Simple wiring diagram for small craft

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

  1. TollyWally
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    TollyWally Senior Member

    Gonzo,
    Are the common everyday switches on pleasure boats spark protected? I feel a little foolish not to have thought of that. I've bought "marine" switches on more than a few occasions and didn't give it a second thought. The ones I like best are epoxy potted with leads that I solder to.
     
  2. Delane
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    Delane Senior Member

    Spark & Vapor = Bad

    Gonzo is so right, and to cover that base one should only place spark proof switches in a location wear fuel vapor may exit due to a leak or venting.

    Otherwise if vapor safe, think out of the box and try something cheap and effective.
     
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  3. CDK
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    CDK retired engineer

    The switch panels you but in boat shops have very cheap, poor switches. Not spark protected, which is not a requirement for normal pleasure boats, but not sealed against moisture and without adequate contact material.
    Finding something reliable that isn't overly expensive (like mil spec or aviation grade) is not easy.
    I use C&K switches, with potted terminals if I can find them. It is one of the few manufacturers who specify in detail what their products can do in term of current, voltage and life expectancy. If the load to be switched requires more current than a C&K switch can handle, I use automotive relays. They are very inexpensive and can carry at least 25 Amps.
     
  4. TollyWally
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    TollyWally Senior Member

    I didn't think those switches looked very high class that I've seen on pleasure boats. I'll try sourcing this C&K brand. The internet is my friend (I hope)
     
  5. Tim B
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    Tim B Senior Member

    The switches I've seen on small craft have been very pretty unimpressive. However, they are easily replaceable. Personally, I'm all in favour of using MOSFETs (Effectively solid-state switches) and controlling them through a microprocessor and serial interface. This has a few advantages:

    1. The high-power system is spark-proof by definition.
    2. The user to keeps all the large switching loads and cables in the engine bay (for example).
    3. The "Human Interface Panel" then only needs to handle very small switching currents (which means small, light, reliable switches, though it does require a microprocessor). Potentially, it could even be a mini touch panel, NavPC etc.
    4. MOSFETs are capable of handling upto 400A (check your current rating) without welding themselves together.
    5. It could even be made ethernet (or USB) capable, depending on how you wanted to integrate the system.

    For cases where 8 lines or fewer are required, the system could be setup following the PC parallel port guidelines, which would negate the need for uPs. Indeed, multiples of 8 could be wired on separate ports to negate the need for uPs on larger systems, though this may risk running out of parallel ports in future interfacing.

    Tim B.
     
  6. Landlubber
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    Landlubber Senior Member

  7. zamgod
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    zamgod Junior Member

    Four Position Battery Isolator Switch

    Hi CDK,
    The battery isolator switch that I purchased has four positions; off, 1, 2 and both. But on the reverse side it only has 3 connectors; 1, 2 and common.
    Does the common on my switch correspond to the '0' on your BS switch?
    Which connector(s) do I use for my main feed to the circuit breaker (and then on to the fuses)?
    Thanks.

    Regards,
    Alasdair
     
  8. CDK
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    CDK retired engineer

    Yes, I labeled the positions (P)ort, (S)tarboard, (B)oth and (O)ff. Common connects to the engine, 1 and 2 to the batteries.
    If you don't have a solar controller, engine bay terminal 5 is the main feed.
     
  9. Bglad
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    Bglad Senior Member

    Regarding the diagram and notes in the absence of an RCD or ELCI type of breaker on the AC inlet how is it wise to leave the green ground on the AC off the battery charger and the DC negative? Bad for swimmers in the water and a potential hazard if the boat is on a trailer plugged in and the charger is putting AC current on the DC system.

    I am assuming this being a minimum system the inlet is not a full blown 30 or 50 amp but more along the lines of a 15 or 20 you might use with an extension cord. If that is the case I don't see why the green ground would not at least be connected to the charger...
     
  10. CDK
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    CDK retired engineer

    There is a heated discussion about the ground lead here: http://www.boatdesign.net/forums/me...l-craft-whilst-afloat-electrolysis-32665.html.

    A ground fault interrupter device is normally behind the marina power socket, but it cannot do harm to have one in your boat as well (I also have one).
    As for connecting the green wire to the charger: that depends on how the charger is wired. I've seen chargers where the ground wire is connected to the transformer core only, with the DC output floating. In that case there is no objection to a ground connection. But others have the negative output tied to it as well, that might cause galvanic corrosion.

