Beginning in 2004, the U.S. auto industry will begin its move from the 12-volt battery (14 volts at the generator/alternator) electrical systems toward a 42-volt standard, with 25 to 50 percent of new vehicles incorporating 42V electrical architectures by 2010, and all new cars by 2020. A 42-volt system will slash weight, improve fuel economy, permit the replacement of many mechanical parts with electrical ones, power all sorts of new gizmos like seat heaters, video, etc, and, of most concern to us, improve efficiency for all automotive electrical devices, opening the door to higher audio amplifier power with far less complexity than the current crop of 12-volt, high-power amplifiers. Not only can will this translate to lower cost and more compact aftermarket power amps, even head units could cheaply integrate 100-plus RMS watts per channel power.
A New Standard
The standard that was recently agreed to by automakers and suppliers in Europe and the U.S. is a 36-/42-volt standard. Specifically, it is a tripling of the current voltage for both battery output (from 12 to 36) and generator voltage output (from 14 to 42). Vehicles with these next generation electrical systems will likely have dual batteries (12-volt and 36-volt) or at least a stepped-down, 12-volt circuit on board so that all electrical components don't have to change over at once. This will be more expensive, but the auto industry is very conservative, and this is the safer way to do it.
Aside from the pressure to meeting state and national standards on automotive fuel efficiency and emissions, the movement to 42-volt electrical systems is being stimulated by a seemingly insatiable demand for electrical and electronic accessories in vehicles, from heated windshields and seats to dash-mounted navigation systems and rear-seat TVs. Expect the first vehicles to switch to this new electrical system to be the big SUVs, premium luxury cars, and hybrid gas/electrical vehicles. Currently, bulky wiring harnesses, heavy power motors, and electronics that are subject to voltage sags and spikes which form some of the compromises of 12-volt systems. Moreover, the potential of breakthrough components like electronically actuated valves, flywheel starter/alternators, electric brakes, active suspensions and, four-wheel steering systems continues to go largely unrealized because there just isn't enough electrical power. More volts mean rethinking everything from light bulbs to the audio systems.
42 Volts And and the Impact On Autosound
Very low impedance speakers, parallel woofers, and bridged amplifiers are commonplace in autosound designs today. We are so used to these expensive kluges that we don't even notice the excess cost, sound degradation, and awkward complexity. The design and selection of the amplifier circuits in autosound are based on the premise that the power supply is 12V. The purpose of the amplifier is to increase signal. This signal increase can be measured in watts, the multiplication of voltage and current (amperes). Since the power supply is limited to 12 volts, the higher power must come from higher current output. To pull the needed current from the amplifier, the speakers must be low impedance. Think of the power from the amp as going through a pipe.
Iincreasing the diameter of the pipe halves the resistance to the signal so more power can passflow. The diameter of the pipe is analogous to the electrical resistance -- the larger the pipe, the less resistance for this power to pass though.
Even the autosound speaker designer has to work around 12V limitations. The gauge of wire used in the speaker voice coil is heavier than optimum in order to keep the speaker impedance low. So either you have a lot of woofers in parallel, or a woofer with a very low impedance voice coil. For sure, with the 42-volt systems and thus speaker impedances shifting upward to the range commonly found in professional sound and home theater systems, your speaker cables will work better and have less signal loss than with ultra low impedance speakers.
Consider that for sending power over long distances, even the power companies use high voltage power lines, and step the voltage down at the power sub-stations. In electrical power (and audio amplifier signals), there exists a phenomenon known as I2R losses, where the power loss (through generation of heat) is worse for high current than for high voltage. So 12-volt amplifier systems send high current (lower voltage) audio signals and have greater loss for the same run to your speakers than a 42-volt amplifier system sending the same power, except with lower current and higher voltage. This is true for all of the wiring harnesses in the car: the switch to higher voltages means to carry the same power, the wire will carry less current, and therefore the wires will get thinner and lighter.
