Emergency lights typically operate at low voltage—4V, 6V, or 12V DC—depending on the fixture. However, buildings deliver 120V AC power. To make this work, each emergency light is equipped with a transformer that steps down the voltage and converts AC to the appropriate DC output needed to charge the battery and power the lamps.
How Emergency Light Transformers Work
Transformers operate on the principle of electromagnetic induction. An incoming AC current flows through a primary coil, creating a magnetic field that induces voltage in a secondary coil. The voltage output is determined by the number of wire turns in each coil. This enables the unit to deliver a safe, usable low-voltage output to the emergency light system.
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Are Transformers Reliable?
Yes—transformers are one of the most reliable components in an emergency light. Unlike sensitive circuit boards, transformers are resilient to heat, current fluctuations, and even moisture. While they can fail, it’s relatively rare. When they do fail, it's often due to long-term stress or wiring faults rather than internal defects.
How to Test an Emergency Light Transformer
Routine monthly tests (using the built-in test button) will also check transformer performance. If the battery fails to charge or the unit does not illuminate, the transformer could be the cause. However, this should be verified with a multimeter:
- Set your multimeter to AC voltage (120V range).
- Check input voltage at the transformer terminals—you should see 120V AC.
- Switch to the appropriate DC voltage setting (typically 6V–24V) and check the output.
- If output is present and correct, the transformer is likely functional. No output indicates failure.
Replacing a Failed Transformer
If a transformer needs to be replaced, it’s important to match the replacement to the original specifications. Consider the following:
- Voltage Output: Must match the original (6V, 12V, or 24V).
- Amperage Rating: Must meet or exceed the original unit’s current rating.
- Physical Size: It must fit within the emergency light housing.
- Connector Type: Some transformers use wire leads, sockets, or direct PCB mounting.
The best solution is to use the OEM (original equipment manufacturer) replacement transformer. If the original part is unavailable, use these criteria to select a compatible third-party transformer.