Chassis earth point for battery maintenance

[ovlov04v]

I have to connect my maintenance battery charger (CTEK) to my wifes 2017 V40 T2 automatic. I understand all the methods etc but what I need help with is:

The manual talks of the negative earth to chassis being made by the right hand engine mount but unhelpfully the diagram doesn't show the location that it recommends. Looking under the bonnet there is on the left hand side adjacent to the battery housing a welded, but painted, bracket fitted to the chassis. This doesnt appear to have any function other than maybe as the chassis earth for battery charging/maintenance. It has what I think is an earth lead from elsewhere on the car which is fixed, with an eye and bolt, to the chassis adjacent to this bracket. Maybe the manuals havent been updated to match the later design?

Question is. Is it the proper earth point and if not where would you use as an earth point. Sorry to be a Jimmy Green about this but I am aware that incorrect connections can cause havoc with modern car electronics.
Thanks in advance

[Dancake]

Any chassis earth point should be suitable. Paint can affect the connection, so an exposed chassis bolt or bracket etc would be preferable. The most important thing to remember with CTEK or similar chargers is to make sure you have the charger connected to the vehicle before you switch on the power.

[Wagon Sailor]

I've never understood why it's not recommended to simply use the + and - terminals on the battery itself. Can you enlighten me, please?

[Zebster]

Originally Posted by Wagon Sailor

I've never understood why it's not recommended to simply use the + and - terminals on the battery itself. Can you enlighten me, please?

There is a battery charge sensor built into the car's battery negative connection (as a series element with a tiny resistance) to measure the flow in and out of the battery to keep the car's battery monitoring system updated. It's OK to connect the charger positive lead directly to the battery, but if you connected the charger negative directly to the battery then you'd be bypassing the charge sensor and so the car would lose track of the battery condition.

I attach the charger negative croc to one of the EGR valve bolts (connecting to the engine is just as good as connecting to the body).

[IainG]

Hi

Originally Posted by Zebster

There is a battery charge sensor built into the car's battery negative connection (as a series element with a tiny resistance) to measure the flow in and out of the battery to keep the car's battery monitoring system updated. It's OK to connect the charger positive lead directly to the battery, but if you connected the charger negative directly to the battery then you'd be bypassing the charge sensor and so the car would lose track of the battery condition.

I attach the charger negative croc to one of the EGR valve bolts (connecting to the engine is just as good as connecting to the body).

Just a thought, is that sensor actually monitoring when the car is in a locked and shut down state? (When it is asleep)
Just wondering
Iain

[Zebster]

Originally Posted by IainG

Hi



Just a thought, is that sensor actually monitoring when the car is in a locked and shut down state? (When it is asleep)
Just wondering
Iain

That particular sensor couldn't know, but the BMS (battery monitoring system) could easily have an input telling it, for example, that the doors were locked. I'm not sure why it would need to though... what were you thinking?

[RS3100]

Originally Posted by IainG

Hi



Just a thought, is that sensor actually monitoring when the car is in a locked and shut down state? (When it is asleep)
Just wondering
Iain

I don't know if it's monitoring constantly or not, but I do know from experience that if you fully charge the battery and lock and leave the car, the system will take it back to 80% charge fairly quickly whilst "asleep". (The BMS on cars with stop/start aims to keep the battery at 80% SOC to allow headroom for smart alternator function). But what happens when the car wakes up if you connect a charger to the battery negative, is that the battery condition will be different to the BMS expectation based on the last known readings, so it disables stop/start amongst other things.

Acording to VIDA, the car has to be left parked with doors locked for 6 - 8 hours to allow the BMS to recalibrate in those circumstances. I know, because it happened to me after the Volvo dealer tech connected the battery maintainer to the battery negative, contrary to VIDA instructions, during a service.

[piotrek]

Originally Posted by IainG

Just a thought, is that sensor actually monitoring when the car is in a locked and shut down state? (When it is asleep)
Just wondering Iain

Yes, the BMS sensor constantly monitors the standby parasitic drain when car is locked. The standby drain from the last 12 hours of sleep is shown as Quiescent current in VIDA or in Car Scanner app on a smartphone (it should not exceed 25mA).

You can also monitor the momentary battery drain when engine is off. Just sitting in the car and listening to music with ignition off consumes 5-7 amps. That's quite a lot, tbh. With ignition on, car electronics draws even more - 15-18 amps from battery.