Alternator charge wire sizing - Chevelle Tech
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post #1 of 9 (permalink) Old Dec 28th, 15, 5:03 PM Thread Starter
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Vince
 
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Alternator charge wire sizing

Can someone explain to me why the factories use such a small charge wire with a larger alternator? For instance, my Yukon has a 145a alternator, yet the charge wire appears to be a 12g (or smaller) fusible link. How does 145a flow through that w/o burning up. Another example is my 96 Mustang, which comes with a 130a alternator. It uses 2 fusible links, probably 14g or 12g also. There seems to be a reason for this.

But yet, when upgrading an alternator there is a lot of talk about up-sizing the charge wire to like 1/0 wiring to get the max benefit of the alt.

Do the hot rodders know something the factory doesn't???

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post #2 of 9 (permalink) Old Dec 28th, 15, 7:09 PM
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Rob
 
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Re: Alternator charge wire sizing

You won't see a fusible link on my car, Ron Francis says they aren't the way to go.

8 gauge is about the right size for the charge wire.

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post #3 of 9 (permalink) Old Dec 28th, 15, 8:26 PM
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Re: Alternator charge wire sizing

Quote:
Originally Posted by 69-CHVL View Post
Can someone explain to me why the factories use such a small charge wire with a larger alternator? For instance, my Yukon has a 145a alternator, yet the charge wire appears to be a 12g (or smaller) fusible link. How does 145a flow through that w/o burning up. Another example is my 96 Mustang, which comes with a 130a alternator. It uses 2 fusible links, probably 14g or 12g also. There seems to be a reason for this.

But yet, when upgrading an alternator there is a lot of talk about up-sizing the charge wire to like 1/0 wiring to get the max benefit of the alt.

Do the hot rodders know something the factory doesn't???
The first question I have is on the Yukon with the 145A alternator is there just one fusible link on it's output post ?. If it is one, what size wire does this then connect to ?.

I'm unsure as to some characteristics of how a fusible link works but everything I've read has the fusible link being a certain size smaller than the wire it is connected to. What I have yet to find is for a particular size fusible link to be connected to a wire, how does the length of the fusible link affect things. I have to think a 4" long piece of let's say 12 gauge fusible link will melt apart at some amperage flow and over a particular time frame but how does this change, or does it, when the same 12 gauge fusible link is let's say 8" long. I have to think the 4" will perform differently than the 8" length.

Another thing you might be seeing is, you say it looks like a 12 gauge fusible link. I wonder is this just looking at the outside diameter of the link or what ?. Maybe this link has a thinner wrapping on it that in previous designs. I know in the car audio marketing you can have two wires having the same outside diameter dimensions but one could have a larger core wire in it with a thinner insulation around it.

As far as you hearing about upgrading the charge wire to a 1/0, it may or may not do anything. It's all how things are now or if things get changed, would this upgrade even be required. GM designed what you have to work (or you hope they did) and if you were to later add some more electronics into the vehicle, this alternator wire upgrade may be needed. At that point you might also have to upgrade the ground connection like what people in the car audio business call the "Big Three".

Some of the newer GM vehicles have computer controlled alternators and maybe the GM design you are seeing on your Yukon allows for the wiring they have attached to the alternator to work. The computer may allow the alternator to put out let's say 145A for a particular amount of time but then the computer backs it's output down so the fusible link does not melt apart.

Jim

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post #4 of 9 (permalink) Old Dec 28th, 15, 10:18 PM
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Re: Alternator charge wire sizing

You need 6" min for link and a 12 gauge link for 8 wire. Mark at M.A.D. gave me this when I talked with him. Link should be four sizes smaller than wire it is protecting.
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post #5 of 9 (permalink) Old Dec 29th, 15, 9:22 AM Thread Starter
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Re: Alternator charge wire sizing

Quote:
Originally Posted by Jim Streib View Post
The first question I have is on the Yukon with the 145A alternator is there just one fusible link on it's output post ?. If it is one, what size wire does this then connect to ?.

