Batteries and Storage Systems

What the rule requires

Aboard ship the storage battery is the source for emergency and portable power — emergency diesel generators, gyrocompasses, emergency radios, ship's boats and forklifts NAVEDTRA 14104 Ch. 12 — Batteries. Exam questions on this topic split into two families: what you do at the battery with a hydrometer and a charger, and what the regulation demands of the installation. Both are worked below.

The five charges, and what triggers each

A discharged battery is restored only by passing a charging current through it. Adding active ingredient to the electrolyte raises specific gravity but does not convert the plates back to active material, so it does not bring the battery back to a charged condition NEETS Module 1 Ch. 2 — Battery Charging.

Initial charge — a new battery shipped dry has uncharged plates. Once electrolyte is added, it is given a long, low-rate charge per the manufacturer's instructions.
Normal charge — the routine charge given in accordance with the nameplate data during the ordinary cycle of operation.
Equalizing charge — a special extended normal charge, given periodically as part of a maintenance routine, which drives all the sulfate off the plates and restores every cell to maximum specific gravity. It is continued until the specific gravity of all cells, corrected for temperature, shows no change for a 4-hour period. That 4-hour stop criterion is the tested detail.
Floating charge — the rate is set by battery voltage rather than by a definite current value. Used to hold a battery at full charge while it is idle or in light duty, at low current, and also called a trickle charge.
Fast charge — starts at a much higher rate than normal, for use only in an emergency, as it may harm the battery.

The charging rate is normally on the nameplate; if the available equipment does not have that rate, use the nearest available, but never a rate so high that violent gassing occurs.

Gassing is your charge-rate indicator

As a lead-acid cell nears full charge it can no longer absorb the energy chemically, so the excess electrolyzes water — hydrogen off the negative plates, oxygen off the positive NEETS Mod. 1 §2-3. Hydrogen is explosive in air above about 4 percent, which is why battery rooms and boxes are ventilated, charging spaces kept clear of flames, sparks and smoking, and the charger switched off before leads are connected or disconnected so no arc is drawn at the terminals.

Read the gassing two ways. Violent gassing when the battery is first placed on charge means the rate is too high; steady gassing developing as the charge proceeds means the battery is nearing full charge . Overcharging accelerates gassing, water loss, plate corrosion and heating; undercharging leaves the plates sulfated .

Specific gravity and routine maintenance

The amount of active ingredient dissolved in the electrolyte cannot be measured directly, so it is measured indirectly as specific gravity, using a hydrometer NEETS Module 1 Ch. 2 — Battery Maintenance. Pure water is 1.0; sulfuric acid and potassium hydroxide are heavier than water, so electrolyte reads above 1.0, and the acceptable range for a given battery comes from its manufacturer. Draw in enough electrolyte to float the float, but not so much that the float rises into the suction bulb, hold the instrument vertical, and read where the electrolyte surface touches the scale. Flush with fresh water after each use, and never use a storage battery hydrometer for any other purpose.

The first step in maintaining any secondary-cell battery is to check the technical manual for that specific type. After that: terminals checked for cleanliness and good connection, case inspected for cleanliness and damage, and electrolyte level topped with distilled water only.

Handling precautions are exam material in their own right. Never short the terminals. Use carrying straps to transport. Wear rubber apron, rubber gloves and a face shield. No smoking, sparks or open flames near charging batteries. Electrolyte spilled on a surface is diluted with large quantities of water and cleaned up at once; on skin or in the eyes, flush immediately with fresh water for a minimum of 15 minutes, pulling the lids clear if it is in the eyes, and notify the medical department. Keep a neutralizing agent to hand — baking-soda solution for lead-acid, boric acid or vinegar for alkaline — and if electrolyte must be mixed, add acid to water, never water to acid . Salt water reaching the electrolyte releases poisonous gases and sets up a reaction that will ruin the battery; report it to the electric shop .

