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NMEA-2000 Network With Split Power for ACSEATSRI
|Author||Topic: NMEA-2000 Network With Split Power for ACSEATSRI|
posted 10-10-2014 11:11 AM ET (US)
I separated this sidebar from another discussion.
posted 10-09-2014 06:19 PM ET (US)
I am confused [about isolated network power], but see if I have this right.
If I were to purchase the Garmin NMEA-2000 power isolator for $20, I could power this side of the network from the main power for both the HDS12T and the LCX-110C gps. The LC-2000 GPS receiver for the LCX would be plugged into this side of the network and would work as long as the power to the units were on. The HDS12T would power on without power on the other side of the network. Since this unit uses an internal GPS receiver, the GPS would still work regardless of whether the network was powered or not.
The other side of the network (the EP85R, 2 Honda multifunction gages, and a Lowrance LMF-200 display) gets its power from the Honda engine data cable and would only be on when the engine keyswitch was on.
To add another wrinkle, if I were to add the Lowrance autopilot which uses a Point 1 GPS receiver (available next month), I could put this on the isolated side of the network so that it would power up when the main power for the GPS' was turned on. (In this instance, I would think that the HDS would have to use the Point 1 receiver)
posted 10-09-2014 08:20 PM ET (US)
I am afraid I am confused. You will have two isolated power segments. Let's call them Segment A and Segment B.
Just tell me what devices are in Segment A and what devices are in Segment B. Then tell me what powers Segment A and what powers Segment B.
If I follow your narrative, I think it goes like this:
SEGMENT A powered by "main power from HDS-12"
SEGMENT B powered by Honda engine
There are three things I don't understand:
--how is SEGMENT A powered? The HDS-12 does not power its network connection.
--where is the Honda engine connected?
--how is SEGMENT B powered?
Designing a network for split power is really very simple. You just connect the two networks to power as if they were completely separate networks, but they are joined together by the GARMIN NMEA-2000 Power Isolator.
The early Lowrance NMEA-2000 capable chart plotters had the ability to provide power to the network via their NMEA-2000 power cable connections. The network power works independently of the chart plotter power, that is, the network will have power if the network power leads are connected to power, even if the chart plotter is switched to OFF. This needs to be considered in the design of the network power. See the operating guide for more details
Re the POINT-1 GNSS receiver and heading sensor: you'll need to wait to see what Lowrance requires in their autopilot before proceeding with the networking of that receiver and heading sensor with all the other devices.
posted 10-10-2014 09:40 AM ET (US)
Sorry, I'll try again.
Both "displays" (HDS12T & LCX-110C) are powered on by a dashboard switch.
Segment "A" consists of the LGC2000 GPS receiver and (possibly) later on a Lowrance Point 1 GPS receiver and a Lowrance 3G radar unit.
Segment "A" derives its power from the LCX, so if the LCX is on, segment "A" has power.
Segment "B" consists of the Honda data cable, 2 Honda multifunction gages, a Lowrance LMF200 multfunction gage, and the EP-85R.
Segment "B" derives its power from the Honda data cable via the engine keyswitch and would only be powered when the engine is running.
What I understand is that as long as segment "A" has power, data will still be able to flow to and from segment"B", meaning that even without the engine running, the HDS would still be able to see the Point 1 receiver and any other devices connected to segment "A".
If the engine is "off', all devices on segment "B" would be off (especially the EP-85R).
posted 10-10-2014 09:44 AM ET (US)
OOPS, the LCX is connected to segment "A".
posted 10-10-2014 10:29 AM ET (US)
I got this arrangement from your most recent description:
SEGMENT A --powered by NMEA-2000 power cable of LCX-110C
SEGMENT B--powered from Honda engine via data cable
Where is the HDS-12 Gen2 Touch?
Note that the network power via the LCX-110C does not follow the power to the chart plotter. It is a completely separate circuit. It can be powered ON when the chart plotter is OFF.
posted 10-10-2014 02:25 PM ET (US)
ASIDE: How do you get the chart plotters to power on by an external switch? On my HDS the front panel button POWER must be pushed to start up the chart plotter.
posted 10-10-2014 06:07 PM ET (US)
The plotters still have to be powered on with their own "on" buttons. I don't believe it makes difference which side of the network the HDS is connected to, as long as it sees data from both sides of the network.
At any rate, I believe as long as segment "A" is powered and the HDS is on, it should still see anything on the "A" side of the network and will see the accessories from the "B" side of the network when the engine keyswitch is on.
posted 10-10-2014 07:55 PM ET (US)
Wrong! If the HDS--or any other device--is on the network segment that is not powered, it won't see any data. It's NMEA-2000 interface won't work.
posted 10-11-2014 04:29 AM ET (US)
Here is my suggestion for your network with two power segments:
When the Honda engine is not powered on, the two Honda gauges, the EP-85R, and the LMF-200 gauge will not be operational. As soon as you turn the ignition key of the Honda to RUN, those devices will have power and begin to work.
The chart plotters will be powered by their front panel switches. The LGC-2000 and the POINT-1 will get their power from the network. The network power will be controlled by an switched power source that feeds the NMEA-2000 power cable that is part of the LCX-110C. You will need to switch on power to the network whenever you want the GPS receivers to function or the chart plotters to communication via the network.
If you want to get fancy, you can power the SEGMENT A network with a relay, and drive the relay coil with two sources, isolated by steering diodes. One source will be your manual switch and the other will be from the ignition key switch ACCY circuit. In this way, the SEGMENT A will always be powered if SEGMENT B is powered, or you can manage SEGMENT A power manually with the switch.
posted 10-11-2014 08:59 AM ET (US)
If the HDS was on the non-powered "B" side of the network, it wouldn't see the GPS receivers even if they had power on the "A" side of the network? I thought the signal would pass thru, it just wouldn't see the devices that weren't turned on.
posted 10-11-2014 11:48 AM ET (US)
The data wiring in a network with split power is intact across the entire network.
Devices which attach to a NMEA-2000 network that is not powered will not have their NMEA-2000 interface operating. The network interface of a network device is powered from the network. If there is no power on the network, the network interface is not operational. If the network interface is not operating, the data on the network is not available.
You might benefit from reading some of the material about NMEA-2000 that is presented in several linked resources that are mentioned in my NMEA-2000 primer at
NMEA-2000 Instrumentation for Modern Outboard Engines
In particular, see
See the diagram on page five with the legend, "Typical Isolated Network Interface."
posted 10-19-2014 06:02 PM ET (US)
Thank you for your help. The network worked exactly as I had hoped. The Lowrance fuel mismanagement issues will have to wait until next year. Maybe by that time they'll have a non-secret cure in the public realm to get these things to read properly.
posted 10-19-2014 11:03 PM ET (US)
I think my fuel management is back to working condition, but I also have to wait until next season to find out. Glad you got the network power worked out. Did you use the Garmin isolator?
posted 10-20-2014 09:16 AM ET (US)
Yes on the Garmin isolator.
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