help me -control engineering

Discussion in 'OnBoard Electronics & Controls' started by jollyricard, Mar 10, 2012.

  1. jollyricard
    Joined: Jul 2009
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    Location: italy

    jollyricard Junior Member

    Dear ALL,

    My name is riccardo, I have received question regarding some procedure on board of ships . I don't understand what to do for Prepare for starting, paralleling and change-over of alternators or generator.
    Moreover what is reverse power? What does it mean ?

    Many thanks in advance
    B/R
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    What is your background in electronics?
    By reverse power, do you mean power to reverse the vessel?
     
  3. Submarine Tom

    Submarine Tom Previous Member

    Or do you mean reverse polarity?

    -Tom
     
  4. gdoug
    Joined: Mar 2012
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    Location: Stuart FL

    gdoug GD

    Some boats with larger engines have parallel switches. A parrallel switch completes a circuit that couples multiple batteries so that you have more power than 1 battery.
    Normally each engine has it's own starting battery. However starting engines draws a lot of power. For this reason circuits are created that couple each starting battery so that you have more power available.

    A parallel switch parallels the starting batteries. When you parallel two batteries you connect them in such away that you keep the same voltage as 1, but increase the amperage therefore increasing power. Power in watts = Voltage X current (in amps).
    For example if you parallel two 24V 80 amp batteries the resulting voltage is 24V, but the resulting amperage is 160. This gives you twice the power.
    You parrallel batteries when starting to give you twice the starting power.
    It's just a safety to protect each individual battery from getting over drawn during start up. Over drawing some batteries can perminately damage them.

    About reverse power. I personally have never heard this term. I'm not sure what you're referring to, but if you explain I may be able to help you out.
    Cheers,
     
  5. gdoug
    Joined: Mar 2012
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    gdoug GD

    Generators are combustion engines that essentially have an electric motor arts Ted to them. And electric motor uses electricity to power copper windings which turn magnets. The magnets are then usually fastened to a shaft (simple example). So when you apply a volage to an electric motor you power the windings which move magnets which move a shaft. Transversly if you use a shaft to turn magnets in windings you will create a electricity. This is how a generator works. The shaft of a combustion engine turns an electric motor creating a voltage.

    Generators on boats have 2 purposes. 1 to charge batteries, 2 to power electronics. The only way they would be needed for starting is if your starting batteries are drawn and need to be charge. BUT! Starting batteries aren't usually hooked up to a generator. You shouldn't need to start a generator to start the boat.

    Unfortunately every boat is different. It's not safe to run or work on a boat if you don't understand the electrical system. You need to find wire diagrams for the boat and have a Marine electrician review them with you.
     
  6. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    he will mean one generator powering another, common problem with older systems when lightly loaded and you are trying to get another online/parallel it
     
  7. gonzo
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    gonzo Senior Member

    If they are A/C the cycles need to be synchronized
     
  8. jollyricard
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    jollyricard Junior Member

    ok thanks but I don't understand the term "reverse power" used for diesel generator on board ships.
     
  9. gonzo
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    gonzo Senior Member

    There isn't such a thing. Are you translating from Italian? There may be a misunderstanding due to that.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Are you mistaking REVERSE for BACKUP ?

    Backup or manytimes labeled STANDBY typically means that DC to AC inverters take over when the generator or shorepower shuts down
     
  11. powerabout
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    powerabout Senior Member

    geez sometimes you guys...

    http://www05.abb.com/global/scot/scot296.nsf/veritydisplay/c1256d32004634bac1256e0f006bf54f/$file/1mrk509042-ben_en_reverse_power_relay_and_protection_assemblies_rxppk_2h__rappk.pdf

    reverse power means one gen set it motoring another, its a common term and problem on large gen sets
    The vessel will have control circuits to trip the gen set off line to prevent it being motored as above
     
  12. michael pierzga
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    michael pierzga Senior Member

    I have never used generators in parallel that have a user controled circuit labeled REVERSE. It is protected, but this protection is in the background.
     
  13. powerabout
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    powerabout Senior Member

    it isnt a user controlled circuit and it usually isnt on gen sets of up to a couple of hundred kw
     
  14. michael pierzga
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    michael pierzga Senior Member

    I trust what you say. Load distribution on the yacht size gen sets Ive used is automatic.
     

  15. powerabout
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    powerabout Senior Member

    yep me too and you dont have a situation where more than 50% of your load is coming off and on like many other suituations so a yacht is quiet straight forward.
    Electronic govenors have almost made this go away which are on almost all high speed diesels but not on medium speed so they hardly exist over about 2mw
    Its a VAR issue ( Volt Amp Reactive) at low load
     
    Last edited: Mar 22, 2012
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