How Battery Backup Systems Function in Explosion Proof Emergency Exit Lights During Blackouts

When the mains supply drops, a battery backup system senses the loss within a fraction of a second and switches the lamp over to a sealed, rechargeable battery. In hazardous area emergency exit lights, that battery and its charging circuit sit inside a certified Ex enclosure, so the changeover never creates an ignition risk. Most units then keep running for 90 minutes or more, or until power returns.

Anyone who has been on site during a blackout knows how quickly a busy plant turns disorienting. Exit lights are the one thing that has to keep working, and you can Learn More about certified fittings built for these zones before you settle on a specification. This guide walks through what really happens inside the fitting, from charging to switchover to recharge.

How Does the Battery Backup Work?

Mains power keeps a sealed battery topped up through a built-in charger. A monitoring circuit watches the supply. When it fails, the circuit connects the battery to an LED driver and the exit sign lights up. When power returns, the unit switches back and the charger refills the battery.

What Is a Battery-Backed Explosion Proof Exit Light?

A battery-backed explosion proof exit light is a certified luminaire or sign with its own internal power source that keeps escape routes lit when normal power fails. It is built so that no part inside it, including the battery, can ignite the flammable gas or dust around it.

This is the heart of emergency lighting for hazardous areas, where a dark exit is far more than an inconvenience. Smoke, gas and darkness together make routes hard to read, and people may be wearing respirators. A clear, steady exit marker is what gets everyone moving the right way.

The Main Parts Inside the Fitting

Most certified fittings, including the ranges supplied by MineGlow, are built around the same handful of parts. Knowing them makes inspections much easier.

•         Battery pack: sealed and rated for the temperature range of the site. It stores the energy used during an outage.
•         Charger: fed from the mains, it holds the battery at full charge and tops it up after every outage.
•         Monitoring and switching circuit: watches the incoming supply and changes over the moment it falls below a set level.
•         LED driver: converts battery power into the steady current the LEDs need.
•         Ex enclosure: a flameproof (Ex d) or increased safety (Ex e) housing with certified glands, sealing everything away from the surrounding atmosphere.

What Happens Step by Step During a Blackout

Here is the sequence, start to finish:

1.       Normal running. Mains power feeds the unit while the charger keeps the battery full.
2.       Failure detected. The monitoring circuit sees the supply drop below its threshold, usually in well under a second.
3.       Switchover. The battery connects to the driver and the LEDs light at emergency output.
4.       Discharge. The unit runs for its rated duration. Australian practice under AS/NZS 2293 commonly sets 90 minutes, and some sites specify 3 hours.
5.       Recovery. When mains power returns, the unit reverts to normal and recharges, often within 12 to 24 hours depending on the battery chemistry.

Maintained vs Non-Maintained Operation

Exit lights are wired one of two ways. Maintained units stay lit all the time, while non-maintained units only light when the supply fails.

Feature	Maintained	Non-maintained
Normal operation	Lit all the time from mains power	Off until the mains supply fails
During a blackout	Switches from mains to battery	Switches on from battery
Typical use	Exit signs and marked escape routes	Standby lighting in work areas and corridors
Fault visibility	A dead lamp is obvious at a glance	Needs a test or self-test to show a fault

Battery Types Used in Hazardous Area Units

Modern explosion proof LED emergency lights draw very little power, which is why a compact battery can carry them through the full rated period. The chemistry still matters, mainly because of heat.

Battery type	Strengths	Watch points
Nickel-cadmium (NiCd)	Tolerates heat and rough handling, long track record	Cadmium needs proper disposal, capacity fades if never exercised
Nickel-metal hydride (NiMH)	Good capacity for its size, no cadmium	Higher self-discharge, less happy at temperature extremes
Lithium iron phosphate (LiFePO4)	Light, long cycle life, stable chemistry	Needs a proper battery management system, limits on charging in the cold

Heat shortens battery life more than anything else, so check the ambient rating on the nameplate against the real conditions in the plant.

Testing and Maintenance That Keep the Backup Reliable

A battery you have never tested is a hope, not a backup. A sensible routine looks like this:

•         Monthly function test: simulate a supply failure and confirm the lamp lights.
•         Full duration test: commonly every six months in Australia under AS/NZS 2293.2. Confirm the interval your site follows.
•         Physical inspection: look at the lens, seals, glands and enclosure for damage or corrosion.
•         Battery replacement: use only the manufacturer’s approved part, fitted by a competent person under permit and isolation.
•         Records: log every test so you can show the system works, not just that it exists.

Short runtime usually points to an ageing battery or heat exposure. A unit that never lights during a test often has a charger or supply fault. Either way, fix it before the next real outage.

Frequently Asked Questions

1. How long do emergency exit lights last during a blackout?

Most are rated for at least 90 minutes, and some run for 3 hours. Check the nameplate and your site standard.

2. Can the battery be replaced on site?

Yes, but only with the manufacturer’s approved battery, fitted by a competent person following permit and isolation rules. Never open the enclosure in a live classified area without proper controls.

3. What is the difference between maintained and non-maintained units?

Maintained units stay lit on mains power and move to battery in a blackout. Non-maintained units stay off until the supply fails.

4. Do the batteries recharge automatically?

Yes. A built-in charger refills the battery after power returns, usually within 12 to 24 hours.

5. How often should I test the system?

A quick function test monthly and a full duration test about every six months is common practice in Australia. Follow the schedule your site standard sets.

6. Why can I not use an ordinary emergency light in a classified zone?

A standard fitting can spark at its battery, switch or enclosure joints. Certified units contain any fault inside a protected housing.

Keep the Lights On When It Counts

Battery backup is simple in principle: charge, monitor, switch, discharge, recharge. What makes the difference in a classified area is certified construction, regular testing and a battery that is healthy on the night it is needed. Treat your explosion proof emergency lighting as a safety system you prove regularly, not a fitting you install and forget.

If you are reviewing exit lighting for a site, MineGlow is a trusted Australian name for certified hazardous area lighting, and its team can answer technical questions about duration, battery options and zone ratings.