# Fusing big 3 upgrade?



## WinWiz (Sep 25, 2013)

Yesterday I installed a new battery and decided to do the big 3 upgrade while I was at it.
The stock wire from the 75A alternator was connected to the battery through the fuse box located just beside the battery. I located a 80A fuse between the input from the alternator and the output to the battery. But when I tried to disconnect the fuse I could still measure connectivity between the to sockets on each side of the fuse. I don't get it, what's the purpose of a fuse if the fuse can't break the connection??
My 30mm2 (2.5 awg) cable was way to big for the fuse box so I decided to leave the stock wire and add my 30mm2 cable directly from alternator to the battery. The cable I used is high quality NGK cable that I know can handle pretty high temperatures (please don't ask how I know this) and I sleeved the cable for extra protection, but now I'm thinking that I really should have fused the new cable. I'm thinking the cable from alternator to battery should be fuse twice, near the battery and near the alternator as both battery and alternator generates current. How come this isn't standard procedure?
Pics show old vs new engine groundwire, the old was pretty bad!


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## gijoe (Mar 25, 2008)

You shouldn't have messed the the OEM cable in the first place. It's fused appropriately for the alternator in the car. You will need to fuse the new cable, but replacing it in the first place only wasted your time, and running without a fuse is risking a fire. 

This is exactly why you don't mess with this cable with doing "big 3" unless you add a high output alternator. You haven't improved anything at all, and you've made your car more dangerous.

It doesn't make sense to fuse twice on the same cable, the current passes through both parts equally, why have 2 fuses? If one blows the whole circuit is broken anyway. 

If you can put the OEM cable back on, I highly recommend it.


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## WinWiz (Sep 25, 2013)

The stock cable is still there and functional.
About fusing both ends of a cable. If I only fuse near the battery, and the cable melts or breaks somewhere between alternator and fuse, I risk a short from alternator to ground, and the fuse near the battery won't break this short, so this might start a fire...
Your statement that I haven't improved anything isn't true, the new thicker wire has lower resistance so the voltage drops less.


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## wr3nchmonkey (Aug 31, 2017)

Are you measuring voltage with the car running? because then you could be measuring the alternator voltage on one side and the battery voltage on the other.


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## gijoe (Mar 25, 2008)

WinWiz said:


> The stock cable is still there and functional.
> About fusing both ends of a cable. If I only fuse near the battery, and the cable melts or breaks somewhere between alternator and fuse, I risk a short from alternator to ground, and the fuse near the battery won't break this short, so this might start a fire...
> Your statement that I haven't improved anything isn't true, the new thicker wire has lower resistance so the voltage drops less.


I'm well versed in voltage drop, but the OEM cable is sized for the OEM alternator, upgrading it won't improve anything. Sure, there is technically less resistance, therefor less voltage drop, but in this case it doesn't matter. The OEM cable can pass all of the current that the OEM alternator can produce, adding thicker cable won't suddenly make the alternator capable of producing more current. 

Think about your double fuse idea a bit longer. One fuse is all that is needed. If the cable melts or breaks the fuse will blow and therefor no current will be traveling through any part of the cable. The blown fuse completely breaks the circuit.

There is simply nothing to gain from messing with the OEM cable if you still have the OEM alternator, and there is a lot to loss if it's not fused correctly. 

So many people like to do "upgrades" for the sake of doing them, without an understanding that the "upgrade" isn't improving anything, and in your case, the "upgrade" could cause a fire. The OEM cable is perfectly suited to send current from the OEM alternator. Adding bigger cable will reduce resistance and voltage drop (negligibly) but how do you think that helps anything?


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## FordEscape (Nov 23, 2014)

Don't know what car and associated charging system controls the OP has (he didn't disclose that important info), but one might wish that for most modern car owners all the old-school 'Big 3' lexicon were lost to eternity.

I suspect that most folks don't undertake the effort (or maybe don't have the wherewithal) to _really_ understand how charging system mods do or don't help or hurt or in some cases introduce risk in modern vehicle applications.

IMHO evidence of that is frequent discussion of these mods absent reference to the specific vehicle involved and acknowledgement of it's particular charging system and logic controls (relating to both system output and system protection), both on the part of OPs and on the part of respondents.

end of rant, I'll crawl back in my cave


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## WinWiz (Sep 25, 2013)

gijoe said:


> I'm well versed in voltage drop, but the OEM cable is sized for the OEM alternator, upgrading it won't improve anything. Sure, there is technically less resistance, therefor less voltage drop, but in this case it doesn't matter. The OEM cable can pass all of the current that the OEM alternator can produce, adding thicker cable won't suddenly make the alternator capable of producing more current.


