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Old 03-04-2013, 09:20 PM
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jigster jigster is offline
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Any reason not to run alternator wire direct to battery?

Getting ready to swap out the alternator charging lead on my '03 x10 to 4 gauge wire.

When i traced down the oem wire i found that it terminates at the starter rather than the battery, the charge then passes thru the battery cable that is on the same post. I dont imagine it matters if the alt wire terminates at the starter or goes direct to battery, but just want to make sure im not overlooking a specific reason this was done especially since it is a marine application.

Also, the factory wire doesnt appear to have a fuse or circuit breaker in it. Should i install one? If so, which end, alt or battery or both? And should i use a fuse or breaker or does it matter?

Thanks - jason
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Old 03-04-2013, 09:40 PM
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Yellow X9 Yellow X9 is offline
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Up-grade the Ground wire to 4ga as-well
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  #3  
Old 03-05-2013, 03:46 PM
gotta_ski gotta_ski is offline
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It terminates there because its easier to use that large gauge wire that is already running to the battery than to run a new wire. The current from the battery to the starter when cranking will be greater than the charging current from the alternator to the battery, so the battery cable will be plenty big enough.

Why do you want to run a new wire? I see no advantage to having an additional wire run this way. It's also another connection on the battery to deal with.

I've never seen a fuse or breaker on an alternator feed. I believe that you can damage the alternator if the engine is running and that breaker were to trip, leaving the current being generated with no place to go. That is why they say never to move a battery switch to "OFF" when the motor is running, and why some battery switches have alternator field disconnect features built in.

I'm not sure on this part, but running a separate wire this way may give you trouble if you ever have a very dead battery and need to jump it. The engine will be having to push whatever current it needs to run through a dead battery first before it can come back along the battery cable and go to the fuel pump, ECU, injectors, etc. Is it likely that this would happen? Probably not, but I like to be prepared for the worst. Again, why change the current set up? It works just fine on everyone else's boats.
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Old 03-06-2013, 09:30 AM
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jigster jigster is offline
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Quote:
Originally Posted by Yellow X9 View Post
Up-grade the Ground wire to 4ga as-well
Totally overlloked that, thanks!
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  #5  
Old 03-06-2013, 09:53 AM
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Quote:
Originally Posted by gotta_ski View Post
It terminates there because its easier to use that large gauge wire that is already running to the battery than to run a new wire. The current from the battery to the starter when cranking will be greater than the charging current from the alternator to the battery, so the battery cable will be plenty big enough.

Why do you want to run a new wire? I see no advantage to having an additional wire run this way. It's also another connection on the battery to deal with.

I've never seen a fuse or breaker on an alternator feed. I believe that you can damage the alternator if the engine is running and that breaker were to trip, leaving the current being generated with no place to go. That is why they say never to move a battery switch to "OFF" when the motor is running, and why some battery switches have alternator field disconnect features built in.

I'm not sure on this part, but running a separate wire this way may give you trouble if you ever have a very dead battery and need to jump it. The engine will be having to push whatever current it needs to run through a dead battery first before it can come back along the battery cable and go to the fuel pump, ECU, injectors, etc. Is it likely that this would happen? Probably not, but I like to be prepared for the worst. Again, why change the current set up? It works just fine on everyone else's boats.
Why I want to run a new wire....

Out of necessity.

Last year I added a second battery to my boat and roughly tripled the total amplifier watt output from the factory. I did use JL HD amps which are more efficient, so I know my total amplifier power consumption hasn't triple but it is likely substantially more than the factory two Clarions.

In addition, a third battery is in the works along with two more JL MHD amps, which at that point I will be upgrading the alternator as I'm likely already pushing my luck with what I have.

So although I proactively addressed the battery issue last year for my current setup by adding a second large 31 series AGM battery and isolated it from the starting battery, I knowingly turned a blind eye to the charging system to leave it for this year's project. The low hanging fruit to knock out is upgrading the charging wire to handle more amps, especially in light of knowing an alternator amp upgrade and third battery are on the horizon.

Reason for wanting to run the alternator leads direct to battery vs. OEM location is trying to minimize lengths of all wiring in the boat, especially high amperage lines such as the alternator, stereo, and starting leads. I can eliminate about 3-4 feet of wire if I go direct to battery vs. alt to starter to battery. I was guessing the factory ran the alt lead to the starter because Indmar probably delivers these engines to Mastercraft prewired. The simplest way to deliver a complete package would be to have everything plug and play. If the alternator wire is ran to the starter, all Mastercraft would have to do is hook up a positive battery cable to the starter, a ground to the block, and plug in the ECU. If they didn't connect the alt lead to the starter there would be a loose wire that they would need to leave hanging off at an undetermined length for each boat the motor would go in.

