What are Autotransformers and Isolation Transformers For?

auto Transformer

It can be a challenge to figure out exactly which transformer you need for your specific application. One common stumbling block is autotransformers and isolation transformers. Should you go for the cheap efficiency of an autotransformer, or the better power quality and safety of an isolation transformer? Let’s discuss the difference between these two transformers and the general applications they are best suited for.

1. Autotransformers

Autotransformers have one voltage winding, shared by both sides. You tap the winding along its length to provide some of the primary voltage across its second load. You should use autotransformers in applications where you need to step up or step down three-phase line voltages (i.e. the standard voltage in outlets or junctions). Ideally, when you’re using a protected piece of equipment, so you need the voltage to match its need exactly. Other uses for an autotransformer include:
  • Reducing starter voltage for an induction motor
  • Start-up for a fluorescent light fixture
  • Compensation for voltage losses, boosting at the end of a long transmission line
  • Enable rectifier output control
When you can get away without the complexity of an isolation transformer, you may prefer an autotransformer because they are cheaper and more efficient. They are smaller than isolation transformers, even when delivering the same voltage, and have a simpler construction. You will also find they have less leakage inductance between the input and output. Autotransformers are typically less expensive than isolation transformers. However, if you need a voltage ratio of 3:1 or more, then you will find that an isolation transformer is more economical, just due to size.

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isolation transformer

2. Isolation Transformers

Isolation transformers are more complex than autotransformers. They are also called insulating transformers, as the primary and secondary don’t share a single coil, but each has their own coil. Thereby, they can isolate circuits, which is usually their primary use. A few uses for an isolation transformer include:
  • Telecommunications equipment
  • Medical equipment
  • Computers and peripherals
  • Remote control equipment
If you need the complexity of an isolation transformer, you may prefer them because they deliver a better power quality. They are safer, with fewer surges, and aren’t as noisy as other transformer options. There is no conductive connection between the Earth and the circuit, which means you can touch one part of it without hurting yourself. However, isolation transformers are larger, more expensive, and more complicated than autotransformers. So, unless you need the functionality or safety of an isolation transformer, you may prefer to use an autotransformer. There are many things to consider when you’re comparing transformers, and these aren’t your only two options. If you want to learn more about what type of transformer you will need for your project, contact the experts at VCM Solutions.

Transformer Selection Guide