Technical Battery and aircon

[euroben]

My twin air panda runs pretty well but when idling at traffic lights etc, when the air con compressor kicks in the engine seems to shudder a little and seems like it is under some stress. It’s definitely when the aircon kicks in and when I switch it off it idles so smoothly and quietly it is like it has stopped (but it hasn’t). Additionally the start stop never works. I don’t get any message saying unavailable but it just never stops the car like it should. It had a new battery in January with the previous owner and it is a varta N60 which is described as an entry level start stop battery. I am wondering if the battery is not sufficient enough for the start stop to work and also when the air con cuts in it is not managing the additional battery draw. Anyone else feel their air con kick in and cause some strain? Anyone have experience of these varta batteries? I did read on an Alfa Romeo forum that varta batteries were nearly always the issue with start stop not working but I haven’t seen anything in here.

 

[JayAre]

seems you’ve deduced the likely cause is the battery, but the a/c takes no battery load as the compressor is driven by the engine (unlike, say, the electric power steering which is powered by the battery and will lose power assistance if the battery is dodgy)
I’ve only had my 2016 TA since May but the a/c operates seamlessly - there’s no sensory feedback of when the compressor is off / kicks in, so it seems something is not right mechanically (I’ve not even noticed any performance drop off when it’s running, even tho there must be some)
The stop/start is permanently off - I hate the delay/uncertainty will it work when I try to pull out/suspicion that it prematurely wears out the DMF (there again some say idling in neutral waiting for the green light or at junctions damages the DMF…).
The battery - I can check the brand+capacity tomorrow +report back if that helps

 

[Panda IIs]

My twin air panda runs pretty well but when idling at traffic lights etc, when the air con compressor kicks in the engine seems to shudder a little and seems like it is under some stress. It’s definitely when the aircon kicks in and when I switch it off it idles so smoothly and quietly it is like it has stopped (but it hasn’t). Additionally the start stop never works. I don’t get any message saying unavailable but it just never stops the car like it should. It had a new battery in January with the previous owner and it is a varta N60 which is described as an entry level start stop battery. I am wondering if the battery is not sufficient enough for the start stop to work and also when the air con cuts in it is not managing the additional battery draw. Anyone else feel their air con kick in and cause some strain? Anyone have experience of these varta batteries? I did read on an Alfa Romeo forum that varta batteries were nearly always the issue with start stop not working but I haven’t seen anything in here.

Hi Ben, the drop in engine revs as the aircon compressor clutch engages, I would say, is not unusual. The system adds load and so the engine has to adjust fuelling etc to allow for this, there's just a bit of hysteresis in the feedback. I experience this with my T5 Volvo too.

Stop start (SS) is a whole other issue - as you say it seems to be battery volts related. Mine worked briefly on two occasions; the first, a brand new battery, high end SS, the second having had the battery voltage sensor replaced (on the negative battery pole.

The voltage sensor is a crazy priced part in OEM form. There's a thread on here https://www.fiatforum.com/threads/ibs-compatibility-and-pin-issues.509500/ that talks about alternatives I think, there is a further thread too if memory serves. This may or may not provide some resolution for you? I can't comment on battery brand but I know some folk on here have strong views! Given my SS stopped working again a while after the voltage sensor was swapped I think there is more to it. Also my car tends to do shorter runs so the battery may never be achieving an appropriate condition for SS.

One thing I did find when teaching my daughter to drive was that, apparently without SS available, if the car was stalled (say pulling away from standstill) the engine would restart when the clutch was depressed... I never could work that one out.

 

[JayAre]

One thing I did find when teaching my daughter to drive was that, apparently without SS available, if the car was stalled (say pulling away from standstill) the engine would restart when the clutch was depressed... I never could work that one out.

pretty sure that is SS

 

[jrkitching]

If the car is fitted with S/S, pressing the clutch should restart a stalled engine, even if S/S does not usually stop the engine when the car comes to a stop in neutral.

If the car doesn't have S/S fitted at all, pressing the clutch won't restart a stalled engine.

 

[Panda IIs]

If the car is fitted with S/S, pressing the clutch should restart a stalled engine, even if S/S does not usually stop the engine when the car comes to a stop in neutral.

If the car doesn't have S/S fitted at all, pressing the clutch won't restart a stalled engine.

Yes, my point was that even with SS being notified as not being available it does still allow a start off the clutch pedal in a stall situation - something I wasn't expecting.

 

[Herts Hillhopper]

Yes, my point was that even with SS being notified as not being available it does still allow a start off the clutch pedal in a stall situation - something I wasn't expecting.

Two different but related things. A car with the stop-start option will always restart after a stall if the clutch is pressed (even if stop-start is turned off on the dash). But the car may choose not to stop the engine when you come to a standstill if it feels the battery isn’t up to ot. Generally after two or three years the system tends to start to disable itself (a function of the battery degrading). Frequent (or only) driving in town tends to see stop-start disabling itself — the car needs a good run (20-50 miles in a day, more than one day a week), based on my experience.

Varta N60 is the correct battery (matches the spec of mine in a 2018 MultiJet 4x4) and is not a cheap one either. (It costs more than the Exide battery I have, for example - see here https://www.tayna.co.uk/car-batteries/types/027-efb/ ). I think it’s more than just a simple measurement of voltage that decides if stop-start works. It seems to relate more to the ability of the battery to recharge, or to the rate of discharge?

