Run Engine to Charge Batteries

[fritzdfk]

I have a a Volvo Penta 280 sterndrive with a gas engine. My question relates to running the engine to charge batteries while anchored for an extended period. I have read somewhere that it is not good to run the engine in neutral for extended periods because of lubrication issues in the outdrive. The problem is that the top end does not get lubrication unless the drive is in gear. First is this true and if it is would putting the drive in gear every so often prevent problems and allow one to run the engine for an hour or so per day?

[CDK]

No, that is nonsense.
There is plenty of oil in the upper gearcase and no load whatsoever because the drive is in neutral.

But unless you get your gas for free, this is a terribly expensive way to store a few Ah's in your battery. I estimate that more than 95% of the gasoline's energy content is converted to heat and pumped overboard. And your engine gets lots of carbon deposits.

If you really need the extra charge while anchoring, a small generator with 12 VDC output is the way to do that. It can run at an efficient rpm, reaches its normal operating temperature and provides a much higher charging current than your idling Volvo.

[powerabout]

there is an oil pump on the prop shaft that wont be turning.....
and with only the input shaft and cone clutch turning I think they will be above the static oil level??
so maybe if it sat for a long time fully down it might be an issue but I doubt it.
Just check the dip stick and you will see where the oil level is

[pistnbroke]

in the uk the canal boats run there engines 12 hrs per day to charge the batteries...they run about 1500 rpm and a 4 :1 up ratio to drive the alternator is normal as is 2 alternators of 100A output capacity each...so unless you are going to fit an alternator with about 8:1 gearing and disconnect its belt when at sea you are wasting your time at 800rpm and a 2 :1 ratio. YOu should size your alternator for 25A per 100AH of your house battery . However big your alternator you will not get a charge current of over 25A initally into a 100AH discharged battery. A small 4 stroke driving an alternator would be a better soluton ...a motor driven gen with a 12 A output is a bit small for the job.

[CDK]

I have a tiny, lightweight Mase silent-500, made in Italy. It delivers 12V/20A, 24V/15A or 230V/500W with very precise electromagnetic load/rpm control.
If I wouldn't have had it I'd make a charger from the smallest Briggs&Stratton and a 3:1 belt driven alternator.

[pistnbroke]

you can actually drive the alternator direct with a briggs either horisontal or with it under the motor on a vertical shaft ...just change the warning light bulb for 21 watt and it will start charging early ...engine quite safe to run at 4000 rpm without modification . alternators driven direct with small honda are popular camping gen in australia

If we knew how many AH the OP was trying to charge then it would be easier to advise .