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Old 02-01-2013, 17:49   #1
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NEMA 2000 Fittings

Hi All:

I find the price for NEMA 2000 fittings to be quite expensive. I can see where they are handy but when I priced out the fittings I need for a little remodel job I want to do it was close to $100. If I could get that cost down to nothing if I could just use a terminal block. Would that work or am I creating a future problem?

I would be putting the terminal block in the middle of the system at the base of the mast. The terminal block would connect the power and the other wires. to what I think is called a backbone cable. On the other end I would have the displays.

Thanks in advance for any replies.
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Old 02-01-2013, 18:07   #2
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Re: NEMA 2000 Fittings

Quote:
Originally Posted by Charlie View Post
Hi All:

I find the price for NEMA 2000 fittings to be quite expensive. I can see where they are handy but when I priced out the fittings I need for a little remodel job I want to do it was close to $100. If I could get that cost down to nothing if I could just use a terminal block. Would that work or am I creating a future problem?

I would be putting the terminal block in the middle of the system at the base of the mast. The terminal block would connect the power and the other wires. to what I think is called a backbone cable. On the other end I would have the displays.

Thanks in advance for any replies.

NMEA 2000 is exactly the same as Truck CAN Bus J1939. See link how they make them in Trucks for almost no costs and without the use of the extremely expensive T-Pieces, Connectors and Terminators. A Terminator is nothing more then a $ 0,05 120 Ohm resistor packed in an expencive connector.

CAN Primer Creating Your Own Network


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Old 02-01-2013, 18:17   #3
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Re: NEMA 2000 Fittings

You could try it but...
Panbo: The Marine Electronics Weblog: Impedance-driven NMEA 2000, & SimNet gets a "Noise Filter"

Let us know how it works out...
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Old 02-01-2013, 18:26   #4
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Re: NEMA 2000 Fittings

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Look at the hardware layer of NMEA 2000 vs J1939, its exactly the same.

For over 10 years we hook our Truck CPU's by cutting the CAN wires and making a T-Joint. Of cource Water tight sealed.

2 Important thinks about the CAN Bus Backbone.

#1. Minimal 20 twists per meter. Also for the drop lines.
#2. Both Ends to be terminated with a 120 Ohm Resistor.

Old Technologie with a changed name, NMEA 2000, and new very expensive "Marine" Connectors, T-Joints and Terminators.

But of cource now it has the name MARINE in it.

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Old 02-01-2013, 19:12   #5
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Re: NEMA 2000 Fittings

Actually there is a post near the bottom of that article of a guy who did exactly what you want to do. It seems the N2000 is quite tolerant of impedance mismatches. However impedance mismatches can be a bitch if you ever run into problems with them.
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Old 02-01-2013, 19:23   #6
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Re: NEMA 2000 Fittings

CeesH can you give us a description in layman terms? Would I need to put the resistor at the very end of the backbone or at the end of each run.
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Old 02-01-2013, 19:51   #7
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Re: NEMA 2000 Fittings

At each end of the backbone.

Many long cables, such as masthead cables, have the terminator built in to the cable. Check with the supplier.
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Old 02-01-2013, 20:12   #8
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Re: NEMA 2000 Fittings

Or you could just buy Garmin NEMA 2000 fittings. They are priced well.

https://buy.garmin.com/shop/shop.do?cID=162

Garmin NMEA 2000 Field Installable Connector, Male

Garmin NMEA 2000 Field Installable Connector, Male (010-11094-00) - iowa sports equipment for sale - backpage.com

http://www.newegg.com/Product/Product.aspx?Item=9SIA1260CC7043
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Old 02-01-2013, 20:31   #9
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Re: NEMA 2000 Fittings

Not exactly what I'd call 'cheap!'

I've found the lowrance gear about the best prices of the pre-made stuff.
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Old 03-01-2013, 06:10   #10
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Re: NEMA 2000 Fittings

you dont "nned"to use any of the pre made connectors, it ban all be done with simple junctions boxes if you want ).

twin twisted RS422 cable wil also do fine, Also Belden make a good range of can bus specific cables

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Old 03-01-2013, 07:27   #11
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Re: NEMA 2000 Fittings

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Originally Posted by Charlie View Post
CeesH can you give us a description in layman terms? Would I need to put the resistor at the very end of the backbone or at the end of each run.
The maximum lenghts of the CAN Bus (Backbone = the "twisted" cable between the 2 x 120 Ohm resistors) can be found in the following table,

In the top of the mast should be the last 120 Ohm resistor, don't make from this line a dropline up mast...
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Old 03-01-2013, 07:42   #12
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Re: NEMA 2000 Fittings

just so theres no confusion
When building your NMEA 2000 network, keep in mind these cable length limitations:
• The distance between any two points on the NEMA 2000 network must not exceed 100 m (328 ft). To estimate this distance, measure between the terminators on your backbone and add the length of the drop cable for the devices connected to the T-connnectors at the ends of the Network.
• The total length of all drop cables cannot exceed 78 m (256 ft).
• The maximum length of a single drop cable to a NMEA 2000 device is 6 m (20 ft).
• No more than 50 NMEA 2000 devices can be connected to your NMEA 2000 network.

dave
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Old 03-01-2013, 07:43   #13
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Re: NEMA 2000 Fittings

For Sale at every Volkswagen Service;
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Old 03-01-2013, 07:46   #14
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Re: NEMA 2000 Fittings

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Originally Posted by goboatingnow View Post
just so theres no confusion
When building your NMEA 2000 network, keep in mind these cable length limitations:
• The distance between any two points on the NEMA 2000 network must not exceed 100 m (328 ft). To estimate this distance, measure between the terminators on your backbone and add the length of the drop cable for the devices connected to the T-connnectors at the ends of the Network.
• The total length of all drop cables cannot exceed 78 m (256 ft).
• The maximum length of a single drop cable to a NMEA 2000 device is 6 m (20 ft).
• No more than 50 NMEA 2000 devices can be connected to your NMEA 2000 network.

dave
Please read the J1939 specs, the so called "Hardware Layer"

NMEA 2000 = J1939 with a +100 time higher price tag...

Expensive :-) Cable Twist Machine;
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Old 03-01-2013, 07:55   #15
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Re: NEMA 2000 Fittings

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Please read the J1939 specs, the so called "Hardware Layer"

NMEA 2000 = J1939 with a +100 time higher price tag...
Im in the middle of a J1939 and hopefully N2K hardware development project, theres not much left to know.

Firslty J1939 is NOT nmea2K, J1939 is actually a far more defined spec, whereas N2K suffers from NMEAs lack of resources to finish the spec.


Under J1939/11 and J1939/15 the baud rate is specified as 250 kbit/s, with J1939/14 specifing 500 kbit/s.

NMEA is 250kbits/sec and while devices can co-exist on the same network, ( because the Address claim is the same), NMEA2K protocols is not a direct copy of J1939, it has extensions that are not supported in J1939 and vice versa. ( of course underlying its all Can 2.0b)

In my view its a great pity that J1939 wasnt just lifted bodily into boats, but it wasnt.

Dave
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