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Discussion Starter #1
I am planning on upgrading my grounds and battery/alternator wiring. I have read on other sites where one should have a fuse in the wire that runs to from the alternator to the battery. The idea was to have a fuse with a lower rating than the wire so that if it were to dead short or something the fuse would blow rather than melt the wire.
I am looking for opinions on this.
Also, I can't find a positive answer on running this wire in addition to the original. I read somewhere that the wire has some sort of a capacitor inline somewhere below the factory air box. Can anyone comment on this?
I would prefer to leave the original wire in place and run an additional wire.

Thanks,
Shawn
 

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there is already such a fuse called a fusable link that is in place in every other car I've seen - I'll assume VW is no exception.

you do NOT need to upgrade the wiring from the alternator to the battery. spend your money and your time doing the big three grounding upgrade and be done with it.
 

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When i did mine i did from the battery to the front and back of the head, to the ABS module, and then to the chasis all from the battery. i didnt do the alternator because of is already being bolted to the block and i grounded the head twice,

heres the website that i used as a guild only i changed the alternator to a chasis ground
http://home.comcast.net/~hhong4/grounding.htm
 

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Discussion Starter #6
Well, I guess I am going to have to make some waves here :poke: I tend to disagree that the alternator wire is not important enough to upgrade.
The definition of the Big Three is:
The "Big Three" upgrade means improving the current capacity of three cables: 1) alternator positive to battery positive, 2) battery negative to chassis, and 3) engine ground to chassis.
The Alternator is supplying the power to the car, not the battery. The battery is for starting the car. The battery can act as a buffer if the demand exceeds the supply, but should not be relied on as a power supply. So basically the entire car is being powered by the one 8ga power wire that runs from the alternator. In the Passat, this wire is also extremely long, which also decreases its performance. I feel that this wire is important enough to not be overlooked.

Respectfully,
Shawn
 

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What performance are you referring to? Voltage drop? Ampacity? If you are having problems, remove the wires and clean all the connections especially all the grounds q_s, mentions. First, it's not 8 AWG wire from the battery to the alternator. It's 16 mm^2 wire running from the alternator to the battery which is equivalent to about 5 to 6 AWG. Second, the ground wire is 25 mm^2 equivalent to 3 to 4 AWG. So even at full load (assuming your alternator is a 90 A), the total voltage drop of the wires for the supply circuit is maybe 0.3 volts or so. Third, the ampacity of the stock wiring exceeds the 90 Amps.

So unless you are upgrading your alternator and adding significant load there is really no need to replace any of the wires you mention. You are simply wasting your money on a useless mod.
 

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Discussion Starter #8
I have not yet had a performance drop, perhaps that was a poor term to use. As far as the alternator using 8 awg, I was just guessing on that. My point is that up sizing the grounds is a great idea, but the supply wire should not be overlooked. I currently have the Valeo 90 amp unit, but am planning to upgrade to the 120 amp version. I am also adding a modest system of ~800 RMS.

Shawn
 

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Well, I guess I am going to have to make some waves here :poke: I tend to disagree that the alternator wire is not important enough to upgrade.
The definition of the Big Three is:
The "Big Three" upgrade means improving the current capacity of three cables: 1) alternator positive to battery positive, 2) battery negative to chassis, and 3) engine ground to chassis.
The Alternator is supplying the power to the car, not the battery. The battery is for starting the car. The battery can act as a buffer if the demand exceeds the supply, but should not be relied on as a power supply. So basically the entire car is being powered by the one 8ga power wire that runs from the alternator. In the Passat, this wire is also extremely long, which also decreases its performance. I feel that this wire is important enough to not be overlooked.

Respectfully,
Shawn
Yes, but current flows from negative to positive...
 

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The OEM wiring should accommodate the 120 Amp alternator. It's basically right on the rating but the rating is conservative. With a larger alternator than the 120 Amp, you should definitely upgrade the wiring. If it were me, I'd probably up the wire size from the OEM 5-6 AWG to 2 AWG which should be plenty of capacity on the supply size and allow for a future upgrade to a 180 Amp alternator.

As far as running a parallel connection between the alternator and battery, a problem that you could encounter would be that if a path developed high resistance then a portion of the current that would normally flow through it would be shunted to the other wire possibly causing an overload. So, for parallel paths you generally want each wire by itself to be able to handle the full load. Thus, it's best to replace the OEM wiring with a bigger wire. But, in this case it should be okay to run a second wire since the OEM wiring can handle the 120 Amp alternator.

Also, I don't believe that the Passat has fusible links. The links are usually near the battery + terminal and are a different color wire covering. Bentley's does not show them in the wiring diagrams and I looked at my Passat and can't see anything that looks like a fusible link. Maybe some else knows for sure. Also, don't know why there would be a capacitor on any supply line from the alternator to the battery. The battery is, in essence, a huge capacitor filtering voltage spikes and noise.
 

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Discussion Starter #11
I would have to agree with you on the capacitor. I can't see why there would be one. I have not torn mine out of the loom yet to investigate it. I believe the wire "should" run from the battery positive to the starter, where another wire goes from the starter to the alternator.
I think I am going to replace the current wire, with either 4 or 2 guage. Probably 2 guage so it will be sufficient if I do go to a 180 amp alternator in the future. I may put a fuse holder in there just 'cause with maybe a 200 amp fuse.
As far as grounds, I think I will replace the factory negative battery terminal with a 0 guage. I will leave all other stock grounds in place and add a second from chassis to engine also in 0 guage.

Shawn
 

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with a system that is capable of producing 800 WRMS, the max instantaneous current you'll see would be about 57 amps. that would be a momentary current output, because very seldom would you see that 800 W as output from any amp.

as for fusible links, there may not be any on the Passat; I haven't dug thru the wiring diagrams that deeply - but if you say it is so, ken, I'd believe it. on a previous car, there was a fusible link hanging off the alternator (the battery was on the opposite side of the car); when it blew, I lost the ability to charge the battery and ran it down!

my present system is powered with a 5 gage wire. I have a Viper d1200.1 for the sub (presently 800W max with the sub as a 2 ohm load), and a the front channels of a JL 300/4 for my front speakers. only at full load (the max volume I'll ever listen to it at) do I ever see any dimming of the front headlights, and that's only at idle. oh, and I have a V6, so I have a 120 amp alternator.
 

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YOu guys don't want to know how much current I can pull during peaks and I haven't done the big 3. The only ground I touched was the battery to chassis because I HAD to.
 

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oh. c'mon, Paul, tell us already! :rolleyes:
 

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Yes, but current flows from negative to positive...
Irrelevant. Current flows in a loop and a weak link in any part of the loop will cause problems, that's all that matters.

Anyway, it strikes me that if the alternator is capable of supplying as much output as the battery (which it must be capable of doing, since it can power everything the battery can, and more), then it needs wiring of the same gauge that the battery has. 8ga on an alternator is a joke. I have thicker wiring on the electrical system in my battery-powered remote control car.
 

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Irrelevant. Current flows in a loop and a weak link in any part of the loop will cause problems, that's all that matters.
It's NOT irrelevant. You're forgetting that the chassis is the main ground conductor. You can run a remarkably small cable since it's only going from the components to the chassis.

8ga on an alternator is a joke.
For that short a run it's PLENTY big enough.

I have thicker wiring on the electrical system in my battery-powered remote control car.
No you don't. I have 4, and NONE of them has wiring over a 12 gauge.
 
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