big alternator necessary with diesel genset & AC charger?

[P69]

I'm dealing with a possible bad alternator and wonder if it is necessary to have a large alternator if primary charging is done with diesel genset and 40amp AC charger?

Existing alternator is unknown brand, likely some kind of GM automotive alternator, age unknown and capacity unknown.  It was working last time i checked.  I did find out that the BAT stud on the alt is lose, its and specs are unknown, it's a GM alt for automotive use, and, because the engine rotates clockwise, the alt has been spinning backwards all its life (don't know when PO installed it or how many hours it ran backwards). 

Anyway, I have a 4.3kw diesel generator and 40 amp AC charger with ~460AH battery bank.  Since gen/battery charger are primary source of charge, is there any need to get an alternator that has capacity of 25% of house bank capacity?

Thanks

[SV THIRD DAY]

I personally wouldn't because who wants to run your main diesel proposition engine to make power while at anchor inefficiently, when you can run your diesel generator that is set-up for that type of load running.  Now I would have a larger battery charger than 40A for for less generator run time, but in terms of an alternator.....once you have a generator aboard, that becomes your primary AC charging mechanism and the power you get while motoring is just a bonus. 

[Firefly]

I have a "stock" alternator that serves fine since I primarily charge with 3 x 135w solar panels and a Honda generator. The solar panels and regulator were purchased new (scratch and dent company in Arizona) all for $1100 shipping included. Rarely run the Honda; pretty much only when heavy overcast for multiple days.

This also avoids all of the alternator drive belt problems that others have with big alternators. Downside is that the panels do take up some space. I put two on a custom bimini and the third on my davits.

Regards,
Stew

[RockysMate]

Stew, do you have pics of custom bimini?  We are trying to find solar panels for Rocky.  We are trying to max out the capacity.  The Kyocera ones we like would stick out beyond the davits about an inch each side and we are afraid we would knock them off.

[P69]

Hey ya'll, thanks for the input on the alternator question. That's kinda what I was thinking, but wanted to hear it from others because sometimes my mind takes me way out into left field. 

Stew, I'd like to see that bimini also, I'm thinking of building a hard-top bimini.

[SVJourney]

We also primarily charge from solar and Honda.  If we are running the engine its because we have to motor somewhere and the trip is usually long enough that it doesn't matter what size the alternator is.  (3rd year of continuous cruising)

Also, and we have talked about this in another thread, our 105 amp alt rarely runs higher than 45 amps.  The batteries would have to be flatter than a pancake to be able to use all 105 amps. (flooded cell, 450 amp/hrs)

So, I would recommend spending the money on solar or wind rather than worry about a spendy alt.

[INCOMMUNICADO]

We also have 165 amps solar 264 amps 6 volt battery bank and a Honda generator. Our boat is mainly used for six month winter trips to the Bahamas. Our Honda is seldom used, we did use it to top off the battery's three times this past winter. I think the best combination would to add a small wind generator. I do hope this helps with your options.  Allen

[Maddie]

Stew, do you have pics of custom bimini?

+1 on "would love to see custom bimini pics".