Wire Guage for Dual Battery Setup

[Splash]

Hi Team.

What guage wire do u rec. to use in circuit shown in attached link:

http://bluesea.com/category/2/productline/overview/329 (http://bluesea.com/category/2/productline/overview/329)

Splash

[peterbo3]

The same size as your battery cable with the the same lugs.

[cobia]

hey mate 8Gauge should be enough..its rated to about 55A give/take some...thats what my dual battery system is using in my car and its made by tjm..

[MitchCalcutt]

Hi Team.

What guage wire do u rec. to use in circuit shown in attached link:

http://bluesea.com/category/2/productline/overview/329 (http://bluesea.com/category/2/productline/overview/329)

Splash
Hi Splash
I read the product overview which would lead me to believe you will be putting 120amps through the system at times when you start you motor. It appears to be a marine surge protector of sorts. Anything with a current load of 120amps is going to require cable that will take 120amps and no less as the cable will heat up rapidly and begin to burn.
I strongly recommend you take the specks to a marine electronics expert before installing it or you might just be having a BBQ at your boats expense.
Take care
Mitch Calcutt

[TheRealAndy]

Hi Splash
I read the product overview which would lead me to believe you will be putting 120amps through the system at times when you start you motor. It appears to be a marine surge protector of sorts. Anything with a current load of 120amps is going to require cable that will take 120amps and no less as the cable will heat up rapidly and begin to burn.
I strongly recommend you take the specks to a marine electronics expert before installing it or you might just be having a BBQ at your boats expense.
Take care
Mitch Calcutt


I can do the maths if required. A few things need to be considered such as current, max permissible voltage drop, length of the run. Temperature can also affect calcs, but unlikely to be a significant factor unless its stuck in an engine room.

[oldboot]

simple rule of thumb.

10 amps per square mm.... minimum

so if you are drawing 120 amps...... 12 mm2 minimum which is close to the 6 guage in the american terms.

personlay I'd go 16mm2

with extra low voltage systems ( 12 v) it does not pay to be cheap on the wire.

You problay need to be looking at battery cable or a welding cable.

the welding cable will be flexible & get someone to crimp the lugs for you.

cheers

[PWCDad]

Real Andy is on the money there .....

To size wire .....

Amps drawn ...

Total distance of wire run .... (that includes earth return) so if you run 3 metres of positive to a bus, say, the run is really 6 metres because of 3 metres of earth.

As far as acceptable voltage drop goes ... I use 200 milliamp as a max drop over between measured voltage at battery verses measured voltage at bus or from alternator to battery ..or from battery to electric motor. 150 mA is even better.

Most 4WD cables I've made up are 25-32 sq mm for longer runs to Andersen Plugs etc... to get the 200 milliamp drop as max (once again depends on run length/amps drawn).

If doing a marine cable .... its the same cable but I use Carroll Terminals (expensive) via its specific crimper ... then water sealed at the cable/terminal interface with double wall epoxy heatshrink .... this makes the cable virtually submersible. See pic.

Regards
PWCDad

[FrankFWM]

PWCDad and TheRealAndy are correct, It comes down to a number of factors like they said regarding the distance of the wiring from the battery including the negative run as well as the positive run and the amount of amps and acceptable voltage drop.

See below for a copy of the ABYC standard relating to this subject - you can use this as a guide...

I also only use tinned marine wire to avoide additional resistance as the wire ages in the salt water environment along with waterproofing the joints to the connectors etc. using something like liquid tape.

:)

[Splash]

Thanks boys - great posts!

Do both batteries have to be same amperage?

I have one(1) crank battery @660CCA and another smaller auxilury battery (NPH 18-12).

Can I link these up together - or should I simply have 2 crank batteries?

Splash

[Splash]

I will be using 6AWG (16mm2) for both relay and isolator shown in circuit (first post) - but what guage should I be using for the isolator to Auxiliary switch board shown on top left corner of diagram?

Splash

[Splash]

ok team - i did the deed - made up circuit with brand new welding cable - good as gold!

Now, what happens to the -ve terminals on both batteries shown in the link in first post?

And, can I place two batteries next to each other or do they need to be placed apart by a certain distance?

SPlash

[Splash]

Team,

This new link shows where the -ve terminals go.
http://bluesea.com/files/resources/instructions/990310020.pdf

I see a rectangular bank of 4 studs which is earth.

Is this rectanular bank a standard item with part number?

Where should this earth bank be located on the boat?

Must I use the same same bank for both batteries or can I have separate earth points for each battery?

Splash

[finga]

Mate be careful with that picture.
It shows a starter and an alternator in what looks just like a starter.
Outboards do not use the body of the boat as a return.
All the negative wires are bonded together to get the return path. Do not use the hull as a return.

[Splash]

thnaks Finga.

Where then should I mount this powerbar earth bank?

SPlash

[finga]

as close as practical to the batteries

[Splash]

When u say "don ot use the hull as a return" - what exactly do u mean?

Is it still ok to use the BLUESEAS powerbar studded bank I purcahsed?

What if I have each battery on either side of boat - where then should this earth bank be?

what are the potnetial dangers of having each battery sitting next to each other?

Splash

[finga]

When u say "don ot use the hull as a return" - what exactly do u mean?

