Can the 120 amp optional alternator drop right in if you have the 105 amp standard?

[smdk2500]

Well, what I really really would do is just get nicer bracket from later truck lol

Going that route would be a lot of work. You would have to use both brackets, get new ac lines and compressor, redo all the wiring for the altenator since it would live on the other side of the engine. I think the only thing OP would be able to reuse is the PS pump but I could be wrong since I've never had a 96+.

 

[1998_K1500_Sub]

the CS130 comes with the brace hole.

I want to highlight the brace in the picture.

GM put it there for a purpose. IMHO it's there for at least two reasons,

- handle the load from the belt driving the AC compressor as it repeatedly tugs on alternator pulley during cycling, and

- manage the inertial forces of the alternator, e.g., due to engine vibration, road shock, etc.

Maybe others will add.

 

[AuroraGirl]

I want to highlight the brace in the picture.

GM put it there for a purpose. IMHO it's there for at least two reasons,

- handle the load from the belt driving the AC compressor as it repeatedly tugs on alternator pulley during cycling, and

- manage the inertial forces of the alternator, e.g., due to engine vibration, road shock, etc.

Maybe others will add.

Im not sure how well the aluminum bracket its mounted to is itself electrically grounded to the block(Like, a good case to bracket but then bolted to a painted engine is not very well grounded)
and that is a dedicated ground stud, its just a sturdy boss with a threaded insert yes, but in case yourt alternator isnt grounded quite as well as we would hope(damn near any original alternator by this point is gonna be having aluminum oxide buildup blocking its ability to nicely pass ground without issue. this can be substituted, to be clear, but if your TBI ecm grounds over on the intake like an idiot GM was (at least in 1987 lol) then it may just be intended to make sure the ground path of the alt does not pass over or past or near the ECM ground. of course, if they moved it nvm

 

[1998_K1500_Sub]

Im not sure how well the aluminum bracket its mounted to is itself electrically grounded to the block(Like, a good case to bracket but then bolted to a painted engine is not very well grounded)

There's a current (ground) path from the alt/bracket, though the bracket's mounting bolts (three of them AFIAK) and into the block (threaded bolts into threaded holes, drawn tightly). In addition, the brace might act as an notable current path.

Current will pass across all paths from the alternator to the engine block, but it will proportionately favor those of lower resistance.

and that is a dedicated ground stud, its just a sturdy boss with a threaded insert yes, but in case yourt alternator isnt grounded quite as well as we would hope(damn near any original alternator by this point is gonna be having aluminum oxide buildup blocking its ability to nicely pass ground without issue. this can be substituted, to be clear, but if your TBI ecm grounds over on the intake like an idiot GM was (at least in 1987 lol) then it may just be intended to make sure the ground path of the alt does not pass over or past or near the ECM ground. of course, if they moved it nvm

I would be interested to see what sort of voltage drop occurs between the alternator case and engine block. I'm guessing it's "negligible", e.g., 10mV (0.010V) or less, but I should go out to the garage and measure it before I spout off too proudly.

A good voltmeter and a DC current clamp will tell interesting tales under the hood, some expected and... some not.

 

[351FUN]

There's a current (ground) path from the alt/bracket, though the bracket's mounting bolts (three of them AFIAK) and into the block (threaded bolts into threaded holes, drawn tightly). In addition, the brace might act as an notable current path.

Current will pass across all paths from the alternator to the engine block, but it will proportionately favor those of lower resistance.



I would be interested to see what sort of voltage drop occurs between the alternator case and engine block. I'm guessing it's "negligible", e.g., 10mV (0.010V) or less, but I should go out to the garage and measure it before I spout off too proudly.

A good voltmeter and a DC current clamp will tell interesting tales under the hood, some expected and... some not.

I read .3 ohm from alternator case to battery negative, fwiw. 4.6 ohm from alternator positive to battery positive, so that's gonna get some attention soon too.

 

[98 Nitro]

I second the Powermaster cs-130d 120 amp made in USA alternator with 3 yr warranty. I have one in my 98 after the AC Delco made in Mexico one crapped out in less than 2 years which had a 12 month warranty. Probably buy their starter when mine bites it too.

 

[1998_K1500_Sub]

I read .3 ohm from alternator case to battery negative, fwiw. 4.6 ohm from alternator positive to battery positive, so that's gonna get some attention soon too.

I kinda question those numbers. In fact, they're wrong. Here's why.

.3 ohms would cause a 30V drop if it carried 100A. And you know *that's* not happening under your hood.

You likely don't have the equipment to measure resistance at milliohm levels, but what you *can* do is measure the current and voltage drop simultaneously... and then calculate the resistance by dividing the voltage drop by the current. That's one way to measure milliohm resistance using everyday, inexpensive instruments.

(edit) Not trying to insult anyone here, just provide some guidance.

 

[351FUN]

I kinda question those numbers. In fact, they're wrong. Here's why.

.3 ohms would cause a 30V drop if it carried 100A. And you know *that's* not happening under your hood.

You likely don't have the equipment to measure resistance at milliohm levels, but what you *can* do is measure the current and voltage drop simultaneously... and then calculate the resistance by dividing the voltage drop by the current. That's one way to measure milliohm resistance using everyday, inexpensive instruments.

(edit) Not trying to insult anyone here, just provide some guidance.

I may have misread it, it was just a fluke multimeter so nothing fancy. I'm an industrial tech so I've only got basic electrical training in the grand scheme. At this point I had no voltage change because the alternator wasn't putting anything out.

 

[1998_K1500_Sub]

I may have misread it, it was just a fluke multimeter so nothing fancy. I'm an industrial tech so I've only got basic electrical training in the grand scheme. At this point I had no voltage change because the alternator wasn't putting anything out.

You're on the right track.

I try to keep in mind that we're looking at 100A-plus currents in these charging circuits, and much greater in the starting circuits. So after a moment's thought, it's obvious that any resistance in those circuits has to be in the .003-.001 ohm range or less. Why? Because a 100A current though a .003 ohm resistance will suffer a .3V drop (V = IR)... and that's about the highest voltage drop that I would consider allowable an a high-current automotive circuit (esp. when there's only a 13.6V budget!). So any reasonable circuit has to less resistance(!).

So we're dealing with resistances that are much, much less than the resistance of the leads on the DVM. One can't measure such low resistance values without using some other means (such as I described in my prior post).

That's enough pontificating for one night. Sorry if I was droning on.

 

[351FUN]

You're on the right track.

I try to keep in mind that we're looking at 100A-plus currents in these charging circuits, and much greater in the starting circuits. So after a moment's thought, it's obvious that any resistance in those circuits has to be in the .003-.001 ohm range or less. Why? Because a 100A current though a .003 ohm resistance will suffer a .3V drop (V = IR)... and that's about the highest voltage drop that I would consider allowable an a high-current automotive circuit (esp. when there's only a 13.6V budget!). So any reasonable circuit has to less resistance(!).

So we're dealing with resistances that are much, much less than the resistance of the leads on the DVM. One can't measure such low resistance values without using some other means (such as I described in my prior post).

That's enough pontificating for one night. Sorry if I was droning on.

Nah you're good. I usually work with 460v ac or 390dc so current is usually around 2 amps max. If I see a motor pulling more than a couple amps it's time to investigate lol.