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Old 23 February 2012, 13:49   #1
Country: UK - England
Town: plymouth
Make: Ribtec
Length: 6m +
Engine: Mercury 175 optimax
Join Date: Feb 2008
Posts: 351
Wiring up for 2 batteries??

Now this is probably a simple question for most people...but not for me.

I m redoing the electrics on my rib so that I can have 2 batteries; that opti takes a lot of juice to turn over!!

Now, if I wire the 2 batteries in parallel, i ll basically have one big ass battery. Do I have to fit anything for the charging of the batteries or will it just charge as one big battery?

I was looking as this one ebay, do I use anything like this


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Old 23 February 2012, 14:09   #2
Country: UK - England
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Engine: Outbaord mariner 75
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If they are wired in parallel then it acts as one large battery.

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Old 23 February 2012, 14:12   #3
Country: UK - England
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The split charge relay is for charging second batteries in a trailer - it makes sure the trailer battery is connected to the car one onlly when the car engine is running - to stop the trailer electrics flattening the car battery when you stop, and to stop the car trying to draw on the trailer battery when starting (as the trailer cable and wiring are not exactly jump leads!). So it's not what you want.

On my boat whenever you put the isolator switch on "both", the two batteries are in parallel and they operate and charge up together, that works so is all you need to do. Although including an isolator switchable "off-1-2-both" gives you options to run on just one battery when the engine's off, keep one for starting only, etc
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Old 23 February 2012, 14:14   #4
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Are you wanting to start using the 2 batteries together or as a back up, you may as well get a more powerful battery
Don't know enough about split charging but it needs to be done properly have a look on off road forums they use split charges a lot
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Old 23 February 2012, 14:18   #5
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Country: Australia
Town: Sydney
Boat name: Lunasea
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Length: 8m +
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You could wire them up together in parallel, that is connect the positives together and the negatives together. The problem with this is if one battery goes flat, chances are so will the other one.

With an isolator you usually connect all the accessories on to one battery and the engine to the other. If you use your accessories with the motor off and flatten the battery, the other battery will still be charged. When you start the engine the isolator will charge the start battery first and when it reaches a certain level then it will charge the accessory battery.

If you choose to use an isolator, somebody more knowledgable than I may advise you if 30A is enough. I suspect not.

Some people just use simple cutoff switches. There are many different designs and you can spend as much as you like. Personally I prefer the simple design with a red removable key, one for each battery. The advantage is you can see exactly what is happening through the position of the switches. You only turn on the second battery when you want to start and run. One battery operation for when you are stopped and using accessories.

A single decent size battery should not have a problem starting your outboard. I suspect your wiring may be starting to corrode or your battery is no longer up to the task.
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Old 23 February 2012, 14:36   #6
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Kubcat is spot on, check your current set up if it is not starting properly. Corroded contacts or a less the fit battery will cause you problems with an Opti which needs to have good voltage to start.
If you want to go twin batteries, house and start batteries, Merlin in Poole do very good split chargers, which unlike simple switches do not suffer from corrosion. (no I am not on their staff )

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Old 23 February 2012, 19:37   #7
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I don't like the idea of split charging systems on boats, I knew someone that owned a Barge hiring business that seemed to have more than his fair of trouble from such systems.

If you are to redesign your battery set-up I would go for a simple two batteries in Parallel design, these will terminate in a heavy duty 1+2+both Isolator switch and that's it. I would suggest you get in to the habit of checking voltage condition of each battery before each trip (this will help varify battery condition) then run the boat on the both setting all day.

If you stop for a spot of fishing or something and want to use the electrics and are worried about flatening the batteries you have the option of selecting one battery as your active power source and the other for starting.

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Old 24 February 2012, 01:58   #8
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I used to be plagued with flat battery when I only had one. I now have two 120 ah's wired per Hightower's post and never looked back. Hope it helps.

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Old 24 February 2012, 02:59   #9
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I used this on the last rib and on the current one, never let me down and no thinking or remembering to mess around with switches.

Add-a-Battery*—*Blue Sea Systems

Or a cheaper way if you're handy with a bit of wiring would be a 1-2 or both type battery isolator switch and one of these

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Old 24 February 2012, 05:03   #10
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Boat name: Half Cut
Make: Cobra 8.6
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Bep vsr

I have a Verado with full electric power steering. Plus cooler, music, lights plotter, VHF, pump for inflatables, etc. The demand for power is huge. The BEP system is highly regarded. I fitted one two years ago with two batteries and it has been faultless.

This is the unit Power Store

And this article explains how it works and looks at some alternatives Battery Rigging for Verados: The club recommendation

The other part of the equation is a really good set of batteries. AMGs are the way to go for relaibility and these are highly recommeded. (Again I use them)
Power Store

Not a cheap option but a proper solution, very reliable and a great safety feature. Not being able to start your engine at the start of a day out is a pain. Not being able to start it halfway through is much more worrying!

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