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Old 04-20-2012
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Grounding a Battery?

I have a Catamaran of course its all Fiberglass but i am installing a marine battery for a Stereo and some switches to turn things off! Where would i ground this battery at can anyone give me any ideas?


thanks
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Old 04-20-2012
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Re: Grounding a Battery?

Take what I say with a grain of salt and hopefully Mainesail or one of the other frequent contributors with more knowledge will chime in, but I assume you are talking strictly DC? If that is the case then my understanding is that a DC system on a boat should only be grounded back to the negative terminal on the battery. NOT to any portion of the boat itself. Connecting electrical equipment to the boat hull will turn your boat into an anode, if I remember Chem 1 class correctly (plus yours is all glass and wouldn't work anyway). I believe you install a DC bus and the bus gets connected to the negative terminal on the battery. Think it is referred to as a "free floating" system.
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Last edited by Silvio; 04-20-2012 at 09:30 AM.
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Old 04-20-2012
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Re: Grounding a Battery?

It's not like a car, where you connect the battery to the body/frame and then use that as the common ground for everything else. You run a positive and a negative wire in parallel to each powered device. You can use a busbar as a common distribution point to avoid a mass of wires going back and forth, if you want, but in the end you will still be able to trace both a positive and a negative wire from each device all the way back to the battery.
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Old 04-20-2012
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Re: Grounding a Battery?

If you have an engine with alternator for battery charging, you will have to run a ground wire to the engine. At the flange connected to the transmission, you could put in an isolation coupling that does not conduct electricity so that no stray currents can reach the prop and cause electrolysis (severe corrosion). There are through hulls that are bronze that may also be an issue. There is some controversy on whether to ground everything together or isolate. The latest I know of is to isolate. There are also separate grounds for lightening and radio transmitter installation. Do not run the lightening ground to the engine as a strike can weld components like ball bearings in the transmission. If you use shore power to charge the battery and also to float the battery to prevent it from slowly discharging and sulfating where you need a new battery many years before the guarantee runs out, you will need a marine battery charger. An automotive type charger will not isolate the ground in the boat from the ground to the rest of the marina and this can cause electrical currents that severely corrode metals completely destroying a stern drive for instance in a year, or maybe your own propeller if not isolated at the transmission. Instead of a battery charger, it might be best to use solar panels for each battery with intelligent voltage regulators to not overcharge the batteries.
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Old 04-20-2012
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Re: Grounding a Battery?

ABCY E-11 section 11.16:

DC Grounding - If a DC grounding system is installed, the DC grounding conductor shall be
used to connect metallic non-current-carrying parts of those direct current devices identified in 11.15.2.1 to
the engine negative terminal or its bus for the purpose of minimizing stray current corrosion and ensuring a
fault current path in the event of a short circuit.
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Old 04-20-2012
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Re: Grounding a Battery?

You have to trail a really long wire behind you that plugs into a grounded outlet at the dockside
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Old 04-20-2012
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Re: Grounding a Battery?

For the purpose of a "car" stereo you don't need any ground. Just run the stereo to the positive and negative battery leads, and if the stereo has a "ground" connection that goes to the negative as well.

Do use a suitable fuse, installed as close to the battery positive terminal as practical.
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Old 04-21-2012
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Re: Grounding a Battery?

Quote:
Originally Posted by hellosailor View Post
...Do use a suitable fuse...
You will need an electrical panel with fuses. If you want jerry rigged setup you will still need fuses to prevent an electrical fire with possible loss of boat

Last edited by LakeSuperiorGeezer; 04-21-2012 at 12:02 PM.
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Old 04-21-2012
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Re: Grounding a Battery?

Quote:
Originally Posted by ImASonOfaSailor View Post
I have a Catamaran of course its all Fiberglass but i am installing a marine battery for a Stereo and some switches to turn things off! Where would i ground this battery at can anyone give me any ideas?


thanks
On a 21 footer with no in-board engine an isolated ground is fine. This means the battery - post is your ship ground...

Quote:
Originally Posted by LakeSuperiorGeezer View Post
If you have an engine with alternator for battery charging, you will have to run a ground wire to the engine.
Most likely and outboard on a 21 footer and the battery can still suffice as ship ground when the motor is lifted..


Quote:
Originally Posted by LakeSuperiorGeezer View Post
At the flange connected to the transmission, you could put in an isolation coupling that does not conduct electricity so that no stray currents can reach the prop and cause electrolysis (severe corrosion).
This is strongly advised against if you have an inboard engine. The ABYC uses the term "MUST" when referring to alternate means of grounding the shaft to the vessel if using an isolating coupling. Isolating the shaft does not solve anything as the motor is still has an electrolyte inside it and also has MANY dissimilar metals. On the vast majority of inboard boats the engine is the ships main Earth/grounding point. It only means your engine will have less protection when you isolate the shaft..

Quote:
Originally Posted by ABYC P-6
6.5.5.2 If a non-conductive flexible coupling is used, an alternative means of grounding the shaft must be provided.
Quote:
Originally Posted by LakeSuperiorGeezer View Post
There are through hulls that are bronze that may also be an issue. There is some controversy on whether to ground everything together or isolate. The latest I know of is to isolate.
The only way to know for sure is to have a corrosion survey inspection by a COMPETENT ABYC trained corrosion specialist. Without this you are basically throwing craps like in Vegas..

Quote:
Originally Posted by LakeSuperiorGeezer View Post
There are also separate grounds for lightening and radio transmitter installation. Do not run the lightening ground to the engine as a strike can weld components like ball bearings in the transmission.

See below...

Quote:
Originally Posted by ABYC
A lightning grounding terminal for a boat should consist of a metal surface (copper, copper alloys, stainless steel, aluminum or lead) which is in contact with the water, having a thickness of at least 3/16 inch (5 mm), and an area of at least 1 square foot (0.1m≤). It should be located as nearly as possible directly below the lightning protective mast in order to minimize any horizontal runs in the primary (main) conductor.

In order to avoid routing grounding conductors horizontally through the boat, boats that use a lightning ground plate or strip located forward should ground backstays, or other metallic objects aft, to the engine negative terminal, a metallic rudder, or other external ground at the aft end of the boat. These grounds should also be interconnected with
the ground plate or strip located forward.

The aft end of a lightning ground strip should be connected directly to the engine negative terminal. This will provide a path inside the hull for any DC stray currents that might be imposed on the thru-hull bolts and the lightning ground strip.

The above has been the industry accepted method for lightning grounding for many years. Even boats from the late 60's & 70's were using this and they still use it today. In a lightning strike it is darn near impossible to isolate the engine as it is connected to the electrical system anyway.
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Last edited by Maine Sail; 04-21-2012 at 12:53 PM.
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  #10  
Old 04-24-2012
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Re: Grounding a Battery?

One can use an electrical conducting brush on the propeller shaft and have the engine isolated. Here is some research on lightening protection with a lot of various links on the subject: http://www.kp44.org/LightningProtection.php and http://www.kastenmarine.com/Lightning.htm and http://www.sailmail.com/grounds.htm

Last edited by LakeSuperiorGeezer; 04-24-2012 at 06:34 PM.
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