Larger crank pulley for more amps

[Rotten Ricky]

After some time to let it sink into BOTH my brain cells, I am thinking of changing my tack on the question of getting more amps for battery charging. I think I will follow Blue Stockings example of simply installing a second alternator driven by a suitably larger pulley, instead of messing around and trying to upgrade the original arrangement. I am fortunate that I have the room to make this change - many people cannot consider this as they simply do not have the room.

Several reasons for this tack:

1. It is easier for me to machine a pulley - even a double pulley - to match the face and attach to the existing crankshaft pulley. The new pulley will be about 6" to 7" compared to the original 4".
2. The stock water pump revs will remain the same so it will not ruin its bearings or possible aerate the coolant. And I don't need a larger pulley on the pump to get in the way of my access if I wanted to try to keep the pump revs down.
3. By making up a simple frame that bolts to the arms on the front engine mounts, the new alt. will not be able to break off any cast ears, lugs, etc on the block or cast covers to which the alt. is attached, due to increased belt tension and torque on the existing location.
4. The new location for the new alt. is likely to give it better cooling, have easier belt tension adjustment and put out more power from the oversized pulley that is only for that alt.
5. It should be less expensive as I do not need to buy costly high-output alternators, serpentine kits etc and instead I can use a cheaper, more common, larger-framed alternator with greater stock capacity, like the Delco CS130D or CS144, both of which are about 100 amps or more.
6. The larger alt. should last longer if I expect it to not be at full amps all the time - as per a 40% de-rating for marine use dictates. However, I do have plans to increase the output somewhat from the stock characteristics. If I can get close to 70 amps for several hours for my 350 amp-hour banks that will be a huge improvement for little outlay.
7. Redundancy is a great thing incase one alt. dies.
8. More money to spend on my wife of 40 years, this last August! Every husband is like that, right?

I think the question about whether increased revs will produce more output amps will depend on the particular alt. in question, as it appears they are constructed differently in many cases, so you are probably all correct!

Thanks again for everyone's suggestions.

Rotten Ricky.

[TeddyDiver]

Originally Posted by Maka

dridas is right. More RPMs on an alternator do not = more amps.
The old generators were like that ,,,the faster they turned the more amps.
But alternators these days put out the same amps at almost all speeds ( RPMs )
If you want more amps get a higher rated alternator ,,, dont speed up the one you have.

Nope, there's allways an alternator specific minimum rpm to get out the nominal output and after that point the output curve becomes "flatter". IE if you run the alternator below that rpm you never get the nominal output of it. Running higher rpm's helps also to cool the alternator even the output doesn't grow so much more. Just to say a couple of points

[Jim Cate]

Originally Posted by TeddyDiver

Nope, there's allways an alternator specific minimum rpm to get out the nominal output and after that point the output curve becomes "flatter". IE if you run the alternator below that rpm you never get the nominal output of it. Running higher rpm's helps also to cool the alternator even the output doesn't grow so much more. Just to say a couple of points

Agreed! And I do believe that for a given output, higher rotational speed requires less field current, and that means less heating in the alternator... always a good thing.

Jim

[wooden head]

Buy the correct alternator for the aplication in the first place. Yes the performance changes at different rpm but the engineers that design them compensate for this. Alternators are speed/load matched for the aplication. Diesel engines in automobiles, trucks and equipment also turn slow. In many equipment aplications they run even slower.
Perhaps the problem is installing a gasoline engine alternator on a diesel. I hope you are not running a true automotive alternator because even on a diesel powered boat potentially explosive fumes from other sources can accumulate.