upgraded alternator, dual parallel batteries. Fuse ?

[mikez71]

Right on. Yep I wasn't going to power the inverter from the fuse (in my truck it's on the battery terminal) Instead I have a little midi fuse box I was going to mount up near the aux battery.

I just thought it might limit alternator output. Instead of upgrading those battery + cables, I was hoping to just add the second alt cable with fuse and upgrade ground cables..

Regarding the wires to the back, I was hoping to run two 4 gauge vs one 1/0. Mainly because it might be easier to run it inside, but I haven't looked closely if you know where the best/safest/easiest routing would be. Maybe it's better underneath along the frame rail..

 

[iamdub]

Right, so when running an inverter that can pull 175A, all that juice has to go through the 175A fuse?

By saying "the 175A fuse", are you still referencing the factory 175A fuse? Just pretend that doesn't exist. That's for the factory stuff. Leave it alone.

If your inverter requires a 175A fuse, then that's the size fuse and corresponding fuse holder you place inline of the power wire connecting the battery to the inverter, wherever it's mounted. You want the fuse to be as close as reasonably possible to the battery terminal.

Here's a 175A fuse and holder as an example: https://a.co/d/6rRdt9z

I keep reading that it's good to have a larger fuse than your alternator can provide (assuming you have adequate wiring I guess)

This makes no sense. The alternator is a source of amperage. So are the batteries. If you have two batteries with a combined capacity of 2,000 amps, does that mean you have a 2,000+ amp fuse somewhere? No. Fuses are to protect the circuits and loads connected to the battery(ies). If you have a 1,000 watt bass amp in the back, you're gonna have about a 100A fuse on that amp's power wire connected at the battery. If you have some underhood LEDs connected to that same battery, you're gonna have something like a 2.5A - 5A fuse on that power wire.

In reality, I doubt I will need it, but just like planning for 'what if'. Also the car uses some juice while running, but that is hooked up to the same side of the fuse as the alternator.

Right. Among many other systems, that fuse also protects the alt and the circuit (wire) in between.

 

[iamdub]

Right on. Yep I wasn't going to power the inverter from the fuse (in my truck it's on the battery terminal) Figured it might limit alternator output. Instead of upgrading those battery + cables, I was hoping to just add the second alt cable with fuse and upgrade ground cables..

Ah. Yours is a newer year. '07 to '08 and maybe '09 has the main fuse on the firewall. Same setup and termination, just alternate location. when modding, the older setup is much more ideal.

Here's mine:

Growing up doesn't have to suck

Y u gotta b a h8a? Just wait til I black up a lot more of my Tahoe. Pretty sure I'm gonna do the roof and maybe the hood. Maybe a pillar or two. :think:

www.tahoeyukonforum.com

Growing up doesn't have to suck

Y u gotta b a h8a? Just wait til I black up a lot more of my Tahoe. Pretty sure I'm gonna do the roof and maybe the hood. Maybe a pillar or two. :think:

www.tahoeyukonforum.com

Growing up doesn't have to suck

Clean af as always dub. One of these days I'll get around to cobbling something together for mine:) Good yob (hecho en USA)

www.tahoeyukonforum.com

Growing up doesn't have to suck

Instead of a long typed response, here is the jest of it: "The bypass valve – otherwise known as a pressure relief valve – is an integral part of the oil filter. The valve is designed to open when the oil filter becomes clogged or when the oil is too thick. This allows the oil to bypass the...

www.tahoeyukonforum.com

 

[mikez71]

Yep the factory fuse. Right the batteries will end up providing juice, but say your demand is high enough to run them down? (400A lets say like a 5000W inverter) Now say for the sake of exaggeration that you had a 400A alternator, wouldn't the 175A fuse restrict the charge rate? I'm sorry if I'm missing the obvious, like I said, reading basic electrical guides online makes my head hurt! (But the few articles I've seen all seem to recommend a larger fuse than the alternator output)

 

[iamdub]

Yep the factory fuse. Right the batteries will end up providing juice, but say your demand is high enough to run them down? (400A lets say like a 5000W inverter) Now say for the sake of exaggeration that you had a 400A alternator, wouldn't the 175A fuse restrict the charge rate?

No. The inverter will be pulling the power (amperage) off the batteries. They'll be dead and inverter shut off long before the batteries are depleted to the point that their amperage supply is lower than what the alternator is supplying. Basically, the charging amps (the load that the batteries present to the alternator) are still much less than the alternator's output.

