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Downlight Transformers

This web page describes:

  • What downlight transformers are.
  • What downlight transformers do.
  • What can go wrong with downlight transformers.

What Downlight Transformers Are

A transformer changes (transforms) an alternating voltage from one value to another value, for instance from 240 volts to, say,12 volts.


A downlight transformer changes the mains voltage to a value that downlights use.


Transformer schematic diagram


Downlight transformer

What Downlight Transformers Do

A downlight transformer changes the input voltage, usually from the ring mains (UK 240 volts) to, typically, 12 volts.


The bulbs in downlights use a low voltage input.


‘Standard’ ceiling lights use, in the UK, 240 volts; 240 volts is too large for downlights, downlights are ‘low voltage’. The bulb in the downlight would blow if the input was 240 volts.


What Can Go Wrong With Downlight Transformers

  • The transformer becomes unserviceable:
    • Replace the transformer – cost about £10 (UK).
  • Part of the transformer becomes unserviceable:
    • There is usually more than one set of output connections – move the wiring to an unused pair of connections (remove power to the transformer first).
  • Wiring deteriorates and becomes loose:
    • Remake the connections.
  • Transformer overheats:
    • Can cause an intermittent problem, for instance flickering lights.
    • Transformers are mostly in the loft or ceiling space – something could be covering the transformer, for instance loft insulation. Remove what is covering the transformer to let the transformer cool down.
  • Downlight does not work with a dimmer.
    • Cheap downlight transformers often don’t work with dimmers, buy a better quality downlight transformer.


Judge Electrical Limited
15 Mulberry Court, Huntington, York, YO32 9TU
Telephone 01904 764845 (Landline), 07919 033113 Mobile)
Email info@judgeelectrical.co.uk
VAT No. 852917405. Company Number 6359328