Johnson Controls will show a 48-volt Micro Hybrid battery system using a traditional 12-volt lead-acid battery and a 48-volt Lithium-ion battery at NAIAS next week. As AutoInformed has reported (Read Exhaust Gas Regen and 48-Volt Cars – Next Efficiency Breakthrough?) the technology is well underway in Europe with cars expected to be on the road this year.
A huge potential market is possible because of pending global CO2 emission targets. The auto industry has about a decade to achieve another 30% reduction by 2022. The move to 48 volts, little noted in the U.S. media, has significant implications for a new generation of potentially cost-effective mild or semi-mild hybrid vehicles.
At the 15th Automobil-Elektronik Congress in Ludwigsburg in 2011, five German automakers – Audi, BMW, Daimler, Porsche and Volkswagen – jointly announced their decision to push for the rapid implementation of 48-volt systems. Ford in Europe and Jaguar are also exploring the technology.
The proposed 48-volt standard in Europe could be a major factor for enabling the required motor-generator efficiency and power levels to make a practical hybrid at a much lower cost than current production models that use much higher voltages. Increasing the voltage beyond 60 volts requires expensive safety systems to avoid electrocution leading to a significant increase in cost. The specification for 48 volts is still evolving, and there may yet be more than one as different approaches are possible in different countries.
The 48-volt system appears to be a good compromise for performance and cost in the development of a new generation of affordable, fuel-efficient cars. However, the automotive road is littered with engineering ideas that never made it to production, as an aborted 42-volt movement decades ago proves.
“Even as Start-Stop vehicles become part of the mainstream in Europe and start to take hold in the U.S., Micro Hybrid technology has the potential to deliver the next level of fuel efficiency along the spectrum of vehicle performance, reaching upwards of 15%-20% in fuel economy,” said Alex Molinaroli, president, Johnson Controls Power Solutions.
The 48-volt battery could support higher power loads such as electric air-conditioning, active chassis technologies and the capture of direct regenerative power energy braking. The 12-volt battery would continue to provide power to the vehicle starter, interior and exterior lights, and entertainment systems such as radios and DVD players.
To elaborate, Ken, initially, the cars are expected to have two batteries, a lead-acid 12-volt unit supplying juice to conventional hardware and the lithium-ion 48-volt battery handling things like Start/Stop, electrically boosted steering and other subsystems profiting from higher voltage.
Hybrids, of course, already have dual batteries, 12-volters for door locks, lights and other “hotel loads,” higher-voltage battery packs for electric propulsion. A Toyota Prius’s battery pack is a nominal 273 v; a Chevrolet Volt’s, 300 v.
Battery electric vehicles run higher voltages. Typical of today’s BEVs, a Mitsubishi i’s battery pack operates at a nominal 330 v; a Nissan Leaf’s, 400 v.
In time, automakers will consolidate things in conventional cars into a single 48-volt battery. One reason for the higher voltage is an ever-increasing electrification of automotive functions. Another is enhanced efficiency—gained by lighter wiring harnesses.
The reason for the latter traces back to Ohm’s Law, V = I x R, where V is the difference in potential measure in volts, I is current measured in amperes and R is resistance measured in ohms. (At least Georg Simon Ohm got that much for discovering the law.)
One implication of Ohm’s Law is that higher voltage pushes more current through a given wire. A hydraulic analogy helps explain this: Think of voltage as water pressure and current as its volume of flow.
Or, engineers can work the other side of things: Employ thinner—and hence lighter—wiring harnesses.
But wait, haven’t we heard this song before? as you point out?
Indeed, way back in 1998, there was talk of replacing the conventional automotive battery of 12-14 volts with one of nominally 36-42 volts. It was all going to happen in a few years.
What went wrong?
First, back in (pre-hybrid) 1998, automotive electrical loads were growing — but nothing like today. Back then, the first priority was thinner wiring for lighter weight, not the need for higher voltage per se.
Second, by 2002, automakers got cold feet, partly because of the costs of re-engineering components and also on safety considerations. Harmless sparks of a 12-volt system could become sustained high-voltage arcs. Connectors, plugs—and shop practices—would have to be significantly upgraded.
Aircraft already use higher voltage, but this is with another dimension of inspection and maintenance. And not without its own issues, eh, Boeing?
(See http://simanaitissays.com/2013/01/30/48-v for more. Truth in editing caveat: Dennis and I worked together at Road & Track for a decade, an experience I thoroughly enjoyed. – Ken Zino)