Low Voltage Transformer

Transformer is a familiar word at least to the ears of ordinary folks in the streets. What is not known to many is what a transformer is. The post will explain what a transformer is, what low voltage means, factors to consider in acquiring one and the applications. A transformer is a device that changes the magnitude of supply voltage in a given ratio while ideally input and out power being equal. Literally it transforms or converts power from one voltage level to another. Broadly speaking there are two types of transformers, classified according to magnitude of voltage it handles; low voltage and high voltage.

Low Voltage Transformer uses

Low voltage transformers are used by electrical loads. The utility service provider supplies power to clients at a fixed voltage levels accepted nationally. In my country 3 phase supply to residential and commercial use is 415V, factories or big power consumers may be connected by 11kV, 33kV or 66kV. A transformer that lowers supply voltage from 415V three phase or 240V single phase to any lower value is referred to as low voltage transformer. It is a step-down transformer. This device is needed whenever there are voltage discrepancies between the power supplied and electrical device voltage rating. It’s worth to note that devices that work with low voltage are safer given that the lower the voltage the less the effects of faults.

Construction and operation

There are two broad classifications based on construction namely; magnetic and electronic types. Electronic transformers are made of a circuitry with components that achieve lower voltage such as resistors and capacitors. The most common type is magnetic type which has four main parts constitute the device, there are;

  • The core- they are from a material that is magnetic and poor conductor of electricity. It provides magnetic linkage while offering electrical isolation.
  • Windings- there are two windings that is primary and secondary. The secondary one has less turns than the primary to make it a step-down transformer.
  • Terminal – the ends of the winding makes the terminals that is a connection point to power supply side on primary and the load on the secondary.
  • Casing- this is the outer cover of the device; this depends on protection class that’s defines its installation conditions. The casing should allow heat dissipation, protect from external factors if exposed to such as water and dust.

It works on the principle of electromagnetic induction. The current flowing in primary winding creates magnetic field in the core and secondary winding. The changing magnetic fields induces electromagnetic force (emf) or voltage. When a load is connected and secondary circuit closed, current flows powering the device.

Factors to consider in acquiring the transformer

  1. Voltage rating- check the rating on the primary as well as secondary side. The primary voltage rating should be available to you (from your supplier) and the secondary voltage should be the one the device you want to power demands.
  2. Power – the wattage rating of the transformer should be higher that the device to be powered. As a rule of thumb, pick a transformer with 20% higher rating than the load.
  3. Casing – where is the transformer to be located will determine the casing to go for. The insulation class notation is the word ‘ingress protection (IP)’ followed by a number depending on what it protects the transformer against.
  4. Construction type- identify whether you need magnetic or electronic type. Electronic type is cheap, light, and small, less heat dissipation and have low life span. Magnetic type on the other hand are heavy, dissipate heat, a bit expensive and durable.


With technological advancement especially in LED lighting, the electrical devices are using less and less voltage rating that the one supplied by power producers. This will call for low voltage transformers to be in demand for lower this voltage. When the power the device the power first goes through the transformer where the voltage is lowered. Where the device is not operational, always check whether your transformer is health electrically. This article only provided basic knowledge on this device. I will not leave without asking you to grab a book and in a quiet space read farther on these transformers.

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