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power connection to NMEA 2000 network

Old 12-03-2017, 11:52 AM
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Default power connection to NMEA 2000 network

Hello THT:

would like to have your knowledge and wisdom regarding this issue: can NMEA 2K network work without a connection to 12V power?

Here is the story:

I sent my boat to a dealer to install engine interfaces on the twin motors and a NMEA 2K backbone so I can display engine data on the MFD units. Took the boat back after he was done. The guy told me he was able to display engine data on the MFD and everything tested out fine. But when we tried there is no engine data displayed at all. We examined the connections and found no power cable from the NEMA network to the battery. He said the power from the MFD will supply the NMEA network, a connection from battery to NEMA network is not necessary.

This sounds really odd. My understanding is that you have to have a 12V power connected to the NMEA network. The MFDs will need their own power supplies too. To me, there is no way he could have made it work without connecting a power cable from 12V source to the NMEA network.

Am I misunderstanding how NMEA 2K works or missing any new updates on NMEA 2K? Or is this guy lying to me?

Many thanks in advance for your help.
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Old 12-03-2017, 11:59 AM
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You are right and he is wrong. The NMEA needs a power source unless they somehow connected the power lead from the MFD to the network.
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Old 12-03-2017, 12:10 PM
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Thank you dave. They surely didn't connect any power source to the network. So he never got it to work. Seems he has been lying to me. Good to know that.
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Old 12-03-2017, 02:04 PM
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He is wrong. Network must be powered to work.

To see engine data on the network, you need the network power to be on, and the engine key must also be turned on. In that regard, the engine is the same as anything else connected to the network - for the network to recognise a device, the device has to be powered on.

In the early days of N2K networks, GPS pucks made by Lowrance (I think the LCG2000) were able to be connected direct to the old Combo units used at the time, and those pucks had to have their own power connection. If a N2K network was then established and the puck was connected to it, the puck connection would supply power to the network. Quite a few people were caught out because they didn’t realise this and included another power supply to the network.

This is the only situation I am aware of where a separate network power connection to a T was not done. But of course, that was years ago and those old pucks are rarely seen these days.
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Old 12-03-2017, 02:18 PM
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Actually, the early Lowrance units did have a separate, internal N2K power supply. Unless, the OP happens to have one of those old units (that used the old, unreliable blue connectors), the network needs it's own switched power.
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Old 12-03-2017, 03:04 PM
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All Lowrance units with NMEA 2000 prior to HDS had a separate pair of power wires dedicated for NMEA 2000 in their power cable. The difference is just where the power is inserted, from a separate connection in the MFD or by a T-coupler in the network. This allowed the use of a single cable with integrated termination to connect the GPS puck, this was used both with LGC-2000 and LGC-3000. They also had a Y-adapter where the GPS puck was connected to one branch and a 60 ohm terminator to the other. Some of the units were also shipped with full NMEA 2000 networks.

The big problem came when people upgraded to HDS and suddenly their NMEA 2000 stopped working. HDS could use the older power cable, but did of course not utilize the NMEA power connection.

Last edited by abbor; 12-03-2017 at 03:10 PM.
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Old 12-03-2017, 05:09 PM
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He’s wrong and lying to you.
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Old 12-03-2017, 05:39 PM
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I think you might all be jumping to conclusions. Yes, N2K requires power, but a number of MFDs can be that source of power. Abbor noted some Lowrence units, and I have seen this on Furuno, and maybe some others, but don't recall exactly which ones. It's worth looking at the manual for your specific MFD, or call the guy who did the installation and ask how he powered the network.
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Old 12-04-2017, 09:57 AM
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Thank you everyone. My MFD is Simrad nss12 evo2, I am not aware this unit can power a NMEA network.

My buddy added a NMEA power cable for me and connected to the 12V battery, now everything is working, I am getting engine data fine.

It is now clear to me that he didn't do the job right and he lied to me. Never going to let him touch my boat again.

Thank you all again. It amazes me how a mechanic can be this dishonest about his work.
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Old 12-04-2017, 10:59 AM
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Originally Posted by capecodtuna View Post
T...It amazes me how a mechanic can be this dishonest about his work.
The fundamental problem is that many old-school mechanics knew nothing about electricity to begin with, and now know even less than that about modern digital networked instrumentation systems. The guy may be great with a wrench in his hands, but clueless with the probe for a digital voltmeter.
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Old 12-04-2017, 11:08 AM
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I'd go back to him, tell him what you did, and ask for money back on the work he charged you for.
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Old 12-05-2017, 03:08 AM
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Originally Posted by capecodtuna View Post
Thank you everyone. My MFD is Simrad nss12 evo2, I am not aware this unit can power a NMEA network.

My buddy added a NMEA power cable for me and connected to the 12V battery, now everything is working, I am getting engine data fine.

It is now clear to me that he didn't do the job right and he lied to me. Never going to let him touch my boat again.

Thank you all again. It amazes me how a mechanic can be this dishonest about his work.
Great you got it working but sucks that the guy lied and didn't do it right. The sad part is this isn't just old school guys doing this.

I've had a particular dealer's service center ask me how I installed a blue seas add a battery kit.

If the guy that did it doesn't own the shop I'd talk to the owner.
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Old 12-05-2017, 10:11 AM
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The guy owns the shop. What bothers me is not that he didn't know how to do it, but the fact that he lied to me and tried to fool me. I am going to talk to Suzuki and file a complaint.
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