New Concept for 42 V Automotive LIghting System

[Cadillac Jim]

In 1955, all the auto companies agreed to switch from a 6 V DC system to a 12 V DC system to cut copper weight by 3/4 and enable improved technology like alternators. A 42 V DC system has been in the works since 2001 or so to cut copper weight by another 88%. In 2002, I saw proposed a 42 V AC automotive power system something like this:

• 42 Volt standard (three small 12V batteries each with 1/3 the ampere-hour rating of current batteries and about the same total weight)
• Weight of copper wiring reduced by more than 80%. This is major for any car, and truly momentous for small cars where copper can approach 20% of vehicle weight.
• Three-phase 400 Hz with neutral as a radial power bus at major points in the car (headlights and front lights, rear lights, interior and HVAC power, etc.) eliminates the need for a large ground return, further reducing copper weight.
• Most relays become unnecessary because AC can be turned on and off with triacs controlled directly by the modules.

Now that we have reduced copper weight by 80-90%, other cost and reliability improvements become simple and inexpensive:

• Fiber optic ring bus controlling all lights and functions, similarly to what we do now with the CAN bus with GM cars.
• New devices run from 42 V 400 Hz for higher efficiency and reliability, lower weight.
• Vastly reduced numbers of connectors in wiring harnesses. Standard "wire" would consist of a four-wire power line and a few fiber optic data lines. Even switches can be optical signals to a module not attached to the button or knob. LEDs run directly from the AC through a diode and limiting resistor at the "switch" or button switch light on and off in a fiber optic line, and the optical signal is used by the IPM or PZM.
• Incandescent lighting can be "soft-on" for longer bulb life. Combining with "soft-off" allows for effects like turn signals rolling across the rear of the car from the CHMSL through the stop light. Safety additions like strobing the brakes when the ABS is invoked are simple.
• Flashers for the turn signals and hazard warning would cease to exist, their functions having been absorbed by the modules -- just as the points & condenser, distributor & spark advance, and mixture control have been for years.

The technology for 400 Hz 3-phase lighting and motors is with us now as the standard for aircraft, for the reason that we should look at it for cars -- it gets the job done with best reliability, highest efficiency, lowest weight. The new system would cost less than what we have now, and backward compatibility would be maintained to provide a value-added transition support for suppliers of existing equipment.

The use of two-phase or three-phase allows a balanced load to draw power with very low ground currents, so a simple neutral for a voltage reference is all that is required. Unbalanced loads, with higher neutral currents, would be used to turn off the power at the inverter as a safety feature, like a GFI interrupt on any power system. Use of three-phase allows very simple 12-phase DC power to be provided with little or no additional filtering for DC lighting or powering electronics; your alternator already does this.

About the only thing that would run on 42 V DC would be the starter and solenoid, and the main 400 Hz inverters, and even the starter would probably become a 400 Hz 3-phase motor pretty quickly because it would draw less power and could be made to work at lower battery state.

A 42 V DC system will cost slightly less than existing 12 V DC systems because of more efficient -- and thus less expensive -- motors and alternators. A 42 V AC system would add a 400 Hz inverter, but this is simpler and less expensive than you might imagine, using technology you see now in the UPS battery backups for your phones and the more important office computers and servers; I have one on my home computer. That cost would be far more than offset by replacing relays with triacs, far cheaper motors and generators, etc. Using 400 Hz uses a whole lot less iron or ferrite than 60 Hz, too.

[Cadillac Jim]

Logan Diagnostics just posted this:

Saw another post that mentoned 42 volt systems. The 42 v systems are worthy of a post. See this link for issues related to 42 volt systems.

http://www.mbmw.com/eye_on_electronics_mike_dale.htm

The main problem is that pulling apart the contacts in a live 42 V system can cause arcs, and fuses can be a problem that drives them to larger sizes, sand packing, or circuit breakers, just like we see for household use.

One area that wasn't mentioned was the fact that 22 V is the magic line below which no one has ever been electrocuted. There have been deaths reported in accidents regarding 24 V farm lighting systems.

I would hope that the AC system, with inherent ground-fault interrupt protection designed in, would fix this. The AC system was never briefed to GM.