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I have read every post concerning LowranceNET, ep-10 and NMEA2000, and I am more confused now than ever.
I currently have an LMS-337 connected to an LGC-2000 GPS module. The GPS module is connected to the LMS-337 via the standard 25' Y-adapter expansion cable. The expansion cable is terminated with a 60 ohm terminator. This is a very minimalist installation, and lowrance describes this as a "dedicated NMEA2000 network".
I want to add an ep-10 fuel flow sensor.
Now I know I can buy a backbone cable with 2 120 ohm terminators and set up a real backbone down the center of the boat like they show in the marketing diagram. I have read Lowrance's NMEA2000 Network General Info document(http://www.lowrance.com/manuals/File...172_101005.pdf) and it states that if you want 3 or more devices on a network, you have to buy a network expansion cable and throw out the 60 ohm terminator. I wonder if this is really true, or lowrance is trying to sell cables. The reason they give for the linear bus architecture is expandability and maintenance, and knowing where the ends are. I don't care about expanding anything beyond the ep-10 (although I really like Got Salt's setup!).
I have also read the "Network Expansion Cable and 120-ohm terminators" manual (http://www.lowrance.com/manuals/File...121_031804.pdf). This manual explains things VERY differently. It says that the network needs 60 ohms of termination - either 1 60 ohm or 2 120s in parallel. In fact, it shows a network with 4 devices and only one 60 ohm terminator. This is a direct contradiction to what Lowrance says in their NMEA2000 General Information document about linear architecture. The copyright on Network Expansion Cable document is 2004, and the General information document is 2005. So somewhere along the way Lowrance changed their story on how to properly expand a bus.
In a previous post about the ep-10, THT member "boling" said he had the same config I had. He replaced the 60 ohm with the supplied t-connector, then reattached the 60 ohm and attached the ep-10. He said this worked.
Any thoughts on this? Why the contradiction? Are they just avoiding customer support headaches, or is there a functional reason for the linear architecture?
I am inlcined to just get the ep-10 and use the t-connector and keep the 60 ohm terminator. I hear the ep-10 comes with 10' of cable. Is this a seperate cable or is it directly attached to the probe. I'm not sure if 10' will make it from my console to the transom.
Drew's full install obeyed Lowrance's "new rules" where a backbone cable is terminated on both ends with 120 ohms - he kept a linear architecture. I am trying to avoild the new cable and terminators and just use what comes with the ep-10. The old lowrance documentation for the expansion cable says it is possible, the newer documentation on General NMEA2000 networks says it is not. I'll try to draw a picture to illustrate. Thanks.
Here are some pictures from the manuals to illustrate my point. First, this is how lowrance now says you have to do it - backbone cable with 120 ohms on each end...all devices connected to the backbone with t connectors. This is from the "NMEA2000 Networks General Info" copyright 2005.
This is an illustration taken from "NMEA2000 Network Expansion Cable and 120 ohm terminators" copyright 2004. Here Lowrance is showing that a nonlinear architecture with more than 2 devices and only one 60 ohm terminator will work.
Pioneer197,
I have just installed an EP-10.
I have a LMS330C GPS/Sounder with a LGC2000 antenna.
I had a T piece existing, [I assume it was the LGC2000 connection] with the 60 ohm terminator, I unplugged the terminator, plugged in the EP-10 and put the terminator back on the available end of the new T [it will only connect in one direction].
The 10' lead is hard wired to the EP-10.
Just watch the orientation of the EP-10, I didn't and it was pretty erratic [mind you I have yet to test it after correcting it ] Keep the sensor vertical with the flow indicator pointing upwards.
Good Luck
__________________ Northernblue
Etec replaced by 90hp Honda
Thanks Northernblue. What type of boat did you do the install in? It sounds like this configuration will work but the only question for me is will 10' be enough to make the run to the back of the boat from the console. I don't think so.
Where did you get your EP-10 from? I see from your signature, Australia, but wondering if you bought it online from the states. I have been told that they are on back order from Lowrance. Will you post a pic of your ep-10 placement? Did your numbers straighten out after training the unit? Thanks.
What will be interesting to see is if Northern fixes his eratic readings by correcting the orientation of the ep-10 (horizontal to vertical), or if the problem is coming from his non-linear network architecture. I have no idea (any electric engineers here?), but I can see Lowrance updating their protocol thru the trial and error phase from '04 to '05 for reasons other than evil commercialism (or just keeping the instructions simple - kiss).
pioneer - you might be hitting on the other main reason for networking - length of cable w/ the modules. That said, you might be able to use an extension cable if the non-linear structure works in your set-up.
Kitebuz,
Did you check out the maretron (sp?) website listed in another nmea 2000 thread? They have an engine interface module that looks like it converts data coming from an older engine into nmea 2000 format. Interesting! And as I recall, something you were looking to do?
