12v Battery Charging

[Ian Key]

Last night when I checked the 12v battery voltage on the iSmart app it was showing 12.2v. This morning at 7:00am it had gone down to 12.1v.
I haven't driven the car or unlocked it since yesterday afternoon and the last time it was on charge was 6 days ago. I've just checked it again (10:00am) on the iSmart app and it's showing 14.7v
Finally proof that the car charges the 12v battery even when it isn't on charge.

 

[pollenface]

Nice. I'm going to put a victron battery sense on mine to monitor the voltage.

 

[PristDean]

That's interesting, as I put elsewhere my 12v went flat when left for days but subjected to unlock / lock and mobile app use. If what you have found is true, not sure how my car's 12v went dead.
So two questions,
1. Do you know what charge % was left at over that period ?
2. Would you by any chance know what BMS firmware your car is on ?

 

[Rolfe]

When I left my car for just a couple of days it seemed to stop responding to the app at all. Don't know if this was just a coincidence, but it wasn't the usual error message when the app's on the fritz, or whether it's supposed to happen. When I went to drive the car, all was normal.

 

[Ian Key]

That's interesting, as I put elsewhere my 12v went flat when left for days but subjected to unlock / lock and mobile app use. If what you have found is true, not sure how my car's 12v went dead.
So two questions,
1. Do you know what charge % was left at over that period ?
2. Would you by any chance know what BMS firmware your car is on ?

Why yours went flat I don't know but I did double check the battery terminals a couple of days after I got it and sprayed the them with lithium grease.

1. The main battery was at 58%
2. I've no idea. The car hasn't had any updates since I got it at the end of March.

When I check 30 mins later the 12v battery was showing 13.8v and now it's at 12.5v.

 

[Surfdog]

When you took the snapshot above showing 14.7v I believe the smart charging would be activate and charging up your 12v battery. Once smart charging stops it should fall back down to something like 12.7v. I have never seen this voltage on app except when main battery charging is taking place. It shows your smart charging is working as it should and you should never have a flat 12v battery. My battery fluctuates between 12.3 and 12.7v when not charging.

 

[PristDean]

Why yours went flat I don't know but I did double check the battery terminals a couple of days after I got it and sprayed the them with lithium grease.

1. The main battery was at 58%
2. I've no idea. The car hasn't had any updates since I got it at the end of March.

When I check 30 mins later the 12v battery was showing 13.8v and now it's at 12.5v.

58%... So possibly the main battery needs sufficient capacity (over 30, 40 or 50%) to attempt charging the 12v ?. Mine was under 30% when the 12v went dead. Will be interesting to test

 

[Rolfe]

That doesn't make a lot of sense unless "sufficient" is about 2%. What good is it to protect the HV battery if the car goes dead because the 12v is flat? 30% or even 20% should be able to keep the 12v charged, surely.

 

[PristDean]

I have you on ignore Rolfe, but viewed this one and it's the usual eristic remark i'd expect.

Of course it makes sense, sufficient capacity to undertake servicing external demands without effecting the range left. In this case, the 12v won't take much but just in the same manaer that VTL can have a cut off to prevent drain, this may too. With this car and it's developers and BMS firmware versions, who knows !
My car's 12v going flat, but Ian's charging when over 50% seems to suggest just this, BMS firmware variable aside. As i said, i'll test mine

 

[tsedge]

I have seen mine drop to 12.1V before my car charges the 12V battery. It seems to charge it reliably, not had any problems.

 

[Rolfe]

I have you on ignore Rolfe, but viewed this one and it's the usual eristic remark i'd expect.

Of course it makes sense, sufficient capacity to undertake servicing external demands without effecting the range left. In this case, the 12v won't take much but just in the same manaer that VTL can have a cut off to prevent drain, this may too. With this car and it's developers and BMS firmware versions, who knows !
My car's 12v going flat, but Ian's charging when over 50% seems to suggest just this, BMS firmware variable aside. As i said, i'll test mine

I don't know what we're arguing about. I thought my comment was perfectly innocuous. It seems a very high % charge to be cutting off protection of the 12v battery at. Perhaps there is another reason?

 

[Rolfe]

I have seen mine drop to 12.1V before my car charges the 12V battery. It seems to charge it reliably, not had any problems.

Are you monitoring it frequently with the app, to be aware of this?

 

[tsedge]

Are you monitoring it frequently with the app, to be aware of this?

I run the app pretty regularly so yes.

 

[Rolfe]

I've never seen a 14v+ figure unless the car is on charge, but then I don't run the app that often. I just wondered if you had some other way of knowing.

 

[tsedge]

I've never seen a 14v+ figure unless the car is on charge, but then I don't run the app that often. I just wondered if you had some other way of knowing.

Just the app.

 

[johnb80]

That doesn't make a lot of sense unless "sufficient" is about 2%. What good is it to protect the HV battery if the car goes dead because the 12v is flat? 30% or 30% should be able to keep the 12v charged, surely.

I completely agree, the 12v battery is 55 a/h which equates to 600w or 0.6kW. 12v batteries should never be discharged more than 50% (12.23v), 12.1v is 40%. so 0.36kWh is needed from the high voltage battery to charge the 12v to 100%. 30% of the HV battery would do that with ease 100's of times.

 

[pollenface]

The obvious answer is a solar panel on the roof charging our 12v batteries

 

[Jto]

Last night when I checked the 12v battery voltage on the iSmart app it was showing 12.2v. This morning at 7:00am it had gone down to 12.1v.
I haven't driven the car or unlocked it since yesterday afternoon and the last time it was on charge was 6 days ago. I've just checked it again (10:00am) on the iSmart app and it's showing 14.7v
Finally proof that the car charges the 12v battery even when it isn't on charge.

View attachment 19608

I think you got your car was in ready mode as 14.7v is what the battery char at on all MG cars, attached is from the MG4 user manual as to how the 12v battery gets charged. Also battery’s show a higher voltage you you where to put a meter on the battery and five minutes later will get a lower voltage.

 

[Ian Key]

If you mean ready mode as in sat in driver's seat and the brake pedal has been pressed then no. The car was locked about 20 hours previously and hadn't been unlocked or touched and the voltage readings were through the iSmart app.

 

[Jto]

I could only think this old screen and a up to date one, as the car battery is not charged when charging the HV battery.