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The current 12-volt system is running out of puff.


The 12-volt electrical system has been with us for many years, but is now running out of capacity. A dual 12V-48V system is the first step towards a higher-voltage solution.


Remember when you could turn off your 4WD engine and listen to the radio for a couple of hours or so, with the ignition switch on ‘Acc’? In a new 4WD that radio-time is down to around 5-10 minutes, after which you get a dashboard message to run the engine to replenish the battery.

Partly, the cause is a move to lighter, lower-capacity starting batteries, but the main reason is the high electrical power demands in modern vehicles.

Even on standby the battery needs to keep ‘alive’ various vehicle ECUs, the navigation system, sound system powering multiple speakers, visual entertainment system, power outlets, central locking, immobiliser, door security, external cameras…the list grows almost daily.

Running all this stuff from a 12V battery is becoming difficult and wiring looms are growing in girth and length. Voltage drop in lengthy 12-volt circuits is another problem and voltage-critical components need to be fed power by thicker, heavier wires.

Medium and heavy trucks from Europe and Asia have employed 24-volt electrical systems for many years, to cope with engine-start power demands and voltage drop at the rear of long combination vehicles.

Early model Nissan Patrols also had a 24-volt system.

In the 1990s the major German vehicle makers decided to triple automotive electrical system operating voltage from 12 volts (14V when charging) to 36V (42V when charging).

The reasoning was simple: because power (W) = voltage (V) x current(A), raising the operating voltage reduces current draw and wiring that carries lower current can be thinner and lighter.

In the then-proposed 42-volt charging system, alternator output could more than double from about 3kW to 8kW, providing much more power for electric systems, such as communications, navigation, power steering and dynamic suspensions.

Early discussions found agreement in the need to have parallel 12V and 36V systems on a vehicle, to avoid the need for completely new sub-systems: lighting, communications, sound, locking and instrumentation, for example.

It looked like the 36-volt movement had stalled by the early 2000s, mainly because of increasing use of low-current-draw components, such as LEDs; the use of more efficient electric motors and digital multiplexing that shrank and lightened wiring looms.

However, the swimming duck’s feet were very busy under the surface, powered largely by the need to comply with ever-tightening regulations for CO2 emissions.

An increase in sub-system voltage had the potential to reduce CO2 emissions, by improving stop-start efficiency, allowing ‘free’ battery regeneration when slowing or braking, the ability to employ electric motor assistance at lift-off and electric supercharging at low engine speeds.

In 2010 UK-based Controlled Power Technologies installed a 12/36-volt system on a VW Passat with a 1.4-litre TSI engine and it almost matched 1.8-litre TSI performance. CPT later developed a turbine energy recovery system capable of generating 2-4 kW of electricity from the exhaust.

48 volt electrics Parallel with this development, R&D in Europe and the USA indicated that a dual 12/48V system would be even better than 12/36V and would take advantage of the fact that there were many 48-volt lithium-ion-battery, charging and motor components already developed for electric vehicles.

Major automotive electrical system component makers in Europe and the USA, including Johnson Controls, Continental and Delphi developed 48-volt systems and Audi was been the first European car maker to announce this technology.

Audi showcased its 48-volt electrical system with two technology demonstrators: an Audi A6 TDI concept and an RS 5 TDI concept.

Both models were fitted with an electrically-powered compressor that acted like a supercharger from practically zero rpm, eliminating turbocharger lag. It operated independently of engine load and therefore improves acceleration.

48 volt electrics In later versions, a compact lithium-ion battery supplied 48 volts as the energy source during engine off phases and a DC/DC converter integrated the 12-volt electrical system.

The lithium-ion battery was fed by an optimised alternator that virtually made the drivetrain a mild hybrid, because of its 10kW energy-recovery capability. That added up to a saving of up to 10 grams of CO2 per kilometre, equivalent to around 0.4 litres of fuel per 100 kilometres.

Continental’s 48 Volt Eco Drive system was designed so the alternator/starter, electric motor, DC/DC converter, lithium-ion battery and powertrain and energy management modules could be integrated in virtually any vehicle.

In Conti’s demonstrator vehicle’s 48V system, the alternator starter was belt-driven (BAS), but could be directly-mounted on the transmission. The demonstrator’s lithium-ion battery was also relatively easy to integrate, because its dimensions were virtually identical to those of a 12V lead-acid battery.


4WD ramifications

A 48-volt electrical system is working very well in mild hybrid 4WDs, because the power demands of 4WDs are even greater than those of highly-specified passenger cars.

If an electric winch and third battery were integrated into a 12/48 system the winch could have a smaller, lighter motor with much more power. If the third battery were lithium-ion, it could have much more amp-hour capacity, to run a fridge for longer periods and with a faster charging rate.

Transitional 48-volt systems in mild hybrid 4WDs have followed passenger car practice and are dual, 12/48V types, so popular 4WD extras, such as electrically-actuated diff locks, driving lights and radios work fine.




























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