Will a second power source on my NMEA backbone fry my devices?

[BassCPT]

Does anyone know if having two power inputs connected to the NMEA Backbone will damage anything on the network?

Recently I got my boat back after repowering and the G2 on her utilizes a NMEA network and so the mechanic just integrated the motor's network with my existing Lowrance network.
After reviewing the wiring diagram and inspecting the backbone, I noticed that there was another fuse block coming from the digital throttle control. upon closer investigation that cable was labeled "power out to accessories" which I confirmed was power to the NMEA network.
So basically when they put it all together, there were two power sources plugged into the network and I fear it could have fried something.
Luckily I didn't have any of my graphs connected to the network but my Point-1 and my Thru-hull Temp sensor, along with my icon gauges were all connected to the network...

[NoCAL]

I don't think anyone can answer this with direct experience. We all have heard the warnings about having two power sources but I've never seen anyone who actually did it AND reported back about the problems. I suppose you will figure it out once you get your graphs connected. At least they weren't connected because the warnings must have come about for some reason. And frying a Point 1 is a lot better than a head unit.

NoCAL

[BassCPT]

Valid point...
I've gotten some feedback from the evinrude board on how I need to redo my network and I've ordered a power isolator tee to separate the circuit.

[Ben Danbleume]

I accidentally did that once, it didn't burn anything up but I did have some strange things happen. For one thing my front graph went unreliable, it would work then it wouldn't, I thought I had a bad unit. It took a while to figure it out, so my units operated for quite some time, set up that way.

[Moonlighter]

All networked devices have internal network circuits that are powered by the network. You risk burning those circuits out.

The devices themselves may also be affected with power being fed back in directions it shouldnt be. Ive seen reports of Suzuki engines ecu’s being damaged from voltage feedback from failed circuitry in network devices. At the very least, damaged network circuitry means they wont communicate reliably or possibly at all with other devices.

NMEA2000 networks max power supply = 15 V, introducing a second 12v supply ...... I dont know exactly how that works but if you end do up with 24 volts things designed for max 15 v are going to get damaged.

NMEA also says there is a risk of harmonics between 2 power supplies.

All of which means messed up network communications and flaky performance at best.

In short, dont do it.

Remove one of the power supplies.

Or, if the first power supply is connected to the engine harness such that it turns on and off with the key, and you need the network to continue to operate when the key is off, you have 2 choices:

2. Put a power isolating T between the 2 “sides” of the network so the engine and gauges are on one side, and everything else on the other.

or

2. Just have one power supply that you can turn on and off with a fused switch. It doesnt matter if the engine digital gauges stay on when the engine is turned off, they use negligible power anyway and it wont hurt them at all to stay on. Saves them going thru a startup procedure every time the key is turned on too.

[rbarrow]

OK... The bottom line is no... you will not damage a device from having two connections to the same 12v circuit. The major impact of having two power connections is the inability to remove power from the NMEA system reliably because you are not aware of the 2nd power feed. We see this often in installations from some boat dealers where their less-than-knowledgeable installers just plug up anything and everything...but don't get me started <LOL>

A power isolator provides the data connection but not the power from devices that do provide their own power to NMEA such as some electronic devices (not normally on used on most bass boats) and/or engine systems.

Alternatively you can choose to use the device provided power as long as it functions in the way you need. In some cases, the power from an engine is only available when the engine is on. It is best practice to use a power isolator when in doubt.

In any case, you will not damage anything and it does not result in any more than the source voltage being applied (12 v) but it may leave power on the network when you think you have it turned off.

[BassCPT]

Thanks guys! The information here will be most helpful as I'm readjusting my network.

I think I've got it figured out using a power isolator tee between the motor side and the electronics side.

NMEA 2K G2 Network V2.jpg

It's some what of a pain but I'll be able to run everything with the cables I currently have. I'll just have to order a Lowrance isolator tee (P/N 000-12259-001).