Capacity and rating

Capacity is in ampere-hours: current in amperes multiplied by the hours the battery will supply it, and it varies inversely with discharge current NEETS Module 1 Ch. 2 — Capacity and Rating of Batteries. A 400 ampere-hour battery delivers 400 amperes for 1 hour or 100 amperes for 4 hours. Most batteries are rated at the 20-hour rate — 20 amperes for 20 hours is a 400 ampere-hour rating — and a battery delivers its full rated capacity only when discharged in 20 hours or more. Discharge it faster and you get less than the rated ampere-hours out of it.

A bank is rated 300 ampere-hours at the 20-hour rate. What is the largest current at which it will still deliver rated capacity, and how long will it hold 5 amperes?

300 ÷ 20 = 15 amperes. Any higher discharge current returns less than 300 ampere-hours. At 5 amperes: 300 ÷ 5 = 60 hours.</details>

Cell and battery types

A cell converts chemical energy into electrical energy and has three parts — electrodes, electrolyte, container NEETS Module 1 Ch. 2 — Summary ¶1. A primary cell cannot be recharged, because the chemical action eventually destroys one electrode. A secondary cell can, because charging current reverses the chemical change to the electrodes and electrolyte.

Lead-acid — the most widely used secondary cell. Anode lead peroxide, cathode sponge lead, electrolyte sulfuric acid and water.
Nickel-cadmium (NICAD) — charges faster, delivers more power, stays idle longer and takes more cycles than lead-acid. Anode nickel hydroxide, cathode cadmium hydroxide, electrolyte potassium hydroxide and water.
Silver-zinc — mostly emergency equipment; light, small, large power capacity for its size. Anode silver oxide, cathode zinc, electrolyte potassium hydroxide and water.
Silver-cadmium — combines the better features of nickel-cadmium and silver-zinc.

The installation: classification, placement and protection

A battery installation is classified by the output of its charger, computed from the highest possible charging current and the rated voltage of the installation: large above 2 kW, moderate between 0.2 kW and 2 kW, small below 0.2 kW 46 CFR §111.15-3. Batteries that generate less hydrogen than an equivalent category of lead-acid, such as sealed types, may have the category reduced.

Placement then follows from the category 46 CFR §111.15-5:

Large — a room used only for batteries, or a box on deck, with installed electrical equipment meeting the hazardous location requirements of subpart 111.105.
Moderate — battery room, box on deck, or a box or locker in a space such as an engineroom or storeroom; the box or locker is not required if the installation is in a ventilated compartment such as the engineroom and is protected from falling objects. Never in a sleeping space.
Small — not in poorly ventilated spaces such as closets, and not in living spaces such as staterooms.

An engine cranking battery goes as close as possible to the engine or engines it serves. Trays are chocked with wood strips or the equivalent, with non-absorbent insulating supports beneath and spacer blocks at the sides for air circulation, and left accessible for installation, maintenance and removal. Battery rooms and lockers get a watertight lining — 3 inches up each shelf or 6 inches up the deck, 1.6 mm lead or equivalent for lead-acid, 0.8 mm steel or equivalent for alkaline; a battery box gets the same lining to at least 3 inches. Each battery carries permanently fixed nameplate data: manufacturer, model, type designation, cold cranking amp or amp-hour rating, and for lead-acid the fully charged specific gravity value.

Cell construction under Subchapter J: no electrolyte spillage when a cell is inclined 40 degrees from the vertical, hydrogen evolution no greater than a similar size lead-acid battery under similar charging conditions, and construction accounting for marine temperature, vibration and shock 46 CFR §111.15-2.

Protection. An overload protective device goes in each battery conductor except conductors of engine cranking batteries and batteries of 6 volts nominal or less; for large installations the overcurrent devices sit next to, but outside of, the battery room 46 CFR §111.15-25. Charging equipment for batteries whose nominal voltage exceeds 20 percent of line voltage must protect automatically against current reversal, except where a converter is used. Chargers must suit the size and type of installation they serve, and chargers incorporating grounded autotransformers are prohibited 46 CFR §111.15-30.

