Adding alternator wires. Big-3

[Kamilo]

Iam planing to upgrade my alternator from 55 to 105-120 amp on mercruiser 5.7 carb. In car audio it is called big-3 wire upgrade.
Should i also add wires from alternator straight to battery and negative to negative to engine ground also instead chassis ground connect battery negative to negative on alternator. 120amp fuse on positive from alt to battery?
Thnx!

 

[Kamilo]

Re: Adding alternator wires. Big-3

Pls help

 

[Slide]

Re: Adding alternator wires. Big-3

In a boat this is just the "big 2." Alternator to battery positive, battery negative to engine block. The block is not in turn grounded to the hull.

DO NOT put a fuse on your alternator to battery lead. Size it right.

 

[Kamilo]

Re: Adding alternator wires. Big-3

In a boat this is just the "big 2." Alternator to battery positive, battery negative to engine block. The block is not in turn grounded to the hull.

DO NOT put a fuse on your alternator to battery lead. Size it right.

Thank you!

 

[Kamilo]

Re: Adding alternator wires. Big-3

Would it be bad to put also connection from negative on battery to negative on alternator?

 

[Joel_CA]

Re: Adding alternator wires. Big-3

Would it be bad to put also connection from negative on battery to negative on alternator?

Its not necessary to run a ground from the battery negative to the alternator since the alternator is already grounded being bolted to the block. You should, however beef up the ground from the block to the battery negative to match the same gauge as the battery positive to alternator.

J

 

[Kamilo]

Re: Adding alternator wires. Big-3

Thnx!

 

[NYBo]

Re: Adding alternator wires. Big-3

You should, however beef up the ground from the block to the battery negative to match the same gauge as the battery positive to alternator.

J

That wire should already be plenty big enough since it carries the current load from the starter.

 

[Slide]

Re: Adding alternator wires. Big-3

That wire should already be plenty big enough since it carries the current load from the starter.

It needs to be the same gauge as the battery positive to alternator.

 

[Kamilo]

Re: Adding alternator wires. Big-3

Thnx!

 

[bruceb58]

Re: Adding alternator wires. Big-3

It needs to be the same gauge as the battery positive to alternator.

No, the negative battery cable needs to be the same size as the positive wire to the starter. In other words, it doesn't need to change.

 

[Slide]

Re: Adding alternator wires. Big-3

No, it needs to be the same size as the positive wire to the starter. In other words, it doesn't need to change.

It absolutely does need to be the same gauge, unless the positive to the starter is for some reason larger. In that case both need to be larger.

 

[bruceb58]

Re: Adding alternator wires. Big-3

unless the positive to the starter is for some reason larger.

Of course the positive to the starter is going to be larger than the alternator wire...that was my point! The OP's battery cables are probably already at least 1 or 2 gauge wires. You think the alternator is putting out more current than a starter draws?

The OP has a 357 mercruiser. Even my 90 HP Mercury outboard has 4 gauge cables on it.

For a 100Amp alternator, he only needs an 8 gauge wire going to it. His battery cables are already going to be way bigger than that.

 

[Slide]

Re: Adding alternator wires. Big-3

Of course the positive to the starter is going to be larger than the alternator wire...that was my point! The OP's battery cables are probably already at least 1 or 2 gauge wires. You think the alternator is putting out more current than a starter draws?

The OP has a 357 mercruiser. Even my 90 HP Mercury outboard has 4 gauge cables on it.

For a 100Amp alternator, he only needs an 8 gauge wire going to it. His battery cables are already going to be way bigger than that.

Regardless of what loads he will realistically see, his battery negative and positive leads must be the same gauge. You do not want unequal voltage drop in that circuit. Because OP mentioned "big 3" automotive, I'm assuming he's adding a large stereo or other heavy duty electrical equipment and feels he needs heavier duty battery cables. Beefing up these cables is a common fix for voltage drop problems from heavy stereo loads.

 

[bruceb58]

Re: Adding alternator wires. Big-3

Regardless of what loads he will realistically see, his battery negative and positive leads must be the same gauge.

Of course...that is what we have been saying.

Positive and negative battery cables...same size. Therefore , keep what he has.

New alternator wire ...8 gauge.

 

[Slide]

Re: Adding alternator wires. Big-3

Of course...that is what we have been saying.

Positive and negative battery cables...same size. Therefore , keep what he has.

New alternator wire ...8 gauge.

"Big 3" upgrade implies he is getting larger battery cables.

 

[sam am I]

Re: Adding alternator wires. Big-3

Iam planing to upgrade my alternator from 55 to 105-120 amp on mercruiser 5.7 carb. In car audio it is called big-3 wire upgrade.

New alternator wire ...8 gauge.

Thinking JUST a tad bit higher than 8AWG, more like 3 min to 2, 1, 1/0 would be wiser considering the proposed alt's current capabilities

 

[bruceb58]

Re: Adding alternator wires. Big-3

Almost every alternator manufacturer recommends 8 gauge for a 100A alternator. The facts are that that alternator will likely never be putting out 100A and if so, only for a short time. If you want to be conservative, 4 would be plenty.

On boat engines(Volvo, Mercruiser) and even in your car, the wire size that comes standard is 10 gauge for a 60A alternator if you want to compare.

Could actually just run another 10Ga wire in parallel and you will be fine.

 

[sam am I]

Re: Adding alternator wires. Big-3

You'll tend to typically find more and more and even in the past, the HO alt's such as this, the manu's have since "up'd/recommending that into the 2's and even into the 1/0's, short term or not, it tends to be based on what the device is capable of during standard/rated output.

 

[bruceb58]

Re: Adding alternator wires. Big-3

You'll tend to typically find more and more and even in the past, the HO alt's such as this, the manu's have since "up'd/recommending that into the 2's and even into the 1/0's, short term or not, it tends to be based on what the device is capable of during standard/rated output.

Post a link to the manuals. Balmar recommends 8 gauge for a 5 foot run to a battery with 100A. If you are using remote sensing(which you should) , the little bit of voltage drop gets compensated for anyway.

Here is one example:
http://www.tuffstuffperformance.com/pdf/1-wire_alternator_instructions.pdf

Depends if remote sensing will be used and he wants to get full 100A out of it. The drawback of voltage drop is that full current won't be produced, not overheating of the wire. Without remote sensing, I would bump it to 4 gauge.