N2K Power Tap dual 12V source?

Laying out a NMEA2000 network on the boat. I have different parts of the network powered from different sources, such as the left and right engine display power by the associated engine start switch such that it would power up when the switch is in the run position just as the gauges do now.

What about a single component that has input from both engines. An example would be a Maretron TMP100 for EGT measurement. One unit but measures temp on both engines. I want it to be powered if the port or starboard or both engines are running.

Can I have 2 12V sources powering a single power tap? God/bad practice? I dont see why it cant be done this way, but maybe a better way?

No, not per the NMEA implementation guidelines. Technically, it probably could be done but if there is a differential in supply voltage problems could ensue as current is flowing through the network. So, the way around it is to create three independent power zones using power isolation tee's whereas each engine is a power zone and the helm and instruments is the third. In this fashion, as the helm network is always on when an engine is powered on the instruments on the engine will power up separately. With all that said why not have everything powered up regardless the engines running or not?
Tom

I have laid out several power zones, but the issue is when both engines share 1 input device, Specifically the Chetco Digital unit...its looking at sensors on both engines. I'll have to go back and look to see if there is an always on device that account for both engines...maybe the fire shut down system? Or add a relay (and complexity).

I've attached a preliminary layout, still needs some work and thought.

ttmott said:

No, not per the NMEA implementation guidelines. Technically, it probably could be done but if there is a differential in supply voltage problems could ensue as current is flowing through the network. So, the way around it is to create three independent power zones using power isolation tee's whereas each engine is a power zone and the helm and instruments is the third. In this fashion, as the helm network is always on when an engine is powered on the instruments on the engine will power up separately. With all that said why not have everything powered up regardless the engines running or not?
Tom

Click to expand...

I see what your talking about...I think your assuming two power taps and in that configuration. I could see current flow between the power taps if at slightly different voltages.

I was thinking about having the port and starboard dc systems connected to 1 tower tap. In that config, not current should flow?

Thinking a little more about it, that wouldn’t wouldn’t work if the batteries were at a Big differential, that would end up being a battery equalization path, and would have to be sized accordingly.

dtfeld said:

Laying out a NMEA2000 network on the boat. I have different parts of the network powered from different sources, such as the left and right engine display power by the associated engine start switch such that it would power up when the switch is in the run position just as the gauges do now.

What about a single component that has input from both engines. An example would be a Maretron TMP100 for EGT measurement. One unit but measures temp on both engines. I want it to be powered if the port or starboard or both engines are running.

Can I have 2 12V sources powering a single power tap? God/bad practice? I dont see why it cant be done this way, but maybe a better way?

Click to expand...

The network power tap is for devices that need power to function like tank senders and gps devices. The power circuit is independent of the data circuits. Other items like engines and MFDs have their own power sources independent of the network. In those cases the interface transfers just the data from the source to the network. I didn’t look up the device you mentioned, but my guess is that takes data from the engines (SAE J1939 perhaps?) and provides an interface to the nmea2000 net.

This arrangement allows the nmea2000 net to be live all the time regardless of whether the engines are running, or MFDs, or your Fusion stereo.

Can there be two power taps? Not supposed to be. But it is possible, as long as they do not connect. In fact it’s the only way to connect a Raymarine SeaTalkNG network to a nmea2000 net. On our boat we have both nmea2000 and SeaTalkNG. STNG is nmea2000 plus SeaTalk 1 to allow legacy SeaTalk devices to be connected. In the connection between the STNG and nmea2000, the power circuits are not linked, just the data circuits. The far end of the nmea2000 net has one terminal resistor and the far end of the STNG net has the other resistor.

dtfeld said:

I have laid out several power zones, but the issue is when both engines share 1 input device, Specifically the Chetco Digital unit...its looking at sensors on both engines. I'll have to go back and look to see if there is an always on device that account for both engines...maybe the fire shut down system? Or add a relay (and complexity).

I've attached a preliminary layout, still needs some work and thought.

Click to expand...

Ah, I understand better. Probably the best solution is to still have a separate NMEA 2000 power zone for the Chetco unit then provide dual power sources to that NMEA 2000 zone however install common Shottky diodes and fuses on both power sources. The diodes are like a check valve that will allow current to flow into the device but not reverse. Common 15 amp, 45 volt Shottky diodes would work just fine. I did a quick sketch below -

ttmott said:

Ah, I understand better. Probably the best solution is to still have a separate NMEA 2000 power zone for the Chetco unit then provide dual power sources to that NMEA 2000 zone however install common Shottky diodes and fuses on both power sources. The diodes are like a check valve that will allow current to flow into the device but not reverse. Common 15 amp, 45 volt Shottky diodes would work just fine. I did a quick sketch below - View attachment 79318

Click to expand...

Thanks Tom...that is exactly what I want/need to do at least for a couple of the nodes. Having slept on it, I'll have to revise some things.

The dont think the Chetco device is powered off the network but I'll have to confirm, but I will still need a couple/several separate power zones.

dtfeld said:

Thanks Tom...that is exactly what I want/need to do at least for a couple of the nodes. Having slept on it, I'll have to revise some things.

The dont think the Chetco device is powered off the network but I'll have to confirm, but I will still need a couple/several separate power zones.

Click to expand...

Possibly another way to do it and also protect the data component of the NMEA 2000 network is something like how I did the configuration (I learned a lot from the lightning strike that took out my boat's electrical). I have three independent data and power zones but yet still communicate data between the zones. This is done using Maretron NBE100 Network Expanders. Below is my configuration on the 52DB; the P's are power supply and the T's are terminating resistors:

ttmott said:

Possibly another way to do it and also protect the data component of the NMEA 2000 network is something like how I did the configuration (I learned a lot from the lightning strike that took out my boat's electrical). I have three independent data and power zones but yet still communicate data between the zones. This is done using Maretron NBE100 Network Expanders. Below is my configuration on the 52DB; the P's are power supply and the T's are terminating resistors:
View attachment 79418

Click to expand...

I have seen those, but have not considered these units. My basic understanding of them was to be able to build larger networks were distance limited what could be designed due to voltage drop or cable length restrictions.

Is this any different than using a power block Tee?

https://www.ancorproducts.com/en/270113

dtfeld said:

I have seen those, but have not considered these units. My basic understanding of them was to be able to build larger networks were distance limited what could be designed due to voltage drop or cable length restrictions.

Is this any different than using a power block Tee?

https://www.ancorproducts.com/en/270113

Click to expand...

Yes quite different; besides allowing a larger network they provide complete electrical isolation between the networks including the two CAN Bus conductors so in the event of a voltage spike the adjoining networks are protected. They probably implement some sort of an optical isolator. The NMEA 2000 power isolators do not electrically isolate the CAN Bus data conductors.

Ah yes.. I see.