upgrading alternator wiring

Sean778

NAXJA Member
NAXJA Member
My experience with using a breaker to replace a fusible link on my XJ left me stranded on more than one occasion. I upgraded my battery cables to 4 gauge welding cable, and installed a higher output alternator at the same time. My alternator was rated at 144 amps, and I used a 140 amp breaker. I had no indication in the cab when it would trip, and the rare time that it did trip it would run fine until I had no juice left in the battery. I have since switched it out for a 150 amp ANL fuse and had no problems.
 

donthelegend

NAXJA Member
NAXJA Member
My experience with using a breaker to replace a fusible link on my XJ left me stranded on more than one occasion. I upgraded my battery cables to 4 gauge welding cable, and installed a higher output alternator at the same time. My alternator was rated at 144 amps, and I used a 140 amp breaker. I had no indication in the cab when it would trip, and the rare time that it did trip it would run fine until I had no juice left in the battery. I have since switched it out for a 150 amp ANL fuse and had no problems.
Obviously you actually use the full output your alternator is capable of, I don't think that has anything to do with the fuse vs breaker argument, except that fuses are generally available in smaller increments. Increasing the amperage is what fixed your problem, not going to a fuse. (Slow blow fuses may give a bit more leeway than the same size breaker but ultimately it comes down to sizing everything correctly for whatever components you want to use).

Blowing the fuse isn't going to give you any more indication while driving than the breaker did, but now you better have an extra fuse or you're stranded. The breaker can be reset in less than 30 seconds and assuming there's not an actual short, you're good to go.
 

Kejtar

PostMaster General
Board of Directors
NAXJA Member
So scratching my head thinking about this - I could wire up an "alarm" indicator of sorts that would trigger if a voltage drops below a certain level. I do have a gauge that gives me current voltage but I don't keep looking at it the whole time as it's off to the right on the center console.
 

ehall

NAXJA Member
NAXJA Member
I would trust megafuse over anl fuse. Those anl fuseholders Re a joke compared to a mega fuse holders.
The ANL holders are junky but its much easier to visually inspect an ANL fuse and they come in much higher ratings than the Mega fuses
 

donthelegend

NAXJA Member
NAXJA Member
The ANL holders are junky but its much easier to visually inspect an ANL fuse and they come in much higher ratings than the Mega fuses
While you're not wrong, mega fuses are available up to 500 amps so they shouldn't exactly be a limiting factor for the charging systems people on this site are using.

They're also a third of the price compared to ANL fuses of the same rating
 

Heavyopp

NAXJA Member
NAXJA Member
So I get that a 160 amp alternator only puts out 160 if the demand is there -- my question is what fuse would you use as the main?

If your wire is big enough are we really just protecting agains a dead short?

That would mean a 175 mega for a potential 160 amp draw

Am I thinking right?
 

Jeep Driver

New member
This is pretty much all incorrect.

1.Alternators aren't constantly putting out max current. They aren't putting out any more current than is being drawn by the system they're attached to. It has EVERYTHING to do with draw.

2. A 160 Amp alternator will only put out 160 amps under certain conditions, namely, when turning fast enough to produce that much current, and when there is that much current being drawn by the battery, engine, lights, radio, and whatever else is using power in the system.

3. Because of 2, if you don't ever need more than 150 amps, there's nothing wrong with 150 amp breaker/fuse on a 160 amp alt. The breaker/fuse is there to protect your wiring first.

4. Nothing wrong with the breakers instead of fuses, I run a 125 amp breaker in my daily driver XJ with stock alt. I run a 150 amp ANL fuse in my trail rig with a 160 amp alternator. Have never popped the breaker or fuse. Installed 125 amp breaker in two other XJs with stock alternator output without problems. All with 4 gauge cables I made.


To the OP:
Get rid of the fusible link/stock alternator positive wire entirely. Replace with 4 gauge or larger wire, with either a fuse or breaker sized to protect the wire or to match the output of the alternator, whichever is smaller. (IE: 0 gauge wire will handle more power than a 136 amp alternator will ever produce, so i'd suggest a 150 amp fuse/breaker which is probably the closest to 136 you'll get without being under sized). Alternatively, if you don't ever need the extra power, you'd probably be fine with a 125 amp breaker, but there's no real reason to undersize the breaker since the wire will handle the extra current without a problem.


There is nothing there that I said that was wrong or incorrect.


He will not be fine with 125 amp breaker.


There is plenty of scenarios in which he will be a full load, or that the alt will sense a full load.

Cruising the back roads at night with AC, aux lights, Efan, head unit with amp......etc.........

Jump starting another vehicle.

Or any thing else that will drain the battery...........like running a wench.

Mine puts out 100amps at idle..........not 5amps here and 30amps there.........100amps.

 

Jeep Driver

New member
So I get that a 160 amp alternator only puts out 160 if the demand is there -- my question is what fuse would you use as the main?

If your wire is big enough are we really just protecting agains a dead short?

