Charging two batteries

[JD76]

Hi guys,<br />Could do with a little help. I have a small cruiser (16.5 feet) which I use mainly for fishing. My power is a 2004 50hp Tohatsu ELP.<br />I carry two batteries (both 12v), one for cranking the motor and the other for powering the VHF, fish-finder, log and lights. This is a big 110 a/h job and it's a bit of a strain taking it out after every trip to recharge.<br />The cranking battery is charged by the engine alternator which pushes out 135w /11 amps.<br />What I need to do is somehow rig up a system whereby both batteries can be topped up by the engine when I'm under way. <br />I do a few all night trips and, out in the North Sea, it's a good idea to have all your nav lights showing bright and clear!!<br />Any help or ideas would be greatly appreciated.<br />Thanks,<br />John

 

[Silvertip]

Re: Charging two batteries

Your 11 amp alternator would need to run for hours to replenish even a half flat battery. That said, purchase a Perko or similar battery switch and make sure it's a "Make-before break" type. The switch generally has OFF, BAT1, BAT2, and BOTH settings meaning all electrics can be turned off, or you can select BAT 1, BAT2, or BOTH to power everything on the vessel. At anchor or adrift, select just one of the batteries to run accessories. Switch to BAT 2 upon restart as it will be topped off. You can charge both, or just BAT 1 or BAT 2 while under way. If the switch is not marked "Make before break" NEVER switch it while the engine is running as you will very likely pop the voltage regulator rectifier.

 

[Richard Petersen]

Re: Charging two batteries

Buy a battery voltage meter and connect it between a ground (earth) point and the input to the selector switch. Check the voltages to decide who needs the charging. A percentage of battery power meter is a good type to use.