Small passenger vessels under Subchapter T are the other set worth knowing: ventilation, natural or induced, sufficient to dissipate the gases wherever charging is done; batteries as high above the bilge as practicable, secured against roll and pitch, clear of splash and spray; permanent type connectors at the terminals, with spring clips and other temporary clamps prohibited; trays lined with or built of material resistant to the electrolyte; an ammeter in the charging circuit of every charger; and a fuse in series in the battery lead, as close as practicable to the battery, where the batteries are not adjacent to the distribution panel or switchboard 46 CFR §183.350.

Emergency power from a storage battery

Five load groups must be connected to an independent emergency source capable of carrying all connected loads continuously for at least three hours: navigation lights, fire protection and detection systems, communications equipment, general alarm, and emergency lighting 46 CFR §28.870. The source goes aft of the collision bulkhead, outside the machinery space, and above the uppermost continuous deck. Where that source is solely storage battery: lead-acid or alkaline type able to withstand pitch, roll, vibration and a salt water atmosphere; no electrolyte spillage at 30 degrees from the vertical; installation in a battery room, box on deck or well ventilated compartment, protected from falling objects; trays secured and lined with material corrosion resistant to the electrolyte; each bank fitted with its own drip-proof charging system; and any deck box weathertight with holes near the top to let gas escape.

Where the battery serves emergency lighting and power, or starts an emergency diesel or gas turbine generator set, it must have apparatus to keep it automatically fully charged, with a continuous trickle charge while the ship's service plant is available and an automatic higher rate after a discharge 46 CFR §112.55-10. Charging operations must not cause an absence of battery power, and instruments must show the rate of charge.

Telling it apart

Charge types get confused because three of them are "normal" in some sense. Separate them by what governs the rate or the endpoint NEETS Module 1 Ch. 2 — Battery Charging:

Normal — governed by the nameplate data, during the ordinary cycle of operation. Restores a battery that has been used.
Equalizing — an extended normal charge on a maintenance schedule. Endpoint is specific gravity steady in all cells for 4 hours, not a voltage or a clock.
Floating — governed by battery voltage, at low current, on a battery that is idle or lightly loaded. The synonym on exams is trickle.
Initial — governed by the manufacturer's instructions, long and low rate, on a dry-shipped battery once electrolyte is in.
Fast — much higher than normal rate, emergency use only.

The two tilt angles are the classic trap. The criterion is which part you are under:

40 degrees from the vertical — general battery construction, Subchapter J 46 CFR §111.15-2.
30 degrees from the vertical — a battery serving as the sole emergency source of power on a fishing industry vessel 46 CFR §28.870.

Series against parallel, where the criterion is which quantity increases NEETS Module 1 Ch. 2 — Summary ¶1: series gives higher voltage with no increase in current; parallel gives higher current with no increase in voltage; series-parallel gives both.

Working a question

A 32-volt bank in the engineroom, not used for engine cranking, is served by a charger whose highest possible charging current is 30 amperes. Ship's service line voltage is 120 volts. What does the regulation require of the installation?

Compute the charger output. 32 V × 30 A = 960 W = 0.96 kW, from the highest possible charging current and the rated voltage of the installation 46 CFR §111.15-3.
Classify. 0.96 kW falls between 0.2 kW and 2 kW, so this is a moderate installation. Not large — a large installation would need a dedicated battery room or deck box and hazardous-location electrical equipment.
Place it. A moderate installation may be in a battery room, a box on deck, or a box or locker in the engineroom. Because it is in a ventilated compartment and protected from falling objects, the box or locker is not required 46 CFR §111.15-5. Had the same bank been proposed for a crew berthing space, that is prohibited outright.
Overload protection. An overload protective device is required in each battery conductor. The cranking-battery exception does not apply here, and 32 volts is above the 6-volt nominal cut-off 46 CFR §111.15-25.
Reverse current. 32 ÷ 120 = 26.7 percent, above 20 percent of line voltage, so the charging equipment needs automatic protection against reversal of current unless a converter is used.
Charger itself. Enclosure per § 111.01-9, suitable for the size and type of installation, and no grounded autotransformer 46 CFR §111.15-30.

Note step 1. Nothing in the classification depends on the battery's ampere-hour capacity, its physical size, or how many cells it has.

