NMEA-2000 Network; Power Isolation; Automated Power Relay

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Location: Michigan, Lower Peninsula

NMEA-2000 Network; Power Isolation; Automated Power Relay

Postby jimh » Fri Nov 08, 2019 11:57 am

In Figure 1 (below) the NMEA-2000 network on my boat is shown in a sketch. In terms of its NMEA-2000 network, my boat is somewhat abnormal because it has the Evinrude ICON electronic shift and throttle (EST) control system. The ICON EST system isolates the usual engine NMEA-2000 interface and uses it for connecting data between the engine and ICON EST controls, but it then provides a GATEWAY module to send public data from the engine to the NMEA-2000 network. The public data fro the network is available from a NMEA-2000 interface on GATEWAY module, which attaches to the NMEA-2000 network. This device interface also supplies power for the network. While this feature is not a standard practice for NMEA-2000 devices, it is employed by Evinrude for (what I believe to be) the purpose of simplification of installation by elimination of a network power node. In my network, I exploit this feature, but also work around it.

Fig. 1. NMEA-2000 network with power isolation and automated power relay.
networkSketch.png (116.64 KiB) Viewed 1132 times

The network has two sources for power and is isolated into two branches for power distribution. The left side network branch (as drawn above) receives its power from an attached device, the Evinrude GATEWAY MODULE. The right side network branch (as drawn above) receives its power from the boat HOUSE battery via a relay contact on a relay I installed for that purpose.

The relay coil will operate from either of two sources:
  • from HOUSE battery supplied by a manually-operated switch
  • from the HOUSE battery) via the ACCY PWR Relay

The action of this arrangement is as follows:
  • the left side branch gets power only when the (E-TEC) engine ignition key switch is in the RUN position
  • the right side branch gets power when either the (E-TEC) engine ignition key switch is in the RUN position or the manually-operated switch is in the ON position

The devices attached to the left side of the network are:

  1. E-TEC GATEWAY Module
  2. EP-85R Date Storage Module
  3. ICON Pro RPM Gauge

The devices attached to the righ side of the network are:

  1. a Power Node T-connector
  2. HDS-8 Multi-function Display
  3. any other NMEA-2000 device not associated with the engine

The design seems complicated. Some explanation may help in understanding.

A fundamental problem to be overcome existed with the EP-85R Data Storage Module. If this device was on the NMEA-2000 network and receiving network power at any time when the NMEA-2000 engine data source it had been configured to monitor for fuel flow rate information was NOT powered on and attached to the network, the EP-85R would lose its configuration and stop working. In some simple installations, this problem was avoided by simply powering the network from the engine ACCY circuit. If that were done, however, then the engine would have to be powered on at all times in order to get the NMEA-2000 network to operate. That means using a $20,000 engine as a toggle switch for network power and accumulating hundreds of hours of run time on the engine management module (EMM). Such a configuration was not attractive to me.

By isolating all the devices that must have the engine powered up onto the left-side power branch of the network, those devices will only get network power when the engine is on, and the engine is operating normally, that is, powered-on when propulsion was needed and not powered on just to provide network power. When the engine is off, the NMEA-2000 network can still be used, but the operator has to throw a manual switch to ON in order to energize the relay coil and deliver power to the network.

In operation, the operator involvement is very simple. If the engine is running, the network has power, and no operator involvement is necessary. If the engine is not running and it is desired to use the NMEA-2000 network, the operator throws a toggle switch to ON. To remind the operator the network has been manually powered-on, the switch is illuminated. The switch lamp lights when the switch is ON as an indictor of power to the network.