Over the years many battery configurations have been proposed. Isolators, Eliminators and Combiners were developed and sold to allow charging the various battery configurations.. We have looked at all of them, had most of them on our boat at one time or another, and all have worked reasonably well.  

However, we were never quite thoroughly satisfied. Some were too complex and most were expensive. We have designed a system that is inexpensive, easy to install, occupies little space, and is user friendly because it requires no attention by the user. Simply use a 60 amp Schottsky Diode and a 30 amp Thermal Circuit Beaker to charge all the auxiliary batteries. .We connect all the house batteries into one bank, and all charging sources charge only that one bank. Whenever the house bank rises 0.4 volts above the auxiliary batteries they will be trickled charged and floated 0.4 vo1ts 1ess than the house battery. Since auxiliary batteries are not used very often, as compared to house batteries, keeping them charged at a lower voltage is better for long period f1oat charging. Liquid batteries will not gas or loose water, and both types of batteries will be kept full at the lower voltage, ready for use.   

When an auxiliary battery like the starting battery is used, it will drop to about 9 volts while cranking the engine. The house battery at 13 to 14 volts will try to put large amounts of current into the auxiliary battery. If over 30 amps flows to the auxiliary battery, after about 20 seconds the thermal circuit breaker will open stopping the high charging current. Once the engine starts the starting battery will return to about 12.5 volts. After another 30 seconds the thermal circuit breaker will close and charging will resume from the house battery to the auxiliary battery at 5 to 15 amps. As the auxiliary battery returns to full float charge the charging current will fall back to a trickle charge.  The thermal circuit breaker protects the wires between the two batteries and large size wire is not required. 

The addition of two simple on-off battery switches provides some very good benefits. The Start Switch provides an easy way to stop engine cranking should the starter hang up and the engine not start. Just turn off the starter. This switch has a removable handle, which should be taken with you when you leave the boat. This makes it very difficult for someone trying to steal the boat to start the engine. 

Should the starting battery become discharged, simply turning the Emergency Switch to ON will put every battery in the house bank onto the starting battery to start the engine. The Figure below shows the basics of the circuit.  It can be expanded to include all the charging sources on one's boat, i.e. alternator, battery charger, auxiliary generator, alternator, wind, solar, or water generators.  

If you already have an amp hour monitor on board, we can help you combine the Simpler Solution into your system thereby monitoring all your charging sources. Give us a call or email us at techsupport@fourwinds-ii.com

Our kit that includes: One Diode with heat sink, one Thermal circuit Breaker and four ring terminals