Dead 12 volt battery

[Jeps]

Hi. Has anyone else experienced to have a dead car because the 12 volt battery is suddenly very low?
We didn't use the car for 5 days, and when it was time to use it again, we couldn't open the car. Luckily I have seen a video on how to enter the car with the secret key. But everything was dead in the car, the 12 volt battery measured 2.85 v when we measured it.

 

[CDR]

Its possible that you left something on like a light. This happened to me when the boot didnt properly close and the light stayed on. The 12v died. I believe the 12v is charged from the HV battery via a contactor fed from the 12v battery, so if the 12v battery is dead there is no way the contactor will energise.
I have a small booster pack for a back up. I connect it across the leads and then I can hear the contactor energise and the car boots up.

 

[Jeps]

Hi CDR. To my knowledge I shouldn't have left any light or the likes on the car. I locked the car without the car's horn alarmed. ( Once I didn't close the boot completely, and then it warned me)
I have had a problem with the car radio. I can't change channels, it showed this message on the radio for the last 3 days before I didn't use the car for 5 days. Maybe it's related? I still wait for an answer from MG Denmark on that issue.
What battery booster do u use?

 

[CDR]

That issue could have caused it, maybe it stayed trying to initialise when the car was off?
I use a cheap 1.2amp one I got in lidl for 70€

 

[Jeps]

Could you boot up the car just after you connected the booster?

 

[ARealHuman]

Stupid question - but why does a battery powered car have a separate 12v battery?

 

[CDR]

Could you boot up the car just after you connected the booster?

Yes. All the booster did was provide enough power to energise the coil of the contactor which allows current to flow which in turn charges the 12v battery and thus the car starts

 

[CDR]

Stupid question - but why does a battery powered car have a separate 12v battery?

The 12v powers the car electronics and all that while the high voltage battery powers the motor and provides charge to the 12v

 

[Frank]

Stupid question - but why does a battery powered car have a separate 12v battery?

Quite simply it is because the DC current that runs the motor is at about 400v and over, lights, horn, windscreen wipers, windscreen washers, interior lights, radio, etc etc are 12v. So ALL ev motors have a 12v battery to run all the ancillaries and the electronics. The main battery pack when up and running charges the 12v battery and the only other time the 12v battery is charging is when you are charging the main battery pack.

I will say this again for ALL you guys that have home chargers, charge your car EVERY time you are not using it even when the SOC is high, you will NOT then have any issues with the 12v battery and lastly when listening to the radio or wanting the HVAC on whilst waiting from someone/something when stationary LEAVE the car in the run mode, again you will NOT have 12v battery issues no matter how long you are waiting and whilst stationary the drain on the main battery pack even when charging the 12v battery is minimal. Also don't worry about the HVAC being on whilst stationary, you would have to be waiting for a LONG time before that drains your main battery to any significance.

Regards

Frank

 

[Jeps]

Hi Frank,

I Thank you for your input.

I start now to realise, that I have to change my charging behaviour. Before we had an Peugeot iOn with a 16kwh battery for 4 years. With the bigger battery I thought I could go for many days without changing, but I guess I must rethink that idea....and maybe start to check the 12 volt gauge that the MG is equipped with ?

 

[Frank]

Hi Frank,

I Thank you for your input.

I start now to realise, that I have to change my charging behaviour. Before we had an Peugeot iOn with a 16kwh battery for 4 years. With the bigger battery I thought I could go for many days without changing, but I guess I must rethink that idea....and maybe start to check the 12 volt gauge that the MG is equipped with ?

Hi,

If your mileage is low then yes you could go for many days without charging. I only do about 10-20 miles a day if that and its all urban so in theory I could only charge the car maybe every two weeks but I don't see the point. If one has a home charger then for the sake of a couple of mins I just plug it in and leave it charging with the knowledge that if the unexpected happens I always have a full charge in the morning. I never worry about overcharging or letting the battery go too low as the Battery Management System looks after that and in most cases due to PCP and leasing most households change their car every 3-4 years so I also never worry about my main battery packs health, I will let the 80000 7 year warranty worry about that besides I will most likely have a new car in four years time.

