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Discussion Starter · #1 ·
So today I melted the negative terminal off one of my batteries. I am restoring an Ericson 32 and the boat hasn’t been in the water in 10 years. In the battery compartment there were two red wires around maybe 2 or 4 gauge and one black wire around 2/0 gauge along with a short black jumper of 2/0 gauge. I hooked up the two red cables to the positive terminals, then I hooked up the black wire to the negative terminal and connected the jumper to the negative terminal on the other battery. Seemed pretty straight forward to me, nothing too crazy. I turned the switch to battery #1 and within about 5 seconds I had melted the terminal where the negative cable was connected. Just my luck. Obviously I have a direct short. Apparently the previous owner decided that the color of wires doesn’t matter and you can use red and black interchangeably. Lesson learned, never trust that the previous owner knew what they were doing. After tracing the wires here is what I found. (see diagram attached)
Wire #1 – Red – Attached from Switch Battery 1 post to the Starter
Wire #2 – Black – Attached from the Switch Common post to Battery #1 Negative terminal
Wire #3 – Red – Attached from the Switch Battery 2 post to the Battery #2 Positive terminal
Wire #4 – Red – Attached from the Battery # 1 Positive terminal to the engine block

Clearly this is all wrong. Here is what I plan to do to correct it (see diagram)

Wire #1 – Red – Remove it from the Switch Battery #1 to the Switch Common and then connect it to the starter.
Wire #2 – Black – Remove it from the Switch Common to Battery #1 and connect it to the Positive terminal on Battery #1.
Wire #3 – Red – Keep it the same. Attached from the Switch Battery 2 post to the Battery #2 Positive terminal
Wire #4 – Red – Remove it from the Positive terminal on battery #1 and move it to the Negative terminal on Battery #1 and keep it connected to the engine block.

Does this sound correct to you? I am a car guy and just getting into boats with inboard engines. I just want to double check that there aren't any strange boat nuances. From now on I will not trust that back means negative and red means positive.
 

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Master Mariner
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9,225 Posts
One battery should be for the house system and feed your 12 v dc electrical distribution panel. The other should be to start the engine. They need to be completely separate until the battery switch goes to both.
Wire size is dependent on load, so figure out run (length of wires) and load, in amps, and size your wire correctly using an electrical wire size guide, available by searching the web.
Use tinned boat cable, not cheap welding, solid, untinned copper or aluminum cable.
 

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Don't call me a "senior"!
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I would redo the color coding (even if you have to wrap some of the cables with colored electrical tape) so that all the negatives are black and all the positives are red. In your second diagram this isn't the case. You may know that wire #2 is really positive, and wire #4 is really negative, but no one else will (without tracing them). You also might forget in the future (at least momentarily). Either way, you could wind up with fried components, or worse, in the future. Do it right --- there is a reason for the red/black convention.

And get some terminal fuses to protect your wiring/terminals in the future.
 

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Discussion Starter · #5 ·
Thanks for the input. I plan on using colored tape so the next guy doesn't have the same problems as me. As for the fused terminal all that I have seen in the store is 200A fuses. I have an an Atomic 4 (small gas 4 cyl inboard) would this be enough to blow the fuse when starting?
 

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Don't call me a "senior"!
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Thanks for the input. I plan on using colored tape so the next guy doesn't have the same problems as me. As for the fused terminal all that I have seen in the store is 200A fuses. I have an an Atomic 4 (small gas 4 cyl inboard) would this be enough to blow the fuse when starting?
The best thing to do is to find out what the current (amp) rating is for you starter motor. But, 200A should be plenty (I think I used 100A fuses for my boat with a Yanmar 2gm).
 

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Learning the HARD way...
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120 amps is light for a starter and would likely suffer from nuisance blows. Better to change the wiring to a heavier gauge - 1/0 or 2/0 - and fuse at 250 or even a bit higher. I have measured 175 amps during starting small easy to start diesels. I generally do not wire batteries or starters with wire smaller than 1/0.
The larger wire allows a larger fuse and less chance of a nuisance blow, especially when the engine is needed quickly.
 

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Bombay Explorer 44
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BTW if you really did melt the terminal off a good battery it is a simple job to melt some lead and cast a new one in situ.

Battery suppliers/auto electricians used to do it before Health and Safety got started.
 

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If it wasn't being charged there wasn't much chance of an explosion. As long as the short is removed quickly the heat build-up stops and the only damage is to the post. A friend did this to a new bank of golf carts when he was installing them, new posts at the dealer and they have been in use for several years since.

I don't recommend it though.:)
 

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I've personally blown the entire top of a battery off, under similar circumstances. As soon as the battery is shorted, it starts producing massive amounts of hydrogen.

I was covered in battery acid and had to feel my way to a nearby sink to wash it off my face and out of my eyes! Good times!
 

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Don't call me a "senior"!
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I've personally blown the entire top of a battery off, under similar circumstances. As soon as the battery is shorted, it starts producing massive amounts of hydrogen. ...
Shorting a lead-acid battery causes it to discharge. Hydrogen gas is only produced during charging; specifically during over-charging, as that is the only time electrolysis of the water in the battery can happen. In your case, there may have been an accumulation of hydrogen gas prior to the short, which ignited the gas. But the short itself didn't produce the gas.

That's why some large battery banks have ventilation fans that only actuate when the system exceeds a certain voltage (usually something like 13.7V or so; IIRC, hydrogen gas production doesn't get severe until something in excess of 14V is reached, but 13.7 leaves a margin for error), as that is when the batteries start producing lots of hydrogen gas.
 

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One of None
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I have this phobia of exploding batteries. This discussion brings this youtube vid to mind.. scary stuff!

 
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