I'm sorry if I'm missing the obvious, like I said, reading basic electrical guides online makes my head hurt! (But the few articles I've seen all seem to recommend a larger fuse than the alternator output)

I think I see where the confusion is coming from. The fact that the alternator is connected to the "downstream" side of the fuse and the inverter is on the other side ("upstream", towards/on the battery). I see the point of a larger fuse to exceed the new alt's output. I just don't see how, with two batteries (that do nearly all of the work), the 60A difference warrants this. It doesn't outweigh the "risk" as you should always have the minimum, or a small percentage above the minimum fuse rating to cover the loads. Most of the loads are very short-term, as with starting up of a motor. That 2,000 watt inverter powering up a circular saw or something will present an extremely short spike (surge) in amps when you first pull the trigger but will quickly drop to just a few amps once its running. This is known as inrush current or FLA (full load amps). Most fuses have a bit of a cushion to not blow so easily near their rated capacity. Of course, there are slow-blow and fast-blow fuses to accommodate various needs.

Play it safe and play it by ear. If the sustained loads pop a fuse, first, determine if it popped due to too small of a fuse and not due to a short. Increase the fuse size and carry on.

 

[mikez71]

I thought i got it, but..

Batteries are not charging with that many amps anyhow and the rest of the FACTORY electrical draw is connected to alt side of fuse. ok

Batteries are parallel on starter, also bypassing fuse. ok

BUT if there was a draw of 200A direct from either battery, wouldn't the factory fuse/wiring still be a bottleneck for the alternator? conceivably a big enough alternator could supply the juice, thus not running the batteries down? (probably moot point on the 220A alt as the truck requires however many amps to run) I know I shouldn't up-rate the fuse with stock cables, but how about on your upgraded cables? That's what led me to think about adding ONE additional alt charge wire to the aux battery, paralleled in the same way the batteries already are on the starter and block.

Why do all upgraded alternator manufacturers suggest a larger fuse? Where do the extra amps we should have available go?

https://www.mechman.com/content/instructional-pdfs/General-alternator-installation-instructions.pdf

Regarding power wires, planning to use this little box, 1/0 cable might just fit.. (.5" opening)

 

[iamdub]

I thought i got it, but..

Batteries are not charging with that many amps anyhow and the rest of the FACTORY electrical draw is connected to alt side of fuse. ok

The batteries would have to be dead and shorted beyond bringing back to put 200A of load on the alternator. You'd be aware of problems LONG before that point!

Batteries are parallel on starter, also bypassing fuse. ok

Yup- the starter wire isn't fused. The starter wire goes to the solenoid and is only a closed circuit for very short times. The solenoid would be more of the fuse than anything. Some cars have a fusible link in the starter wire, though.

BUT if there was a draw of 200A direct from either battery, wouldn't the factory fuse/wiring still be a bottleneck for the alternator?

The 200A draw isn't being supported by the alternator. It's being supported by the battery that can support an 800+ amp load. And you have two batteries so you're good for 1,600 amps. The alternator is just recharging the batteries. It having a higher amp output means it'll support the batteries discharging as they feed that 200A load faster and for a longer time period.

conceivably a big enough alternator could supply the juice, thus not running the batteries down?

Yes. This is the idea and is why audio system competitors run multiple alts on their multiple batteries.

I know I shouldn't up-rate the fuse with stock cables, but how about on your upgraded cables? That's what led me to think about adding ONE additional alt charge wire to the aux battery, paralleled in the same way the batteries already are on the starter and block.

Fuses protect the circuits. If the wiring feeding an electric motor, like a cooling fan, can only withstand 20A before it burns up, it'd have something like a 30A fuse. If that fan motor shorts out or the insulation on the wiring rubs through and shorts on the body- whatever would make it pull more than 20A, the fuse would pop so the circuit immediately goes dead instead of letting it heat up and burn. Larger cables don't "push" more amperage to the circuits. The point of upsizing the wiring, as with a Big 3, is because all the electrical circuits on the car are somewhat starved for power because the wiring is too small. Actually, providing the proper voltage to the loads makes them draw fewer amps. All my fuses are the stock specs.

I see what you're saying about the extra charge wire to that extra battery. To directly answer that- yes, if that battery has its own ground, then that charge wire would help. It's still all stock wiring that's barely adequate in a stock setup. You're far from stock electrical loads with a 2,000 watt inverter.

