Charging from Outboard

[Drascomber]

My Mercury 6HP 4T outboard gives me 2 amps at cruising speed and about 2.5 flat out.

In the days when cars had ammeters the charge dropped when the barrery was recharged.

However, the outboard seems to always give the same output whether the batteries are fully charged or not. Is this right?

 

[VicS]

Yes probably because the open circiut voltage from your o/b will be way above the normal regulated output of a proper alternator. If you have a good sized battery it should be able to take that current for a lengthy period but if you find the battery needs regular topping up disconnect the charging connection, or fit a switch so that it can be switched off. If you must then find a suitable regulator, one intended for solar pnels or wind turbines perhaps. I think there is something in the Maplin catalogue. Better still sail more and motor less!

 

[Otter]

Our Yamaha 9.9HP does exactly the same, I assumed it was a fault and was going to try and fix it. On the very rare occasions we have to motor for more than a couple of hours the charge state led's on the Marlec controller are stuck at maximum - a state they never acheive other than in prolonged 40+knot winds with the Rutland 913 in full helicopter mode.
If we were to disconnect the charging leads or fit an on/off switch, isn't that like running a diesel with the alternator disconnected from the batteries, doesn't that fry the alternator?

 

[FullCircle]

Unlikely you will run the outboard so much that it will blow a decent size battery. I presume you have something between 70-85Ah? Should be no problem at all, rather the opposite usually.

 

[Drascomber]

If it helps my batteries are two sealed lighting standby batteries of 26 amp hours each.