NMEA 2000: Micro/mini/mid? Power taps, T taps... What does it all mean?

[Toubab]

I'm adding some new electronics to my old boat and I'm starting from scratch, so I'm trying to figure out how to make a NMEA 2000 network. I think I get the basics of it: power line comes into the backbone which then goes in two directions, then you put T's on the backbone to put drop lines to your devices. Finish it all off with terminators at each end.

I'm getting confused about the specifics though. I see things about micro, mini, and mid type connectors and I'm not sure what the difference is or what I should use. Then I also see a few different types of connections for the power cable. I think a lot of that might only be for Maretron, but I'm not sure.

Then once I figure out all the stuff I need, can I get some recommendations on brands and where to buy and all that?

Thanks!

[twistedtree]

It is indeed confusing at first. You just need to get used to the terminology. Here's a quick summary:

First, there are two sizes of cables and connectors; Mini (bigger) and Micro (smaller)

Mini (bigger) is used exclusively to build larger, longer backbones. For a boat under50' or so it's unlikely that you will need to use a Mini backbone, but can instead use Micro size parts

Micro (smaller) cables and connectors are universally used to connect to devices. I don't think devices ever have Mini connectors on them. My boat is 47' and has a N2K backbone that runs from the top of the mast to the very stern with 20+ devices on it, and it is built entirely out of Micro cables and connectors.

The only thing that will drive you to build a backbone out of the larger Mini components is if your network ends up with too many devices and/or too much length. Since power gets distributed to the devices by the network, there is a voltage drop every foot, and every device. There are limits on how much drop is allowed before things stop working reliably. The larger Mini cables have fatter wires and can carry more power, hence are called for in bigger networks.

I think the best way to sort this out is to use Maretron's N2KBuilder program. It's a free download (you might have to register first), and let's you "build" the network on paper and check to be sure you are within spec on everything. If you have a problem, it will tell you. I'd assume you are building everything out of the smaller Micro parts unless N2KBuilder tells you it's not possible.

You are correct that devices are attached to the backbone by inserting "T" connectors, then running a "drop" cable from the T to the device. The drop cables are always Micro cables, and the very same cables you will use for your Micro backbone as well.

"Mid taps" are all about how you supply power to the network. Ideally, you want to locate the power tap near the middle of the backbone. That way the longest distance to a device, and hence the largest possible power drop, is half the length of the backbone. In contrast, if you put the power tap at one end, then the longest distance is the full length of the backbone and you are twice as likely to have unacceptable power losses.

Building your network with N2KBuilder can be a bit tedious, but it's worth the time. Not only will it give you a network that you can be confident in, but it also serves as a great way to document it for future reference.

As for parts, the Maretron stuff is very high quality, but expensive. If you shop around, I have found the Garmin cables and Ts to be more affordable, however the fittings are plastic as compared to metal on Maretron. Actually, in either case shopping around pays.

Once you get comfortable with all this, then we can talk about how you can tie your N2K bus to the various proprietary variants like Simnet and SeaTalkNG. The good news it that it's just a matter of connectors and cables.

[Toubab]

OK, that N2KBuilder thing is pretty cool. I only played around with it for a minute but my network is going to be pretty simple to start off with. 2 issues came up. First, what's the difference between micro and mid? Second, the power tap tee has 2 female ends, so how is it supposed to connect to the backbone where everything else is male on one end and female on the other? I got it to work with a "bulk cable grey" that is male to male. Is that how I'd have to do it in real life?

Here's what I came up with:
It's not pretty or anything but you can see it's pretty simple.

[smac999]

Originally Posted by Toubab

Second, the power tap tee has 2 female ends, so how is it supposed to connect to the backbone where everything else is male on one end and female on the other?
It's not pretty or anything but you can see it's pretty simple.

the maretron power tee is the same on both sides. so you'd end up with 2 resistors the same sex. and the backbone would be leaving the T facing opposite ways.


the garmin kit has a male and female power T and 2 different resistors. so everything on the whole backbone ends up facing the same way.

[delmarrey]

If you go to the Maretron web site they have a Knowledge Base page that gives a lot of info. Maretron | Knowledge Base

Also, a FYI, try not to mix brands of N2K connectors if you can help it. The threads are tight fitting from one brand to another, but will work.

Just lay out a plan with the male/female fittings and backbone so you know what to order. And you'll never need more the two terminators.

[Toubab]

Oh, and with the cable going to the transducer, it told me it was too long unless I made it 4m. I don't actually know yet how long that will be but I thought the limit was 6m...

[twistedtree]

I think Mid and mini may be synonyms? Does N2KBuilder give you 2 or 3 choices for cable type? I just don't remember since I did my whole system with micro.

On the power tap, just take your group of 3 Ts and flip them so their male end goes towards the power T. The cable runs with both end with male terminators, but that's fine.

For you transducer, I see you have a lead on the transducer itself, plus a cable to the T. The total of both of those needs to be 6M or less. If you look at the properties of each you should be able to check the lengths and make them correctly match the transducer and cable length you plan to use.

Back to the idea of placing the power tap near the middle of the backbone, it should ideally go between the GPS and transducer taps, more or less, rather than at one end as you have it currently.

[Toubab]

Originally Posted by twistedtree

I think Mid and mini may be synonyms? Does N2KBuilder give you 2 or 3 choices for cable type? I just don't remember since I did my whole system with micro.

I'm not by my computer right now but I think it has mid and micro together and when you right click it lets you change a cable from one to the other.

On the power tap, just take your group of 3 Ts and flip them so their male end goes towards the power T. The cable runs with both end with male terminators, but that's fine.

Wow... smart and simple. I wish I had thought of it!

Back to the idea of placing the power tap near the middle of the backbone, it should ideally go between the GPS and transducer taps, more or less, rather than at one end as you have it currently.

Yea I'm planning it out like that because I'm planning on running the other end up the mast in the future.

[gordwedman]

I am working on a Furuno system with instruments, chartplotter, repeater and compass. Maretron has a six page guidance document which, I believe, has example networks.
Furuno USA also has a guidance document in the Support section. Some of this is specific to Furuno equipment but a lot is basic N2K. There does not seem to be a big difference in the cost of Maretron mini and mid cables so mid is possibly the way to go for backbone. Most of the cost will be for T's, drop cables and terminators. The prices at at Blue Heron Marine seem pretty good.

[Dockhead]

You're getting good advice here.

Use all Micro -- no need for anything bigger on anything less than a superyacht. The N2K Builder program will calculate losses and let you know if you have any problem, but I have Micro cabling from the top of my 75' mast to the engine room and up to the helm of my 54' boat with probably 40 devices on it, with no problem whatsoever.

I have mixed connectors with no problems.

I did split my network into two separate sub-networks with a joiner between -- that was for power control -- but now realize that this was probably unnecessary.

N2K is really great -- hard to screw it up. If you design it first with N2K Builder you can just about just screw it together and plug 'n play. I'm already finding it hard to imagine life before N2K.

[twistedtree]

Once you get it electrically correct, then you will need to be sure it's configured properly. In particular, you need to understand instancing and be certain that all devices emitting the same data type (like GPS) have unique instances. Otherwise you will get unpredictable results. Not all devices properly support instancing, so it may take some fussing around.

But once done, you can tell each device which data to listen to, and switch to a backup source with a few clicks. No rewiring required, unlike with 0183.