Why do all upgraded alternator manufacturers suggest a larger fuse? Where do the extra amps we should have available go?

https://www.mechman.com/content/instructional-pdfs/General-alternator-installation-instructions.pdf

Because if you're maxing out the alternator, too small a fuse can blow. Typically, larger alternators are to support the batteries powering heavy equipment, large amplifiers, etc. You shouldn't be within a dangerous range with your proposed plans and with having two batteries. You might be close, but if the stock fuse rating reliably supports your loads, leave it. It's safest and that's the point of fuses. If you have a DC amp clamp, then you can put some factual numbers to all of this.

Regarding power wires, planning to use this little box, 1/0 cable might just fit.. (.5" opening) View attachment 399689

Well, that's cool. There's that fused distribution block we were talking about earlier. lol

 

[mikez71]

I see what you're saying about the extra charge wire to that extra battery. To directly answer that- yes, if that battery has its own ground, then that charge wire would help. It's still all stock wiring that's barely adequate in a stock setup. You're far from stock electrical loads with a 2,000 watt inverter.
.....
Because if you're maxing out the alternator, too small a fuse can blow. Typically, larger alternators are to support the batteries powering heavy equipment, large amplifiers, etc. You shouldn't be within a dangerous range with your proposed plans and with having two batteries. You might be close, but if the stock fuse rating reliably supports your loads, leave it. It's safest and that's the point of fuses. If you have a DC amp clamp, then you can put some factual numbers to all of this.

Yep, aux battery grounds to left head next to the alt bracket..

I think I will run that second alt wire. I have read about a few people doing this.. (@doubelieve?)

I think with two batteries and two sets of wires, I will only need to upgrade grounds and add that aux charge wire.. Sounds like the alt fuse is to protect the wiring between battery and alt. I will add another 175A to the new aux battery charge cable (of adequate size). If the fuse somehow provides protection for the alternator itself, then maybe I will go with a 100A fuse (100+175=275A for 220A alt) Though I have not yet read any evidence for this..

You say the factory circuits have borderline power, then I should upgrade the cable from main battery fuse (downstream alt side) to fusebox as well..

Regarding a DC amp clamp, I'm assuming I need to load it up to get meaningful numbers?

The distribution block is a daimler/chrysler product.. smallest/simplest multi fuse holder I could find.
That's the plan.. for now. Thanks for you patience!

 

[iamdub]

You say the factory circuits have borderline power,

The factory wiring is borderline big enough to carry the amperage. Copper is expensive so using the bare minimum or even undersized for the millions of vehicles you produce adds up to big savings. Case in point: On my '02 S10, I replaced the wiring to the headlights from the fuse/relay center with 10 AWG. Just replaced the factory stuff, in the factory loom with the 10 gauge, nothing else. That was the largest wire that would fit in the 9006 bulb plugs. Against a wall, the low beams were then just as bright as the high beams. Different pattern, of course. But the brightness was much improved just from getting that extra ~2 volts to the bulbs. I never got around to giving the high beam circuits the same treatment. Surely, they would've been even brighter.

then I should upgrade the cable from main battery fuse (downstream alt side) to fusebox as well..

The one that runs along the firewall? It's tempting to do so, but probably not so necessary. If I estimated mine correctly, it's 4 gauge. That's good for at least 100A and I don't see any devices drawing anywhere near that, singularly or collectively.

Regarding a DC amp clamp, I'm assuming I need to load it up to get meaningful numbers?

Right. To see what that inverter, the factory stuff... anything is pulling to have a solid idea of what fuse rating to get.

The distribution block is a daimler/chrysler product.. smallest/simplest multi fuse holder I could find.
That's the plan.. for now. Thanks for you patience!

It's nifty, for sure. With the fuses in it and wire size capacity, I'd say it's for loads that aren't all pulling at the same time. This is a rare occurrence, anyway.

 

[mikez71]

It's nifty, for sure. With the fuses in it and wire size capacity, I'd say it's for loads that aren't all pulling at the same time. This is a rare occurrence, anyway.

yeah, the buss bar does look small, but if it can handle a 200A fuse, I should be ok.

good info on the headlight wiring.. guess the thing to do is look for voltage drops anywhere. new headlights are next on my list. (all front lights while bumper is removed)