A transformer provides alternating current (a.c.) output of 12 or 24 volts; 12 volts a.c. is normally used to power halogen lamps in low voltage garden lights. A dc power supply provides direct current (d.c.) output (same as a battery). L.e.d.s consume a lot less power than incandescent lamps but are vulnerable to overvoltage, so if you are using a small number of low power lights such as Navigator Minor, Major, Quo or Quad models which are made especially to work from both a.c. and d.c. supplies, you should use a regulated 12 volt 10w DC power supply such as the 10w T9201 to ensure stable voltage for l.e.d. loads less than 10w. If you are using an a.c. transformer for a larger group of led lights or if you are using higher power led lights such as the Navigator Major, Eye or Quatro models which are designed for ac operation, then load a 20va or 50va magnetic (wire wound) transformer to at least 50% of its rating to ensure stable voltage. Even though many led products are now designed for ac supply rather than dc as they used to be, it is advisable to run them from a magnetic (wire wound or toroidal) transformer, not an electronic type as the circuitry in the led units and electronic transformer can interact to cause flickering, especially on longer cable runs.

Magnetic transformers for garden lighting come in 2 forms - wire wound types around an "E core" producing a cube-shaped transformer, and a toroidal type which is donut shaped. Elipta's standard surface mount garden lighting transformers are magnetic (wire wound) types housed in black weatherproof IP66 boxes to be mounted on a wall or post, in manholes, outbuildings or under decking. Where a wall or fence post isn't available for mounting, use a mounting spike or post to locate the transformer behind planting or a landscape feature. Only an IP68 ground burial transformer can be left lying on the ground where water may pool after heavy rain, and it is in any case essential that 240 volt junction boxes used for connecting transformers to an armoured cable are clear of possible water ingress. For safety 12 volt and 240 volt cables must be segregated, which often means a "3 box" installation - a 240 volt IP rated enclosure (jargon for weatherproof junction box) to connect to the armoured supply cable, the sealed transformer and another IP rated enclosure for the connections to the 12 volt cables running out to the lights.

Ground burial 12 volt transformers are used where standard surface-mount transformers can't be hidden above ground, such as in lawns or gravel areas, and it is not possible to use a 240 volt light instead. Elipta's Ground burial transformers feature a polycarbonate enclosure into which the magnetic (wire wound) toroidal transformer has been resin-sealed. To avoid "wicking" of moisture into the transformer, connection to mains supply cables and multiple lighting cables must be via resin sealed underground joints; connection to a single 12 volt lighting cable may be by means of a heat shrink cable joint kit of a type where a melting adhesive provides a waterproof seal around the joint. The transformer incorporates a thermal overload cutoff and is connected via the 1.5m rubber cables fitted. As it is common to mix several led models on the same transformer supply it is best to stick to using an ac transformer in most installations. The examples shown illustrate use of 20va and 50va magnetic transformer types to power a range of led products.

Copyright 2010; Information based on products supplied by Lighting for Gardens Limited and is advisory only. The company accepts no responsibility for incorrect use or application of information given. Light fittings can become hot in use; exercise appropriate precautions. Exterior electrical installations should be undertaken by a qualified electrician.