[Public-List] Yamar 2cyl 15hp

[Robert Kirk]

Mike... I wouldn't worry about the alternator load in any case. On a very 
low battery, it's putting out about 25 amps - which is all a 100 Amp-hr 
battery can take. So, 25 amps X 13 Volts X 2 [wild guess 50% 
mechanical/electric efficiency- probably conservative) / 746 (Watts/HP = 
7/8 of a horsepower. That's not much of an extra push. Plus, if you turned 
off the alternator, you've still got some mechanical friction load left.

In the more likely event in your example below where you are normal 
steaming with a battery  not fully discharged, you are probably only 
drawing 5 amps from the alternator to maintain charge [check your ammeter 
gage], so with the same arithmetic, you are only drawing about a fifth of a 
horsepower. Not worth the trouble of turning off.

Bob Kirk
Isobar #181

At 08:59 AM 3/15/2012, Mike Lehman wrote:
>I recently went to a seminar on marine electric systems and learned 
>something that was quite interesting...if you have a diesel and the engine 
>is in the process of charging the battery, it can take a significant 
>amount of HP to run the alternator, depending on the size of the 
>alternator and the state of charge on the batteries. But it you need the 
>extra HP to go through an inlet, or bridge, or fight some strong current, 
>you can turn of the ignition switch, which will turn off the tach and the 
>alternator and give you the extra power you may need. The engine will 
>continue to run, but you will not be charging your batteries. I have never 
>tried this, and am a bit scared to do so. Has anyone ever tried this?


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