Cruising RPM.

[jviss]

Most of the time if I have to charge the batteries I use my Nextgen 5.5KW generator and run my AC powered charger. A lot more amps for the fuel use. I probably should upgrade my alternator though. Otherwise it seems like when I do cruise in the somewhat narrow restrictions we have here I end up motoring long enough on the transit that it takes care of some of the charging and the solor panel finishes it up. And yes, the admiral pefers to get a slip and plug in more often than not. Not my perference but as I have said many times before - If mamma ain't happy ain't nobody happy.

Just for my education, do you really need to run at 80% rpm to reach maximum alternator output? Seems awfully high. I would think more like 1500 to 2000 rpm or so (40% to 55%).would do trick but then again I would appreciate your input on this.

No, you don't have to run at 80% max RPM to get maximum alternator output; though this is a statement that may or may not be so for everyone, as there are so many variables to consider. I have a 125A alternator, and the belt and pulley setup I have is such that i probably could get 125A before I reached 2880 RPM (80% of 3600), I really don't want to charge that hard. And, at such a high current I wouldn't stay in bulk mode very long with a 230AH bank, and the speed would be wasted as the regulator took the current down by holding the acceptance stage voltage (14.8V for me). Battery charging is really no good for diesels when the power output of the engine far exceeds the charging requirement. I bulk up at 80A, and I can achieve that at 1500 RPM. Once I enter acceptance phase I can trim that down as the current drops until I'm doing most of my charging at only 1,000 RPM.

One thing that I still don't know is whether loading an engine at 80% of output at a particular RPM is just as "healthy" for a diesel as loading it at 80% of maximum power output.

What kind of AC charger have you? I'd be surprised if it put out more DC current than your alternator. Most chargers I've seen on boats like this are in the 20 to 40A neighborhood.

 

[smokey73]

One thing that I still don't know is whether loading an engine at 80% of output at a particular RPM is just as "healthy" for a diesel as loading it at 80% of maximum power output.

What kind of AC charger have you? I'd be surprised if it put out more DC current than your alternator. Most chargers I've seen on boats like this are in the 20 to 40A neighborhood.

With regard to RPM vs load. That's a tough one to answer - too many variable. But assuming the boat design team did a pretty good job matching the drive train to the boat, then with a clean hull and prop, the 80% of RPM probably is fairly close to the 80% rated load. Your increased alternator may have added a load but I'm not sure how much? But then again, the builder may have gotten a "deal" on a particular diesel model. Who knows for sure? Lacking anything else its the only thing we have to go on. I did some more research and am starting another thread tited "Crusing RPM research" so take a look.

With regard to alternator. I am ashamed to say that I still have the stock alternator with no external control so I am sure I don't get much out of it when its hot. I have a Sterling 50A charger that I have more confidence will give me a better charge profile and the Nextgen sips fuel. (I generally load it with the Air Con to keep the Admiral happy so it is loaded pretty well ) The Yanmar is too much power for just the charger if I have an alternative available.