As to the air con, there’s a thermostat in the aircon circuit (otherwise it would freeze solid). That turns the power to a clutch on the aircon compressor on and off. When that clutch engages the compressor it adds a significant mechanical load to the engine which, if just idling, will be detected as a drop in revs briefly, until the engine ECU corrects for it. That’s all perfectly normal behaviour and not related to the battery.

 

[Herts Hillhopper]

The stop/start is permanently off - I hate the delay/uncertainty will it work when I try to pull out

It will always restart… if it sits with the engine off for long enough for there to be risk it won’t (eg sitting for a long time at a level crossing) the system starts the engine without you needing to press the clutch before the battery drains too far. A sign of failing battery is the s-s restarting itself in this way more often: mine used to stop then start straight away in the weeks before the battery failed abruptly. It can’t have any effect on a dual mass flywheel… they are damaged by poor clutch action (releasing too abruptly) or allowing the engine to ‘labour’ too much (revs too low for the gear/road speed)

 

[euroben]

Two different but related things. A car with the stop-start option will always restart after a stall if the clutch is pressed (even if stop-start is turned off on the dash). But the car may choose not to stop the engine when you come to a standstill if it feels the battery isn’t up to ot. Generally after two or three years the system tends to start to disable itself (a function of the battery degrading). Frequent (or only) driving in town tends to see stop-start disabling itself — the car needs a good run (20-50 miles in a day, more than one day a week), based on my experience.

Varta N60 is the correct battery (matches the spec of mine in a 2018 MultiJet 4x4) and is not a cheap one either. (It costs more than the Exide battery I have, for example - see here https://www.tayna.co.uk/car-batteries/types/027-efb/ ). I think it’s more than just a simple measurement of voltage that decides if stop-start works. It seems to relate more to the ability of the battery to recharge, or to the rate of discharge?

As to the air con, there’s a thermostat in the aircon circuit (otherwise it would freeze solid). That turns the power to a clutch on the aircon compressor on and off. When that clutch engages the compressor it adds a significant mechanical load to the engine which, if just idling, will be detected as a drop in revs briefly, until the engine ECU corrects for it. That’s all perfectly normal behaviour and not related to the battery.

Thanks for all the info. I’m glad the N60 is the right battery and it is only 8 months old so should be fine age-wise. I have cleaned off the negative battery terminal today and also there was quite a bit of corrosion on the intelligent battery sensor so I have cleaned that carefully off as well. I haven’t taken it out for a drive yet to see if it has had any impact on the start stop.

I’m glad the air con load seems to be normal. I did observe a similar thing on a fiat 500 I hired on holiday but then didn’t notice it on a subsequent fiat panda cross I hired in Greece.

Many thanks

 

[JayAre]

A car with the stop-start option will always restart after a stall if the clutch is pressed (even if stop-start is turned off on the dash)

has this been confirmed in a stall test? (can’t see anything in the handbook)

(SS) can’t have any effect on a dual mass flywheel… they are damaged by poor clutch action

many references in various threads about needing to declutch when starting and switching off the engine to preserve the DMF - SS won’t do this

dual mass flywheel… damaged by… allowing the engine to ‘labour’ too much (revs too low for the gear/road speed)

the dash screen continually indicates “change up” even before 2500 rpm is reached - there is no way to disable this and sometimes I’ve found myself obeying only to hear the uneven engine note as it drops back below 2000. Doubtless Fiat would say this is a “characteristic” of the engine and not labouring…

 

[Herts Hillhopper]

has this been confirmed in a stall test? (can’t see anything in the handbook)

Yes. Mine does it and other replies confirm it.

many references in various threads about needing to declutch when starting and switching off the engine to preserve the DMF - SS won’t do this

The stop-start only starts when you put the clutch down….

the dash screen continually indicates “change up” even before 2500 rpm is reached - there is no way to disable this and sometimes I’ve found myself obeying only to hear the uneven engine note as it drops back below 2000. Doubtless Fiat would say this is a “characteristic” of the engine and not labouring…

Yes - the TwinAir can sound as if labouring, but isn’t; not at 2000 rpm. My deisel shows change up at 2000 rpm if being driven gently, which then gives 1500 rpm (peak torque) in the next gear. It also shows ‘change up’ if you try and ask it to pick up with revs less than 1500. The system is there (in part) to protect the DMF.

As in another post: don’t try and over-think this: just let it work. It’s well proven, well tested technology used in all modern cars without issue.

 

[JayAre]

many references in various threads about needing to declutch when starting and switching off the engine to preserve the DMF - SS won’t do this

The stop-start only starts when you put the clutch down….

and switching off the engine?

 

[euroben]

Thought I would come back and say that following cleaning off the negative battery terminal and in particular cleaning off some corrosion on the copper part of the intelligent battery sensor, my start stop now works flawlessly!

 

[Herts Hillhopper]

and switching off the engine?

It’s in neutral so no load on the clutch

 

[Herts Hillhopper]

Thought I would come back and say that following cleaning off the negative battery terminal and in particular cleaning off some corrosion on the copper part of the intelligent battery sensor, my start stop now works flawlessly!

Good to know - thank you.