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Digital Switching: Packing a boatload of benefits, part 2

A lot of what happens behind the scenes system-wide aboard boats these days is compliments of developing technology called digital switching. Not only does it simplify and centralize much of the onboard electrical circuitry, digital switching eliminates the maze of traditional wiring connections, switches, fuses and other components that are potential trouble spots, which can lead to failures.

Last week we described the basics of the technology and some benefits that digital switching offers—CLICK HERE. This week we look at the differences between digital switching and analog systems along with a few other aspects of the technology. We published the article originally in Marine Electronics Journal.

By Ev Collier

Big differences between systems

In contrast to traditional, or analog, electrical distribution systems, DSS systems do not use electromechanical switches such as those in toggles and circuit breakers. This eliminates excess voltage drops, intermittent connections and overheating due to corrosion, arcing, and loose and faulty connections, all the result of vibration, wear and tear and salty air ingress. The principal differences between the two systems are actually few, but of considerable significance.

First, in the traditional system, the main source of power is a short length of heavy gauge copper bus bar, tapped and threaded for contact screws, and located in the electrical distribution panel, centrally placed in the boat. Power for each of the boat’s motors, pumps, and electronics is run via heavy-gauge, high-conductance copper wire from the panel to the individual devices. In a DSS, the primary source of DC power is via a single high-conductance bus, or "backbone,” such as that used in a CAN (Controller Area Network) or NMEA 2000 network (below), that runs the length of the boat. Connections to devices require only short cable "drops.” Failure-prone components such as electrical distribution panel, switches, and fuses and/or electromechanical circuit breakers are eliminated.

Second, connection, protection and control of electrical and electronic equipment are done by a circuit control module (CCM). It is the interface device between the brains of the system and the device being controlled. Different manufacturers refer to this device by a variety of names—output interface (OI), power distribution unit (PDU) or DC module (DCM)—but we’ll use the term CCM to avoid confusion. The CCM is located close to the device it’s controlling, in series with the short "drop” to the backbone. It is solid-state and capable of serving four to 16 different circuits, depending on the particular system.

Third, a keypad control and display module, which may be a separate handheld device or incorporated into the boat’s MFD, offers soft switches marked with telltale icons indicating their function.

As you might expect, digital switching systems vary widely in their sophistication, depending on the target market. Some are fairly basic, performing only the essential on/off, protection, duration, etc. functions, while others have greater capabilities.

One approach

Blink Marine’s DigiPack system is a basic DSS aimed primarily at boat builders. When connected to various functional utilities, such as lights, electric motors, pumps, or the solenoid actuator of a hydraulic arm, the KeyBox component allows you to activate/deactivate them by way of a keypad. The KeyBox reacts to signals from the keypad according to how it has been configured—toggle, dimmer, momentary, etc. It executes the command and sends a return signal to the keypad turning off the LEDs present on each button. A rotary index pushbutton knob makes it possible to manage complex scroll functions and interface with onboard systems via various CANbus protocols.

Managing Director Riccardo Arienti says, "The system uses proprietary RS-485 connections between controllers and keypads, can be used with other controllers and has the ability to communicate over NMEA 2000.” He says the Europe-based company is planning to open an office in the US.

More whistles and buzzers

Raymarine’s DSS is much more than an electronic way of turning onboard systems on and off. It’s a fully networked solution for automation on any onboard system. It can be accessed from anywhere on the boat or remotely by sending a signal to your smartphone if a problem occurs. The system has been installed on boats ranging from 130 foot motor yachts to trailered boats.

The system uses solid-state digital CCMs, each customized to meet the requirements of the equipment being monitored and controlled and each supports multiple circuits. Each CCM is connected to a NMEA 2000 backbone, enabling it to communicate with other CCMs and with MFDs on the boat. This allows the CCMs to be located close to their devices, significantly reducing the amount of high-gauge wire needed. Based on its ability to interpret input signals, the CCM may output configurable thresholds for alarms and graphical functions, dimming, soft start/stop, etc. Raymarine’s system uses EnOcean wireless energy-harvesting switches and sensors. The company offers a CCM designed for vessels equipped with a CANbus.

A Master Control Unit (MCU) is the central processing unit that drives the system, providing computing power, intelligence and decision-making. There are also various interface connections to external devices and a remote control unit. The MCU is a NMEA 2000 device that talks to other system components via the NMEA 2000 network. The MCU stores and executes configuration files for holding installation data for each DC module in the system. A dedicated SIM card slot allows the MCU-200 to connect to a mobile GSM network and communicate with smartphones via text messaging. A dedicated CANbus link connects to third-party systems such as air conditioning and battery management. System control is through a graphical interface on Raymarine MFDs or through Raymarine’s control/remote apps for users of tablets and smartphones.

Installing the sophisticated system is usually a cooperative effort by Raymarine’s technical experts, the owner and his representative or a marine electronics dealer and the yard doing the work. The team figures out which inboard systems are suitable for DSS control, and where these items should be controlled from. A detailed list of equipment and individual power requirements is developed and used to design the overall system. Raymarine’s experts then match that list of requirements with the best combination of CCMs and accessories. Finally, the customized touchscreen user-interface is designed and uploaded into the boat’s MFDs and tested to ensure the system is fully operational.

Like many marine electronics dealers, Atlantic Marine Electronic’s Tally is enthusiastic about what’s ahead for DSS: "There is no doubt in my mind that DSS will continue to evolve and proliferate in the future.”

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