I'm unsure as to some characteristics of how a fusible link works but everything I've read has the fusible link being a certain size smaller than the wire it is connected to. What I have yet to find is for a particular size fusible link to be connected to a wire, how does the length of the fusible link affect things. I have to think a 4" long piece of let's say 12 gauge fusible link will melt apart at some amperage flow and over a particular time frame but how does this change, or does it, when the same 12 gauge fusible link is let's say 8" long. I have to think the 4" will perform differently than the 8" length.

Another thing you might be seeing is, you say it looks like a 12 gauge fusible link. I wonder is this just looking at the outside diameter of the link or what ?. Maybe this link has a thinner wrapping on it that in previous designs. I know in the car audio marketing you can have two wires having the same outside diameter dimensions but one could have a larger core wire in it with a thinner insulation around it.

As far as you hearing about upgrading the charge wire to a 1/0, it may or may not do anything. It's all how things are now or if things get changed, would this upgrade even be required. GM designed what you have to work (or you hope they did) and if you were to later add some more electronics into the vehicle, this alternator wire upgrade may be needed. At that point you might also have to upgrade the ground connection like what people in the car audio business call the "Big Three".

Some of the newer GM vehicles have computer controlled alternators and maybe the GM design you are seeing on your Yukon allows for the wiring they have attached to the alternator to work. The computer may allow the alternator to put out let's say 145A for a particular amount of time but then the computer backs it's output down so the fusible link does not melt apart.

Jim
Its just one fusible link coming off the alt. but it's only like 6-8" and its connects directly to the positive battery/starter cable.

I'm sure the 145a rating is just a max potential and it would only by for a very short period of time. These guys with stereos and such probably have a more continuous demand I guess which would warrant the heavier charge wires. Some of the newer GM (07+) have 160a alternators with that little 12g wire, and their loaded down with electronics I will have to assume that the normal operating amps are WELL below any max threshold.

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post #6 of 9 (permalink) Old Dec 29th, 15, 9:23 AM Thread Starter
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Re: Alternator charge wire sizing

Quote:
Originally Posted by saltygog View Post
You need 6" min for link and a 12 gauge link for 8 wire. Mark at M.A.D. gave me this when I talked with him. Link should be four sizes smaller than wire it is protecting.
That makes sense right there. I think auto wire is rated higher than household wire, so 12g auto is rated at like 40+ amps I believe.

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post #7 of 9 (permalink) Old Dec 30th, 15, 8:58 PM
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Re: Alternator charge wire sizing

The ability for a wire to carry current varies with:

The material the conductor is made out of

The temperature in which the wire must operate in

The length of the wire

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post #8 of 9 (permalink) Old Dec 30th, 15, 11:28 PM
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Re: Alternator charge wire sizing

well 14 gauge (15a circuit) house wiring can handle 1800 watts
165 amps at 12v is around 2000 watts. Doesn't seem like a problem with 12g wire.
Is my math wrong?
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post #9 of 9 (permalink) Old Dec 31st, 15, 12:51 AM
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Re: Alternator charge wire sizing

Quote:
Originally Posted by RamIt View Post
well 14 gauge (15a circuit) house wiring can handle 1800 watts
165 amps at 12v is around 2000 watts. Doesn't seem like a problem with 12g wire.
Is my math wrong?
Well, kinda. A given size wire has a certain amount of resistance per foot. Smaller wire has more resistance to current flow which translates to heat as current increases. A larger wire has a smaller resistance and therefore less prone to heating for a given current flow.

For wire sizing purposes, an amp is an amp. Amp rating for a given size wire will vary based on rated operating temperature. Voltage and temperature rating for wire is determined by level of insulation. Your watts numbers are a measure of the power consumed by the load (lights, fans, etc.), which is amps x volts dropped across the load.

Having said all this, the load can do more work with a higher voltage for a given amp draw. That's the reason high voltage is transmitted through the power grid and stepped down via transformers at your utility pole; it allows smaller wiring to be used efficiently over long distances.

Wiring is sized such that the wire itself doesn't become a significant part of the load, wasting power needed by the load it feeds.

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