TST Engineering Services | Module 31 Batteries & Emergency Power Infographic

1

Rules, regulations and emergency-power function

SOLAS Ch II-1 route

Purpose of the emergency source

Emergency electrical power exists to keep essential safety services available when the main source of electrical power fails. The source may be an emergency generator, batteries, or a combination, but it must be independent and arranged so that an engine-room or main-source casualty does not disable the emergency supply.

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45 secondsAutomatic start, connection and supply of emergency circuits within the common SOLAS oral figure.

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Independent sourceEmergency source, switchboard and route are separated from the main source of power.

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Fuel supplyIndependent fuel supply with closed-cup flash point not less than 43°C.

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Damaged attitudeEmergency power equipment remains capable at 22.5° list and 10° trim.

Requirement area	Detailed fact to include	Engineering reason
Location and independence	Emergency source, associated transformers/converters, transitional source and emergency switchboard are outside and away from the main machinery space/main source, normally above the uppermost continuous deck, not forward of the collision bulkhead and accessible from open deck.	Emergency power should remain available after main-space fire, flooding or loss of normal electrical supply.
Construction / separation	Emergency generator space and emergency switchboard are separated from the main source. Fire boundaries, ventilation, access and cable routes are ship/Class specific; machinery-space construction is generally treated as a protected space.	One casualty should not disable both normal and emergency electrical power.
Automatic connection	On main-source failure, the emergency generator starts automatically, connects to the emergency switchboard and supplies emergency circuits within the required time; 45 seconds is the common oral figure.	Escape, communications, fire detection and essential safety circuits cannot remain unavailable during a blackout.
Fuel	The emergency-generator prime mover has an independent fuel supply. Closed-cup flash point is not less than 43°C.	Independence and safe fuel storage preserve emergency operation when normal systems are unavailable.
Starting energy	Starting arrangements are independent and capable of repeated starts. The teaching answer is at least two starting arrangements and stored energy for at least three starts without recharge.	The set must start even if the first attempt fails and the normal supply/charger is unavailable.
List and trim	Emergency power equipment remains capable of operation with the ship listed up to 22.5° and trimmed up to 10°.	Emergency systems must remain available during damaged or abnormal ship attitude.
Emergency battery source	Where batteries supply emergency loads, they carry the load for the required duration without recharge and without excessive voltage drop, and are not normally in the same space as the emergency switchboard.	Batteries must not depend on failed normal supply and should not introduce a single-point failure.
Testing	Emergency source and changeover arrangements are tested under SMS/PMS, including starting energy, breaker/changeover logic and emergency load availability.	Readiness must be proven and recorded, not assumed.

2

Main failure to emergency supply

Blackout recovery

Emergency switchboard supply logic

In normal operation, the emergency switchboard is commonly fed from the main switchboard through an interconnector.
When normal supply fails, undervoltage/no-voltage detection initiates emergency-generator auto-start logic.
Transitional batteries or UPS arrangements support critical services that cannot tolerate the 45-second changeover period.
Breaker and changeover logic prevents unsafe paralleling, reverse feeding or overload of the emergency generator.
When normal supply is restored, changeover back to normal supply is carried out automatically or manually according to vessel design.

Emergency loads are vessel-specific. Common examples include emergency lighting, escape-route lighting, navigation lights, radio/GMDSS, internal emergency communications, fire detection, fire alarms, fire-door release, emergency fire pump, selected bilge/firefighting services, watertight doors/indicators, steering control or one steering motor as applicable, and equipment required to restart a main generator.

3

Emergency-generator automatic start sequence

Signal → cranking → load

Normal condition

Emergency switchboard is supplied from the main switchboard. Emergency generator is on standby; heaters, charger, control power and starting energy are maintained.

Main supply fails

Undervoltage/no-voltage relay detects loss of normal supply to the emergency board or main bus failure.

Start command issued

Emergency generator control panel receives the automatic start command after the designed time delay or logic confirmation.

Cranking

Battery starter, air motor/direct air or hydraulic starter operates. Fuel rack/solenoid, governor, pre-lubrication and start-permissive logic operate as designed.

Engine fires and proves running

Speed pickup/frequency, oil pressure, voltage build-up and excitation are confirmed. Failed-start logic may initiate another attempt.

Voltage and frequency acceptable

AVR and governor stabilise the output. Protection verifies that the set is healthy enough to close onto the emergency switchboard.

Emergency breaker closes

Normal feeder is opened or isolated by changeover logic. Emergency generator breaker closes and energises the emergency switchboard.

