(11) Charging More Than One Battery Bank from a Common Alternator or Charger

What is necessary to charge two battery banks from a single alternator?

A way to parallel them while charging and isolate them while running.

Name the options for managing charging between two battery banks.

Manual Battery Selector Switch, Battery Isolation Diodes, Battery Paralleling Relays, Series Voltage Regulators, and Remotely Operated Battery Switches

What are the more common solutions for charging multiple battery banks?

Battery paralleling relays, series voltage regulations, and remotely operated battery switches.

What is the function of a battery selector/isolation switch?

It parallels the various batteries when charging and isolates the banks when finished.

What positions does a typical battery selector switch have?

OFF, 1, BOTH, 2.

What should generally not be wired to the battery side of the selector switch?

Loads should generally not be wired to the battery side to maintain the isolation function.

What are exceptions to the rule against wiring loads to the battery side of the selector switch?

Exceptions include bilge pumps, battery charging devices, and safety/memory devices like propane alarms.

What is the purpose of having Overcurrent Protection (OCP) as close to the battery as possible?

To protect equipment that needs to be continuously connected to the battery.

What is the field disconnect function on some battery switches?

It disables the alternator before the switch circuit is broken to prevent damage.

What damage can occur if the bank switches are changed while the engine is running?

Alternator damage can occur if banks are switched while the engine is running.

What type of switch is necessary to avoid alternator damage?

A Make-before-break switch is necessary.

What is the operation process of a Make-before-break switch?

It brings both batteries online before disconnecting one.

What is a Zap Stop or Snubber?

A cheap device wired from alternator output stud to ground to safely short out spikes to prevent damage.

What can happen if two different battery types are charged in parallel?

One battery is likely to be overcharged while the other is undercharged.

What is a remotely operated battery switch?

A heavy duty relay that allows switches to be inaccessible and closer to batteries while still being operable.

What are key criteria for remote battery switches?

Continuous and intermittent current ratings suitable for application, manual on/off, safety lockout, local and remote indication of on/off, power only used when switching to prevent power drain, ignition protection

What is the primary issue with using diodes in battery charging circuits?

Diodes cause a voltage drop of 0.6V-1V, leading to incorrect sensing by regulators.

How does split charging with diodes work?

Alternator output is fed to diodes that get assigned to each battery or bank so batteries can be charged in parallel but are isolated when running, since diodes only allow current flow in one direction.

What happens when a regulator senses 14.2V due to diode voltage drop while the battery is at 13.6V?

The regulator may stop charging the battery, thinking it is full, resulting in an undercharged battery.

What is the recommended alternative to diodes for battery parallel configurations?

Using a Battery Paralleling Relay, Automatic Voltage Relay (AVR), Automatic Charging Relay (ACR), Voltage Sensitive Relay (VSR), Zero Drop Isolator, or a Combiner

What type of device can be used instead of diodes to prevent voltage drop in battery charging?

Battery Paralleing Relays, which use a heavy-duty relay, solenoid, or solid-state switch.

What is the function of a voltage sensing circuit in a battery paralleling relay?

It triggers the relay to close when battery voltage rises, allowing charging.

What happens when a heavily discharged battery bank is paralleled with a well-charged one?

There may be a high short-term inrush current flow when the paralleling first occurs.

What can a high inrush current cause in terms of relay operation?

It can cause the voltage on the higher voltage battery to drop below the relay's recognition threshold and open the relay.

Where should the alternator be wired to avoid issues with battery paralleling?

The alternator should be wired to the house bank side of the relay since it will be the more discharged one.

What is the difference between latching relays and conventional relays?

Latching relays only need power to actuate them and then have no power drain, while some relays require power to hold them closed.

What do 'smart' paralleling devices prioritize?

They prioritize the starter battery until a set point, then isolate it and bring another battery to the same voltage until the first battery falls back under the set point.

How many batteries can 'smart' paralleling devices typically manage?

They can work for up to 4 batteries and will parallel them all when they reach the same voltage.

What happens if the voltage drops on a battery managed by smart paralleling devices?

The device will isolate the other batteries and focus on the one whose voltage has dropped until voltage is restored.

What is the problem with paralleling charge sources for different types of batteries (cranking vs house)?

One charge source sends charge to several different types of batteries that accept charges differently.

How can you get around the problem of paralleling different types of batteries?

By having a voltage regulator for each bank, having an alternator for each bank, or with one alternator, using a series regulator or a battery-to-battery charger.

What is the function of alternator to battery chargers?

They take the output of one or more alternators and apply multi-step regulation to prioritize cranking.

What is a key difference between alternator regulators and alternator to battery chargers?

Alternator to battery chargers do not push alternators to a higher voltage and won't cause problems with electronically controlled engines, instead they use DC-to-DC converters to boost alternator output voltage.

What kind of converters do alternator to battery chargers use?

They use internal DC-to-DC converters to boost alternator output voltage.

Why are electronic devices often put on their own battery bank?

To protect against voltage sag and spikes that can cause electronic failure and interference.

Why is it beneficial to have a separate battery bank for windlasses?

It saves money on heavy cabling since the windlasses are often at the bow and batteries at the stern of the boat.

What should the cables to the windlass battery be rated for?

Maximum alternator output.

How much current can bow thrusters use?

Up to 700 amps at 12 and 24 volts.

What can leave batteries undercharged?

The distance from the charging source unless a Battery-to-Battery charger is installed.

What is Point Charging?

Point Charging is when, even at different voltages, all charging devices connect to a common charging bus, and end up with common voltage using a constant voltage regulator. Each bank is then charged with a dedicated Battery to Battery charger that is specifically set to their banks CAR

What is the purpose of dedicated chargers for each battery bank?

To ensure each bank is charged at the appropriate voltage specific to that bank.