Battery separators are used to connect a house battery to a starting battery, so that each can be charged from the others’ charging source. The separator only joins the batteries when one is fully charged.

There are two types of separator: one way (or unidirectional), and two way (or bidirectional).

Wiring either type is very simple:

• heavy gauge wire from each battery to the appropriate stud on the separator
• light-gauge wire (14AWG is recommended) from the earth tab of the separator to chassis ground

Separators vs isolators

I don’t talk much about isolators in these pages. Isolators use a diode to isolate one battery from the other; voltage traveling across this diode experiences a loss of about 0.6 volts. This can result in a charge voltage too low to be effective. If the isolator fails, the batteries are left in a separated state.

Separators use a solenoid switch, with no voltage drop. If the switch fails, the batteries are left in a connected state.

One way separators

These allow charging of both batteries from a single side of the separator. Usually, this is set up to allow the house battery to be charged by the alternator, once the starting battery is fully charged.

Recommended units:

	Sure Power 1314
	Blue Sea Systems automatic charging relay

Two way separators

These allow charging of both batteries from a charging source on either side of the separator. In this way, the alternator will charge the starting battery always, and the house battery once the starting battery is charged; also, a charging source on the house battery side (such as a shore power charger or solar panel) will charge the starting battery when the house battery is charged.

Recommended units:

Sure Power 1315A