Selecting Equipment

Continued charging of a fully charged battery will cause a rise in battery temperature and excessive gassing. When connected to shore power, the batteries are kept charged by an onboard charger. Small 12-volt boat refrigeration systems will run many hours per day in warm climates while drawing current from the batteries. The current is then replaced by the charger. Many battery chargers cannot handle the continuous balancing of current flow. The simplest way to determine it your charger is over stressing batteries is by the loss of water or battery temperature. Although all of these charger examples are not marine equipment their charging patterns are similar to the different chargers found in many boats. These example voltages only apply to common lead acid batteries. Other type Batteries may require lower voltage

Fixed Output 12-Volt Charger

Fixed output chargers have no automatic control over voltage. Their transformers are wound to produce from 14.2 to 15 volts. These chargers are designed to be left on batteries for only the length of time it takes to bring them up to full charge. This type charger may have been the best way to do it 25 years ago but not today.

Automatic Shutoff Charger

Automatic shut off is the answer to over charging batteries only if there is no load connected to the battery. The basic operating principle of this type charger is to shut down when full charge is reached and reactivate when charge drops to 90%, which would be several hours or days. When a 12-volt refrigerator 5-amp load is added, the automatic charger turns on to its fixed output of 15-volts that will overload a fully charged battery for several hours each day.

Fully Automatic Charger

Some fully automatic chargers are nothing more than an auto shutoff with a trickle charger added. When these chargers see a full charge, they switch to a pulse charge of less than one tenth amp. Again, when a refrigerator load is added to the battery, the charger switches to full output voltage overcharging the battery.

Fully automatic 3 stage charger

The new step voltage regulators for alternators and battery chargers have become the boat battery's best friend by reducing the voltage several times during charging. The final charge step is know as the float phase and should maintain the battery and act as a power supply for small current drawing equipment such as a refrigerator The more expensive chargers provide various settings for operator control to compensate for seasonal battery temperatures and battery types.