    The danger for swimmers is non-existent, the boat on a trailer connected to shore power could be a potential hazard if the charger isolation (2500 V breakdown) fails. You should add a ground switch or a galvanic isolator for that situation, I could also imagine a circuit that would audibly warn in such a case.
    Please bear in mind that this post was meant as a guideline for small craft that normally stay in the water during the season, have a single engine and only basic equipment.
     
  11. Bglad
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    Bglad Senior Member

    I get that it is a basic diagram and I will say right up front your knowledge way exceeds mine in the technical aspects of the various systems aboard. I'm a bit of a lug trying to learn enough to keep myself out of trouble doing my surveying business.

    Check out electric shock drowning at this site to see how swimmers are at risk although primarily in freshwater http://qualitymarineservices.net/ when a vessel is plugged into AC power.

    My basic idea is to think of the boat hull as a refrigerator frame. The green ground needs to be connected to the hull or in the case of wood or plastic hulls the DC (-) and bonding system to protect you in the event the AC current runs amok. The metal parts touching the water are a path to ground when plugged into dock power it would be no fun to make the connection while rummaging around while aboard!

    I have been lurking for a couple of weeks doing a lot of reading seeing if might add anything here or there but mostly just trying to catch up and take notes. Maybe this discussion can help someone out...
     
  12. CDK
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    CDK retired engineer

    The qualitymarineservices link provides some interesting items. Some seem to contradict my assessment of an ungrounded hull, but if you read carefully nearly all cases where the cause of electrocution was established, there was a small current carrying object like a cable or submerged socket in the water. Only in such cases a voltage gradient steep enough to paralyze a swimmer can exist.

    The guy leaving his berth without removing the cable is a striking example. Wiring or not wiring ground shore in the boat wouldn't have made a difference.

    Exactly for cases like this it is of paramount importance to have a ground fault interrupter installed near every waterfront socket. Such a device measures the current flowing through the two power leads and trips whenever there is an unbalance of more than 5 milli-amps, cutting off the power to the socket immediately. This threshold is reached even when rain gets inside a socket or plug. The device is normally behind a panel, so a technician must be called and the reason of the ground fault explained.

    Such devices are mandatory in all European countries, even in the not-quite-up-to-standards country I live in.
     
  13. Bglad
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    Bglad Senior Member

    One of those instances was aboard an IO boat that did not have the AC green ground DC negative connected. A DC wire burned through a AC wire in the harness and sent the outdrive up to 80 or 90 volts. It killed a young child floating by in a lifejacket (freshwater). Not likely in a simple system but not beyond possibility. Had the AC green ground and DC negative been connected the circuit breaker would have tripped eliminating the fault. Most boats have this connection somewhere unentionally if they have a generator, inverter or even a battery charger that is grounded properly.

    Saltwater is not nearly so hazardous since it is a better path than the human body.

    Here in the US ELCI circuit breakers are going to be required soon on new boats. If current is leaking off the boat they will trip requiring a visit from an electrician.
     
  14. patrick1973
    Joined: Mar 2011
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    patrick1973 New Member

    WOW !!!!!!! Tank YOu for these simple print outs... You saved my life. I bought the 12v bible and big book of marine electronics. There's some nice lesson plans in there and basic science. BUT NOT very good diagrams or photo's These 2 pieces of paper are helping me more than both books.. So Tanks YOU!

    By the way, the black 6 switch panel with rubbers over the switches and round fuse holders next to switches.... Is that panel "SPARK RESISTANT" ???? Just spent 60 bucks one. Also how much ventilation do you suggest on a console. I have four slots on the panel door. But I feel like I should have more air ? It;s my 1st boat rebuild. Should I add a few clam shell vents? Fog humidity VS fumes. I like humidity more than fumes.

    Anyways, great website here. Thank you.
    Pat
     

  15. Tim B
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    Tim B Senior Member

    It's more important to make sure that any fuel tank vents are routed properly, so that no fuel fumes end up in the "living quarters". The switch panel is generally going to be on a cupboard or some form of facing board, which probably has a direct route from bilge to deck behind it anyway. Ventilating said cupboard is only important if you expect to generate heat in it (eg. running a PC or possibly a NAV console).

    Is your console spark resistant? Probably not. But it's probably not an issue as long as you have adequate ventilation in the living quarters.

    Tim B.
     
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