Automobile Propre answers your questions. Since electric cars carry a traction battery with a large energy capacity, has the 12 V battery for accessories become useless?
Our reader’s question
After reading Soufyane’s article entitled ” Electric cars: which equipment consumes the most? “, one of our readers reacted this way in the comments: “ So, silly question, is the 12 V battery decorative? ».
Our answer
It is more particularly this sentence that has created doubt: “ All this equipment draws its energy from the traction battery “. Yes, it is true in a certain way, in a shortened way.
For my part, the information that I had obtained a few years ago from manufacturers’ EV technicians was that it is always the 12 V battery which supplies the accessory equipment, this element inherited from the thermal models being maintained in charge by the lithium ion pack. Several comments following the article also go in this direction.
And now the doubt sets in. Impossible to treat the subject without contacting Soufyane, the author of the article. This is also the strength of Automobile Propre, enriching each other with our personal knowledge and questioning ourselves when necessary. Technologies evolve, it is necessary to know how to integrate these evolutions.
We both discussed the subject at length, comparing our sources. A very interesting exercise that made us think back to our own experiences with thermal models. When a gasoline or diesel car is started, is it the 12 V battery that supplies the consumers or does the flow come directly from the alternator. And there, it became obvious, it is not so binary.
And on a thermal?
Let’s take a classic 30-year-old thermal car with a moderately discharged 12 V battery. By turning on the headlights without switching on the ignition, we can see that they illuminate less than usual. Provided there is enough juice left and the alternator is operational, if the engine is started, the light intensity of the headlights increases markedly. It can even be stronger when accelerating. The role of the alternator appears obvious.
Car started, if the alternator is dead, does the 12 V equipment still work? Yes most of the time, sometimes in degraded mode. The electric windows go up more timidly, for example. What if the 12 V battery is very discharged and the alternator is in good condition? Same, it works.
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Another scenario, is it possible to drive with a started petrol car when the 12 V battery is completely discharged or the alternator is out of order? Yes, in both cases, the ignition receives what it does with electricity, at least with certain models. And this thanks to a rather fine but rather simple electronic management. It is more complex with the current models.
When an electric is started
Thinking about what happens on a thermal car has allowed us to be sure of two things. First of all, when the car is started, the supply of electricity to 12 V equipment potentially comes from the battery and/or the alternator, depending on the situation. On the other hand, if the engine is cut, there is only one source left: the 12 V battery.
Second point: there are differences in behavior depending on the models. And for electric cars? Wouldn’t there be an intermediate element playing a bit the same role as the alternator when the engine is started? A converter for example. How to know ? Ah but, yes, of course, I’m revolted not to have thought of it sooner! Who better than e-Garages to answer these questions?
Hence a phone call to our friends in Carquefou, near Nantes. ” When the car is started, a converter supplies the 12 V and recharges the accessory battery. It is he who powers everything, and it is completely transparent for the 12 V “, replied the EV repair professionals. Specifying : ” This operating mode is identical for all EVs equipped with a 12 V battery ».
What if the electric car is not started?
When an electric car is not started, it’s like on a thermal model, ” it’s the 12 V battery that powers everything “. And this, thanks to a few computers which then quickly go to sleep. This operation serves what is of the order of telemetry and makes it possible to communicate remotely with the vehicle.
During this period, the 12 V battery can be kept level by drawing on the traction battery, still passing through the converter. Some electric cars clearly indicate this. Thus the Kia e-Soul, by a flashing blue light at the top of the dashboard, when it is not plugged into a terminal or a socket.
On the other hand, when the ignition is on, but the vehicle is not started, Revolte noticed 2 scenarios: ” On the Citroën C-Zero and Peugeot iOn, the 12 V battery alone supplies the equipment with the necessary energy. It’s different on the Renault Kangoo where the converter is already active “. Thanks team!
Do without a 12 V lead battery
Could we do without the 12 V battery? This lead element is most often identical to that of a thermal. When my Kia e-Soul died, the repairman suggested that, given the distance from the Kia dealership, I go to Renault next door: “ It’s the same battery model as on their Mégane or their petrol Clio ».
However, it is not so simple, because depending on the electric car model, even if the 12 V battery is identical, there is often a specific manufacturer protocol to follow when replacing it.
Note that, in accordance with Revolte’s explanations, with a dead 12 V battery, it is impossible to start the Korean SUV. But by connecting a booster, it works, and you can drive without problem. You just have to not cut before being able to solve the problem. Manufacturers have already considered adopting a 12 V lithium battery instead of lead chemistry. So Tesla.
And do without this element completely? Same, many have already thought about it. This is technically feasible, but would require an alternative, potentially more expensive than a 12V battery.
With this new Green Stamp section, Automobile-propre journalists are there to answer your questions on electromobility. Choice of a vehicle, need for technical information… Send us your questions in the comments below or by email at this address:
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