3gm30f 55amp or 35amp alt

[Emmalina]

Originally Posted by lateral

Depends what life you want out of your belt.
At 50% SOC and 110A——>60ish in first hour I’m getting 100+ hrs out of a single gates green stripe. I designed my own tensioner to do a belt change in a couple of minutes. Changing my setup to serpentine or double wasn’t an option.
Max 80A you should easily treble that life. Also I suspect the thermistor will derate the output of that alt promptly as it heats up. If it’s anything like the IR in the
Hitachi.
Anyway, it’s only a stop gap. You’re going Li aren’t you? Just match pulleys and move on.
Rule of thumb, < 90 Single, >90 double or serpentine I’ve heard. I use the standard yanmar belt size on gm series and ignored that.

Wow Im looking at 3-4000 hours between belts and thats running lifepo charging at 120A.. Something sure is wrong with your setup.

[lateral]

Thats good to know! I have been replacing mine at oil change . (100hrs)
Didn't seem anything wrong with them. Now have four spares.
So much for the > 90A mantra.

The one I had trouble with was when i swapped the Hitachi with the 10SI clone.
But it came with the boat so don't know how old it was. Different pulley as well.
I just assumed the mantra was right.
I am interested to see if 2x 115A bosch's derated to 90A, with forced air will live with the Li install. (one will be dual pulley)

[RaymondR]

The ratings for auto alternators are only for a ten minute run, after that they will overheat if run at full rated amps. The design rationale is that by ten minutes of running the increase in battery voltage will wind the output current back.

[AA3JY]

Balmar 150 amp single (Gates) belt with external (belt saving mode)regulator .

[RaymondR]

Originally Posted by Notyetsinking

I am asking about the fitment, I am new to marine alternators and the whole process of working with parts that aren't OE. I am pretty handy with automotive engines, but for some reason I have psyched myself out a bit with the Marine application.

I understand the current aspects of the alternator, I am very comfortable with that. What I am not comfortable with is how the whole system will play together when a harness designed for 35 or 50 amps is brought up to 80 amps (I understand it will never be this value, but the design considerations I imagine remain the same). Said another way, a system designed to 35 amps seems like it would struggle with an 80 amp alt.

Will I need to add protections to the battery to handle this new current? Or is that more of something to be handled along with the li batteries?

Just replace the B+ wire with a bigger one and that's all you need. The regulator on the alternator will respond to the batteries needs as commanded by the battery so you don't have to worry about that.

The biggest potential problem is the belt size on the alternator as the load on the belt increases significantly with the 80 amp alternator. Probably not a problem when jumping up from 35 to 55 amp but could be a problem in jumping up to 80 amp.

A bigger alternator increases the lateral loading on the crankshaft which might be significant on a relatively small motor so unless you really need the extra charging ability of the 80 amp alternator I would avoid it.