Can you overload a 12 volt battery? - SailNet Community
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Old 09-02-2015 Thread Starter
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Can you overload a 12 volt battery?

I am getting ready to rewire my entire O'Day. PO had everything a big mess and stated the interior lights didn't work because of a lightening strike near his boat. I found that hard to believe so I ripped out all the wiring and found the wires for the cabin lights and hooked them straight to the battery and of course every light worked. I am replacing ALL wiring, fuse panels and lights (going to LED's) and adding several other electrical items. I understand DC and AC systems but my question is this, "Can a person overload a battery to the point of being a safety issue?" OR will it just make the battery last that much shorter?

I know 50% of all boat fires are electrical related and most of those are due to wires chafing. I am installing two 6 gang fused panels. I am running all 12 gauge stranded wire because I have dozens of rolls of it already sitting in my pole barn. The items I will have running on the two 6 gang panels are listed below and the list names indicate each separate circuit.

Cabin lights (5 LED lights)
Running Lights
Masthead light
Cockpit lights (2 LED's)
Head night light (1 LED)
Bilge Pump
Shore Radio
AM/FM radio
12 volt power socket (for charging phones)

I always have two deep cycle batteries and the boat does have shore power which I will have hooked up at my slip and be able to charge those batteries at any time. I am not worried about a dead battery...I am just worried about anything that could happen IF all circuits were powered on at the same time.....would it be just a quickly drained battery or is there more to this and possibly a fire issue (even using 12 gauge wire).

1985 O'Day 26'

I spent all my money on booze, boats and broads. And the rest of it, I wasted. - Elmore Leonard

Last edited by Bruce3966; 09-02-2015 at 09:42 PM.
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Re: Can you overload a 12 volt battery?

I had to do almost the same thing this past spring. The previous owner rewired the boat. and he did a pretty good job for most of it, but I wanted to make changes.

This is how my boat is wired...

All devices negative (black) wires go straight to battery. So, 12 gauge is fine because each device has its own wire to the battery.

A heavy gauge red wire (welding cable) goes to 30 amp fuse then to a distribution block.

From there, 12 gauge red wires goes to a 10 amp fuse then to a switch then run out to the device/light to complete the circuit.

If you plan to install a power inverter, run it straight to battery, using appropriate fuse on red wire. I have a 400 watt and 200 watt inverter and neither work well when plugged into the lighter sockets installed in the boat.

You don't have to run the black wires all to the battery, you can make a distribution block somewhere, then run a piece of welding cable to it, if you have to, depending on the loads you expect.

On my switch panel I also installed a recessed LED volt / amp meter which is really handy. Get them on Amazon for a couple bucks.
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Re: Can you overload a 12 volt battery?

Absolutely. But figure a size 24 can do 600 amps for starting and probably 25 amps on a longer draw for extended time. What you list is maybe 12 amps, tops, all running simultaneously. Put in a 10 amp fuse for the rest but run the bilge pump on its own 15 amp fuse. You can easily do five days on a charge provided you turn the lights off in the day and the pump only runs 10 minutes a day. THAT's the one on you list that sucks current.

LEDs and the phone charger are less than an amp an hour I'm guessing.

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Re: Can you overload a 12 volt battery?

It sounds like neither of you guys is planning on using boat cable (tinned wire) and that will pretty much make your hard work a waste of time. Welding cable is NOT acceptable on boats these days, nor is untinned copper wire, stranded or otherwise. Ask anybody with a boat from the 80's who has ripped out apparently good welding cable, and replaced it with very expensive boat cable. A friend actually had a fire from a corroded spot in a welding cable start system.
There are certain standards for wiring a boat that are not needed in other applications, and that is why we use different cabling and wire.

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Re: Can you overload a 12 volt battery?

Yup, studying this a tad more I have decided to spend another $200 and get marine wire to rewire the entire boat. Whats another couple hundred!
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1985 O'Day 26'

I spent all my money on booze, boats and broads. And the rest of it, I wasted. - Elmore Leonard
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Old 09-03-2015
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Re: Can you overload a 12 volt battery?

Quote:
Originally Posted by Bruce3966 View Post
I understand DC and AC systems but my question is this, "Can a person overload a battery to the point of being a safety issue?" OR will it just make the battery last that much shorter?
You won't overload the battery. Please ensure that you have the correct size wires, fused for, at most, their rated load. You also need to be careful to get the earthing right when on shore power - it can be lethal if not correct.
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Re: Can you overload a 12 volt battery?

Yeah, I agree with Capta. If you have the budget go with the tinned copper. It will be safer and last 10x longer than plain copper. I didn't have the budget this year, and neither did my boat's PO apparently.

I don't have anything that requires high loads so I'm not terribly worried about it, hopefully the fuse will catch any shorts. But there will be a day (sooner rather than later) when it will all have to be replaced. The sailing season is so short in Canada that the wires don't get a chance to get corroded anyway!

Just as Delirious suggested, my bilge pump also goes direct to battery, fused of course. It's connected with the original wires, so I would imagine it uses proper tinned wire. But it blew it's fuse recently, then stopped working altogether and needs replacing before I go out again.
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Re: Can you overload a 12 volt battery?

I will for sure order marine wire today. Looking at the O'Day original wiring diagram I see all circuits were run with 16/2 except for the wires from the battery to the fuse panel which they list as 12 gauge and the the cabin lights which were 14/2. I am assuming LED's take less amps, and the Whale Gusher bilge I am putting in pulls 2.4 and specs recommends a 5 amp fuse.

O'Day's original fuse panel had a 15 amp fuse for cabin lights, a 10 amp fuse for running lights, a 5 amp fuse for masthead light and a 10 amp for accessory. I will try to figure out amperage for each circuit and go from there.

1985 O'Day 26'

I spent all my money on booze, boats and broads. And the rest of it, I wasted. - Elmore Leonard
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Old 09-03-2015
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Re: Can you overload a 12 volt battery?

I think 12 gauge from the battery to the panel is WAY too small! It would get to a 3% voltage drop with a 12 foot loop at just 10 amps. I would use at least a 6 and would fuse it at the battery. Instead of setting up for a large voltage drop and a fire do it right!

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Last edited by Don L; 09-03-2015 at 10:07 AM.
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Old 09-03-2015
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Re: Can you overload a 12 volt battery?

When I rewired my batteries, I bought 00 gauge cables pre-made from Genuine Dealz. They use the right boat cable, and 4-jaw hydraulic crimper, and they pretty much just charge you for the materials. Quality is top-notch.
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