Cooper - I looked at their site a while back, but did not see the interface you mention. I'll have to take a look. Now that you've shown us how to splice the wires, it could be a pretty easy conversion to the LN system - thanks.
Forgive me but I am an electrical idiot....Does any one know where I can go for information on connecting my E-tec to my 337c? I don't see and plugs on the E-tec wiring and assume I will have to splice....but to where?
Now I feel stupid because I am an electrical engineer.
I did some poking around online. Keep in mind I am NOT an NMEA expert obviously - just reporting what I learned, so take it for what it is.
The NMEA 2000 standard is very similar to the CAN Bus (Controller Area Network) used in the automotive industry. They share the same physical interface defined by ISO 11898-2. The physical layer is a high speed serial interface and uses a RTZ (Return to Zero) bit encoding. The serial data is transmitted on a pair of differential lines. When the bus is not being driven by any device/node the bus must return to it's 'recessive' state. 60 ohms of resistance is required between the differential lines to pull it back to the recessive voltage level. So this is accomplished by one 60 ohm, or two 120 ohms in parallel. Either way is fine - for THIS part of it at least.
Where there IS a difference is bus termination to reduce reflection. The ISO 11898-2 standard supports a data rate as high as 1 Mbps with a bus length up to 40 Meters. At this data rate, the bus must be terminated at both ends to minimize reflection. Also, devices attached to the bus should have a drop length no longer than 0.3 Meters. Each drop is an unterminated offshoot of the bus and will introduce reflection onto the bus (the shorter the better). If the data runs at half this rate, 500 Kbps, the drop length on devices attached to the bus can be 6 meters.
NMEA 2000 runs at a data rate of 250Kbps, so the requirements are a little more forgiving. I don't know the exact numbers on maximum drop length at this rate. Every device supplier I've come accross says it's 6 Meters, but I think it can tolerate more than that. What I'm getting at is without a linear architecture, we don't have these hard and fast rules for maximum backbone length, maximum drop length, cumulative drop length, etc. Every cable in the system is essentially an unterminated drop, so length should be kept to a minimum. But at 250 Mbps, I think there is a good amount of room for error.
I think the way Northern did it is fine, and I'm going to do it his way, and even extend it another 12 feet. Any other way leaves a lot of extra cable having to be tucked away. I can convert to a backbone by adding 120 ohm resistors and a T later if I need to. I'll report back any problems.
The NMEA 2000 higher level protocols have error detection, so corrupted data would be discarded. In other words I would expect either the fuel data is recieved, or NOT, but it wouldn't be inaccurate. I would imagine the flakiness Northern saw was because of the actual fuel flow turbine not working properly due to orientation...but that is just my feeling.
There is a nmea 2000 cable connector (CANbus, I think etec calls it) under the cowling. You'll need an ep-20 probe from lowrance, which should ship at the end of this month (so says lowrance).
Thanks, Pioneer. Interesting read. It's always good to hear from people who know what they are talking about - especially in electrical. Keep us posted. It will be interesting to hear if this set-up works for you both. Post a diagram of your set-up if you can.
Maybe one day I'll undertand why you need double the resistance (120 vs 60) instead of half when using two terminators instead of one...
Cooper knows about the e-tec module - I think he's 1st in line for normal people (not GotSalt).
Wow, this is just the post that is most needed at this time.
Recently talked to a Lorwance Rep and said that the y-coupler that came with my 3300c was too long and needed an 18' cable to the LGC-2000 instead of the original 25' extension that came my 3300. And introduces the 120 ohm terminated network.
This changecould help the theory on keeping the Network closer to under 6 meters. Maybe this and the EP-20's were designed to correct this. Do the EP-20's have a shorter dropline?
Thanks and would like to know what features are available on the 3300c update besides the fuel tank level reading upgrade.
Maybe one day I'll undertand why you need double the resistance (120 vs 60) instead of half when using two terminators instead of one...
I always think about it using the water flow analogy. Instead of electrons flowing through copper, it's easier to think of water flowing through a pipe. Water flows downhill, from the positive terminal uphill to the negative terminal downhill. The higher the positive terminal, the higher the voltage drop. The amount of water flowing is the current. Resistance is inversely proportional to the diameter of the pipe - bigger pipe, less resistance. So think of it like this...the same current will flow through one large pipe as it will through 2 pipes of half the size in parallel.
I really don't know where you guys get your info from but I personally ordered everything from b.r.p and received all of the components for attaching e-tecs to lowrance back-bone cable , Ive got simm module , adaptor cables , etc. nothing backordered
Lowrance NMEA2000 - Expansion confusion 
] Keep the sensor vertical with the flow indicator pointing upwards.
