# 250 AMP Alternator Upgrade



## WIPensFan (Jan 31, 2009)

So I have a 2007 Chevy 3500 classic 4x4 with the 6.0L engine. Has towing and snow plow prep. Truck is the one in my Sig. Currently running stock 145 AMP alternator and just ordered a 250 AMP upgraded Alternator.( just put a new 800cca Interstate Battery in ) I think most of my wiring is good as far as gauge of wire is concerned but I'm not sure. There is a 250 AMP fuse wired in line, I'm not sure if that's factory or when the plows were installed. So I've read a million online comments on this upgrade and one of the tips is to run a 1 gauge wire from the alternator to the positive battery terminal. My truck has a red junction box that a smaller black wire runs from the alternator to that box and then a larger red wire goes to the battery terminal. Do I run this new larger gauge wire from the alternator to the junction box?? And then leave the larger red wire as it currently is?? Or is my current wiring good enough??Any help would be appreciated, I suck at mechanical things and am probably worse at electrical things.


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## Philbilly2 (Aug 25, 2007)

I cannot give any real world on high output output alternators as I think they are the wrong approach, but a 1 gauge off the alternator seems like it would be hard to even hook up to the alternator in my option, not to mention it will most likely look like hell. What is the post on the alternator like a 10MM head?


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## WIPensFan (Jan 31, 2009)

Philbilly2 said:


> I cannot give any real world on high output output alternators as I think they are the wrong approach, but a 1 gauge off the alternator seems like it would be hard to even hook up to the alternator in my option, not to mention it will most likely look like hell. What is the post on the alternator like a 10MM head?


I'm not sure but it's not real big.


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## Mebes (Feb 7, 2004)

Run it from the post on the alt directly to the positive terminal of the battery.
The reason for this upgrade is that your factory wire and terminals are not rated for the extra amperage that your new alt puts out and could get too hot.
It's also a good idea to run a larger ground wire directly from your neg bat terminal to one of the studs that mount your new alt if possible for the same reason.


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## Randall Ave (Oct 29, 2014)

There isn't a spot to put a second battery behind the driver's side headlight? Are you having issues, or just doing this as a precaution?


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## Philbilly2 (Aug 25, 2007)

Randall why would you do more batteries rather than a big alternator? More amps is better!


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## Randall Ave (Oct 29, 2014)

That's what I've always had, never had a problem, and have never had an alternator fail. If he's putting out 250 amps, he may have problems. Now does that alternator put out a constant 250, or is that it's rating at full RPM?


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## Philbilly2 (Aug 25, 2007)

Over charging is an issue... huh...

Water tower is all I have to say... Water Tower...


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## WIPensFan (Jan 31, 2009)

Mebes said:


> Run it from the post on the alt directly to the positive terminal of the battery.
> The reason for this upgrade is that your factory wire and terminals are not rated for the extra amperage that your new alt puts out and could get too hot.
> It's also a good idea to run a larger ground wire directly from your neg bat terminal to one of the studs that mount your new alt if possible for the same reason.


Are you sure? That fuse isn't inline anymore though is it? I need to look at it again and take some pics. I don't think I can bypass that junction box.



Randall Ave said:


> There isn't a spot to put a second battery behind the driver's side headlight? Are you having issues, or just doing this as a precaution?


I have dual batteries and the aux is running the dump bed.



Randall Ave said:


> That's what I've always had, never had a problem, and have never had an alternator fail. If he's putting out 250 amps, he may have problems. Now does that alternator put out a constant 250, or is that it's rating at full RPM?


I read the alternator only puts out as much as you need, not 250 always.


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## Philbilly2 (Aug 25, 2007)

Why does the second battery only run the dump bed????


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## WIPensFan (Jan 31, 2009)

Plow seemed slow and lights dimmed more than usual it appeared to me. Next day the truck labored a bit to start and it doesn't usually do that, so I thought I better get a new battery in there. Still had the original AC Delco! That may be a world record for battery age.


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## WIPensFan (Jan 31, 2009)

Philbilly2 said:


> Why does the second battery only run the dump bed????


That's how Monroe set it up.


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## Philbilly2 (Aug 25, 2007)

WIPensFan said:


> That's how Monroe set it up.


Wow... I would change that if I was you.


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## WIPensFan (Jan 31, 2009)

Philbilly2 said:


> Wow... I would change that if I was you.


I think the aux may run back to the trailer plug as well. Why change??


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## Philbilly2 (Aug 25, 2007)

There is no need to have a second battery run just the dump box that you might run once or twice a day.

If you just take a 12v positive 2 gauge and connect your two batteries, you have a ton more amperage storage. Your plow draws a ton of amps when your are running the motor and the more storage that you have available, the less draw it puts on the total system. Hence the "Water Tower" annoligy. You are trying to force the power into a small holding cell when you could just have more storage and let the regular alternator do the same work over a lengthened time. High charging rate gives wears the crap out of the cells. Think like when you charge with a trickle charger. You get a much more quality charge at 2amps than at 20amps. Battery gets hot, cables get hot... slow and steady wins the race.


