MG5 System Fault - HV Battery Shut Off

[Barryf67]

Whilst charging on a Public rapid charger the charge stopped at 94% and when I disconnected, the car was showing a system fault; HV battery shut off
After turning everything off and leaving for 5-10 minutes the car came back on,
Has anybody else encountered this and do they think its a safety mechanism protecting the battery?

 

[Jomarkh]

Lots of this on the forum

 

[Maciej]

It was discussed in the last podcast. Apparently happened to few people. Advice given was to take car to dealership so they can read error message from computer and note what charger it was.

 

[5teep]

It has either to do with main battery temperature or the 12v being low.
It's happened to me once at 95% and same result wait 10 and its fine. My solution is not to rapid charge past about 85%, never had the issue again.

If you run the electrics on 12v during the charge (i.e.not in ready mode) the main battery cannot recharge it and if the voltage drops too low you get the hv batt cut off error. Once charging stops the main battery can supply power to the 12v again.

 

[Maciej]

seems really strange that it only happens at very specific battery %. It's still an issue I would take it to dealership so it can be reported back to MG and fix in some update if possible or in future versions.

 

[Barryf67]

Yeah car is going back in to get checked over, only had it three weeks and was only my second charge.
They advised to only charge to 80% using rapid chargers.

 

[bob876]

Not sure it always happens for the same reasons.
Just got back from a holiday in Scotland in my MG5 LR.
Had the system fault twice at different chargers, the first happened at a slow charger, the car wouldn't move , eventually got it going by disconnecting the 12v battery.
Happened again at Gretna Green ecotricity charger, this time I got it to move but wouldn't charge at all, on any of the chargers up there, tried IONITY, ECOTRICITY AND BP PULSE.
Left the 12v battery disconnected for a longer period and it would take a charge again!
Its going in this week to be checked out

 

[Jomarkh]

Are these all rapids and what percentage are you charging from and to?

 

[5teep]

Not sure it always happens for the same reasons.
Just got back from a holiday in Scotland in my MG5 LR.
Had the system fault twice at different chargers, the first happened at a slow charger, the car wouldn't move , eventually got it going by disconnecting the 12v battery.
Happened again at Gretna Green ecotricity charger, this time I got it to move but wouldn't charge at all, on any of the chargers up there, tried IONITY, ECOTRICITY AND BP PULSE.
Left the 12v battery disconnected for a longer period and it would take a charge again!
Its going in this week to be checked out

The HV disconnect issue most folk get clears itself after 5-10 minutes. If yours doesn't then I think you should get it checked out yes.

 

[bob876]

The first time it happened was at just a fast charger ie 7kw as the rapid was broken and I was at about 40% charge.
Then the other times were on rapid chargers again roughly between 40 and 50 %.
The first time it happened we waited ages as I wasn't sure what to do and we were in such a remote area on the Isle of sky and it didn't clear on its own.
Was very scary after disconnecting the battery the car is free to move but you get about 10 more warnings of safety features not active, however these sort themselves after you start to drive the car.

 

[5teep]

The first time it happened was at just a fast charger ie 7kw as the rapid was broken and I was at about 40% charge.
Then the other times were on rapid chargers again roughly between 40 and 50 %.
The first time it happened we waited ages as I wasn't sure what to do and we were in such a remote area on the Isle of sky and it didn't clear on its own.
Was very scary after disconnecting the battery the car is free to move but you get about 10 more warnings of safety features not active, however these sort themselves after you start to drive the car.

That's definitely not the same issue then, I hope the dealer finds the problem for you.

 

[bob876]

Thanks. Will post what they find if anything.

 

[Douma]

Happened to me yesterday PM, great drive around Dumfries and Galloway, battery at 32% used a local garage with a 50 kWh ccs, went for a walk, when we came back battery at 94%, stopped charging, tried to get car to go!!! Absolutely nothing, HV error showing in dash, walked away came back an hour later, problem seemed to have sorted itself out, but will contact nearest MG dealer for a diagnostic check.

 

[Jomarkh]

I wouldn't rapid charge above 90%, the car doesn't really like it and the charge rate drops off anyway.

 

[BugEyed]

Whilst I agree that a Rapid is relatively slow above 90% charge and some may consider it anti-social to take up a resource that others may need when charging on a Fast AC is as quick, surely it is still a fault that should not happen? If the car doesn't like Rapid charging it should either stop the charge or reduce it to the levels that match the AC charging.

I assume that Rapid charge points stop charging when the levels being requested get too low for them to want to supply, and that may in turn throw an error code in the car (to the effect "charge terminated by supplier"), but why should this cause it to not start?

 

[Petriix]

Whilst I agree that a Rapid is relatively slow above 90% charge and some may consider it anti-social to take up a resource that others may need when charging on a Fast AC is as quick, surely it is still a fault that should not happen? If the car doesn't like Rapid charging it should either stop the charge or reduce it to the levels that match the AC charging.

I assume that Rapid charge points stop charging when the levels being requested get too low for them to want to supply, and that may in turn throw an error code in the car (to the effect "charge terminated by supplier"), but why should this cause it to not start?

No one has quite figured out the exact circumstances that cause the issue. The CCS protocol is notoriously wooly and there are certain combinations of EV and charger that don't play nicely together. However, the MG software is certainly more than a little buggy.

I suspect that they (MG) have programmed in a very crude 'failsafe' which decides that something has gone wrong with the charging session and cuts it off without terminating the session correctly. That likely entails simply disconnecting the battery as if it's an emergency situation, which is why you see the errors.

Unfortunately MG have a bit of a culture of secrecy and absolutely zero interest in responding to questions or feedback so we are unlikely to ever see a fix. That means you really should avoid rapid charging above 90%.

 

[Maciej]

I wouldn't rapid charge above 90%, the car doesn't really like it and the charge rate drops off anyway.

While this is true it doesn't matter. Car shouldn't break because you charged to full. This isn't user error this is software error.

 

[Douma]

Whilst charging on a Public rapid charger the charge stopped at 94% and when I disconnected, the car was showing a system fault; HV battery shut off
After turning everything off and leaving for 5-10 minutes the car came back on,
Has anybody else encountered this and do they think its a safety mechanism protecting the battery?

Yes it happened to me whilst on holiday, I went back to the car an hour later & it worked just fine, checked the car into my nearest MG dealership when I got home but no fault found. I'm now very wary of public chargers & will only go upto 85%.

 

[Geo68]

Happened to me once at a public charger, think I got the sequence wrong on starting the charge and I could hear the gate opening and shutting continuously as it was looking to start. I eventually managed to disconnect the car only to have the HV fault. Left it for 10 mins and alll was ok. I'm a bit more carefull when charging now

 

[Prof1967]

In 15 months of ownership this has happened to me 3 times. Car has always reset itself after being left for 5 minutes and have never had to reach for the 10mm spanner.