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Old 27-05-2015, 12:40   #16
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Re: Alternator Output Lead Sizing

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Sure if you have an old leaky engine that keeps everything nice and oily so the ends don't corrode and you're not going to keep the boat for another 30 years because that's about how long it takes for the insulation to fall off welding cable
Yeah, the insulation does go after 30 years or so. Whatever you use I hope you seal the ends of your cable well.... not just crimp something on.
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Old 09-06-2015, 08:21   #17
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Re: Alternator Output Lead Sizing

[QUOTE=Maine Sail;1834765

Also don't forget that the regulators black wire is part of the voltage sensing circuit so both the red/v-sense and regulator black wires need to sense the bank directly.[/QUOTE]


Interestingly, the manual for both the reg and alt say to connect the reg ground to the alt, vice battery. I wonder why?
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Old 09-06-2015, 09:32   #18
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Re: Alternator Output Lead Sizing

1/0 wire is massive and a lot to hang on to a vibrating alternator. You can make it work if you are able to secure it to the alternator bracket so the mount vibrates the same as the alternator lug where the terminal goes and then secure the cable again as it goes away from the motor. The lugs on most small frame (if that is what it is) alternators are not really big enough for a cable that size. IMO

You shouldn't have that long a run to make so IMO I would get the right size wire and lugs and do it right. As far as mixing and matching wire sizes it shouldn't make any difference if you have a small size in the middle or whatever compared to the other pieces EXCEPT that you have to have multiple connections which is never a good thing for a high amp circuit.

You should "ground" the alternator to the same stud as the main engine DC negative "ground" and it should be lug to lug. You could also ground to the main DC common ground as well. The ground wire should be the same size as the alternator positive (or at least as big as the amps call for). They don't have to be identical if the positive if bigger than necessary.

If it were me I would put on #2 wire for both. Sell your surplus lugs on ebay or something. Don't be penny wise and pound foolish.
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Old 09-06-2015, 10:25   #19
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Re: Alternator Output Lead Sizing

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Interestingly, the manual for both the reg and alt say to connect the reg ground to the alt, vice battery. I wonder why?
Why? Because it was poorly written.....
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Old 09-06-2015, 11:02   #20
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Re: Alternator Output Lead Sizing

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1/0 wire is massive and a lot to hang on to a vibrating alternator. You can make it work if you are able to secure it to the alternator bracket so the mount vibrates the same as the alternator lug where the terminal goes and then secure the cable again as it goes away from the motor. The lugs on most small frame (if that is what it is) alternators are not really big enough for a cable that size. IMO

You shouldn't have that long a run to make so IMO I would get the right size wire and lugs and do it right. As far as mixing and matching wire sizes it shouldn't make any difference if you have a small size in the middle or whatever compared to the other pieces EXCEPT that you have to have multiple connections which is never a good thing for a high amp circuit.

You should "ground" the alternator to the same stud as the main engine DC negative "ground" and it should be lug to lug. You could also ground to the main DC common ground as well. The ground wire should be the same size as the alternator positive (or at least as big as the amps call for). They don't have to be identical if the positive if bigger than necessary.

If it were me I would put on #2 wire for both. Sell your surplus lugs on ebay or something. Don't be penny wise and pound foolish.
Rusty's alternator is specifically built to handle this type and size of wire and is far more robust than the vast majority of phenolic starter solenoids you see connected to 2/0 - 4/0 wire. The 5/16" positive post on Rusty's alt is through bolted to the rectifier not a wimpy press fit #10 stud like you'd find on a factory Hitachi alt... I wire high performance alts with 1/0 to 2/0 wire on a regular basis but these alts are designed for this...
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Old 09-06-2015, 12:42   #21
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Re: Alternator Output Lead Sizing

Rusty-
Presumably you are derating the alternator to 120A in order to run it cooler and more reliably, or to be kinder to the belt?


Consider that using the heavier cable will allow the alternator to operate at a lower voltage, which will mean lower wattage, and therefore also LESS HEAT and less load.


Be kind to your alternator, use the heavier cable if you can. Even if that means buying one length of #2 with lugs, from genuinedealz.com
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Old 09-06-2015, 12:56   #22
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Re: Alternator Output Lead Sizing

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Rusty-
Presumably you are derating the alternator to 120A in order to run it cooler and more reliably, or to be kinder to the belt?

Consider that using the heavier cable will allow the alternator to operate at a lower voltage, which will mean lower wattage, and therefore also LESS HEAT and less load.

Be kind to your alternator, use the heavier cable if you can. Even if that means buying one length of #2 with lugs, from genuinedealz.com
I'm primarily detuning to benefit the alternator, since I also installed a Grasser ribbed belt setup (aka "serpentine", though that's a misnomer in my application, since only two pulleys are involved).

I created a new route across the underside of the cockpit for the 1/0 cables (two for alt, one for starter), and finished installing them last night. As a side benefit, that created lots of free space in the primary wiring bundle.

Now I just need to finish up the regulator wiring, and I'll be ready to fire up and do some load testing.
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Old 09-06-2015, 13:44   #23
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Re: Alternator Output Lead Sizing

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Originally Posted by Rusty123 View Post
I'm primarily detuning to benefit the alternator, since I also installed a Grasser ribbed belt setup (aka "serpentine", though that's a misnomer in my application, since only two pulleys are involved).

I created a new route across the underside of the cockpit for the 1/0 cables (two for alt, one for starter), and finished installing them last night. As a side benefit, that created lots of free space in the primary wiring bundle.

Now I just need to finish up the regulator wiring, and I'll be ready to fire up and do some load testing.
Don't know if you saw this but it goes into much greater detail on the regulator voltage sensing question.

Alternators & Voltage Sensing



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