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post #1 of 9 Old 04-10-2010 Thread Starter
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Question Battery grounds: Individual or common?

I've been combing threads and diagrams to no avail, and hoping someone can slam the lid on this question for me...

I have two battery banks (one battery in each bank) on my boat. Is it *best* to take the negative terminal from each battery individually to a ground bus, or to join the two negative terminals, then take it to a ground bus?

When purchased, the boat was wired with the two negative posts joined, but since I'm re-doing almost everything right now and replacing the battery wires it's a now-or-never moment to get it right. Unfortunately, all diagrams seem to just show things going to ground without specifying the actual path... (Or maybe I'm just not in on the secret code!).

Thanks in advance,
Chris

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post #2 of 9 Old 04-11-2010
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Quote:
Originally Posted by cghubbell View Post
I've been combing threads and diagrams to no avail, and hoping someone can slam the lid on this question for me...

I have two battery banks (one battery in each bank) on my boat. Is it *best* to take the negative terminal from each battery individually to a ground bus, or to join the two negative terminals, then take it to a ground bus?

When purchased, the boat was wired with the two negative posts joined, but since I'm re-doing almost everything right now and replacing the battery wires it's a now-or-never moment to get it right. Unfortunately, all diagrams seem to just show things going to ground without specifying the actual path... (Or maybe I'm just not in on the secret code!).

Thanks in advance,
Chris
There is no secret. Electrically they are the same. Electrons cannot tell the difference one way or the other. Just make sure the size/gauge of the wire is the same or able to handle the batteries you have. Two terminals on one wire = heavier wire gauge. One terminal and cable for each = lighter gauge wire. Most setups I have seen usually put the two terminals on one wire/cable.
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post #3 of 9 Old 04-11-2010 Thread Starter
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Electrically they are the same. Electrons cannot tell the difference one way or the other. Just make sure the size/gauge of the wire is the same or able to handle the batteries you have. Two terminals on one wire = heavier wire gauge. One terminal and cable for each = lighter gauge wire. Most setups I have seen usually put the two terminals on one wire/cable.
I knew it was essentially the same in an electron's world (assuming proper wire gauges as you metioned). I thought there may be a difference in terms of some safety scenario, or just a best practice / ABYC rule that tends to be used. It surprised me that I didn't find anything specific in some of the books since everything else is so specific.

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Chris

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post #4 of 9 Old 04-11-2010
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When you are connecting batteries and components you want to make sure to use a "star pattern" for the ground wires. What this means is that each battery/device has only one path to ground. If not ground loops can be created and cause all kinds of gremlins. You can daisy chain components, just make sure only one end of the daisy chain is connected to the common ground point.

I like to use ground buses in areas where there are multiple components (radio panel, cabin lights and fans). I then run one wire from the bus to my main ground point.
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post #5 of 9 Old 04-11-2010
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The real concern is to be sure you have only ONE common ground point to the earth. This is usually the engine. You can tie it all into a common buss then from the buss to the engine or ships ground. What you want to avoid is the use of multiple grounds to earth throughout the boat.

Using one ground wire for the batts is fine, and less expensive, but as others have noted make sure it is of a large enough gauge to support the entire system.

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post #6 of 9 Old 04-11-2010
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If you are redoing the wiring I would take each bank of batteries separately to the ground bar. That reduces the number of connections between any load and any battery. When (not if) you have an electrical problem, troubleshooting will be much easier too. If you aren't an expert in wiring it will also keep you from creating inadvertent ground loops that can drive you nuts. When loads share a common path then one load does affect another, with respect to electrical noise and voltage fluctuations. So a single large ground point has many advantages.

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post #7 of 9 Old 04-11-2010
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Aside from ONE common ground point...You also want the shortest possible cable run form the batteries to ground, with the fewest splices/lugs in it. And, if you ever are using the batteries in "combined" mode, in theory you want the cable runs to both batteries being equal. Identical cables, each from one battery to the common ground point, would do that best. Installing a ground bus (bar) or similar at that point would be a good way to ensure that everything else can be joined up to "the same" point, while still not glomming them all on one terminal.
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post #8 of 9 Old 04-11-2010
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I would try not to have more than one connection on each battery post. Negatives from each battery to a big bus, from the bus to the single engine ground point. Same for positives, one connection on each post, to switch and to a bus before the panel.
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post #9 of 9 Old 04-11-2010 Thread Starter
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Ok. I'll install a ground bus very near the battery boxes, give each battery its own wire to the bus, then take that bus to the engine grounding lug. Sounds like a plan. Thanks for all the responses!

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