Managing Voltage: 2 New Approaches to the Legacy 12v System

If you have been active in the automotive sector over the past two decades, you are no doubt familiar with the infrequent debate that surfaces every few years over the increasing electrical load expectations needed for “today’s emerging technologies.” Those technologies included steering by wire, braking by wire, and electric turbochargers. You know these technologies and many others have been incorporated within the existing 12-volt architecture in a seamless fashion with no attendant draining or failure due primarily to efficiencies squeezed from within the existing 12-volt architecture.

You also know new technologies continue to be added to the automotive platform with each new model year. Could it be that we are, in truth, reaching the limit of what can be expected of the 12-volt system? Is it possible the demands of start-stop technology, navigation, 12-inch screens, automated driver assistance systems, electric A/C compressors, telematics, engine management systems, sensors, and tech we haven’t seen yet will indeed exceed the workable capacity of the 12-volt DC system we all know so well?

This article will detail two coming evolutions, one each for the automotive and heavy truck sectors, in their electrical load management systems. While the changes are different for each, they are likely to become more common in the coming years. For the automotive sector, a 48-volt system may become the next emerging standard to supplement the 12-volt system we know and love. For heavy trucks, multi-voltage systems are coming in the form of multi-voltage power distribution systems (MVPDS).

When a 12V System Isn’t Enough

Automotive OEMs, wrestling with this challenge, have begun  to gradually migrate toward a 48-volt mild hybrid system to supplement their existing 12-volt systems. The 12-volt battery and alternator are designed in a synergistic partnership to supply all the electrical power needed regardless of the load asked. The mild hybrid supplement seems to offer both proven technology and enhancements that satisfy OEMs and consumers alike.

Our familiarity is growing with new fuel efficiency strategies that include shutting off the engine during stops as well as utilizing cylinder cut-off systems while the vehicle is in motion. The battery must supply all active loads even as the total number of engine stops is multiplied. The charging system may be modulated even when the engine is running to increase engine performance and/or fuel economy. The battery may even be discharged to boost a running engine to deliver better efficiency or performance. Can the 12-volt system “live” in spite of these demands too?

OEMs agree the expanded in-vehicle electrical grid can be managed well by incorporating a mild hybrid system that replaces the starter with a 48-volt motor generator unit (MGU). Some call it an integrated starter generator (ISG), adding a battery pack along with a DC-to-DC converter. Why? Four significant benefits accrue from this technology, all of which match clear OEM objectives and consumer desires:

• Potential fuel savings estimated at 15 to 20%
• Potential cost savings over utilizing a traditional hybrid system
• Emissions reductions as the electric motor manages some of the power demand previously handled by the internal combustion engine
• Improved performance, particularly in the stop/start process.

These objectives are no doubt popular with the consumer, and with increasing pressure on OEMs to increase Corporate Average Fuel Economy (CAFE) standards, these objectives may approach the level of imperatives for OEMs.

This technology does not mean the end of the 12-volt system; 12-volt systems still operate well with a 48-volt system, as the two can operate concurrently. Standard items such as power windows and seats, door locks, and lightscan still operate within the 12-volt architecture, while more power-intensive loads (e.g., start/stop) will defer to the advanced higher voltage system.

Pioneered by Honda in the Insight first and then by GM in the Saturn in the early 2000s, initial and limited mild hybrid availability was expected in MY-2020 with substantial sales projected for MY-2023. This technology is featured currently in the Ram 1500 (3.6L) and offered in the Jeep Wrangler, the Hyundai Tucson, and in Volvo automobiles (at 42 volts) by Mercedes. Most OEMs now, or soon, will offer this technology in various iterations.

Multi-Voltage Power Distribution Systems are Coming

If you understand the increased electrical loads required by automobiles, you may be able to easily imagine load demands in the heavy truck sector have been exponentially more severe, as most operate within the same 12-volt architecture. As with the automotive sector, the voltage appetite of a heavy truck, impacted by many of the same factors listed above, has steadily increased.

Understandably in a heavy truck, the electrical appetite has largely been satisfied by adding more batteries (12V) and/or increasing alternator capacity and output. The success of this equation has featured variables such as ultra-capacitors, inverters, multiplexing, auxiliary power units, or including a shore power interface — systems that we in government are very familiar with.

The landscape, just as in the automotive sector, is changing for many of the same reasons detailed above. In Europe, the 24-volt system in heavy truck operations is now the norm. As electric truck technology is coming into focus, 12- , 24- , 48- , and even 60 volts or more will be necessary to supply the megawatts needed for a 250-mile range expectation. Those of you with technicians in your employ must be cringing as you consider the potential life-altering result of an error while working on such powerful systems in your shops.

Heavy trucks will soon feature multi-voltage power distribution systems. Experts in the development of these systems agree they will require conductors of a larger gauge, wiring of various gauge thicknesses, and even greater attention to sealed connections to handle the power and resist corrosion as energy demand increases. Clearly, technician training, both in safety and diagnostics, will be critically important along with the acquisition of capable tools and diagnostic and safety equipment. Unfortunately, this is not the best news given today’s lean technician staffing levels.

Continuing Industry Research

The identification, standardization, and marking of cabling is currently being tackled by the Society of Automotive Engineers’ (SAE) Truck and Bus Electrification Systems committee under its new J3176 standard. This will include how power and ground cabling will be identified for the various voltage ranges on board a heavy truck for safety and maintenance purposes. Several other SAE standards are being worked on that also pertain directly to MVPDS.

Additional work is underway by the Technology and Maintenance Council’s S.1 Electrical Study Group as it references these new SAE standards in developing its recommended practices designed to assist technicians in their daily preventive maintenance and diagnostic troubleshooting activities involving cabling in all voltage ranges. The objective of the Multi-Volt Electrical Task Force is to support fleet maintenance management by providing guidance through which MVPDS can be understood and repaired safely and efficiently.

Clearly, MVDPS will be among the many acronyms and new technologies with which fleets, fleet managers, and technicians will become more familiar and challenged by in the coming months and years. Government fleets, characterized by their diverse vehicle inventories ranging from Class 1 to Class 8 plus heavy equipment, are likely to be more greatly challenged than most due to the diversity common to every government’s vehicle inventory.