By that logic upgrading engine ground is even less helpful, because that cable is shorter. Sure the manufacturer used at cable that works, but cost also influenced the manufacturers choice of cable. The resistance in the rather tiny oem cable causes electric energy to be wasted as heat, the lower resistance in my upgrade cable waste less energy because it generates less heat. I also think thicker cables is extra important inside the engine bay, because the engine bay gets hot, and heat causes the resistance in cables to increase.



gijoe said:


> Think about your double fuse idea a bit longer. One fuse is all that is needed. If the cable melts or breaks the fuse will blow and therefor no current will be traveling through any part of the cable. The blown fuse completely breaks the circuit.


If the short to ground happens between the alternator and the fuse, while the alternator is running, the electricity will run from the alternator to ground because electricity runs where the resistance is lowest. So the fuse wont break the circuit from the alternators positive output to ground. Maybe the alternator will break before it starts a fire, but I don't know and I don't like to gamble with fire hazards in my car.

This is also the reason that cables from battery to amp (and other power drawing accessories) must be fused near the battery, this minimize the risk of a short to ground to happen between the battery and the fuse...


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## gijoe (Mar 25, 2008)

WinWiz said:


> By that logic upgrading engine ground is even less helpful, because that cable is shorter. Sure the manufacturer used at cable that works, but cost also influenced the manufacturers choice of cable. The resistance in the rather tiny oem cable causes electric energy to be wasted as heat, the lower resistance in my upgrade cable waste less energy because it generates less heat. I also think thicker cables is extra important inside the engine bay, because the engine bay gets hot, and heat causes the resistance in cables to increase.


Again, I studied EE for 2 years, I am well aware of how resistance works. It's just not relevant here. 

Lets say you used a huge cable with virtually no resistance, so what? The current is still going to get to the battery with the OEM cable, and the OEM cable is sized so that it will not be a hazard. Increasing the awg of the cable might prevent a couple mV worth of voltage drop, but when supplying current to the battery/electrical system, that won't matter. Adding 20k watts worth of amplifiers won't change the fact that the OEM alternator will still only produce the current it is built to produce, and the OEM cable is fine for that.


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## WinWiz (Sep 25, 2013)

gijoe said:


> Again, I studied EE for 2 years, I am well aware of how resistance works. It's just not relevant here.
> 
> Lets say you used a huge cable with virtually no resistance, so what? The current is still going to get to the battery with the OEM cable, and the OEM cable is sized so that it will not be a hazard. Increasing the awg of the cable might prevent a couple mV worth of voltage drop, but when supplying current to the battery/electrical system, that won't matter. Adding 20k watts worth of amplifiers won't change the fact that the OEM alternator will still only produce the current it is built to produce, and the OEM cable is fine for that.


Yes the cable upgrade wont increase the alternators output, but less wasted energy equals more usable energy.


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## gijoe (Mar 25, 2008)

WinWiz said:


> Yes the cable upgrade wont increase the alternators output, but less wasted energy equals more usable energy.


The wasted energy in this case is negligible. That's the point. 

As you drive, the alternator charges the battery. The wasted energy in the wire is so little that you may need to let the car idle for 30 more seconds to make up the difference. You seem to think that the OEM cable is so undersized that you're loosing a ton of energy, which isn't the case at all. The voltage drop on the OEM cable has to be so low that it won't be a fire hazard. You can easily, and safely push 120 amps through 4 ft of 8awg. Most cables aren't that long, and many alternators aren't pushing that much current. In a lot of cases 12awg cable would be perfectly fine.


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## WinWiz (Sep 25, 2013)

FordEscape said:


> Don't know what car and associated charging system controls the OP has (he didn't disclose that important info), but one might wish that for most modern car owners all the old-school 'Big 3' lexicon were lost to eternity.
> 
> I suspect that most folks don't undertake the effort (or maybe don't have the wherewithal) to _really_ understand how charging system mods do or don't help or hurt or in some cases introduce risk in modern vehicle applications.
> 
> ...


My car is a 1996 Honda Civic. I was a little worried that upgrading the alternator cable might **** up the charging system, but I don't think the system in my old car is very intelligent. I have been monitoring voltage while idling and driving, it seems to increase with rpms and nothing else. 
Other people with old cars doesn't seem to report issues after doing the big 3 upgrade so I figured I would try it.