Emergency loads supplied

Essential emergency circuits are fed. Preferential trips or load-management logic prevent overload or unsafe backfeed.

Normal supply restored

Changeover back to the normal source is completed according to vessel design. The emergency generator cools down and returns to standby.

4

Emergency-generator starting systems

Stored energy route

Battery electric start

A dedicated DC battery bank supplies a starter motor through a solenoid/contactor. The motor drives the flywheel until the engine fires.

Checks: state of charge, charger, terminals, cabling, insulation, starter motor/solenoid, fuses/links and low-voltage alarm.

Compressed air start

Stored air in an independent receiver is released through a starting valve, starting air motor or direct-air system to crank the engine.

Checks: receiver pressure, drains, compressors, non-return valves, leaks, reliefs, isolation positions and start-air quality.

Hydraulic start

A hydraulic accumulator stores pressure. On start, oil drives a hydraulic motor coupled to the engine.

Checks: accumulator pressure, nitrogen pre-charge, hydraulic oil level, leaks, pump, valves and manual recharge arrangement.

Repeated starts: the stored-energy system must remain capable of repeated start attempts. The common teaching answer is at least three starts without recharge and at least two independent starting methods/arrangements, but the exact arrangement is ship, Flag, Class and build-date dependent.

5

Battery fundamentals and cell arrangements

Cells, voltage, capacity

A cell is a single electrochemical unit. A battery is two or more cells connected together.
A cell converts chemical energy into electrical energy during discharge.
Electrolyte may be acidic, alkaline or other chemistry depending on the cell type.
Cells in series increase voltage. Cells in parallel increase ampere-hour capacity.
Ampere-hour is a measure of capacity: a 50 Ah battery rated over 10 hours can supply about 5 A over that stated period.
Primary cells are non-rechargeable. Secondary cells are rechargeable and are the normal emergency/standby battery type.

6

Battery type comparison

Selection and risks

Battery type	Electrolyte / construction	Typical voltage and charge indication	Advantages	Disadvantages / risks
Open lead-acid	Lead dioxide positive plates, spongy lead negative plates, dilute sulphuric acid electrolyte.	About 2.0–2.2 V per cell. Specific gravity is useful on open cells.	Low cost, efficient, high cranking current, familiar maintenance route.	Gassing, corrosion, topping-up, sulphation if left discharged, heavy, hidden capacity loss possible.
VRLA AGM/Gel	Valve-regulated lead-acid; sealed with pressure valve, AGM or gel electrolyte format.	Lead-acid voltage range. State of health still requires load/performance testing.	Low maintenance, sealed, reduced electrolyte handling, useful for standby systems.	Should not be opened, sensitive to overcharge/heat, correct charger settings critical.
Alkaline / Ni-Cd	Nickel hydroxide positive, cadmium negative, potassium hydroxide electrolyte.	About 1.2 V per cell. Specific gravity is not a state-of-charge indicator.	Long life, robust, good standby service, tolerant of over-discharge and abuse.	Higher initial cost, lower voltage means more cells, cadmium environmental concerns.
Lithium-ion	Lithium-ion chemistry with BMS, cell monitoring, protection and thermal management.	About 3.2–3.7 V per cell depending chemistry.	High energy density, compact, low self-discharge, useful for hybrid/UPS applications.	BMS essential, thermal runaway risk, cell imbalance, specialist fire detection and firefighting strategy, Class/Flag approval route required.

MGN 550 route
Lithium-ion systems require a specific marine safety case covering BMS, thermal runaway, cooling, fire detection, firefighting and Class/Flag approval.

7

Lead-acid cell operation and condition checks

Chemistry → SG → load test

Condition indicators

Condition	Indication	Meaning
Fully charged	Specific gravity about 1.28 in the module material; approx. 2.0–2.2 V per cell depending condition.	Electrolyte strongest and plates in charged condition.
Discharged / flat	Specific gravity around 1.12; terminal voltage falls.	Electrolyte weakened; prolonged discharge causes sulphation.
On charge	Hydrogen and oxygen may be produced near full charge or during overcharge.	Ventilation and ignition control are critical.
Overcharge / heavy discharge	Heat, gassing, plate damage, loss of active material or sulphation.	Capacity and reliability are reduced.

Voltage alone does not prove capacity. A weak battery may show acceptable open-circuit voltage but fail to deliver cranking current or UPS endurance. Use load/discharge testing according to maker and SMS requirements.

8

Battery maintenance, testing and defects

Practical checks

Routine inspection

Ventilation running, room clean, no corrosion tracking, batteries secure, terminals tight, links sound, cell tops clean and dry, charger healthy, alarms clear.