That's just my guess as I say, so I wanted to make sure there wasn't a safety related reason for doing this. I've managed to eliminate a ton of excess wire in my boat to date as I've been upgrading things, but just a little leery when it comes to areas where ignition/fire/explosion can be a concern.

I see your point on the fuse, so I can skip that unless I am opening myself up to a fire hazard. Given the choice, I'd rather risk burning up an alternator than burning up the boat. Thoughts?
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  #6  
Old 03-06-2013, 10:40 AM
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Tristarboarder Tristarboarder is offline
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I just added a bunch of amps (wetsounds) to my Tristar, and currently have 2 batteries (1 starting, 1 deep cycle) wired to a Perko switch. Knowing that I would be pushing a lot of power through the system, I knew eventually that it was likely that my original stock 51 amp alt would puke probably on some nice day on the water with a bunch of friends on board. To be proactive, I just installed a 105 amp alternator, which was just a "1 wire" setup. I was at my local auto electric specialty shop last week, and I asked the owner about wiring it. He said it would be more efficient just to run the wire from the alt directly to the common lug on the Perko, which is essentially just like running it directly to the battery, as in your case. I asked him about how the original wiring was, as in from the alt to a wiring bus, fuse, etc. and he said that is how it was pre wired from the factory to have a neat little package. I like my setup because I can isolate the system by turning the Perko off anytime not in use.
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Old 03-06-2013, 10:49 AM
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Tristarboarder Tristarboarder is offline
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Oh yeah, and he told me that running 8 gauge wire would be perfectly sufficient.
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  #8  
Old 03-06-2013, 11:12 AM
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Quote:
Originally Posted by jigster View Post
Getting ready to swap out the alternator charging lead on my '03 x10 to 4 gauge wire.

When i traced down the oem wire i found that it terminates at the starter rather than the battery, the charge then passes thru the battery cable that is on the same post. I dont imagine it matters if the alt wire terminates at the starter or goes direct to battery, but just want to make sure im not overlooking a specific reason this was done especially since it is a marine application.

Also, the factory wire doesnt appear to have a fuse or circuit breaker in it. Should i install one? If so, which end, alt or battery or both? And should i use a fuse or breaker or does it matter?

Thanks - jason
The charging wire has terminated at the starter since they began to use a starter. It may not have a fuse, but it may have a fusible link. If the wire looks like it only has two ring terminals, it doesn't have a link. If you add a bunch of accessories (high-capacity alternator, power amps, pumps, blowers and lights), you would need to increase the charging lead. If not, you can leave it as-is.
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  #9  
Old 03-06-2013, 11:59 AM
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Thrall Thrall is offline
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I fail to see how the battery(s) could possibly be closer to the alt than the starter but either way will work just fine as long as the wire is sized properly for the load and run length.
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  #10  
Old 03-06-2013, 12:29 PM
TRBenj TRBenj is offline
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I havent dissected a modern boat's electrical system, but all of the basic electrical systems used into the early 90's had a breaker or a fuse between the alternator output and the battery. Usually a good sized circuit breaker mounted in the engine compartment. Only the battery, starter solenoid and starter were on the unprotected side of the breaker. The alt and all the loads were on the protected side.

Adding additional wires running to components in a different manner than they were from the factory (rather than simply upsizing wires) seems to be a recipe for disaster unless you know exactly how the electrical system functions. You dont want to bypass any part of the system's functionality, and you definitely dont want to bypass any of the safety components.

Basic electrical thought process:
1. Select your wire size such that it can handle the worst case load (current draw) of the components they are feeding.
2. Size your fuse/breaker slightly smaller than the current handling capability of the wire you selected.*
3. Install the fuse/breaker as reasonably close to the source of the current as possible.

*If the wire is sized such that it can handle the maximum current that the power source is capable of providing, then it does not need to be fused. (The fuse is there to protect the wire). This is why the wire coming out of the alternator usually doesnt have one.

Remember that the battery is essentially an infinite current source. The alternator will not put out much more current than it is rated for, and is less of a concern.
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