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## WinWiz (Sep 25, 2013)

gijoe said:


> The wasted energy in this case is negligible. That's the point.
> 
> As you drive, the alternator charges the battery. The wasted energy in the wire is so little that you may need to let the car idle for 30 more seconds to make up the difference. You seem to think that the OEM cable is so undersized that you're loosing a ton of energy, which isn't the case at all. The voltage drop on the OEM cable has to be so low that it won't be a fire hazard. You can easily, and safely push 120 amps through 4 ft of 8awg. Most cables aren't that long, and many alternators aren't pushing that much current. In a lot of cases 12awg cable would be perfectly fine.


What you can push trough a cable is dependent on several factors, cable dimension is only one of these factors.
I know the voltage drop isn't major but the output of my old RF amps is a product of input voltage squared by 2. With 3 amps powered by an old 75A alternator, I want to minimize energy waste as much as I can.

Please educate my why the alternators short ground cable is more important than the alternators much longer output cable?


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## WinWiz (Sep 25, 2013)

I just calculated, voltage drop caused by 75A through a 1.5m 6mm2 cable @ 90 Celsius is 0.82V, so 6.8% off the alternators maximum output is wasted as heat due to the 6mm2 cable...

After upgrading the wire to 35mm2 only 1.17% is wasted as heat.


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## gijoe (Mar 25, 2008)

WinWiz said:


> What you can push trough a cable is dependent on several factors, cable dimension is only one of these factors.
> I know the voltage drop isn't major but the output of my old RF amps is a product of input voltage squared by 2. With 3 amps powered by an old 75A alternator, I want to minimize energy waste as much as I can.
> 
> Please educate my why the alternators short ground cable is more important than the alternators much longer output cable?


The amps are essentially on a different circuit. The only thing the alt-battery cable is doing is passing current from the alternator to the battery. It only needs to be sized for however much current will pass through it, and it's already sized appropriately. Having no amps, small amps, or large amps won't change that part of the circuit, the max current through the alt-battery wire will never exceed what the alternator can put out. 

The only thing that matters is resistivity. The resistivity of the wire depends on material (copper), length, and diameter. The american wire gauge factors all of these into the equation when determining how much current can safely pass through the wire. A short run has less resistivity than a long run.

No matter what you put downstream, amps, head unit, DPS, etc. the alt-battery cable only passes the current created by the power source (alternator), the amount of current that goes through that cable will not exceed the alternators rating, regardless of what you wire downstream, and if it does, the fuse blows (because something is broken). 

Think about speaker wire. We use 18-12 awg wire most of the time, why not wire tweeters with 8awg? Using 8awg will reduce voltage drop, right? We don't use excessively large speaker wire because a tiny bit of voltage drop isn't a problem. The voltage drop from the alt-battery will not affect the power going to the amps. Even with an unregulated amp, the battery conditions the power, so you're not drawing directly from the alternator, any of that voltage drop you're worried about from the alt to battery will already be a non-issue because you're primarily drawing your power from the battery, which holds steady.


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## WinWiz (Sep 25, 2013)

gijoe said:


> The amps are essentially on a different circuit. The only thing the alt-battery cable is doing is passing current from the alternator to the battery. It only needs to be sized for however much current will pass through it, and it's already sized appropriately. Having no amps, small amps, or large amps won't change that part of the circuit, the max current through the alt-battery wire will never exceed what the alternator can put out.
> 
> The only thing that matters is resistivity. The resistivity of the wire depends on material (copper), length, and diameter. The american wire gauge factors all of these into the equation when determining how much current can safely pass through the wire. A short run has less resistivity than a long run.
> 
> ...


Resistance through a cable also depends on temperature and the number of strands. The material surrounding the cable also has some effect.

The alternator and the battery are connected in a parallel circuit, so its not really two separate circuits. And measuring the voltage at the distribution bloc for my amps clearly shows the how the voltage increase from something like 12.5V to about 14.4V when the alternator is running.

Tweeters draw so little power that heavy gauge wire is waste of copper.


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## gijoe (Mar 25, 2008)

WinWiz said:


> Resistance through a cable also depends on temperature and the number of strands. The material surrounding the cable also has some effect.
> 
> The alternator and the battery are connected in a parallel circuit, so its not really two separate circuits. And measuring the voltage at the distribution bloc for my amps clearly shows the how the voltage increase from something like 12.5V to about 14.4V when the alternator is running.


Are your amps unregulated? 

