When to Choose a Magnetic Transformer
Powering 300 Watts or More
Electronic transformers are usually lighter and more compact, but can only power up to 300 watts. Magnetic low voltage transformers are generally bigger and can be a bit noisy, but can power up to 1200 watts.
Multiple or Long Circuits
When a lighting project branches out from one power supply into several different circuits, a multi-circuit transformer allows you to connect more than one lighting system to the transformer. Boost tap and multi-tap terminal boards are convenient features that compensate for voltage drop in 12V and 24V magnetic transformers that are powering a long run of low voltage lights.
Although magnetic transformers are rated for higher wattage than their electronic counterparts, they may not be able to use 100% of it. EI magnetic transformers (named after the stacks of "E" and "I" shaped internal components) should only use up to 80% of their wattage rating. Toroidal magnetic transformers are lighter, quieter, and more energy-efficient but also tend to be more expensive. After determining how many watts you need for your lighting project, check the specs to see what the recommended maximum load is for the magnetic transformer you are interested in.