12 V Battery Charging System Fault

[Martinonline]

@MickeySw, you may be right and I agree that 14.7/8 is too high unless it is charging, hence my request for the conditions under which measurements are taken.

I have never seen a voltage above 12.8V when using the App so I would say that using the App does not normally trigger the DC-DC Converter. However, there is at least one occasion when this does happen which I have just checked, as described below.

My car is connected to my Ohme e-Pod, not charging but with a car-schedule set for 0:30 start to battery set limit (UK Octopus Go). I used the App to check the LV battery which showed with refreshes, 12.3V, 12.2V, 12.1V, 12.2V. I exited the App and checked the Ohme App which showed the car had started charging. Accessing the App again showed the battery level to be 14.2V which, to me, means the DC-DC Converter is active. I have also seen this when the charging has been completed and I have accessed the iSmart App to see if charging had been completed. (Now I use the Ohme App.)

It is probable that the early start of the charging with a car-schedule is part of the software that pauses charging when a locked car is unlocked but resumes charging a little while later, irrespective of the locked state.

As for not needing boosting, it could be that there is an LV battery drain and the car has automatically activated the DC-DC converter and that @DoctorWolf just happened to view the battery level at that time.

@DoctorWolf will need to take a series of readings using the App with the car powered off (not just out of Ready mode) and locked and not connected to an EVSE/Charger to see if the LV battery drains significantly. Perhaps the dealer will do that.

 

[MickeySw]

Accessing the App again showed the battery level to be 14.2V which, to me, means the DC-DC Converter is active.

14.2V sounds about right, 14.8V seems therefore way too high for a MG4

As for not needing boosting, it could be that there is an LV battery drain and the car has automatically activated the DC-DC converter and that @DoctorWolf just happened to view the battery level at that time.

Too much of a coincidence imho.

My best guess is that somehow the low voltage isn't always read correctly which triggers the faults when driving and activates the DC/DC unnecessarily when the car is off?

Perhaps the dealer will do that.

Nice try...

 

[DoctorWolf]

Thought I woulds give a further update. The car worked well for a number of days and 300 miles of driving and then last week had the low battery warning appear again (incidentally after pumping uo all the tyres using the provided electronic pump, which was exactly the same thing I did before the previous low battery). Decided to try fitting a new 12 V battery. Still have the low battery warning with new one although I noticed when I do full lock to either side that drains it from 11.9/12V to about 11.5 but then it returns to previous levels when steering is centered. I haven't done a test with a multimeter yet to see if I'm getting a false reading. When not ready the battery reads at 12.4-12.6 on the app. Most of my research says I don't need to code the new battery, but who knows. Prior to changing the battery my charge port lights didn't work nor the rear left window. Both now work. Something at least! However, I don't seem to be able to get it to charge. It was set at 80% battery health and was at 80% anyway, but I changed it to long journey mode (100%) now and tried but it still fails. Guess I'll have to see what MG say on the 10th April...

 

[MickeySw]

Decided to try fitting a new 12 V battery. Still have the low battery warning with new one.

It’s generally recommended to fully charge even a new 12V battery before you install it (it may have been on the shelf for some time). If you don’t have an external charger, leave the car in READY for a couple of hours.

When not ready the battery reads at 12.4-12.6 on the app.

What you read when READY?

but I changed it to long journey mode (100%) now and tried but it still fails.

Is there a charging schedule active?

 

[DoctorWolf]

It’s generally recommended to fully charge even a new 12V battery before you install it (it may have been on the shelf for some time). If you don’t have an external charger, leave the car in READY for a couple of hours.

What you read when READY?

Is there a charging schedule active?

Thanks for your reply. At the moment it reads 12V when ready. No schedule set for the charge. Should have thought about charging the battery before installing. I do have a trickle charger I could use now.
Out of interest, how would I leave the car in ready for a couple of hours, without being in it? Cheers, Mark

 

[MickeySw]

At the moment it reads 12V when ready.

As mentioned before, when READY, that voltage should be around 14V (provided by DC/DC)? Might be worth borrowing a multimeter and measure directly across the battery terminals..

Out of interest, how would I leave the car in ready for a couple of hours, without being in it?

Turn it on (READY) leave it in P and take the key with you, unfortunately you can’t lock it..

 

[Martinonline]

For clarification, the car just needs to be powered up (bum on seat to power up) to start charging the low-voltage battery. Ready mode involves putting your foot on the brake and is disengaged when you open the driver's door.

When I had 12V battery problems (reported previously) I could not charge the car using AC nor DC. In the end I put my booster across the terminals with the car powered up and the car charging circuit sprung into action.