Transformers & Frequency Converters

Thread Starter


Joined Oct 14, 2011
I have questions about transformers and frequency converters. First, I think I have a decent knowledge of how transformers work, but there is one thing I'm still unsure about. Transformers are rated as either step up or step down as described by the primary versus the secondary ratings. For example, 440/110 would be a 4:1 step down transformer. This makes sense since 440/110 = 4. However, I've seen various other ratings, such as 440/120, 240 X 480, 230 X 460 primary and 120/115/110 secondary which don't make sense to me. For example, 440/120=~3.67, not 4, so would this still be considered a 4:1 transformer? And what about the 240 X 480? Does the "X" denote the options at that particular terminal point?

Let's take this a step further and say, as an example, I want to go from a 440VAC to a 120VAC, 60 Hz, single phase with a 3kVA carrying capacity. What are my options? Would every primary rating equal to or above 440VAC with a secondary equal to or below 120VAC work? Why or why not?

Note: I'm aware of the transformer section available on allaboutcircuits. I'm looking for specific information though. I browsed through the first few pages of the e-book material but didn't find the answers I was seeking.

Now let's shift focus to my next question about frequency converters. First off, how does one even perform a simple frequency conversion using discrete components? Say I want to go from 60Hz to 400Hz, without changing my voltage, current, phase, etc... If I just want to change the frequency, would I use an LC network? I've looked at frequency converters online and they mostly appear to be expensive and very large units intended for not only changing frequency but also voltage and current. Would it be easy to build my own frequency converter if I only wanted to increase the frequency (single phase)?

Thanks in advance!


Joined Mar 14, 2008
Not sure I completely understand you question about turns ratio, but in general, you buy a transformer that accepts the input voltage, and generates the output voltage you want. Some transformers have tapped primaries and secondaries (denoted by the X) and you can select the voltage from the listed fixed values.

A 440/120 would be a 3.67:1 transformer, not a 4:1, for example.

You can always use a transformer with a higher primary voltage rating, but never a lower. The output voltage is, of course, proportional to the input voltage as determined by the turns ratio.

No it's not simple to change frequency of a mains voltage. Generally the converters change the AC to DC and then use an inverter circuit to generate the desired AC frequency from that DC. That's why they are large and expensive.

Another way to convert frequency (often used for high power conversions and also expensive) is to use a motor-generator set.