Hello everyone!

First of all - I'm not in such situation just my curiosity, if someone can answer would be happy  

I don't know much how does e-Tec (mild hybrid) works, but know little more than something about Toyota hybrid tech.

 

In short - what happens if my cars 12V battery is dead? If I understand correctly the engine is started using 48V battery power, so the 12V is needed only to switch some relays. Will it start with really weak 12V battery, for example I have left my 12V kettle in the trunk for a while (kidding)?  

How is 12V generated in the car as DC-DC  (48V-12V) converter like in Toyota or with usual alternator?

 

Thanks everyone!

Once more - I don't have such an issue just want to understand my car little better. 

The 48V battery will drained out first followed by the 12V battery.

 

it is the same scenario as any other cars with just a 12V battery.

 

replace the 12V battery.

17 hours ago, stridercombi said:

The 48V battery will drained out first followed by the 12V battery.

Do you mean that 48V->12V inverter is working even when the car is switched off?

Isn't there any protection for a 48V battery to save it from deep discharge?

 

Dead I mean it is completely discharged - need to charge it, not replace it, which can actually happen with an "always hot" 12V socket.

6 hours ago, lmp said:

Do you mean that 48V->12V inverter is working even when the car is switched off?

I doubt that. I have PHEV, it didn't help me that 13kWh battery was full when 12V battery was flat. Car was even plugged and programmed to start charging during the night. As technician explained me, controllers which are responsible to keep 12V battery charged and are charging it when car is plugged, they too are supplied by 12V battery. Why there is nothing to detect discharge of 12V battery and start charging it (from big battery or plug) is not quite understandable.

Hello!

I'd be happy to help explain how e-Tec (mild hybrid) systems work in cars.

In e-Tec mild hybrid systems, the 12V battery is responsible for powering various auxiliary components in the vehicle, such as lights, infotainment system, and other electronics. The main engine starting is indeed done using the 48V battery system, which is typically connected to an electric motor or integrated starter generator (ISG).

 

If your car's 12V battery is dead or very weak, it can potentially cause some issues with starting the vehicle or powering the electronics. In such cases, the 48V battery system might not be enough to start the engine, as it is primarily designed to assist the engine during acceleration and provide some additional power for efficiency improvements.

 

As for generating the 12V power in the car, it can be done in a few ways. Some e-Tec systems use a DC-DC converter, similar to Toyota's hybrid technology, which steps down the voltage from the 48V battery to 12V to charge the smaller battery. Others may still use a traditional alternator connected to the internal combustion engine to charge the 12V battery.

 

In any case, it's essential to ensure the 12V battery is in good condition to avoid any potential starting or electrical issues. Regular maintenance and checking the battery's health can help prevent such problems.

 

I hope this clarifies how e-Tec (mild hybrid) systems work and how the 12V battery is involved in the process. If you have any more questions or need further information, feel free to ask!

Thanks everyone for your replies. It is little more clear now.  

Only would be great to know how it is done and what is expected behavior with the Octavia e-Tec.

It seems for me that engine is started with 48V electrical motor as engine start is so smooth I have never seen on the 12V system.