87' Merc 5.7 Competition ski alternator upgrade

[jlucas209]

So I have an upgraded audio system in my boat, I decided to upgrade my factory alternator to this unit from Amazon. It seems to be "plug and play" but I have read several places that I need to upgrade my wiring if I'm upgrading the alternator. Is this true and is it just the Orange power wire that I need to beef up that goes to the starter? I have also read that I should add a fuseable link? If so where?

Thanks,

 

[alldodge]

To use the 120 AMP ALT you will need to replace the 90 AMP fuse on the starter with a 120 AMP and increase the wire size going to the starter post.

My above statement means you have but one battery or your using an ACR to charge the second bat.

The issues with using a high output ALT could cause issues if you don't have batteries or battery banks which can accept that much output. A lead acid bat can only take so much at one time, and AGM's can take more.

Why do you think you need a 120 AMP ALT?

You want to charge the bat from the time you float around for a few hours on a 20 minute ride back to the ramp/dock?

What is your plan for setup of the banks?

 

[Scott Danforth]

depending on the distance from the alternator to the starter, you will most likely need to jump to 2 gauge as 120 amps is a lot for 4 gauge. stock wiring is 6 or 8 gauge.

if you didnt upgrade to dual v-belts, your belt will slip if you try to draw 120 amps. single V-belt is good for about 90 amp max, beyond that, they slip.

 

[jlucas209]

To use the 120 AMP ALT you will need to replace the 90 AMP fuse on the starter with a 120 AMP and increase the wire size going to the starter post.

My above statement means you have but one battery or your using an ACR to charge the second bat.

The issues with using a high output ALT could cause issues if you don't have batteries or battery banks which can accept that much output. A lead acid bat can only take so much at one time, and AGM's can take more.

Why do you think you need a 120 AMP ALT?

You want to charge the bat from the time you float around for a few hours on a 20 minute ride back to the ramp/dock?

What is your plan for setup of the banks?

Are you referring to the red wire or orange wire when you say the wire going to the starter post?

I currently have 2 batteries and a perko switch which I keep on "all" when the engine is on.

I have 10 speakers and 2 15" subs, I have my music blasting while floating around for hours "idling" my system draws a lot of power which is the reason I wanted to upgrade.

I also dont see a fuse on my starter, can you elaborate?

Dual V belts? The pulley is for a single V belt, what do you mean?

 

[Bt Doctur]

Don`t you think some people would be annoyed at YOUR choice of music.
Dual V belts? The pulley is for a single V belt, what do you mean?

He means when drawing the 120 amps, the alt requires 2 belts to be able to turn without slipping.

 

[alldodge]

There should be a 90 amp fuse on the starter post, some have removed them, but most have not. This fuse is to protect the battery if the ALT shorts out.

 

[thumpar]

I would go bigger than 120 on the fuse. It is used as a safety so anything that would cause the fuse to blow should be a little more than what you think you will push it. a 120 may blow if you are right at what the fuse can handle. I would probably go 140 or 150. If it is drawing that much something is wrong and it will blow.

It will take a while to charge a battery off the alternator. I would have gone with bigger/more batteries since even with a big alternator it won't extend your music time unless you are running the engine. If you did happened to drain a battery you would be looking at a good chunk of boating time charging it back up.

Like Alldodge mentioned separating the batteries is a good idea. Then you can listen to the music until the battery dies on the accessory side and still start the engine. On my last boat I used an isolator. They work great but do have a slight current usage of their own. I just got an ACR for my current boat. Those are a bit smarter and don't draw much at all. I didn't use a switch and not going to use one this time either.

 

[jlucas209]

There should be a 90 amp fuse on the starter post, some have removed them, but most have not. This fuse is to protect the battery if the ALT shorts out.





Sounds like you need something to keep your starting battery separated from the stereo bat when the motor is not running. Depending on how many amps/watts the system pulls you may need more then one bat for the stereo.

If you use a ACR (automatic charge relay) then the ACR will disconnect and reconnect the ALT when the motor is running. Otherwise you need to figure out how you plan to charge all bats.

Other option is an isolator but do recommend the ACR

I appreciate all the feedback guys.

So, I'm still not sure on what I should do.