Where candidates lose the point

Choosing the open-circuit voltage test to find a weak cell. It reads plausible because a bad cell does drag voltage down, but the method that isolates the cell is comparing the specific gravity of the electrolyte in each cell with a hydrometer NEETS Module 1 Ch. 2 — Battery Maintenance.
Reading violent gassing as "nearly charged." Steady gassing developing as the charge proceeds indicates a battery nearing full charge; violent gassing at the start of the charge means the rate is too high NEETS Module 1 Ch. 2 — Battery Charging.
Topping up with tap water, or with acid. Distilled water restores level; adding active ingredient raises specific gravity without recharging the plates, so the reading lies about the state of charge.
Classifying an installation by battery size. The three categories key on charger output in kW — 2 kW and 0.2 kW are the breakpoints — computed from highest charging current and rated voltage 46 CFR §111.15-3.
Answering 40 degrees for an emergency battery on a fishing industry vessel. That installation is 30 degrees 46 CFR §28.870.
Applying overload protection to every conductor without exception. Engine cranking battery conductors and batteries of 6 volts nominal or less are excepted 46 CFR §111.15-25.
Answering three hours as "the battery capacity requirement" for any vessel. The three-hour endurance attaches to the five specific emergency loads listed in § 28.870(a), and the source must also be aft of the collision bulkhead, outside the machinery space, and above the uppermost continuous deck.
Treating a deck box as sealed because it is weathertight. A deck box used for battery storage is weathertight and has holes near the top so hydrogen escapes.

Check yourself

You are told to charge a battery that came aboard dry and has just had its electrolyte added. Which charge do you give it, and on whose instruction?

An initial charge — long, at a low rate, in accordance with the manufacturer's instructions shipped with the battery; absent those, current Navy directives NEETS Module 1 Ch. 2 — Battery Charging. A normal charge follows nameplate data during the ordinary cycle of operation and is the wrong answer for a battery that has never been charged.</details>

You are running an equalizing charge on the emergency bank. How do you know when to secure it?

When the specific gravity of all cells, corrected for temperature, shows no change for a 4-hour period. The purpose is to drive all sulfate off the plates and bring every cell to maximum specific gravity, so the endpoint is a gravity reading that has stopped moving, not elapsed time or a voltage.</details>

A 24-volt moderate installation is proposed for a locker in the crew berthing space, protected from falling objects and ventilated. Is that acceptable?

No. A moderate battery installation must not be in a sleeping space 46 CFR §111.15-5. The box, the ventilation and the protection from falling objects do not cure the location.</details>

Electrolyte splashes into a shipmate's eyes at the charging station. What do you do first?

Flush the eyes immediately with large quantities of fresh water for a minimum of 15 minutes, pulling the upper and lower lids clear so water reaches under them, then notify the medical department with the type of electrolyte and location of the accident NEETS Module 1 Ch. 2 — Battery Maintenance.</details>

On a small passenger vessel the battery bank sits several feet from the switchboard and its terminals are made up with spring clips. Name the two deficiencies.

Terminal connections must be permanent type connectors; spring clips and other temporary clamps are prohibited. And because the batteries are not adjacent to the distribution panel or switchboard, the battery lead needs a fuse in series as close as practicable to the battery 46 CFR §183.350.</details>

The emergency generator's starting battery is on charge from the ship's service plant. What charging arrangement does the regulation require, and what must be fitted to prove it?

Apparatus to maintain the battery automatically fully charged: a continuous trickle charge while the ship's service generating plant is available, with automatic charging at a higher rate after a discharge, and charging that does not cause an absence of battery power. Instruments must show the rate of charge 46 CFR §112.55-10.</details>

A charger's highest possible charging current is 8 amperes at a rated 24 volts. What category is the installation, and where may it not go?

24 × 8 = 192 W = 0.192 kW, below 0.2 kW, so small 46 CFR §111.15-3. It must not be in a poorly ventilated space such as a closet, nor in a living space such as a stateroom . Note how close the arithmetic runs to the moderate breakpoint — compute it rather than eyeballing the battery.</details>