That would mean a 175 mega for a potential 160 amp draw

Am I thinking right?
That's correct.
 

Jeep Driver

New member
My experience with using a breaker to replace a fusible link on my XJ left me stranded on more than one occasion. I upgraded my battery cables to 4 gauge welding cable, and installed a higher output alternator at the same time. My alternator was rated at 144 amps, and I used a 140 amp breaker. I had no indication in the cab when it would trip, and the rare time that it did trip it would run fine until I had no juice left in the battery. I have since switched it out for a 150 amp ANL fuse and had no problems.
Thank you for making my case.
 

donthelegend

NAXJA Member
NAXJA Member
There is nothing there that I said that was wrong or incorrect.


He will not be fine with 125 amp breaker.


There is plenty of scenarios in which he will be a full load, or that the alt will sense a full load.

Cruising the back roads at night with AC, aux lights, Efan, head unit with amp......etc.........

Jump starting another vehicle.

Or any thing else that will drain the battery...........like running a wench.

Mine puts out 100amps at idle..........not 5amps here and 30amps there.........100amps.

No, it doesn't. That's not how electronics work. It puts out up to 100 amps at idle. Go throw a clamp on meter on there if you don't believe me but without running a winch, a ton of lights, or a big stereo, that alternator isn't putting out anywhere near 100 amps at idle most of the time. Now start your winch and absolutely the alternator will produce that 100 amps but for normal conditions, it's not making 100 amps.

My comments on a 125 amp breaker/fuse being fine were based on the assumption that he doesn't actually need more than 125 amps out of his alternator... Because most people don't and unless you've upgraded the stock alternator, it's not capable of putting out more than that anyway.

You can certainly argue that an individual needs more than 125 amps, in which case they need a bigger breaker/fuse, but most parts stores reman'd alternators barely make their rated current near max rpm, and at or near idle, where most people tend to run winches or jump start other cars, they're only capable of making a fraction of that, and once again the lower rated fuse is not going to cause a problem.

I'm not saying I recommend putting a 125 amp breaker on a 160 amp alt, but it's not instantly going to trip, and is not going to hurt anything either.
 

Jeep Driver

New member
Some needs to tell power master to put "@ 100% load" on their alternator tags.
Maybe you need to think a little harder.


Here's some homework for you-

You add up all the devices that are running on the average vehicle. Fuel pump, ignition, PCM, TCU, headlights, aux lights, AC, amp and radio, maybe a CB or other..........maybe a trailer, lights, Ebrakes, trailer battery,..........etc........Efan........wipers............whatever.

Add it all up......typical summer evening.......running full tilt.



Bet you'll be over 100 amps..........maybe 125 amps............continuous load.


Your alt is running full load all the time
 

Green XJ Jeep

NAXJA Member 4950
NAXJA Member
Maybe you need to think a little harder.


Here's some homework for you-

You add up all the devices that are running on the average vehicle. Fuel pump, ignition, PCM, TCU, headlights, aux lights, AC, amp and radio, maybe a CB or other..........maybe a trailer, lights, Ebrakes, trailer battery,..........etc........Efan........wipers............whatever.

Add it all up......typical summer evening.......running full tilt.



Bet you'll be over 100 amps..........maybe 125 amps............continuous load.


Your alt is running full load all the time
At full load or duty cycle yes a person is going to max out their alt. Just like your alternator when it was tested, it was put under full load and the max amps it was capable of delivering at idle was 100.

An alternator is not going to produce max amps all the time.

Maybe you should quit embarrassing yourself and actually read on how charging systems actually work.
Here let me help,
https://www.lifewire.com/understanding-alternator-output-ratings-534785

Here is a vid that kind of shows it. If you look at idle its only putting out 50 amps until a load is applied,
https://www.youtube.com/watch?v=Q3HKivSo_TY
 
Last edited:

Jeep Driver

New member
At full load or duty cycle yes a person is going to max out their alt. Just like your alternator when it was tested, it was put under full load and the max amps it was capable of delivering at idle was 100.

An alternator is not going to produce max amps all the time.

Maybe you should quit embarrassing yourself and actually read on how charging systems actually work.
Here let me help,
https://www.lifewire.com/understanding-alternator-output-ratings-534785

Here is a vid that kind of shows it. If you look at idle its only putting out 50 amps until a load is applied,
https://www.youtube.com/watch?v=Q3HKivSo_TY
Quoting from your own article, again, making MY point.

In this case, your alt is UNDERcharging and yet the alt is at full tilt most of the time.

Any extras on most of our Jeeps and we are drawing 100amps.


50/120A 13.5V

Since we know that both ISO and SAE standards call for a format of "IL / IRA VTV" actually pretty easy to interpret this rating.

First, we’ll look at IL, which, in this case, is 50. That means this alternator is capable of putting out 50A at the “low” test speed, which is either 1,500 RPM or “the idle speed of the engine,” depending on which standard you’re dealing with.

