Yet most electric cars on the road today still use 12V lead-acid batteries for standby power, despite the development of lithium-ion batteries that provide longer ranges, faster acceleration, and greater horsepower.
The Legacy of Lead-Acid Batteries
It has been more than 100 years since lead acid batteries were introduced, including in the early versions of electric vehicles back in the 1890s, where they were inexpensive and reliable. In cold conditions, it can deliver 500 A for up to 5 seconds when starting an internal combustion engine. In addition, the 12 V battery can power the entire electric subsystem of an ICE vehicle once the engine is shut down.
Hybrid and plug-in hybrid electric vehicles were introduced in the 1990s by the auto industry; however, they still require lead-acid batteries to run their gasoline engines.
What About Cars Without an Engine?
The heavy battery, which is used to supply 12 V power to all electric subsystems when the motor is not running, is still used in most fully electric vehicles even when the gas engine is not running because it does not need to deliver 500 A peak output current to start it.
It might seem straightforward to eliminate the 12 volt battery in a fully electric car, but there are a few more issues to address before it can happen.
There is no cost difference between lead-acid batteries and DC-DC converters, but the latter is usually more costly in order to transform 400 V (from the battery pack) into 12 V for the infotainment/navigation systems and all the lights.
There is a considerable amount of work involved in redesigning anything in a car, since automotive qualification alone can take years to complete. A 12-volt battery can run low-voltage systems in an electric car, which makes engineering easier. Lead-acid batteries offer proven durability and a long lifecycle.
The low-voltage systems outlined above are located very close to passengers, so the idea that they draw power directly from 400 or 800 V batteries can be frightening. Lead-acid batteries can isolate higher voltages from critical systems by disconnecting the main battery back from them. Many layers of safety protection would be needed for high voltage inside the passenger compartment.
Rather than eliminating the 12 V battery altogether, some recent EV designs employ much smaller and lighter lithium-based batteries with lower available output currents as opposed to eliminating the 12 V battery altogether. Another option is re-use of used ev batteries.
So What Does It Take to Eliminate the 12 V Battery?
The 12V battery must be completely eliminated by using a rugged power supply capable of drawing safely from the high-voltage batteries. For functional safety critical applications, it should have a wide input voltage range, ideally 30 to 1000 DC, to cover both 400 V and 800 V nominal battery voltages.
The traction battery needs to be highly efficient, so that it does not discharge as quickly. It also needs to have a low component count, so that space is saved and reliability is enhanced.
This power supply would benefit from Power Integrations’ InnoSwitch3-AQ flyback switcher ICs with 900 V PowiGaN switches which are AEC-Q100 qualified. For secondary-side control, FluxLinkTM feedback links provide reinforced isolation up to 5000 VRMS.
In battery management systems, the circuit can start from 30 V without external circuitry, and the ICs achieve more than 90% efficiency at no load while consuming less than 15 milliwatts.
Frequently Asked Question
1. Do electric vehicles use lead-acid batteries?
Lead-acid batteries don’t work well in electric vehicles. They primarily use lithium-ion batteries, which offer greater energy density, longer lifespans, and lighter weights than lead-acid batteries do.
2. Can lead-acid batteries be used in cars?
Batteries using lead-acid can be used in traditional internal combustion engines. These batteries have been commonly used as starter motors and as electrical power sources for many years in conventional vehicles.
3. What is a lead-acid car battery?
Car batteries with lead dioxide (positive electrode) and sponge metallic lead (negative electrode) are rechargeable batteries commonly found in cars with internal combustion engines. An electrolyte of sulfuric acid is used to charge these batteries. Known for their reliability and ability to deliver high current for short periods, lead-acid batteries are an excellent choice for starting engines.
4. Does Tesla use lead-acid batteries?
Due to lithium-ion batteries’ superior energy density, performance, and longevity, Tesla’s electric vehicles don’t use lead-acid batteries. Lithium-ion batteries have superior performance and longevity compared to lead-acid batteries.
