are long term owners on a tight budget wondering why the battery is done after a few years normal use and they are stranded somewhere spending hard earned on the car, recovery and garage services, (supplier quality issues aside).

 

10 years/100k miles is the achievable lifetime target for the battery set by the OEM for 95 percentile customer usage pattern. Changing the optimised charging strategy reduces that expectation.

 

Tell that to Nissan Qashqai owners!