The Existing Approach
The existing high current output approach came out of necessity for autosound aftermarket amplifiers. The technique uses many parallel high current output transistor devices, which is both a complex and expensive solution. Another common way to pull more power from existing amplifiers on 12-volt electrical systems is bridging. In this case, two amplifier channels work as a single audio channel. In this approach the audio signal is split down the center, with the upper half of the signal going to one amplifier channel and the lower half going to the second amplifier. On the output of the amplifier the two halves are "bridged" together to "swing" the higher voltage. This works fine, and is a common solution, but at the cost of double the amplifiers for a given number of channels! For a given power supply voltage, this roughly provides double the wattage. Another consideration with bridging is that the minimum speaker impedance load you can connect to the amplifier cannot be as low as the same amplifier when not bridged -- so if your amplifier could normally handle 2 ohms, when it is bridged it can only handle approximately a 4-ohm load.
Beyond medium power 12-volt amplifiers, above about 70 RMS watts per channel, designers run out of tricks and must use a DC/DC converter within the amplifier. This is a circuit of high complexity that adds significantly to the cost of the amplifier. The 12-volt (actually closer to 14-volt) power input from the alternator/generator is fed into a DC amplifier that converts the 12 volts to a higher voltage. There are quite a few hidden costs from heat, expensive components like sophisticated power ICs and other trick semiconductors, and pricey wound inductors. Still another aspect is that DC/DC converter designs require a manufacturer that knows what it is doing, which leaves out much of the Chinese subcontractor autosound amplifier manufacturing industry. The new 42-volt standard avoids all this, and enables even the Chinese autosound vendors to jump into the high power autosound amplifier game, which is great news and will represent breakthrough values for the consumer. Since the real electrical system in the car is now about 14 volts, and the real electrical supply in the next generation cars will be 42 volts, the power level that will be easily achieved will be three times what they are now -- perhaps a bit over 200 watts RMS per channel if all the tricks like bridging the amplifiers and low impedance speakers are used. But even 100 watts RMS can be attained with costs close to amplifiers of half the power today.
Remember, the electrical "power" is the product of amperes (current) times voltage, so an amplifier that takes 12 amperes of current at 12 volts requires only 6 amperes at 24 volts or 4 amperes at 36. So tripling the voltage effectively cuts the current by two-thirds, while still providing the same power capability. This creates opportunities to downsize the amplifier and perhaps rethink the amplifier architecture. For example, instead of offering 70 watts into a 2-ohm load, the amplifier can be limited to 4-ohm loads, but still reach 70 watts (at 4 ohms) and the number of output stage transistors in parallel can be reduced, all with a smaller size and lower cost.
Super Power Head Units
Has anyone ever seriously considered the amplifier in the head unit as a viable option for high power sound systems? That will soon change and become not only a real challenge for the aftermarket industry but an opportunity as well. The typical head unit struggles to deliver 15 watts RMS per channel, due to lack of internal real estate for big and hot amplifiers in a 1- or even 2-DIN format radio/cassette/CD unit. The latest switching amplifiers (digital amps) deliver compact size, minimal heat generation and even four separate channels in an IC chip. One 12-volt system example is Sony's MEX-5DI, which uses Tripath Class T technology with 4 x 70 watts output in a 1-DIN format. Imagine a 42-volt descendent in a few years with 4 x 200 rms watts!
