One or two connectors?

As trailer ABS mandate nears, fleets must get up to speed on their options.Since the 1950s, the SAE J560 7-pin connector has enabled truck operators to reliably funnel electrical power from tractors back to trailers for lights and auxiliary equipment purposes. But with the arrival of the trailer antilock braking system (ABS) mandate, complicated ABS powering and bi-directional communications issues

As trailer ABS mandate nears, fleets must get up to speed on their options.

Since the 1950s, the SAE J560 7-pin connector has enabled truck operators to reliably funnel electrical power from tractors back to trailers for lights and auxiliary equipment purposes. But with the arrival of the trailer antilock braking system (ABS) mandate, complicated ABS powering and bi-directional communications issues have been brought front and center.

In the interest of minimizing incompatibility problems between old and new equipment, ATA's Technical Advisory Group and The Maintenance Council have come out with a recommendation that the J560's auxiliary circuit (pin no. 7) be used to provide continuous power for trailer ABS.

When selecting an electrical interface system for trailers with antilock brakes, however, operators currently have more than one option. They can use the single J560 connector with the "blue" circuit dedicated to constant power for trailer ABS. However, this single connector is unsuitable if either of the following conditions exist: Additional auxiliary equipment on the trailer is controlled by means of a dedicated switch in the cab; or there are excessive power needs in the trailer while the vehicle is in motion.

Fleets that need switched circuits in trailers can use either the Cole-Hersee 13-pin connector -- which provides room for as many as six additional circuits -- or go the two-connector route with a modified ISO 3731 connector in tandem with the J560.

In addition, a pair of enabling technologies has been developed to address this issue. "Ultra-Plex" from Grote Industries and "Smart-Plex" from Truck-Lite are multiplexing systems that can be used to provide switched power from tractor to trailer. Grote's approach relies on computer communications technology to transmit control signals through the seven-conductor cable's "brown" wire, while the "black" wire is used for auxiliary as well as normal power.

Truck-Lite's Smart-Plex utilizes declassified military power-line carrier (PLC) technology to control auxiliary equipment on the trailer, with power provided through the seven-way's "blue" wire. PLC works by imposing spread-spectrum signals into the vehicle's electrical system via the power line to which it is connected.

Both the Ultra-Plex and Smart-Plex systems provide a simple means for achieving the in-cab trailer ABS malfunction lamp, which becomes a requirement in March 2001.

Freightliner Corp. has decided to provide a second electrical connector as standard equipment beginning with its 1997 models. Other OEMs will provide a second connector, but only on special request. Most will also supply the Cole-Hersee connector.

Paul Menig, Freightliner's director of vehicle systems development, believes that for the interim a second connector is the "preferred interface." He claims that a tractor with a modified ISO 3731 connector not only provides a simple hard-wired circuit for an in-cab trailer ABS malfunction lamp, but also supplies dedicated ABS power and ground, assuring maximum voltage for ABS electronics. An important side benefit, adds Menig, is that it also increases the unit's total ground capacity.

Other OEMs, however, feel that one connector is the simplest way to meet the upcoming in-cab trailer ABS malfunction lamp requirement. Again, the two multiplexing systems that make this possible today are the aforementioned Ultra-Plex and Smart-Lamp, which is a single-function derivative of Smart-Plex.

In the future, fleets that want to capitalize on J1939 multiplexing capabilities such as "plug and play" will be able to use the J560 and modified ISO 3731, plus an electronic bridge, which will allow new power units to connect with old and new trailers.

Next month, we'll analyze the significance of the Eaton-led Truck Mux Consortium project (FO--9/96, p. 26) and the more recent Truck Technology Demonstration Consortium vehicle (FO--11/96, p.21), with an eye toward determining which multiplexing and connector systems will best help the industry meet future needs -- the most formidable of which will be electronic braking.

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