NMEA 2000 - a simple question

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Ronald_M

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Sorry if this is too simple a question(!), but can an NMEA 2000 network be configured to provide power-only (ie no data) take-offs?

I'm about to rewire the boat, incorporating a canbus system to feed tillerpilot, GPS, charplotter, etc, but I shall be keeping my old Nasa Clipper instruments. It would simplify the whole system of wiring if the Nasa instruments could receive their 12v supply from the canbus backbone rather than from dedicated cables run from the switch panel.

TIA

Ron.
 
Cardo said:
Don't see why you wouldn't be able to take a T with only the power wires hooked up.
Click to expand...

Presumably you could use a "power tee" connected to a load rather than a supply?

It's probably not according to The Rules, but I can't see that it would be a problem.

For what it's worth, my helm plotter (a 4" Lowrance) is powered from the nearby Seatalk bus (original seatalk, not nmea2000 in drag).

Pete
 
Thanks, chaps.

It would, indeed, be important to do a "total amperage audit" for the whole system to ensure that the cabling/fuses could cope.

My main worry though would be that if the T-piece was wired up only to feed 12v power, would the data link be severed? ie would the data-stream carry on merrily to everywhere else in the system, or would it be interrupted?

Sorry, I really don't know very much about NMEA 2000 archtiecture!

Ron.
 
Ronald_M said:
Thanks, chaps.

It would, indeed, be important to do a "total amperage audit" for the whole system to ensure that the cabling/fuses could cope.

My main worry though would be that if the T-piece was wired up only to feed 12v power, would the data link be severed? ie would the data-stream carry on merrily to everywhere else in the system, or would it be interrupted?

Sorry, I really don't know very much about NMEA 2000 archtiecture!

Ron.
Click to expand...

Any T off would be connected in parallel to the system, not in series, so it won't break the link.
 
Not such a simple answer to a simple question. There are two power option for N2K, thin and thick backbone thin is 22AWG and the heavier backbone id 16AWG (I don't have either my NMEA 0400 document or my N2K training manual to hand so both AWG are from memory but I'm pretty sure) It is possible (and compliant) to enhance the loading above usual installl by using power break Tees and inserting power supplies at intervals on large networks. If you down load the free network planning software from Maretron you can easily plan and verify your proposed install, substituting different weight cables and power breaks/insertions if the original plan is not up to the power draw. I have found this software a god send on larger commercial installs. Should you wish to take power only from a backbone the simplest and most economical way is to use a power insertion lead and use the two leads on that for a supply and return, they have an inline fuse holder built in so an appropriate fuse for the instrument can be easily inserted.
 
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David2452 said:
Not such a simple answer to a simple question. There are two power option for N2K, thin and thick backbone thin is 22AWG and the heavier backbone id 16AWG (I don't have either my NMEA 0400 document or my N2K training manual to hand so both AWG are from memory but I'm pretty sure) It is possible (and compliant) to enhance the loading above usual installl by using power break Tees and inserting power supplies at intervals on large networks. If you down load the free network planning software from Maretron you can easily plan and verify your proposed install, substituting different weight cables and power breaks/insertions if the original plan is not up to the power draw. I have found this software a god send on larger commercial installs. Should you wish to take power only from a backbone the simplest and most economical way is to use a power insertion lead and use the two leads on that for a supply and return, they have an inline fuse holder built in so an appropriate fuse for the instrument can be easily inserted.
Click to expand...

That's all true, but for a 21' boat with 3 devices on the network, the simple answer to the OP's question is yes. His installation is not the type or complexity that would use the heavier cables, have multiple power feed in points, or require network planning software.
 
AngusMcDoon said:
That's all true, but for a 21' boat with 3 devices on the network, the simple answer to the OP's question is yes. His installation is not the type or complexity that would use the heavier cables, have multiple power feed in points, or require network planning software.
Click to expand...

But some others may, and the OP will not be the only person reading this, nothing wrong with a definitive answer.
 
Thanks, everyone.

My question seems to have been answered.

I hadn't realised that a power T-piece can operate "in reverse" as it were, ie that it can insert power to a backbone when connected to a 12v source, as well as supplying power from the backbone to a unit that requires it.

I'm relieved to learn that the data flow will not be interrupted by so doing.

Thanks again to all.

Ron.
 
Ronald_M said:
Thanks, everyone.

My question seems to have been answered.

I hadn't realised that a power T-piece can operate "in reverse" as it were, ie that it can insert power to a backbone when connected to a 12v source, as well as supplying power from the backbone to a unit that requires it.

I'm relieved to learn that the data flow will not be interrupted by so doing.

Thanks again to all.

Ron.
Click to expand...

Pleased to see that the comprehensive answer was useful to the OP as well as possibly to other readers, just goes to show the value of a definitive answer rather than a one liner.
 
David2452 said:
Pleased to see that the comprehensive answer was useful to the OP as well as possibly to other readers, just goes to show the value of a definitive answer rather than a one liner.
Click to expand...

Well, I assumed he was replying to my earlier suggestion of using a power tee :p

Pete
 
All boxes ticked!

One of the most pleasing aspects of sailing is the willingness of others to share knowledge when one's own is lacking. Never be afraid to ask!

Now, where are those cable-ties, crimper, heat-shrink, hole-saw, soldering iron, multimeter, etc, etc........

Thanks again,

Ron.
 
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