For sure, 42-volt systems in cars are coming, first in SUVs, high performance and luxury cars, and the hybrid gas/electrics. But don't put off buying that power amp for your car, as 42V audio gear is still a few years away, and you'll need to buy the actual car first! A few of the smarter amplifier companies are looking at what this means for their future product lines -- and you heard it here first. v
Some History and Background
The 12-volt configuration has not always been with us. Up until the mid-1950s, U.S. cars used 6-volt systems and many European brands continued to produce 6-volt cars through the 1960s. General Motors made the switch in 1955, and VW was the last major player to jump to 12 volt, back in 1966. The larger trucks moved to 42-volt systems long ago. Actually, our cars run on 14-volt alternators and generator electrical systems; only the battery is 12 volts. The current thinking (pun intended) is for a triple increase to 42-volt systems. It is generally agreed that safe voltage is limited to 60V. As voltage levels rise, however, the higher voltage can more readily jump the air gap between electrical conductors and "arc." Arcing in a 42-volt environment is a much bigger headache than 12/14-volt systems --the energy in the arcs is much higher. The solution is there is a lot of subtle part redesign that has to be done to prevent arcing. The new 42-volt standard was driven by the industry wanting the highest possible voltage, with the most safety. But higher voltage beyond a point can have its own costs -- a European safety regulation specifies that any voltage above 60 needs to have more heavily insulated wires and connectors. That would add weight and defeat many of the advantages gained in other areas.
The new electrical system architecture will likely help provide a seamless information link between home, office, and vehicle by combining the Internet, GPS, DVD, audio, cellular and satellite info systems. Other benefits of the extra electrical power afforded by the switch to 42 volts will include driving- and braking-by-wire systems, which replace a car's bulky hydraulic and mechanical parts with electronics, enabling electronic brakes, steering, valve control, air conditioning compressors and power steering pumps.
There are dozens of fractional horsepower motors on a car or truck. Electrically controlled mirrors require multiple motors for changing tilt and angles. Adding car sound systems, plus electronically controlled engine management systems, electric heating, ventilating and air conditioning systems has resulted in big increases in power needs. Vehicle electrical demands vary considerably by type, size and model of vehicle as well as by component. In general, it is estimated that typical vehicle electric demands doubled between 1990 and 2000. On small cars, electrical power demand has doubled from 500 watts in 1990 to close to 1 kilowatt today, going to 1.5 kilowatts by 2005 (large cars exceed 2 kilowatts and by 2005 will reach 3.5 kilowatts). Within a decade a typical vehicle's electric demand is expected to approach 10,000 watts of power.
Going to a 36-volt battery, which charges and operates at 42 volts, would permit vehicles to go the other way -- using a lighter, thinner conductor to handle the equivalent loads. Furthermore, having an electrical system in place with 42-volt capabilities permits the OEMs to add even more comfort and convenience items. But beyond those considerations, having a 42-volt electrical system permits the car manufacturers to achieve important goals in improving fuel economy, emissions and safety by replacing belt-driven and crankshaft-driven components with electronically controlled electric motors and solenoids.
There is a lot of room for improvement. According to an article published by MIT, less than 30 percent of the energy in gasoline actually makes cars move -- the rest is heat burned off during idling and waste by inefficient (often mechanical) components. More powerful electrical systems will allow the more efficient electronics parts to replace mechanical parts, such as those driven off of belts connected to the engine. Switching to high voltage architecture also means cars can have starter motors strong enough to provide an "instant start" at the tap of the accelerator, so they can shut themselves of at traffic lights, or any time the vehicle comes to a complete stop, rather than idle and waste gas. One of the real benefits of jumping to 42-volt systems, especially for hybrid vehicles, is the ability of the vehicle to offer regular 110-volt electrical outlets.
This will allow us to plug in, say, tools at a worksite or campground -- or even home audio gear! However, consumers do not have to wait for the 2004 introduction of GM's hybrid full size pickup truck for this benefit. Today they can buy an off-the-shelf product for ultimate power supply reserve, the Auragen. This is a 5kW generator developed by Aura Systems that turns a vehicle into a mobile power generation plant. It generates 60Hz 120/240V AC power whenever the vehicle engine is running, from idle past red line. The AuraGen has no effect on the operation of the engine. Power is clean enough to run any analog or digital electronic equipment. Two 120V AC/20-amp circuits and one 240V AC/20-amp circuit are provided. This would allow a sound system to be designed using audiophile or touring sound reinforcement signal processors and power amplifiers, without any need to modify the equipment's power supply. A dash-mounted control panel provides a power switch and meter with power generation indication.