The next number is 120, which is “IR” or the amperage output at the “rated” test speed. In this case, this alternator is capable of putting out 120A @ 6,000 RPM.

Since this is the “rated” test speed, this number is usually used for the alternator’s rated output.

The last number is 13.5V, which is “VT” or the voltage that the alternator was held at during the test. Since an alternator’s output can vary both up and down from 13.5V in real world situations, it’s actual output limits will vary from the idle and rated numbers.


In this case, stop and go traffic...............your alt will never keep up.
 

Green XJ Jeep

NAXJA Member 4950
NAXJA Member
Quoting from your own article, again, making MY point.

In this case, your alt is UNDERcharging and yet the alt is at full tilt most of the time.

Any extras on most of our Jeeps and we are drawing 100amps.






In this case, stop and go traffic...............your alt will never keep up.
Your whole argument is, an alternator is going to produce max amps all the time regardless of demands. Which is completely false.
At full load yes, sitting in the driveway warming up or idling in traffic with no auxiliary devices running it most definitely will not.
 

Green XJ Jeep

NAXJA Member 4950
NAXJA Member
You must have completely missed this,
Alternator Output Supply and Demand

With all of that in mind, it’s also important to understand that the output of an alternator is tied to the demands of the electrical system in addition to its inherent capabilities and the speed that its input shaft is rotating at any given moment.
In essence, while maximum alternator output is dependent on the rotational speed of the input shaft, the actual output is load-dependent. That basically means that an alternator will never generate more current than is called for by the momentary demands of the electrical system.
What that means, in the real world, is that while an underpowered alternator can cause problems by not meeting the needs of your electrical system, a substantially overpowered alternator represents a lot of wasted potential. For instance, a high output alternator might be capable of putting out upwards of 300A, but it won’t actually provide more amperage than a stock 80A unit if that’s all the electrical system ever tries to draw.
 

Jeep Driver

New member
Your whole argument is, an alternator is going to produce max amps all the time regardless of demands. Which is completely false.
At full load yes, sitting in the driveway warming up or idling in traffic with no auxiliary devices running it most definitely will not.

No, my whole argument is you dont even know what demand is at any given moment.

The argument began when the other posted stated that the OP would likely be OK with a 125 breaker and a 160 alt.


My argument is that a 160 alt will put out 160, at some point, or, all day long, if demand is there, like jump starting another car/truck.
A failing battery will cause a full load on the alt......whatever, whenever.
 

techno1154

NAXJA Member
NAXJA Member
No, it doesn't. That's not how electronics work. It puts out up to 100 amps at idle. Go throw a clamp on meter on there if you don't believe me but without running a winch, a ton of lights, or a big stereo, that alternator isn't putting out anywhere near 100 amps at idle most of the time. Now start your winch and absolutely the alternator will produce that 100 amps but for normal conditions, it's not making 100 amps.

My comments on a 125 amp breaker/fuse being fine were based on the assumption that he doesn't actually need more than 125 amps out of his alternator... Because most people don't and unless you've upgraded the stock alternator, it's not capable of putting out more than that anyway.

You can certainly argue that an individual needs more than 125 amps, in which case they need a bigger breaker/fuse, but most parts stores reman'd alternators barely make their rated current near max rpm, and at or near idle, where most people tend to run winches or jump start other cars, they're only capable of making a fraction of that, and once again the lower rated fuse is not going to cause a problem.

I'm not saying I recommend putting a 125 amp breaker on a 160 amp alt, but it's not instantly going to trip, and is not going to hurt anything either.
That quote from the alternator manufacturer is only a test on a test bed. It is not an indication of the amount of power the alternator will put out on a regular XJ or any vehicle for that matter that have the minimum load applied to it. Case and point, My XJ came with the standard 90 AMP alternator which was perfectly fine running everything the XJ came with at idle. Then I added dual electric fans that require 50 AMPS and everything went to hell after that. I could make the alternator on my XJ put out all 160 AMPS at 2,000 RPM by jumping the switched ground on the back of the alternator to a permanent ground at which point the voltage would get to 18+. And yes, I have done that in the past when I was having some electrical problems.

I too have added a 160 AMP alternator and if the fans are not running the AMP draw is less than 40. Now if throw in plenty of AMP gobbling equipment in the XJ the AMP draw will increase only these equipment are actually working and even so, the alternator will only deliver the amount of AMPS necessary to operate these equipment properly. For most of us it will be less than 100 AMPS. In my case I added another battery of more than 900 CCA's to help to smooth things out at start up.

There is absolutely nothing wrong with a circuit breaker. They are the preferred electrical protector over a fuse in house AC and for the protection of critical implements that need to be on,...think of marine/boats, airplanes etc.. Keep in mind that breakers do go bad and trip prematurely unlike a fuse. Also, they could be bad right out of the box. The only disadvantage I see for a breaker in the XJ is the amount of space they need to mount them.
 
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