Experience with bus based power systems?

Discussion in 'Electrical Systems' started by Nordic Cat, Oct 11, 2008.

  1. Nordic Cat
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    Nordic Cat Senior Member

    I am considering the use of a so called "smart" power distribution system for a new catamaran build, and would like to know if there are any systems out there that someone can reccomend.

    I have done a rough estimate on the weight savings, and it comes to around 40-50 kgs.

    The one that tops my list at the moment is this one:

    http://www.capi2.com/

    Any feedback would be much appreciated.

    Alan
     
  2. CDK
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    CDK retired engineer

    Siemens proposed the bus system for passenger cars in the mid-80's but had very little success. Car makers kept on using the conventional wiring harness because it is cheaper, reliable, easy to understand and test.
    Only very recently the system can be found in several cars because with anti-theft circuits, air bag control and digital injection the environment has changed to such an extend that a bus system isn't scary anymore. Service tools for all passenger cars are diagnostics computers now, the mechanic with just a test lamp has been phased out.

    Using such a system in a boat is something else.
    The main drawback is that except steel barges, boats do not conduct electricity so they do not provide a Faraday cage. The bus system runs from the stern to the bow and acts as a large antenna that picks up electrical discharges from thunderstorms, marine radio's and radar.
    Of course it is possible to design and install a reliable system, but it requires a skillful engineer and high quality materials. Inadequate shielding or improper grounding will be the cause of failures.

    At the present, the average marina technician does not have sufficient education and equipment to install and service such a system.
     
  3. Nordic Cat
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    Nordic Cat Senior Member

    Thanks CDK. I think what you are referring to is probably CAN-bus which was developed by Bosch see: http://en.wikipedia.org/wiki/Controller_Area_Network

    As far as I can see, the NMEA2000 bus is also a CAN-bus. It should offer "plug and pray" between products from different suppliers. To my understanding, it is not for power distribution. Volvo and others have been using this for some time now.

    I fully agree with you that NO mechanic out in the marine industry is likely to be able to help you if something goes wrong.

    The bus system I am asking about is solely for Power distribution. IMO it should not be too difficult to work around if problems arise. It's a bit like the mains supply out on the street that goes into each house. As long as you have your cable thicknesses and fuse sizes right it should be safe.


    BUT, what should I look out for?

    Alan
     
  4. lazeyjack

    lazeyjack Guest

    ca you tell us whata BUS system is? please
     
  5. Nordic Cat
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    Nordic Cat Senior Member

  6. Nordic Cat
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    Nordic Cat Senior Member

    LJ,

    have a look at the capi2 link I posted in post#1.

    If it is not clear, then please ask again....

    Alan
     
  7. lazeyjack

    lazeyjack Guest

    ah Qui, bon, can you find a schematic, cos I do not see one here,
    sounds interesting, I usually witre all our boats, then get an A.C. registered electrician to sign it off, I find wiring to be very saisfying, and relaxing, makes a change from all those hard work parts of the boat
     
  8. Nordic Cat
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    Nordic Cat Senior Member

    Here's a link to the PDF with all the technical stuff...

    http://www.capi2.com/downLoads/NewCapi2Fine.pdf

    I reckon it will save lots of time, cabling and maybe some money, as I have no idea on pricing. They claim weight savings of 50%, but even 30% is a lot of time and money...

    Let us know what you think

    Alan
     
  9. lazeyjack

    lazeyjack Guest

    ok, Alan , will look at it tomorrow, got a new project ready to build
    thanks
     
  10. CDK
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    CDK retired engineer

    All bus systems use callers/listeners or masters/slaves with TTL-level (5V) signals or something like RS232 with 12V signals.
    Electromagnetic discharges from nearby thunderstorms put spikes on the signal lines that are a 1000 times larger, so there must be serious over-voltage protection and shielding, otherwise the whole system is permanently damaged before you can even hear the rumble.

    There is a street light in direct view from our house, on a wooden pole with the supply cable hanging high in the air. It needs to be replaced after EVERY thunderstorm within a few miles radius.
    The ones in the city perform much better: they have underground cables and metal lamp posts. Only a direct hit somewhere in the grid kills them.
     
  11. lazeyjack

    lazeyjack Guest

    thannks Both very interesting
     
  12. Nordic Cat
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    Nordic Cat Senior Member

    Not all Bus systems are voltage based, many industrial systems use a current loop like RS 485. Others use some kind of Manchester coding for the physical layer of the OSI structure.

    These systems are not as sensitive to voltage spikes, but generally all bus systems need to be wired and grounded correctly, and require skill to be used.

    Alan
     
  13. lazeyjack

    lazeyjack Guest

    THE nodes which are just breakers
    They need be accessible So if say you have 25 circuits, that means 25 of these nodes, need to be placed in accesible places
    I usually use BEP switchboards using breakers I have gone a bit overboard often using a separate pair for each and every light circuit, when I should really have just looped them, apart from the nav , which has to be on separate wire
    I wonder how certifaction would see this
    one thing I do see, is the saving in weight
    But having everything on one ac/ and one dc board, seems more convenient to me?
    google up BEP marine, in NZ
     
  14. CDK
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    CDK retired engineer

    I stand corrected. Completely forgot the 20 mA current loops used for industrial communication and sensing. And the old telex of course.

    A far superior bus control system for marine applications would be an optical one. Optical fiber is very cheap and light, doesn't corrode and is not prone to electrical fields. Each node has a photodiode and a LED to emit the signal to the next node. The last one gets a return line to the control panel to report the status of all previous nodes.
    Might be an interesting project..... but what am I talking about, I'm retired.
     

  15. Nordic Cat
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    Nordic Cat Senior Member

    I would put a node in each "room" as a kind of master switch for that room, and then run out to the individual lamps or whatever. Say 4 in each hullfor lighting etc. 1 for refrigeration, 1 for charger, 1 for instruments, 1 for comms equipment, 1 for winches, 1 for nav lights etc...

    All linked to the main control panel, which is programmable, so that you can switch any section you want from this panel.

    Anyway that is what I envisage, but not having tried it yet, was looking for some experience/feedback.


    Alan
     
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