Battery position in boat

[mungindi]

Morning,
I'm at the stage of trying to work out the battery placement in my boat, I'am going to have 2 batteries one for starting and the other a house battery for the electronics and the like. These are connected to a BEP 716 vsr unit so they can be run in parrellel if the need should arise to start the motor.
I was going to house the batteries under the centre console but have been advised it would be better to house the starter battery at the back of the boat as near to to the transom as possible to avoid voltage drop. to do this I would have to modify the transom storage area are a bit which at this stage of the build would be a pain in the arse.
The distance from the console to the motor is just on 2.8 mts would a batterry that distance from a motor suffer to much of a voltage drop and be a problem, the console is pretty big so there is no shortage of room to put a far lump of a starting battery in there if needed. The motor it will be turning over is a new DF 140hp Suzuki . Any help or advice on this would be greatly appreciated as I really want to get this boat finished and on the water as soon as possible
Thank's
Gary

[Fish'n Junky]

Ideally, have it as close as possible to the motor.

The voltage drop you're talking about is caused by the inherent resistance of the cable used to connect the battery to the motor. The end result is less current being available to turn the engine over.
This can be offset by the use of a larger diameter cable, although this brings into consideration other factors such as will a larger diameter cable fit where you want to run it, and also larger terminal connectors will be required.

The cable and it's connectors are the key as you want to minimise the resistance between the battery and the motor to ensure all possible voltage is applied to the starter, and that current draw is ample to turn over the motor.
A bigger battery will mean squat if the resistance of the cable is high.


It can be done, but I'd look at keeping it as close as possible!
It's just easier!

[finga]

I disagree with the batteries have to be down the back theory.
Bung the batteries where it's convenient for you to inspect or change or disconnect or mount or....anything.
The cost of a bit of cable is more preferable to me to the swearing and cursing of getting to batteries when you want too.
A 2.8m run is nothing for some correctly (+50%) sized cables unless your got a high compression V8 in the boat.
Actually where are the batteries in the V8 supercars??? In the back??

My reasons for putting batteries at the back is purely for the softer ride for the batteries for longevity.

If one battery is going to be under the consul why not bung both there?
If one battery is under the consul and you want to be able to use it as a start then the bigger cable has to be run to the back anyways otherwise problems will most likely happen when you want it to work the most.

What size outboard are you talking about?
What length of cable comes with the motor standard?

[mungindi]

G/day Fish'n junky , finga,
I have plenty of room to run larger size cables if needed , it shouldn't be a problem getting larger size cable connectors to fit the size of the cable or battery terminals if that is what is needed hopefully.
The motor is a new 2008 DF 140hp suzuki to be honest Im not realy sure what lentgh cable come with the motor but the wiring harnes is a bit over 6mts in length if my memory is correct.
Thank's for the input fellas I'm just trying to keep this boat build moving as I'm pretty keen to get this boat finished and on the water.
The main reason I'm not overly looking forward to modifing the transom area is because it would mean cutting out an area and having to re-glass and paint it again. Thank's again for your'e help and advice I appreciate it
Gary

[Noelm]

Finga has it right, the back of the Boat is better for the Battery, far less banging and bouncing back there, but with adequate cables, you could put it in the bow if you so desire, good clean connections, quality cable (not from supercheap) and terminals and your set, sure as close to the Motor is best, no question about that, but it also needs to be a compromise with usability.

[cormorant]

Not cheap but you can actually get tinned battery cable and It is worth it if you are keeping the boat long term as if you have correctly swaged or soldeed fittings very little loss will happen over time.

If one is start and the other house you don't need huge cables going to the house battery unless you are running a leccy off it. Think about size of leads on a battery charger. If you need to use the house to start the motor then just pull it out of bracket and either jumper leads or move it to where start battery was. You do carry long Jumper leads so you can help or be helped if desperate?

Now VSR- these can be good or bad
Good- they get one battery chargedand then the second battery gets charged - that's the theory

Bad - reality depending on brands and battery types- 1st battery gets charged - then VSR opens and joins 2 batteries together - if second battery has an issue it can drain 1st battery - neither get full charge.

If either battery has lost a plate you can see where I am coming from

If 1 st battery has an issue the VSR may never change to second battery and give it any charge

Some of the newer batteries ( calcium ones and gels) require higher charging voltage to get a full charge . VSR aren't designed to fully maintain these batteries.

Many a 4wd has been stuck due to a VSR so understand what you are buying and it's limitations.

You really do want on a boat in an emergency is 2 seperate independent batteries. Some of the later motors have a better VSR set up in their Dual battery charging option accessory kit that can be bought for the motor rather than trying a aftermarket one.

I am sure a electrics guru can add to this

[Noelm]

very true, I have never really been a fan of Electronic "gizmos" in Boats, might be OK in a Car, but salt spray and crap soon takes it's toll, far better off to have a simple two battery setup, even if it means charging the "house" battery every now and then, unless you have an Electric Motor, then a good sized Battery will last for yonks in a standard old trailer Boat with "standard" electrics/electronics fitted