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## WIPensFan (Jan 31, 2009)

Philbilly2 said:


> There is no need to have a second battery run just the dump box that you might run once or twice a day.
> 
> If you just take a 12v positive 2 gauge and connect your two batteries, you have a ton more amperage storage. Your plow draws a ton of amps when your are running the motor and the more storage that you have available, the less draw it puts on the total system. Hence the "Water Tower" annoligy. You are trying to force the power into a small holding cell when you could just have more storage and let the regular alternator do the same work over a lengthened time. High charging rate gives wears the crap out of the cells. Think like when you charge with a trickle charger. You get a much more quality charge at 2amps than at 20amps. Battery gets hot, cables get hot... slow and steady wins the race.


You read the part of my first post where I said I don't understand most of what's going on with all this right??
You may as well have posted in French because I would have understood it just the same.


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## Philbilly2 (Aug 25, 2007)

OK sorry.

You will be better suited having 2 batteries than a high output alternator.

If you take a 2 gauge wire and connect your 2 positive battery posts together that will be better.


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## WIPensFan (Jan 31, 2009)

Philbilly2 said:


> OK sorry.
> 
> You will be better suited having 2 batteries than a high output alternator.
> 
> If you take a 2 gauge wire and connect your 2 positive battery posts together that will be better.


Ok, I will keep that in mind. Thank you for trying to help, sorry I'm a dumba$$ on this stuff.


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## JMHConstruction (Aug 22, 2011)

The junction box you're talking about is the red box that flips open so it's easy to hook jumper cables to right? If I remember clearly (I'm not looking at my truck right now) it has the main battery wire coming to it, then splits off into the fuse box and the alternator. If that is correct you can't just bypass it, you'll have to get power to your fuse box.

Out of curiosity, where did they put your second battery? The only open place I can think of on mine is in the back on the fender.


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## WIPensFan (Jan 31, 2009)

JMHConstruction said:


> The junction box you're talking about is the red box that flips open so it's easy to hook jumper cables to right? If I remember clearly (I'm not looking at my truck right now) it has the main battery wire coming to it, then splits off into the fuse box and the alternator. If that is correct you can't just bypass it, you'll have to get power to your fuse box.
> 
> Out of curiosity, where did they put your second battery? The only open place I can think of on mine is in the back on the fender.


That's exactly what I'm talking about. I don't think I can bypass that little red box. My second battery is on the passenger side fender closest to the windshield. I may not need any adjustments to the wiring, this new alt is a direct replacement for my stock unit. Just higher amps.


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## Randall Ave (Oct 29, 2014)

Is the second battery running on a battery isolated circuit? If it's not, and I do not think it is, both batteries are working together. You should replace both at the same time. When you install the new alternator. Run an extra wire to the main battery, A 4 gauge wire should be fine, Leave the trucks power distribution box alone.


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## WIPensFan (Jan 31, 2009)

Randall Ave said:


> Is the second battery running on a battery isolated circuit? If it's not, and I do not think it is, both batteries are working together. You should replace both at the same time.


No, it's isolated.


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## Randall Ave (Oct 29, 2014)

The three chevys I had, one was a mason dump. Ran two batteries, duel terminal high amp Interstates. Just ran them wired together. Never had a problem. If it was mine I would get rid of the Isolator, just my opinion.


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## Mebes (Feb 7, 2004)

WIPensFan said:


> Are you sure? That fuse isn't inline anymore though is it? I need to look at it again and take some pics. I don't think I can bypass that junction box.


Adding a wire from the alt to the battery does not bypass the fuse box that protects all of your wiring it simply provides a second path for the extra amps you are creating to get to the battery without overloading existing wires.

Maybe this spoiler helps
Note: The numbers below are estimated for simplicity.


Spoiler














































WIPensFan said:


> I read the alternator only puts out as much as you need, not 250 always.


This is correct, if your system needs 100 amps it will only make 100 amps.
The engine needs to be spinning at least 2000 to 3000 rpm to develop the 250 max rated amps.
Less RPM's mean less amp output.

Keep in mind that the guys also make quite a few excellent points about large alternators not being necessary for most situations.
My posts here are only to help you hook it up correctly if you still want to go ahead with it.


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## WIPensFan (Jan 31, 2009)

Mebes said:


> Adding a wire from the alt to the battery does not bypass the fuse box that protects all of your wiring it simply provides a second path for the extra amps you are creating to get to the battery without overloading existing wires.
> 
> Maybe this spoiler helps
> Note: The numbers below are estimated for simplicity.
> ...


That's helpful and simple, thanks.


