'99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

[insttech1]

I knew my alternator was the source of some tiny squealing noise,
so I pulled it completely apart.

Not only is there rear bearing noise, the rotor was somehow contacting the stator, at one point in time,
and 1/3rd of it is "scored" and partially melted, but not down to the stator windings.

And one of the main housing screws is stripped out as well. That may have allows the stator to move around a bit...

So instead of messing with it, I'm getting a new one, and want some advice:
I have a 17.5' bowrider, that I'm either tubing with, or fishing.
If fishing, I'm running the engine for four to five minutes, if that, anchoring, and fishing for 1/2 hour to an hour.
Then on the next hole. (I may fab' up a trolling motor mount next summer.....and take a 2nd battery)
If tubing, I'm running about 3200RPM for a few hours until the kids are bored.
I only run WOT if I'm tuning the carb and checking RPM range....I don't run this thing for "max speed".

I have a 2-speaker low-level stereo, and I do have a new battery (which I now know why it wasn't charging too well....but my fishfinder showed 14.3v running, 12.0 not running, and boat gauge said 10v),
but I do run my fishfinder all the time while fishing, and have my anchor lights on when night fishing (load on battery).

So I'm wondering if it's beneficial to go up to 65amps since I go on short runs and keep a load on the battery,
versus keeping a stock 55amp alternator.

And as far as the source (and I'm leaning toward the 65Amp):
Get a VP/Merc/Sierra one for about $180 to 250
Get an autozone marine version for $139
Get an ebay one for about $90
I highly suspect all three are made in the same place, on the same tooling, but not 100% sure.

Any thoughts are welcome....and thanks!!

 

[bruceb58]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Getting your present one rebuilt is another option.

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Bruce there is one more reason not to do that:
It looks like at some point in the past the manifold was replaced.
For whatever reason, this forces the manifold-mounted bracket to be too far forward of the manifold, and cocked to the side by a few degrees, even though it is bolted squarely to the manifold.

Therefore, pulley and belt alignment are off a bit.

The previous owner "tried" to correct this by overboring the foot mount of the alternator housing, and leaving a non-rounded hole that the mounting bolt slides around inside of. (The 3/8" bolt is actually bent a little in the center.....???)

So that's just one more thing I can correct with a new alternator; I can properly modify the foot or bracket by shimming, and getting a new mounting bolt and square up my pulley/belt alignment.

And I looked up parts for a rebuild anyway....with all the internal corrosion, paint flaking off the rotor and allowing rust, damage to the stator, and the stripped out hole that clamps the stator between the front/rear housing, I think I'd be better off just to get a new one, rather than spend all that time/money playing with the damaged unit.

What are your thoughts on the amperage?

 

[Maclin]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

The wire from the alternator to the battery can only handle so much current, but going from 55 to 65 might still be in range for it. I would hate to be wrong though and be smelling cooking insulation just before the wire either starts a fire or melts like a big fuse. Then starts a fire.

The 65 will only output what is needed but also keep in mind that the alternator drive belt may be taxed if demand goes above the 55 amp level for very long. It is nice to have the extra capacity but that does need more HP when the demand goes up.

As long as any extra circuits are well thought out and the wiring can handle the current then the extra amps (when needed) should not overload anything.

 

[bruceb58]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

What are your thoughts on the amperage?

For what you are doing, probably doesn't matter what amperage you get. You don't need to change the wire going from the alternator to go up to 65A although not changing it may negate the benefit of getting the bigger alternator. It won't harm the wire as the voltage drop going to the battery will just cause the alternator to reduce its current output unless you are using a remote sense line which I really doubt.

I do understand your very good reasons not to rebuild.

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Thanks for the info Maclin.
I'll have to brush up on my motor theory (it's been a while....LOL!).
Hopefully this is still correct (if not, please chime in!)
Electromagetic drag is what pulls "more HP" when needed.
The output amps are proportional to the RPM. (So roughly a linear curve of output amperage as RPM's increase?)
Max 65A would only be seen at WOT? Or would that be seen earlier in the RPM curve and then cut off from there?
I know there's a voltage regulator; what I don't know is if there is something that regulates current?

Or is the current draw dictated by the requirement/drain of the battery and what's needed to recharge it?

Thanks Much!

 

[bruceb58]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

The voltage regulator regulates the field current. The regulator increases the alternator output by increasing the field current until a certain voltage is reached at the alternator output. Increasing the field current is what increases the load the alternator puts on your engine since more effort is required to turn the rotor through the stator.

The alternator output vs RPM increases as RPM is increased but it is not linear. More current output increase is greater at lower RPM and tapers off as RPM increases. Typically, max current will be reached at around 2500 RPM depending on the alternator pulley sizes.

 

[bruceb58]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

I would hate to be wrong though and be smelling cooking insulation just before the wire either starts a fire or melts like a big fuse. Then starts a fire.

If the wire is undersized, the wire would have enough voltage drop that the alternator would adjust the current so that the voltage at the alternator was at a certain voltage. This has the affect of the alternator only getting up to a certain current. Of course your 65A alternator would never deliver 65A of current in this scenario which is why you normally bump up the size of the wire.

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

OK thanks for all the info gents.
Bruce I must have been typing as you were, LOL!!

And I just looked up alternator theory and curves (RPM vs amperage) and see the non-linearity.

So I guess it boils down to this: I'm assuming the 65A would "top off" the battery more quickly and more efficiently during the short runs that I tend to make, and then leaving a few things on (with engine off) that tends to put a light load on the battery?

Thanks for your time fellas!!!

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

And I will take a look at the wire size/condition.
It's a short run, so not much drop to consider due to length in addition to gauge size.

 

[Maclin]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Bruce, thanks for the more in depth explanation.

Insttech, I do feel that you will be ok with going up to the 65a. I was concerned about stereo loads, not knowing how much of the lake can feel ya...

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Thanks Maclin....
Nope, I don't crank the stereo. But I let the kids turn it on a little while we swim. Since I'm never running the boat for a long time between swimming or fishing stops, I'm always a bit concerned about draining the battery.
(So when I keep my fishfinder on, I do set a "low battery" alarm on it; anything under 12V and it will go off. But I can only set it in 1V increments....)

So I think I'll go with the 65A, and that will be my birthday present for next month

 

[Walt T]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

55 or 65 just make sure it's a marine alternator.

 

[insttech1]

Re: '99 3.0 GS needs new alternator; stay with 55amp or go up to 65amps?

Yup, got that covered Walt...even if I do "autozone", they now carry approved marine alternators for the 3.0, and other engines.
You just have to call them so they special order it....$139 total; no core.