Electrolyte checks

Open lead-acid: level, colour/contamination, temperature-corrected hydrometer readings and inter-cell comparison. VRLA: do not open; follow maker test route.

Performance proof

Load test or discharge test proves actual capacity. Emergency generator starting batteries should be tested against starting performance and recovery charge.

Defect	Likely significance	Control action
Low SG in one cell	Weak or sulphated cell, electrolyte issue or internal fault.	Compare cells, check temperature correction, investigate under maker procedure.
Bulged case / heat	Overcharge, internal fault, blocked vent or thermal stress.	Isolate if safe, control ignition sources, inform responsible officer and follow SMS.
Corroded terminals	High resistance, poor charging/starting and heat risk.	Clean, neutralise as appropriate, protect terminals and torque to maker guidance.
Charger alarm	Battery may be undercharged or overcharged; emergency starting reliability at risk.	Check supply, output voltage/current, float/boost settings and battery condition.
Failed load test	Battery cannot support required duty even if off-load voltage appears acceptable.	Remove from service or replace according to criticality and approved procedure.

9

Battery room construction, ventilation and safe entry

Hydrogen + acid + fault current

Charging and overcharging can produce hydrogen. Hydrogen is lighter than air and can collect at high points and stagnant pockets.
Ventilation must remove hydrogen and heat. Ventilation failure is a hazardous condition and may require restricted entry or charging control.
Use Ex-rated fixed equipment and intrinsically safe portable devices where the hazardous-area plan requires them.
No smoking, hot work, ordinary portable torches, ordinary phones or ignition sources in the controlled area.
Wear eye/face protection, acid-resistant gloves/apron as required, suitable footwear and remove jewellery.
Use insulated tools, terminal covers and controlled work methods because low-voltage battery banks can deliver very high fault current.
Provide eyewash, spill response, neutralising/containment arrangements and SDS/SMS controls for electrolyte exposure.

10

Hazardous areas, Ex marking and intrinsic safety

Low-energy ignition prevention

Hazardous-area classification

Zone	Explosive atmosphere likelihood	Practical meaning
Zone 0	Present continuously or for long periods.	Highest control level; equipment must be specifically suitable.
Zone 1	Likely to occur in normal operation.	Certified equipment and controlled work practices are required.
Zone 2	Unlikely in normal operation and, if it occurs, only for a short time.	Still requires suitable equipment according to the hazardous-area plan.

The vessel hazardous-area plan is the authority. Do not assume every battery room has the same zone classification; classification depends on ventilation, battery type, charging rate, enclosure and ship-specific design.

Ex marking essentials

Marking	Meaning
Ex i	Intrinsic safety: energy in the circuit is limited below ignition capability under approved normal and fault conditions.
Ex d	Flameproof enclosure: an internal explosion is contained and flame transmission to the atmosphere is prevented.
Ex e	Increased safety: construction reduces risk of arcs, sparks and excessive surface temperatures in normal operation.
Gas group	Equipment must suit the gas/vapour present. Hydrogen is demanding and requires appropriate group suitability.
Temperature class	Maximum surface temperature must be below the ignition temperature of the gas/vapour present.

Intrinsic safety design facts

Intrinsic safety prevents ignition by limiting electrical and thermal energy in the hazardous area.
It is normally used for low-power instrumentation and control circuits, not high-power motors or general lighting circuits.
Voltage and current entering the hazardous area are limited by certified barriers or isolators.
Stored energy in capacitors and inductors must be limited, including field device and cable capacitance/inductance.
Zener barriers require correct earthing/bonding so clamped fault energy has a safe low-impedance path.
IS cabling and terminals are segregated and identified, commonly using light-blue identification.
A system descriptive document/calculation should show apparatus parameters and cable limits.
Non-IS equipment or uncertified repairs must not be mixed into an IS loop.

11

Module 31 assessment checks

Questions candidates must be ready for

Following a blackout, how quickly must the emergency generator start, connect and supply its rated emergency load?
What are the SOLAS requirements for an emergency generator and its emergency switchboard?
Explain the emergency generator automatic start sequence from loss of normal supply.
What types of emergency generator starting methods are used and how do they work?
What is the difference between lead-acid, alkaline, VRLA and lithium-ion batteries?

How is the state of charge of an open ventilated lead-acid battery checked?
What maintenance is conducted on emergency batteries?
What are the battery-room hazards and entry precautions?
What is a hazardous zone and what does an Ex marking mean?
What is intrinsic safety and how does a Zener barrier protect a circuit?