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## chevyhauler (Oct 21, 2014)

WIPens,
To try and clarify what all these guys are talking about I will try to put this into plow guy terms.
Lets say that u r a plow guy. Lets say that you have a shed out back that holds your bagged salt for sidewalks. Your shed is your storage. The bigger the shed...the more salt that you can store and the bigger storms that you can accommodate without running out. All you need to do is go back to that shed and get your salt. 
In this example salt = electricity.
More batteries (hooked up properly) means more storage for power. When your plow needs that push of power...the batteries store it so that it is there and does not have to be made by the alternator. Without your shed...if u needed more salt...you would have to run back out to a store. That's one of the reasons that your lights dim. The battery storage is not enough so the alternator is hustling to try and catch up.
Now the wiring is just like you or someone else running out to that shed to get the salt. Imagine a 80lb tiny dude trying to fill your truck with salt. They will quickly overheat...get tired...and slow down. That is just like a smaller wire trying to push more power. It overheats and looses efficiency. Now imagine a team of football players, hustling your salt out there. They could fill your truck in minutes. That would be the large gauge wire pulling all that juice efficiently.

I have rebuilt several alternator/battery systems before.
That red box that you talk about is what actually brings the power into your truck. Unless you go directly to a battery (which many plows and dump bodies do) all the power for your truck goes through that red box first.
Personally, I like 1o welding cable for high power truck/car systems. It is super thick and is super flexible. It has several very small strands of wire inside it. So many of those small strands bring you up to the thickness of cheaper wires, but because the strands are so small, they are able to move such that you can route the wire around all kinds of obstacles. If you can find the right supplier, you can get the connectors that can connect the welding cable to just about anything. The poor mans way to crimp the ends is with a really large screwdriver and a sledge hammer. Done that several times. After doing it so many times, I finally went out and bought the $200 special crimper that can do wires that large. Also suggest a piece of shrink tube to transition back a couple of inches on the wire and over the copper end. 
I hope that this helps.


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## WIPensFan (Jan 31, 2009)

chevyhauler said:


> WIPens,
> To try and clarify what all these guys are talking about I will try to put this into plow guy terms.
> Lets say that u r a plow guy. Lets say that you have a shed out back that holds your bagged salt for sidewalks. Your shed is your storage. The bigger the shed...the more salt that you can store and the bigger storms that you can accommodate without running out. All you need to do is go back to that shed and get your salt.
> In this example salt = electricity.
> ...


Yes it helps, thank you.


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## Philbilly2 (Aug 25, 2007)

Wow... that made so much sense, I think my wife would get it!!!

Well played sir... well played.


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## chevyhauler (Oct 21, 2014)

Philbilly2 said:


> Wow... that made so much sense, I think my wife would get it!!!
> 
> Well played sir... well played.


thanks.
I was once told (by an Electrical Engineer no less) that you don't fully understand something, if you cant explain it in the simplest of terms.
I don't know if I completely agree. Personally, I think that figuring out how to explain something is a completely different skill set than understanding the original content. Its almost like building a bridge. U gotta know both sides well in order to be able to connect them.


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## WIPensFan (Jan 31, 2009)

Got the 250 amp alt in and added 2 gauge wire from alt to + battery terminal with a 250 amp fuse in line. Also new 2 gauge ground from - battery terminal to the shock mount where it was located previously. I didn't do the engine ground strap because it looks pretty robust. Also two new 800CCA Interstate Batteries for good measure. Thanks to all those who helped me.


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## chevyhauler (Oct 21, 2014)

WIPensFan said:


> Got the 250 amp alt in and added 2 gauge wire from alt to + battery terminal with a 250 amp fuse in line. Also new 2 gauge ground from - battery terminal to the shock mount where it was located previously. I didn't do the engine ground strap because it looks pretty robust. Also two new 800CCA Interstate Batteries for good measure. Thanks to all those who helped me.


And how r the results?
Inquiring minds wanna know!


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## WIPensFan (Jan 31, 2009)

chevyhauler said:


> And how r the results?
> Inquiring minds wanna know!


Works like a charm! No more dimming of headlights at all. Plows are slightly faster which is what I was hoping for.


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## chevyhauler (Oct 21, 2014)

Absolutely awesome!!!
Glad to hear it!


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## leolkfrm (Mar 11, 2010)

usually the isolator is for the camper package so you can still start the truck?
that said, did you have to modify anything as far as mounting? or size of belt?


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## WIPensFan (Jan 31, 2009)

chevyhauler said:


> Absolutely awesome!!!
> Glad to hear it!


Thank you.



leolkfrm said:


> usually the isolator is for the camper package so you can still start the truck?
> that said, did you have to modify anything as far as mounting? or size of belt?


No alterations for the alternator. Only change was buying a new main battery with top and side posts because the side posts had to many add ons to fit in the tight space where the battery is located next to the main fuse box. The 2 gauge wire have huge copper ringlets on the ends that attach much easier to the top posts.


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