Don't use the hull as the negative return from the motor or any auxiliaries.
Use a black wire for the negative to the motor and all auxiliaries.
There should be no wires connected directly to the hull

Is it still ok to use the BLUESEAS powerbar studded bank I purcahsed?
Yes definitely.


What if I have each battery on either side of boat - where then should this earth bank be?
Place the bar where convenient approximately mid way between them

what are the potnetial dangers of having each battery sitting next to each other?
None really. The same dangers as a single battery sitting in the boat.
That is if there is not great temperatures involved.
Most batteries sit side by side. But not all.

Splash

Cheers then
Scott :D

[Splash]

Thanks Scott.

I am having trouble understanding the difference between the powerbar bus bar being mounted to hull (and being ok) and wires connecting directly to hull (and being not OK). What's the difference between the two mounting principles?

My current setup is a basic one crank battery and a baby battery for all auxiliaries.

With my newly proposed circuit dual setup I have now fully commitited to, can I use the existing +ve battery cable from crank battery to one of the +ve studs on the isolator earlier reffered to in this thread?

And, in light of your last post, where would the -ve cable from crank battery end up?

Apologies for gnawing at you like this but I am nto electrically minded and want to get it right first time - esapecially when it comes to marine applications!

SPlash

[driveon]

Hi Splash, if your not use to working with 12 volt wiring it can seem a bit strange.

If you haven’t already got one, you need a bus bar for the negative cables ( wires ) to be bridged together.

This bus bar can be a proper bus bar or just a single earth stud, a single isolated bolt.

You then run a BLACK cable from the negative terminal of your cranking battery to the bus bar and then another BLACK cable from the bus bar to the negative terminal of your auxiliary battery.

These two BLACK cables MUST BE the same size or bigger than the RED cable you use to connect up the positive terminals of the two batteries and the dual battery controller.

You then need to run a BLACK wire from the dual battery controller’s negative or earth terminal to the negative bus bar ( where you connected the two thick BLACK cables running from you two batteries negative terminals ). This wire can be a thin wire as it won’t be carrying much current.

With you positive cables, run a thick RED cable from the cranking battery’s positive terminal to the input of the dual battery controller. Run another thick RED cable from the dual battery controller’s output to a positive bus bar ( or stud ), then a thick RED cable to the auxiliary battery’s positive terminal.

To wire each one of your accessories, for example say your CB. Run a Red wire from the positive bus bar ( stud ) straight into an inline fuse holder and then to the positive input of your CB.

Then run a Black wire from the negative of your CB to the negative bus bar ( stud ).

Run the wires for each accessory the same way.

Although you could actually use the auxiliary battery’s terminals for your bus bar it simplifies everything when you need to work on the auxiliary battery if you have a bus bar set up.

A point of safety, with ANY dual battery set up, before you do any work on the 12 volt wiring, you MUST REMOVE BOTH batteries negative terminals BEFORE you start any work.

You can leave the positives in place and only when you have finished should you reconnect the negative terminals.

Cheers

[Splash]

WOW - thanks Driveon!

WOudl you be abel to draw up a circuit for me to explain your post?

SPlash

[Splash]

ANy chance of a wiring diagram DRIVEON?

SPlash

[driveon]

Hi Splash, I will draw one up for you but it will not be fore few days, I’m absolutely flat out at the present.

:-X :-X :-X :-X :-X :-X :-X :-X :-X :-X

[Splash]

Tahnsk mate - Merry XMAS!

[TheRealAndy]

Splash, where abouts are you? Northside?

When people say dont use the hull as a return they mean do not connect anything with a direct electrical connection to your boat. The busbar should be mounted on plastic, with no electrical connection to your boat. In saying this, I assume you have an aluminium boat. Stray currents in metal boats can do all sorts of strange things, and you can end up with corroded holes in the worst places.

[Splash]

Thansk Andy,

I have a fiberglass hul lin fact.

I have the busbar now.

In light of what you are saying, I assume I can moun this anywhere as long as no electrical conenction exists.

SPlash

[Splash]

Hi DriveON.

Any chance of compleing that schematic for me?
Thanks

Splash

[TheRealAndy]

Something along the lines of... Crudely drawn up in publisher because i dont have visio or any cad tools on this PC.

Yell out if you need more detail.....

[Splash]

Thakns Andy for that great special extra effort!

Does this schematic depict DriveOn's description?

Will deciper it and let u knwo how i get on..

Splash

[TheRealAndy]

Follows driveon's description more or less. I excluded a positive busbar as i think most of theose fused switchboards you buy have the positives commoned up like a busbar anyway. If your switchboard is not fused, then use inline fuses from the switches the radios and lights. Always keep spare fuses handy as well!

Its may also be worth placing a fuse in the wire that runs from the house battery to the switchboard. If you do, mount this fuse as close to the battery as possible.

[driveon]

Hi Splash, my apologies, I just haven’t had time to catch up with my own work yet and TheRealAndy’s diagram is spot on.

Cheers and again, sorry for being so slack.

[Splash]

No probs DriveOn - XMAS can be frantic for many.

Thanks for you detailed assistance an dbcaked up by Andy.

Will let u know how i get on.

Cam