Regards

Frank

 

[KasEV]

Well said Frank.
I understand Tesla has a different electrics initiation process which overcomes these 12VB issues.
Apparently MG and other manufacturers either out of laziness or apathy just superimpose their ICE startup sequence on their EVs and that is why we have these issues with our 12VB.
With a Tesla the standby state is always with HVB on and 12VB on but motors not ready to engage. There is no standby state were only 12VB is on.
The MG have a basic standby 12VB only (yellow)
On standby state HVB plus 12VB on but motors not ready to engage (green, no ready message on message board)
On state motors ready (green plus Ready on message board)
Apparently it is safer the MG way. If you ask me it is a bit impractical but very very safe.
Please make sure when in the ZS EV which is stationary and you want to use radio HVAC etc for more than 2mins that you use the on standby state(Green No Ready message) if not you may end up with a flat 12VB.

 

[CDR]

Well said Frank.
I understand Tesla has a different electrics initiation process which overcomes these 12VB issues.
Apparently MG and other manufacturers either out of laziness or apathy just superimpose their ICE startup sequence on their EVs and that is why we have these issues with our 12VB.
With a Tesla the standby state is always with HVB on and 12VB on but motors not ready to engage. There is no standby state were only 12VB is on.
The MG have a basic standby 12VB only (yellow)
On standby state HVB plus 12VB on but motors not ready to engage (green, no ready message on message board)
On state motors ready (green plus Ready on message board)
Apparently it is safer the MG way. If you ask me it is a bit impractical but very very safe.
Please make sure when in the ZS EV which is stationary and you want to use radio HVAC etc for more than 2mins that you use the on standby state(Green No Ready message) if not you may end up with a flat 12VB.

Stupid question - but why does a battery powered car have a separate 12v battery?

Your welcome

 

[Jeps]

Yes. All the booster did was provide enough power to energise the coil of the contactor which allows current to flow which in turn charges the 12v battery and thus the car starts

Hi CDR.

I followed your example and bought a JumpStart booster. I ended up with seeing very good reviews on the Audew jumpstarter. The one I bought here in Denmark is sold under a different name, but it's the same.
And it worked beautifully
The car could be turned on right away

Audew 2000A Peak 20000mAh Car Jump Starter for All Gas Engines or Up To 8.5L Diesel Engines with LCD Power Display

Your friend shared a website for you! Check it now.

m.audew.com

 

[ARealHuman]

Thanks to all for anwering my daft question! I actually have a portable jump starter, so may keep it to hand once the MG arrives.

 

[CDR]

Hi CDR.

I followed your example and bought a JumpStart booster. I ended up with seeing very good reviews on the Audew jumpstarter. The one I bought here in Denmark is sold under a different name, but it's the same.
And it worked beautifully
The car could be turned on right away

Audew 2000A Peak 20000mAh Car Jump Starter for All Gas Engines or Up To 8.5L Diesel Engines with LCD Power Display

Your friend shared a website for you! Check it now.

m.audew.com

Thats great news.

 

[CDR]

Thats great news.

I leave mine in the car all the time plugged in to the usb port. That way it is always trickle charging and will be full if I need it. The usb ports power supply is cut off when the car is switched off, so no need to worry about draining the 12v by leave the booster plugged in all the time.
Its like having a bit of security.

 

[Jeps]

I leave mine in the car all the time plugged in to the usb port. That way it is always trickle charging and will be full if I need it. The usb ports power supply is cut off when the car is switched off, so no need to worry about draining the 12v by leave the booster plugged in all the time.
Its like having a bit of security.

Yeah, will keep mine in the car too. It is a very SERIOUS power bank to have laying handy.
I am very impressed with the quality of the one I bought. It had 73% when I unpacked it, and it said 72% after I started the car. So plenty power in that one?

 

[Mgkev]

I have one of those bought for exactly that same reason. Never thought to leave it plugged in so thanks for that.

 

[CDR]

Yeah, will keep mine in the car too. It is a very SERIOUS power bank to have laying handy.
I am very impressed with the quality of the one I bought. It had 73% when I unpacked it, and it said 72% after I started the car. So plenty power in that one?

Glad I could be of any help