Emergency lights operate at 4, 6 or 12 volts DC (direct current), depending upon the particular light design. However, the electricity we receive through electrical outlet is 120 volts AC (alternating current). To change one to the other requires the use of a transformer. This means that all emergency lights have a transformer within them.


Transformers operate under the principal that moving electrical current, like what is moving through the wiring in a house, office building, or industrial site, produces a magnetic field. The transformer contains two coils of wire, which are of very particular lengths. As the electrical current passes through the larger coil, its magnetic field produces electricity in the smaller coil. This new electricity is at a different voltage, determined by the number of “turns” of wire in the coil.


While this technical description of the workings of a transformer may not be all that interesting to you, it does illustrate one valuable point; there’s not much that can go wrong with a transformer. While I won’t go as far as to say that transformers never fail, there’s not a whole lot there to fail. Unlike semiconductors, found on the circuit board, they aren’t affected by heat, fluctuations in electrical current or even water.


Due to the design of the circuit board, if a transformer fails, it will probably cause the light to come on and stay on, even in a non-power-loss situation. Don’t assume that it is the transformer though; it could also be a circuit breaker that is turned off.

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Your normal, scheduled monthly test of your emergency light’s function will also test the function of the transformer. A bad transformer will mean that there is no electrical power to charge the battery, resulting in a failed test. If your lights pass their monthly test, using the test button on the units, then the transformer works as well.

However, if you encounter an emergency light that doesn’t work, it is easy to test the transformer with a multi-meter. As I’ve already mentioned, the transformer has two coils of wire; so, you should see four wires coming out of your transformer as two pairs. You might have a fifth wire, which is connected to ground. One pair will be connected to the AC power coming in to the emergency light and the other pair will be connected to the circuit board, possible through a connector.

If there is a connector, disconnect it. Take your multi-meter and set it for AC voltage and whatever setting is the closest above 120 volts. Find a place where you can touch the copper conductor of the wire with your multi-meter probes and carefully connect them, verifying that you have 120 volts coming into the transformer. If you have power coming in, change the voltage setting on your multi-meter to 20 volts (still AC) and check the output voltage. If you have any output voltage, it’s probably the right one. Transformers don’t partially fail, so if you have output voltage, your transformer is good.


While the possibility of a transformer going bad is minimal, there is still some possibility. There are some important considerations when replacing a transformer:

  • The output voltage must be the same as the transformer you are replacing. Too high an output voltage will burn out bulbs, batteries, and circuit boards. Too low an output voltage will not charge your battery and make your lights dim.
  • The amperage (current) rating of the new transformer must be at least equal to the amperage rating of the old one. If it is too low, charge times will be incredibly slow. Too high an amperage rating isn’t a problem
  • It must physically fit in the case, where the old transformer was. Transformers come in a wide variety of configurations. You want to make sure it will physically fit in the space.
  • It must have the right type of connectors. Some transformers mount into a socket, some have wires, and some mount directly to a circuit board.

Obviously, the best replacement is the one supplied by the original manufacturer of the emergency light. These criterion are given in case you cannot find the original manufacturer, or the manufacturer’s transformer. Call us today at 404-224-9365 for more assistance and help in finding a replacement transformer or new affordable emergency lighting unit. You can also email our production team for a prompt response.