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lightyear22 03-03-2006 08:31 AM

Using the outboard to charge battery
On my SailMaster outboard it has a charger in it for charging the 12v battery. I took a reading with the voltometer anf it is putting out alot more than 12v. I am thinking that when it is hooked up to the battery it will put a load on the charger and do what it is supposed to. Is this correct. I have read that people use the 12v outlet in the cabin to connect to the electical and charge the battery from there. Will this effect my other wiring in the boat? Will it cause any damage to my wired in xantrex shore power charger? I do alot of night sails and would like to keep the battery up and the lights on.


GordMay 03-04-2006 06:53 AM

Charging Voltage over 13.8VDC
Depending upon your battery type (and ambient temperatures), typical Charging Voltages are always considerably higher than 12Volts.

Bulk (Absorption) Rate:
Flooded Lead Acid: 14.4VDC (@ normal temp. 77 deg. F - Lower V for Hot temperatures, and Higher V for Cold temps.)
AGM: 14.3VDC
Gel: 14.2VDC

Float Rate:
Flooded: 13.5VDC
AGM: 13.4VDC
Gel: 13.8VDC

Be aware that your small outboard may not have a “Regulated Output” alternator, suitable for Battery Charging. Many small O/Boards only have an “Unregulated” power supply, suitable for operating lights.

Gord May

lightyear22 03-04-2006 07:16 AM

I think it is unregulated. Does this mean I need to install a switch so I may switch just the lights over to the O/B? When I took the O/B in for service last year. The service man said that the charger was working correctly and that it was unregulated.


GordMay 03-04-2006 08:55 AM

SPDT Switch
Yes, a Single Pole Double Throw Switch (Centre Off), applied as a DC Source Selector to the Navigation Lights.
The "Common" (Centre) pole goes to the Lights.
One Switched Terminal comes from the Outboard Alternator Output, & the Other Switched Terminal from the Batrery.

Alt ----------0
Centre 'Off' > 0---- Lights
Batt --------0

BeneteauMark 03-04-2006 10:59 AM

Charge/run lights with outboard -- check amps, too
It wouldn't hurt to check the amp output from your outboard's alternator before proceeding. My 5hp OB's alternator only put out 2 amps at crusing rpm, which wasn't enough to do anything with.

Before rearranging wiring to run your nav lights from the outboard, if you're doing a lot of night sailing, what is the total amp draw from your nav lights? (The aggregate draw from my bow light and stern light is only 2-3 amps. You can get a lot lower than that with LED nav lights.) Realistically, a decent group 24 deep cycle battery should power the lights overnight, and you could recharge once returning to the dock. Seems simpler to me than splicing in a switch to chose between battery and alternator power.

One Step Closer
Lake St. Clair, MI

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