Simple wiring diagram for small craft

Discussion in 'OnBoard Electronics & Controls' started by CDK, Jun 8, 2009.

  1. Joakim
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    Joakim Senior Member

    Well I have done this and seen only very small currents. There are plenty of examples of such parallel connection used without problems for several years. This is standard in many new boats and in some new cars as well.
     
  2. BertKu
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    BertKu Senior Member

    It differs for Sealed Lead Acid Batteries (SLABS) the modern battery today used in most new cars. It is much better to use such a SLAB in the marine environment
    bert
     
  3. Joakim
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    Joakim Senior Member

  4. BertKu
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    BertKu Senior Member

  5. DaveJ
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    DaveJ Senior Member

    http://www.jaycar.com.au/products_uploaded/sc151.pdf

    @CDK can you please show me where in the above that this particular triac will not conduct below 28vdc. From what i can see for the triac to tigger, the gate voltage needs to be between 2.5 to 3.5 vdc (depending on the model number) and the on state are all below 1 vdc. The braw back of this triac is its voltage drop between 1.52 to 1.85 vdc, or am i reading it wrong.

    Yes the triac will stay trigged until a reverse potential is placed apon it and will turn off and not be trigger until the gate is triggered again for either direction. So in a charging cct if you want the triac to turn off you momentaryly apply a reversed voltage, this can be achieve through a small volatge doubling cct.
     
  6. BertKu
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    BertKu Senior Member

    Yes Dave, it will work. However not with a diac. A diac needs first at all +/- 32 Volt to reach the Voltage whereby it "collapses" and supply the current to the Triac to conduct. A diac only revert to its original state if the current falls below a certain value. Thus you need a normal DC Voltage via a resistor to conduct the Triac. But it is indeed not advisable to use a triac due to the high Forward Voltage. The debate was to create a system whereby 2 large batteries with high current capabilites can be professional connected parallel. Regardless whether you have a liquid Acid battery of 12,7 Volt switched parallel to a modern Sealed Lead Acid battery of 13,4 - 13,6 Volt, or a brand new and an at the end of its lifetime battery.

    Diacs are similar in behaviour as lightning arrestors. It conduct as long the current flowing through the device is enough to keep it conducting.
    Bert
     
  7. DaveJ
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    DaveJ Senior Member

    Why, the triac i quoted could handle voltage up to 400V before its turned to toast, unless the rise was higher then 30v/usec, since the system will not get above 15v that parameter will not be reached.

    Oh, ok, i missed the point, what you want is load sharing. How i would try to achive this is to have a voltage/current regulation cct just after each positive terminal of each battery that has a sense line to the other cct of each battery, the lowest battery dictates the supply of voltage until it reaches a level that is too low is dropped out of the cct (and a charge can be placed) and the next lowest battery takes over. This would allow different types of batteries to be used in conjunction with each other. Does that sound like what your looking for.
     
  8. CDK
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    CDK retired engineer

    No I cannot, I never said so.

    And before you start drawing circuits: to let a conducting triac revert to off-state, the current trough the device must be reduced below the holding current or reversed. In a low resistance circuit with LA batteries that can only be achieved with inductance and a short command pulse.
     
  9. BertKu
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    BertKu Senior Member

    Dave, CDK is correct in both paragrahs. It is only wise to use electronics in the marine environment, if it can be substantial better or it cannot be done otherwise. With forward Voltage we mean, the voltage drop over the "contact" of the device i.e. if you have a 100 Ampere load and your Forward Voltage is 2,35 Volt, you have lost 235 Watt in the "contact". Not very efficient. With a Diode this means between Anode and Cathode, with a transistor this means between Collector and Emitter etc.

    The ideal situation is a device which has at 100 Ampere only a loss of 0.1 Volt , thus 0.001 Ohm. Thus during the conducting stage you loss is only 100 Ampere x 0.001 Ohm = 10 watt at a usage at 1200 Watt, this is acceptable. A relay contact is such an example with paladium as contact material.
    Bert
     
    Last edited: Apr 4, 2011
  10. DaveJ
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    DaveJ Senior Member

    You got me, i don't know what i'm talking about
     
  11. boattech2
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    boattech2 boattech

    Hi, I'm a newbie on this forum! Hello all!
    I'm not trying to hijack the post to another subject but this may be a worthy comment:

    Re: Simple wiring diagram for small craft;

    Per the diagram posted, I thought the SHP Shore Power Charger Green wire Must be connected to the chargers A.C. input. To omit it may become a hazard, I think. Possibly this is an automotive type charger? I was taught never use an "automotive" battery charger for permanent installation on boats because a charger made for Marine use safely Isolates the A.C. Ground & D.C Negative internally.
     
  12. BertKu
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    BertKu Senior Member

    No we hijacked the thread and now we are back to the original schematic.
    If you earth the boat's earth to the offshore earth and should the offshore earth have a voltage potential, your boat becomes a nice "Magnet" . Your stray currents will eat your metal up like the most delicious pudding on earth.
    Well that is what I guess.Therefore you notice the warning "Note the green earth is not connected". In principle you could use any charger, provided you know what you are doing concerning the earth and as long your boat has its own earth properly connected.
    Bert
     
  13. CDK
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    CDK retired engineer

  14. BertKu
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    BertKu Senior Member

    Hi Boatech2,

    Maybe we should discuss the shorepower. Somewhere there is agenerator in an electricity company which generates via transformers stepped down 220 Volt/380Volt to the the harbour. The generators are normally configured in star mode, whereby the center of the star is earthed. via all the transformers between phase and this star centerpoint it is 220 Volt and between two phases 380 Volt.
    If the earth is a mile away from your boat and at the same time also used by other users, not nesseccary boat users, you build up a Voltage potential between your earth of your boat and the earth on this "cheap automotive " transformer. For that reason the earth must be taken off. The question then remains "what quality transformers is used in the cheap automotive charger" and that maybe a problem. Although my experience is that as long the casing of the cheap automotive charger is earthed to the offshore, but not to your boat. It is as safe as any charger, provided your boat is earthed to the water.
    Bert
    Sorry CDK, this reply crossed yours.
     
    Last edited: Apr 5, 2011

  15. BertKu
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    BertKu Senior Member

    Dave as long you don't stop asking questions. You know probably more about another subject ,you are an expert on, then us. We all have sometimes made a wrong conclusion. Nothing wrong with that. Even people like Pistbroke are sometimes wrong. I have here 40 Ah / 12 Volt SLABS which are charged to 13.7 Volt (just below the gasdsing voltage) and when the charging leads are taken off, the Voltage drop to 13.6 Volt and after days and days the Voltage is still above 13 Volt ( 13.2) @ 25 degrees Celcius.
    Thus statements like all Lead Acid Batteries are less then 13 Volt is incorrect.
    Don't feel bad about it.
    Bert
     
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