Start/stop voodoo

[snow]

V40 D3 65 plate.

Car doesn't get used overly much so can sometimes be standing for a week. When it does get used its a journey of 80 miles of mixed driving with no heavy traffic. So under these conditions no DPF issues - I've noticed the occasional mpg drop during re-gen and once parked up during mid-gen with the fans whirring away like crazy. Next trip everything back to normal.

Anyway - it's the start/stop system that exhibits what to me is strange behaviour. With infrequent use, the cars start/stop system is often unavailable due to "electrical system" reasons - I would guess the battery needs to be brought up to the right level for the system to be enabled. Fair enough, often on the 80 mile trips the start/stop comes back online at some point. Recently the start/stop was unavailable (electrical reason as usual) and didn't re-enable during the trip. Subsequent shorter trips didn't seem to bring it back online either. Yesterday another long (80 mile) trip and still no sign of start/stop being ready for action. Got home switched off the car with seat/stop still unavailable - by now I'm suspecting some battery weakness/failure - although car starts normally etc. Got back in car later the same day and lo and behold the start/stop is now available - without me having done a thing to it!

What sort of magic is going on here? If I stop the car and the battery is not charged enough to run the start/stop system - how can starting up a few hours later change the state of charge. If anything it would have been marginally drained due slight standing current draw.

What does the team think?

PS sorry long post but trying to get as much info to readers. Thanks for reading his far (if you have done!)

[id5]

Originally Posted by snow

...What sort of magic is going on here? ...
What does the team think? ...

It is really not difficult ‘snow’. If the moon is new to waxing gibbious then you need to park with the front of the car to the south until the moon is waning crescent and then switch to having the front of the car to the north unless of course the moon is dark in which case you need to apply the rules widdershins. Why people cannot understand it I will never know.

[piotrek]

Everything seems ok. If car was parked for longer periods or with many short trips, it takes up to 60 minutes of driving for the secondary battery to reach operating voltage. Main battery sometimes takes even longer to reach 85% SoC (state of charge).

Actually, both parameters can be displayed in "Car Scanner Elm Obd2" app for Android or iOS - useful especially if car is equipped with parking heater.

Excerpts from VIDA:
The time the secondary battery can be charged varies between 3-3600 seconds. A secondary battery voltage of 12.9 V gives a charging time of about 5 seconds after each auto stop throughout the entire current operating cycle. If the secondary battery has a lower voltage, the load time increases for each auto stop.

Every time autostart is activated, the Central electronic module (CEM) continuously reads the secondary battery's voltage (whilst the secondary battery powers the vehicle). The lowest value that is registered is stored in the Central electronic module (CEM). At the next autostart this sequence is repeated and the Central electronic module (CEM) then calculates the average value of the previously registered voltage value and the last read value. The average value is calculated at each autostart. This average value is the basis for the measurement for SoC and capacity. If the calculated average voltage falls below 10.4 V the automatic start/stop of the engine function is not permitted in the current operating cycle, this is to prevent the secondary battery from discharging too much.

As the next operating cycle starts, the Central electronic module (CEM) counts up the stored value by 0.1 V so that an autostop is permitted. This is to enable the secondary battery's SoC and capacity to be recalculated. If the average voltage drops to 10.4 V again, the automatic start/stop of the engine function is not permitted. If the average voltage, on the other hand, is above 10.4 V, autostop is permitted until further notice. Causes of the average voltage being too low at the end may be due to too high energy consumption in the vehicle during autostart. This may be caused by the vehicle having extra connected accessories that draw too much energy.

[ksmi]

Originally Posted by id5

It is really not difficult ‘snow’. If the moon is new to waxing gibbious then you need to park with the front of the car to the south until the moon is waning crescent and then switch to having the front of the car to the north unless of course the moon is dark in which case you need to apply the rules widdershins. Why people cannot understand it I will never know.

Now then ID, How many g&t's have you had? as for the gibbons, I could only find a half eaten packet of baboons,would they do? My 'manager' has been sticky beaking over my shoulder and recons it's a load of rocking horse manure.
Have not had a state of play on the Velo's recently,?

Regards,Keith.

[id5]

Originally Posted by ksmi

Now then ID, How many g&t's have you had? as for the gibbons, I could only find a half eaten packet of baboons,would they do? My 'manager' has been sticky beaking over my shoulder and recons it's a load of rocking horse manure.
Have not had a state of play on the Velo's recently,?

Regards,Keith.

Ah, baboons, I do like the lemon ones Keith

So, two incantations, one mystical and one technical. I am sure that piotrek’s is the better of them. All I can say is that I have had our V40 for over a year now and my incantation works for me and Start/Stop is available most of the time. What I do know though is that the auxiliary battery kicks in to reduce the power dip to the rest of the car whilst the main battery turns the starter and if the goblin that oversees the engine doesn’t think that the aux battery is up for it then it won’t let the stop start spell work. What I didn’t know until I read piotrek’s incantation is that the goblin can be a sulky little bugger and doesn’t ask the auxiliary battery if it wants to come out and play every time, it only ask’s it every other time once it has said No.

We digress from snow’s original reason for the thread, so my apologies to him. The Velo’s, thank you for remembering and asking. I have not been in the garage for over 18 months to do anything on them. Instead all my spare time is taken up with getting a new business off the ground. 12 to 16 hours days are not fun but so far it has been going well but now we are at the dangerous stage of growth where we need to replace the multiple roles that I am doing with lots of other people. If it works then I could have lots of spare time to play with the Velo’s, if it goes wrong it could be another 18 months. I have put the 250 back together and it sits waiting a frame up restoration, she is 85 years old and needs the TLC. The little elf in the magneto of the 81 year old 350 broke all the insulation on the armature windings and escaped so I had to get a new one incarcerated into it and it re-wound to keep the sod in there. All I need to do now is refitting it…just need a couple of days free time…

[snow]

Will pay attention to parking orientation in future

Thanks for the technical explanation and detail. I'm not sure if I understand it enough to see whether it explains the start/stop becoming available after a couple of hours of just being parked up.

Thanks techies and masters of the dark arts!