MG5 System Fault - HV Battery Shut Off

Afternoon all.
This exact issue (charge on rapid charger to 94% and then “System Fault” and HV shutoff) occurred to me twice today on the way back from Wales; both times it cleared after waiting for 5 mins and trying to start up again.
Has there been any progress on identifying what the issue that causes it is?
My observations would be that I’ve had my 5 for a bit over a year and use public chargers exclusively as I don’t have one at home. Usually I would use a 7kW charger to 100% and on for a while perhaps once a month or so but I haven’t for perhaps three months. This issue has never occurred for me before, despite plenty of lengthy multistop trips…I wonder if not having balance charged it for a while might be the culprit? That said, my motor has never indicated it wanted a balance charge.

Ho hum!
 
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It's some wonky rapid charging software. The CCS 'standard' is known to be pretty poorly defined and MG are known to be pretty loose with their interpretation of such things.

It's fairly obvious that a condition regularly occurs where the car decides to terminate the charge based on hitting what it interprets as an error. It's likely to do with how the car and charger negotiate the step down in charging rate at higher states of charge or possibly about the battery temperature and cooling system.
 
Petriix said:
It's some wonky rapid charging software. The CCS 'standard' is known to be pretty poorly defined and MG are known to be pretty loose with their interpretation of such things.

It's fairly obvious that a condition regularly occurs where the car decides to terminate the charge based on hitting what it interprets as an error. It's likely to do with how the car and charger negotiate the step down in charging rate at higher states of charge or possibly about the battery temperature and cooling system.
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OK, cool thanks. That makes sense.
I shall have a prod and see if any error codes/DTCs are stored.
 
I hope people aren’t regularly using rapids to charge over 90% when people are waiting, it’s poor etiquette.

I do however confess to having done it once in a deserted car park at 1am (and would have stopped if anybody else arrived to use it) and having the issue mentioned here.

Just turn everything off for 15 minutes and it’ll restart no problem. Fairly certain I read it was something to do with protection against the battery overheating or something.
 
Alanp said:
Would someone please explain what balance charging is.
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Battery is composed from multiple cells as you use battery those cells discharge at slightly different rate. When you charge to 100% one of the cell may be 100% while other may be 90% car still registers as 100% but your range slightly drops.

Balancing battery discharges the 100% cell to 95% and charges the 90% cell to 95%. Then it brings up both 95% cells to 100% so your cells are all at the same value giving you maximum rate.

You don't need to do it more than once a month and requires nothing more than just leaving car plugged in once it reaches 100% for a bit. If you charge over night chances are your car is doing that every day anyway
 
Maciej said:
Battery is composed from multiple cells as you use battery those cells discharge at slightly different rate. When you charge to 100% one of the cell may be 100% while other may be 90% car still registers as 100% but your range slightly drops.

Balancing battery discharges the 100% cell to 95% and charges the 90% cell to 95%. Then it brings up both 95% cells to 100% so your cells are all at the same value giving you maximum rate.

You don't need to do it more than once a month and requires nothing more than just leaving car plugged in once it reaches 100% for a bit. If you charge over night chances are your car is doing that every day anyway
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Thanks Maciej. I've nearly got it. I had assumed that if you left it charging at home overnight for 100% then charging wouldn't stop until the charge was at 100%, presumably for all cells, ready for full range in the morning. I only charged at home overnight and haven't any experience of on the road chargers. Does balancing only apply to those who only charge to less than 100%? Maybe I don't understand on the road charging but don't they also stop charging when they reach 100% like my home charger?
 
Yes if you leave it over night it will get to 100% and then will rebalance all cells and stop. Balancing is more important to people who rapid charge a lot because their cells tend to be more off balance so it's recommended to do it every now and them most people don't need to worry about it. If you are charging over night your car automatically rebalnces your battery already at the end of a charge
 
Sort of. MG use passive cell balancing - read this detailed explanation:

How Does Cell Balancing Improve Battery Life

There's no reason why DC charging cannot be used when balancing, but as it only takes place at high SoH and takes many hours at low currents it is not recommended. Instead AC charging is recommended, and it doesn't even require a "Fast" 7kW charge point as the power is way below the ~2.3kW a pEVSE provides.

Note - DC charging is controlled mainly by the car, and at high SoH the car calls for low current from the charger. If the charger for some reason exceeds this then the car aborts the charge or if the charger cannot go this low it aborts the charge. Either way this shows as an error on the car as the HV battery has not been shut down correctly and the car throws a hissy fit until it is sure that everything is safe.

Sadly the CCS standard is a mess and is open to interpretation by both car and charger manufacturers as well as charger operators. The result is total inconsistency, a car might work perfectly at one charger with one operator but not at the same model of charger with another operator, or with one model of charger with an operator but not a different model of charger with the same operator. In both cases all the machines may work with another model of car, or not.

To avoid issues avoid going to high SoH with DC charging, "balance" or "equalisation" charge on AC monthly.

FWIW I have an LR and normally only charge to 80% on AC with occasional 100% before long journeys. I have never seen the dashboard instruction to balance charge despite often going for 6-8 weeks between 100% charges.
With my Wife's LEAF we seem to need to balance charge roughly fortnightly to avoid things getting out of line, but we can see the individual cell voltages (using 3rd party software) and its different chemistry.
 
Wakefield5 said:
I hope people aren’t regularly using rapids to charge over 90% when people are waiting, it’s poor etiquette.

I do however confess to having done it once in a deserted car park at 1am (and would have stopped if anybody else arrived to use it) and having the issue mentioned here.

Just turn everything off for 15 minutes and it’ll restart no problem. Fairly certain I read it was something to do with protection against the battery overheating or something.
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Assumptions of “poor etiquette” really make me laugh.
 
So, the plot thickens as the vehicle has done it again this morning but this time at 77%

I’m going to run a balance charge later today and see what that does.
 
Well, there we have it.

No DTCs stored but the car consistently ends a charge and disconnects the HV battery, with it resetting after a while disconnected from the charger. However, performing a balance charge has stopped this behaviour completely with no continuing issues at present.

Perform regular AC charges people, it keeps the battery and the BMS happy!
 
WigglePig said:
Well, there we have it.

No DTCs stored but the car consistently ends a charge and disconnects the HV battery, with it resetting after a while disconnected from the charger. However, performing a balance charge has stopped this behaviour completely with no continuing issues at present.

Perform regular AC charges people, it keeps the battery and the BMS happy!
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AC charging is good for the battery. The HV cutoff can also be a firmware problem, MG have released a patch for it which you'll get next time to go for service (or sooner I guess if you ask).
 
Wakefield5 said:
Where’s the assumption? Charging above 90% on a rapid while people are waiting is poor etiquette.

And to be clear I never said the OP had done this.
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There’s the assumption, right in the front.

Drinking all of that pint you bought is poor etiquette too I suppose, if someone wants the seat…
 
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