###### Asked in Electrical Engineering

# What is the rating of a step-down transformer that can step-down 230 volts AC to 30 volts AC?

## Answer

###### Wiki User

###### August 07, 2008 9:58PM

The way transformers are usually rated is in voltage (primary and secondary) and in watts. In the case of a 230 to 30 volt step-down transformer, there are lots of possibilities. Let's look as some things about the transformer. When we work with transformers, we look at the primary and secondary voltages. In this case, we have 230 and 30 volts respectively. If everything is "okay" in an application, the power in the primary will equal the power in the secondary. Yes, there will be a bit of loss, but let's just do the math. If the load operating at 30 volts draws 10 amps, then the power in the secondary is volts times amps, or 30 times 10, or 300 watts. The 300 watts in the secondary must be supplied by the primary. And since it's operating at 230 volts, and because the volts times amps here will have to equal the 300 watts, the current in the primary will be about 1.3 amps. Simple and easy. But how does that solve the problem? You need to know the voltages (primary and secondary) and the current maximums or the watts (because we can calculate either one if we have the other) to be able to rate your transformer. If your transformer is rated at just 200 watts, it won't work in this application. A 200 watt transformer should never be used to supply a device that requires 300 watts of power to operate it. We usually err on the side of caution, too, and allow for a bit more wattage in the transformer than the prospective load will actually use. Using a 300 watt transformer in this application is "just enough" to supply the load, and, though it may be considered for intermittant use, no one with any electrical knowledge would recommend it for continuous operation. Please, please, please be smart about this one. It is often the case when "marginal" electrical lash-ups are brought online that the problems don't show up immediately. Only after everyone is gone and no one is about does a fire start in the electrical system, and then all the "short cuts" suddently seem foolish and unnecessary. How fortunate we are when all that happens is that property is destroyed and no loss of life occurs.