48 VOLT SYSTEMS: HIGHER VOLTAGE, GREATER BENEFITS
From engine to wheels
In medio stat virtus (virtue stands in the middle): opportunities and benefits - including environmental ones- of higher voltage electrical systems (more than 12 volts), without reaching the hundreds of volts of electric vehicles
Car enthusiasts are quite familiar with the equation: electrical system = 12 V battery. Obviously we find different voltages too in our cars, for example in the ignition system or Xenon headlights, but these are very low and of little relevance to the electrical system as a whole. But when speaking about air conditioners, alternators and starter motors, things change drastically: in this case hundreds of amperes come into play with all the related issues.
It is definitely worth explaining, at this point, the relationship between voltage, current and power. The power of a user unit in terms of direct current (12 volt direct current in case of a battery) is given with good approximation by multiplying the supply voltage by the current (amperes)that goes through it . Yet, if more electrical current runs through a conductor, the losses due to the resistance exercised by the wiring system will be higher, resulting in power dissipation and an overheating of the conductor. Think of a light bulb: its 55 watts imply a current of about 4.6 amps while the alternator of a small sedan delivers 100 amps and even more; a big engine’s starter motor, on the other hand, exceeds 2 kW, with a current consumption - fortunately for very short periods - in excess of 170 amperes. Increasing the voltage to 48 volts can divide by 4 the current consumption for the same power: our light will then need just 1.15 amps, a reassuring value if you think that a USB port of a computer delivers 0.5 amps.
Less current, more power
A system of this type not only allows you to decrease the diameter of the wires, much appreciated in modern cars, since electrical inputs tend to rise steadily, but opens the way to new types of hybrid cars.
While start-stop technology currently in use take 12 volts systems to the limit, the use of more powerful 48 volt technology could produce 10-12 KW “electric vehicles” with a far more efficient start-stop system, allowing them to behave as a mild-hybrid with a slight weight increase. In fact, these solutions may become almost indispensable to meet, in these stormy times in the field of emissions, the limits that will be imposed by 2020: their use, for example, in 100 million cars could reduce emissions by 100 million tons of pollutants every year.
A prototype based on an Audi A6 TDI has an alternator specially designed to recover up to 10 kW and saves about 10 grams of CO2 per km. These developments are very interesting in view of future WLTP (Worldwide harmonized Light Vehicles Test Procedures) approvals, which, being more similar to the actual use of the vehicle, will be more difficult to obtain. An "electrical aid" during acceleration, for example, might limit the surplus of fuel injected into the cylinders, lowering temperatures and thereby minimizing the production of the dreaded and harmful nitrogen oxides NOx. The Hyundai 48V Hybrid Concept combines a 2 liter, 134 hp engine to a 14hp electric motor: despite the limited power of its electric unit, its efficiency and high torque at low revs produce a combined power of 148 hp with emissions limited to 109 grams of CO2/km.
Another possible use for 48 volt systems is in the field of electrically forced induction: a compressor powered by an electric motor, rather than a turbine, overcoming limitations such as a typical slow throttle response or completely dying out at low speeds.
The password: efficiency
Great power output and energy recovery are therefore possible with the 48 volt system, but batteries have to properly manage the high power peaks. Lead-Carbon batteries appear to be very promising in this regard, a technology currently developed by the Advanced Lead-Acid Battery Consortium. The consortium has already produced three experimental vehicles, among which a Passat 1.4 TSI equipped with a Valeo electric compressor and a CPT alternator / motor. This car, already in the early stages of its development, already boasts a reduction of 13% in CO2 emissions, but an 18% reduction is possible in the near future.
Even the Kia Optima T-Hybrid is designed around the Optima series, but its 1.7-liter CRDi turbo-diesel now has a 10 KW Valeo generator / motor, an electric compressor and a 48 volts East Penn UltraBattery. This powertrain allows the car to travel short distances in EV mode, recover energy during braking and increase torque at low engine speeds. The ADEPT (Advanced Diesel Electric Powertrain) concept is produced by a partnership between Ford, using a Focus, and the Ricardo engineering group. This car is clearly aiming to reach the emissions threshold of 75 g/km and looks at reducing it further to 70 g/km with a higher cost / emission reduction rate than a full hybrid vehicle. Furthermore, these mild hybrid vehicles can limit the extra weight to a few kg: the Tucson hybrid quoted above shows, in fact, a total weight gain quantifiable in 20 kg, including a DC / DC converter that supplies 12 volts to the various user units.
The battery’s contribution
These Lead-Carbon batteries (the latter being used in negative electrodes), in addition to being more convenient compared to lithium elements as well as being totally recyclable, combine the high energy density of a battery and the high specific power of a super-capacitor in a single low-cost device. The primary goals of lead-carbon research have been to extend the lifecycles of lead-acid batteries and increase their power. Another big advantage is the substantial lack of sensitivity to low temperatures: they can in fact be charged even at temperatures of - 30C °.
Significant improvements, however, have been recorded even in Lithium batteries: the Wanxiang Group is developing an MIT patent which, through NanoPhosphate technology, will have elements that require little or no temperature management , with great advantages in terms of weight and size of the battery pack.
The potential of the 48 volt systems have attracted the interests of large groups: in addition to the aforementioned Valeo, also Continental, Bosch and Magneti Marelli - to name only the most prominent names - are about to implement a mass production of these types of components. The relatively low voltage also allows operators to "handle" these systems much in the same way as a classic 12 volt system, thereby eliminating the need for assistance networks to purchase new equipment and skills that 200 / 500 volt batteries of electric and full hybrid vehicles require.