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Old 21-02-2010, 20:32   #1
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Need Help with 12vdc System

I am trying to gain some basic knowledge about how a 12v dc system works. Being that my boat is from the late 60s I think it might be time to rewire it. My basic question is does anyone have any diagrams or pictures of a 12v system?

I would like to know if buy a 12v dc circuit breaker distribution panel from some one like Blue Sea systems do I need to think about additional fuses or do I just wire the battery power into the panel and then connect my lights, accessories etc to the breakers?
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Old 21-02-2010, 20:53   #2
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I think you are asking a series of questions that could not be easily or completely answered in short reply on this forum. Best thing you could do is get on Amazon and pick up a couple of books on the subject. Nigel Calder's books are good and I think there are several more that are currently recommended. Any half decent book on boat 12V systems will be loaded with pictures and diagrams.
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Old 21-02-2010, 21:06   #3
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This is a good intro in addition to Calder's book:

Amazon.com: The 12-Volt Bible for Boats (0639785802235): Miner Brotherton, Edwin Sherman: Books
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Old 21-02-2010, 21:07   #4
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This should answer a few questions. Easy Ac/Dc, Boat Wiring and Marine Electrical Questions, Answers and Comments
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Old 21-02-2010, 21:09   #5
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Also here is a tip to test the load on AC electric, have your wife/better half lick her fingers and say hold this.


Dutch
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Old 21-02-2010, 21:58   #6
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Also here is a tip to test the load on AC electric, have your wife/better half lick her fingers and say hold this.


Dutch
Dutch, I take it you single hand a lot.
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Old 21-02-2010, 22:12   #7
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only after the first time i had the wife hold a coil wire to check fire to the plugs. lol
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Old 21-02-2010, 22:19   #8
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Very basically:

You have a power source - usually 12v batteries
You need to charge that power source - Alternator, Solar Panels, Wind Generator etc
You need to regulate that charge to protect the power source - voltage regulators
You need to distribute that power - wire
you need to protect your electrical equipment - fuses or circuit breakers

Now there have been a lot of books written on the subject that go into great theoretical detail on the subject without actually telling you how to re-wire your boat. Mainly, because every boat is different

So, you can either buy a whole load of these books and get very knowledgable on the subject.

Or

You can get hold of a wiring diagram for a similar sized boat as your own, with a similar layout and copy it.

Or

There was once (possibly about 10 years or so ago) a series of articles was done in one of the yachting magazines (could possibly have been Practical Boat Owner or Yachting Monthly). It was great - dead simple overview with big easy to read diagrams. In fact, it was so acclaimed they actually made a separtate publication of the whole series combined. I just can't remember the name or give you a link - maybe someone else remembers it
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Old 22-02-2010, 08:21   #9
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Thanks for all of the responces. I think what i need to to is draw my wiring diagram and post it for feedback.

Does anyone have experience with the Blue Sea prewired breaker panels? Any one know of a cheaper alternative or are they a good value?
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Old 22-02-2010, 08:34   #10
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...
you need to protect your electrical equipment - fuses or circuit breakers
...
I'll just pick one nit:

Fuses/breakers are to protect the wiring, not the equipment. fuses/breakers should be sized to prevent the wiring from overheating and causing fire if shorted (i.e., drawing too much current).

You size the wiring of the circuit to the equipment to be powered.

Kirk
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Old 22-02-2010, 09:12   #11
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Thanks for all of the responces. I think what i need to to is draw my wiring diagram and post it for feedback.

Does anyone have experience with the Blue Sea prewired breaker panels? Any one know of a cheaper alternative or are they a good value?
Blue seas are a great panel, Marinetics are also good panels. Depending on your goals there are a ton of options including building your own.

Blue Seas
Marinetics
Seadog
Perko
Seachoice
Switch Panels by Discount Marine Supplies
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Old 22-02-2010, 09:20   #12
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I did my boat with Square D panels from Lowes, a twenty circuit box with a bunch of breakers for $100. Get a book called The 12 Volt Bible and figure out the loads. I didn't bother with the tinned wire. I did pay a marine electrician to do the installation which worked out well.
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Old 22-02-2010, 09:32   #13
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Not sure how big a boat you have but assume it is modest with moderate loads. If you have more than one battery get a battery switch to switch loads and this will also let you disconnect all loads. But you can dedicate one circuit to lights and another radio or what ever suits your fancy. Size the breaker to the wire size as somebody else said. 12 gauge typically 20 amps. Use marine grade wire. You can ad fuses to indiviual loads like radios other elctronics to protect them and give you ability to disconnect.
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Old 22-02-2010, 09:51   #14
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If you plan to have 120V circuits onboard you should have a separate 120V breaker panel as well. An excellent book is Understanding Boat Wiring, by John C. Payne.
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Old 22-02-2010, 09:55   #15
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Also be aware of voltage drop along long wiring runs. For a low voltage (i.e. 12V) system the minimum required voltage drop will often trump the required current, making a larger wire diameter necessary, especially for critical systems like bilge pumps. Blue Sea has a wire size calulcator: Blue Sea Systems
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