Per your suggestions, I should add 120amp+ fuse to my starter (where exactly) and I need to beef up the wire going to the starter post. Is that the orange wire going from the alt to starter?? (I also tried googling to fuse and couldn't find one, anyone got a link on where to buy?)

Also isn't the perko switch just like an isolator? When my motor is off I switch to the accessory batter so I do not drain both batteries, then when my motor and music is on I keep the switch on "all"

 

[alldodge]

A switch turns things ON and OFF
A isolator is diodes encased in a heat sink. The diodes allow current to flow in one direction only.
The fuse would be between the alternator and the battery (which is normally attached to the starter post).

 

[thumpar]

The main difference between a Perko type switch and the isolator/ACR is that the Perko takes manual turning. The isolator/ACR is fully automatic. There is no chance of leaving it in the wrong position and draining the batteries and also less hassle.

 

[alldodge]

Clarification: a ACR is not an isolator

and in all fairness, the OP does not understand how electricity works. I'm trying to stay and the top level and not go into the weeds.

 

[thumpar]

I used the / as a way to show they are not the same device but how they both differ from manual Perko type switch.

 

[jlucas209]

So the fuse should go on the starter post with the wire that is going to the battery.

As for the orange wire from the alt to starter, is that ok to leave alone? From what I read I need to get bigger wires somewhere.

Thanks,

 

[achris]

So the fuse should go on the starter post with the wire that is going to the battery.

As for the orange wire from the alt to starter, is that ok to leave alone? From what I read I need to get bigger wires somewhere.

Thanks,

The fuse is to protect the battery from draining if the engine harness (or anything attached) goes to ground.. The fuse goes on the same post as the lead from the battery, but not IN that circuit. It's in the circuit AFTER the starter motor (effectively), and the main power feed from the starter post to the engine comes from the 'output' side of the fuse...

Yes, the cable that runs from the alternator to the fuse post is the one you need to increase in size. At 120A, make it BIG! Cooking that cable is a very bad idea.

Chris......

And just as an aside. That sort of audio power and volume will get you universally disliked by about 1/2 the planet. Consider fellow water users and turn it down.Do that and you'll save you ears, the wrath of anyone within 4 miles of you and your wallet. At lower volumes (read: 'sensible') you won't need to upgrade the alternator... I have a 40watt system on my boat, and it RARELY gets put up beyond 1/4 volume. Plenty loud enough!

 

[alldodge]

So the fuse should go on the starter post with the wire that is going to the battery.

As for the orange wire from the alt to starter, is that ok to leave alone? From what I read I need to get bigger wires somewhere.

Thanks,

You want/need simple, this will work, and disregard the outboard, take it as your orange alternator wire

 

[jlucas209]

Thank you I appreciate the help guys..

You guys should really stop judging people on their boats and what they do to them. To each its own, I'm a young boater in NorCal area. Almost EVERYONE has crazy loud sound systems. We tie up and party every weekend.You guys wouldn't understand if you are not from around here lol. Check out this video from last week. Hundreds of boats and not one complaint about loud music lol.

 

[jlucas209]

You want/need simple, this will work, and disregard the outboard, take it as your orange alternator wire

That's pretty much how I am set up now, other than the fact I dont have a fuse in there. Also my orange wire only goes from Alt to Starter, then a red thicker wire going from the starter to my perko. My batteries are wired just as your picture.

 

[alldodge]

In all fairness we use to do that also when I was young. The young still do it around here, they come in with there tunes blasting, and can be heard on the other side of the lake. You should know sounds travels very well on water. Now if a few boats on the other side of the water came over to your group and asked if it could be turned down a bit, what do you think would happen????

Most the time, when the kids come in, we just up anchor and go find another spot where folks are more respectful of others. It will continue to happen until the end of time, so enjoy while your young, you will be older soon enough.

Just something to think about next time your parting, take time to look around as what is happening around the area after you all get going. If your always in the same spot, then maybe not so much, folks learn to stay clear if it isn't their thing

 

[alldodge]

I should edit my previous simple pic, the fuse should be on the Orange alternator wire going to the starter post. The fuse is to protect the battery from the alt if it shorts out. You can do it without fuse, just less protection