The cable isn't whats causing the jump between 12.5v and 14.4v, even after you upgrade the cable you'll still have the same voltage fluctuation, and they won't matter unless your amps are unregulated (unlikely).


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## WinWiz (Sep 25, 2013)

gijoe said:


> Are your amps unregulated?
> 
> The cable isn't whats causing the jump between 12.5v and 14.4v, even after you upgrade the cable you'll still have the same voltage fluctuation, and they won't matter unless your amps are unregulated (unlikely).


Yes I believe my old school RF amps are unregulated. When the engine is off the alternator isn't spinning so I get about 12.5V at my amps. When the alternator is spinning i get about 13.8-14.4V, so I believe this proves that my amp do get power from my alternator, and not only from the battery as you stated.

By the way I never got 14.4V before I did the big 3, so the upgrade must have minimized the voltage drop.


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## gijoe (Mar 25, 2008)

WinWiz said:


> Yes I believe my old school RF amps are unregulated. When the engine is off the alternator isn't spinning so I get about 12.5V at my amps. When the alternator is spinning i get about 13.8-14.4V, so I believe this proves that my amp do get power from my alternator, and not only from the battery as you stated.
> 
> By the way I never got 14.4V before I did the big 3, so the upgrade must have minimized the voltage drop.



You are still ignoring the simple fact that the only current that will ever flow through the alt-battery cable is the current produced by the alternator. That current will max out at whatever the alternator is capable of producing, and the cable is already sized to carry that current. Nothing else matters. Adding bigger cable to allow current to flow to the battery with less voltage drop won't make a single bit of difference, not one!

What you have done is taken a safe, fused cable, and bypassed it with an unfused cable that is not giving you any benefit at all. The battery stores power, getting current to the battery with negligibly less voltage drop will do nothing for the stereo. Any difference you've seen is not from beefing up that cable. 

Upgrading grounds is a completely different argument because when you install amps you need a good way to complete the circuit, in this case OEM ground cables could be holding you back. The ground cable and the alt-battery cables are serve completely different roles. The alt-battery cable will only ever see the current that the alternator produces, every. The grounds are sized for the equipment installed from the factory, adding amps changes that requirement, so upgrading grounds might help, but that doesn't change the amount of current traveling from the alternator to the battery.


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## WinWiz (Sep 25, 2013)

gijoe said:


> You are still ignoring the simple fact that the only current that will ever flow through the alt-battery cable is the current produced by the alternator. That current will max out at whatever the alternator is capable of producing, and the cable is already sized to carry that current. Nothing else matters. Adding bigger cable to allow current to flow to the battery with less voltage drop won't make a single bit of difference, not one!
> 
> What you have done is taken a safe, fused cable, and bypassed it with an unfused cable that is not giving you any benefit at all. The battery stores power, getting current to the battery with negligibly less voltage drop will do nothing for the stereo. Any difference you've seen is not from beefing up that cable.
> 
> Upgrading grounds is a completely different argument because when you install amps you need a good way to complete the circuit, in this case OEM ground cables could be holding you back. The ground cable and the alt-battery cables are serve completely different roles. The alt-battery cable will only ever see the current that the alternator produces, every. The grounds are sized for the equipment installed from the factory, adding amps changes that requirement, so upgrading grounds might help, but that doesn't change the amount of current traveling from the alternator to the battery.


Voltage x Amperage = Power
So if my voltage increase and amperage is constant then power will increase right?

It's really very simple. The battery stores the power from the alternator, when there is surplus. The alternator generates all the electric power in an normal gas powered car like mine. So if less electricity is wasted in the cable from the alternator to the battery, I will have more electric energy available for all the electric stuff in my car.

And please enlighten me, if my amps gets all their energy from my battery, and not from my alternator, then how can a stock ground cable to my alternator "hold back" my amps?

Of course my amps gets voltage from my alternator, alternator and amps share the same positive pole piece and ground. Amps, battery and alternator are connected in parallel, so they have a common voltage. Rather basic stuff.

JL Audio also recommend upgrading the wire from stock alternator to the battery. Are JL complete morons?


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## WinWiz (Sep 25, 2013)

wr3nchmonkey said:


> Are you measuring voltage with the car running? because then you could be measuring the alternator voltage on one side and the battery voltage on the other.


No, when I removed the fuse and checked for continuity between the to screws holding each side of the fuse, the car was off and I had also removed the cable from fusebox to alternator. That's why I don't understand how the fuse can protect against shorts, if it doesn't break the connection when it blows.


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