Bill Roosa;825140[B said:
][/b][FONT="]Also John alternator output is controlled by the regulator not engine RPM[/FONT][FONT="]. Once you get the alternator to "fire up" it will produce it's rated output at idle. You do have to rev the motor initially to get it to fire up but then you can throttle back to idle and the regulator will compensate by running more current (making a stronger magnetic field) through the rotor coil. A common misconception though.[/FONT]
Bill where on earth do you come up with this stuff..?
Let's take a look at this from an alternator specs standpoint based on what the OP most likely has if it is still "factory".
Based on his 2006 Hunter he most likely has a Yanmar 4JH series engine. Most of these shipped with either a 60A or optional 80A Hitachi alt.
The 60A alt develops its rated output of 56A at a MINIMUM alt speed of 5000 RPM per the Yanmar specs. To reach a 5000 RPM alt speed at an 800 RPM idle you'd need a 6.25:1 pulley ratio. There is not a 4JH that has anywhere near a 6.25:1 ratio. The Yanmar 4JH is a 1.9:1 ratio as I have measured it on a customers boat. The crank pulley is 5.25" and the alt pulley is 2.75".
Using a 1.9:1 ratio with an idle speed of 800 RPM, what most 4Jh engines idle at, gets you to an alt speed of just 1520 RPM. A 1520 RPM alt speed on the Hitachi 60A alt is a 20A output no matter how much field the regulator applies. 20 amps is a far cry from the rated output of 56A.
Even on the 80A unit your getting just 20A at an 800 RPM idle. By going to 3000 RPM on the alt you develop 60A at 1580 engine RPM. This is still 15A shy of the rating for that alternator and your getting a decent output but your RPM for the engine is almost double the idle speed. By going to 4000 alt RPM you're now at 70A but also at 2100 engine RPM.
You simply can't apply a blanket statement that alts will produce their full rating at idle as all output curves are different and many engines have different pulley ratios. If the alt is not spinning the needed RPM to match its output curve even full fielding the unit won't produce anything more than it can produce based on its own output curve. Some alts do much better than others at idle but I've yet to see one that can put out its full rated current at normal pulley ratios on marine engines with the engine at a 600-800 RPM..
Even a 100A Balmar 6 series will not produce it's hot rated output of 87A until 5000 alternator RPM. You can hit 80A at 2500 alt RPM which is 1315 engine RPM or 515 engine RPM higher than idle and your still 7A away from max rated output.
I do agree that with many alternators you do not need to race the engine to get good output, as many folks do, but many alts perform poorly at low alt RPM so if your pulley ratio is low then it's a good idea to run the calculation to see where you optimum charging speed is.
A 50A charger, depending upon brand, may be right up against the limits of a Honda EU 1000 and may or may not work without shutting the EU down on temp overload... The Progressive Dynanamics 50A charger for example draws 900 watts but an Iota 75A draws 1000W so it depends upon which brand of charger the OP has, which he's not disclosed as of yet.
We really need to know what the charger is, brand & model, in order to help more.