1
\$\begingroup\$

How much can a transformer go without a failure?

For example, let's say that a transformer is designed to work with 500mA. (obviously you should avoid exceeding this limit)
But as I learned with capacitors - their tolerances are up to 20%. (you can pretty much safely run a 10v capacitor with 12v source)

And now I am wondering - what are transformer tolerances? In other words, can you run a 500mA transformer at 600mA safely and without failure? I know this is really subjective as it depends on the transformers quality but there has to be an average number.

enter image description here

\$\endgroup\$
3
  • 2
    \$\begingroup\$ Look at the datasheet. There is no generic tolerance for all transformers. If the datasheet says 500mA you better don't run it with 501mA \$\endgroup\$
    – PlasmaHH
    May 25, 2016 at 14:27
  • 2
    \$\begingroup\$ No, there is no"average number". The margins used by each manufacturer for each product line vary depending on the intended application and the price point. The only way to get this information is to ask the manufacturer, who may or may not be willing to divulge it. With transformers in particular, exceeding the ratings quickly runs into nonlinearities that make predicting performance difficult. \$\endgroup\$
    – Dave Tweed
    May 25, 2016 at 14:30
  • \$\begingroup\$ You should be designing so the transformer, or any other device, sees less stress than it is rated for, not more. It probably will take more but how much is anybodies guess \$\endgroup\$
    – Warren Hill
    May 25, 2016 at 14:51

2 Answers 2

Reset to default
3
\$\begingroup\$

The tolerance of capacitors refers to their capacitance value in Farad, not to their maximum current. If you want to run a 500 mA transformer savely, you should limit your current to about 450 or even 400 mA. Look for derating due to temperature.

\$\endgroup\$
1
  • \$\begingroup\$ Again, you are missing the point. It's obvious that capacitors are not rated in mA. As well as resistors are not rated at nano farads. I made an example with capacitors based on their tolerance to handle over-voltages and was thinking what is transformers tolerance of over-current. \$\endgroup\$
    – Giedrius
    May 26, 2016 at 10:40
3
\$\begingroup\$

The current rating is in RMS which means the current into a resistive load.

If you think you can get 600mA DC from a 500mA transformer you are wrong. You will need a 1A transformer to get 600mA DC with full wave rectification and filtering. And pay attention to the datasheet ratings for ambient temperature.

\$\endgroup\$
2
  • \$\begingroup\$ DC current is not part of the question. I was asking about tolerances and by that I mean what is the max safe current you can use on a transformer (In other words, can you safely exceed the rated current for long term without blowing up/shorting the transformer) And I really don't get what you meant by 'transforming' 500mA AC to 600mA DC. To me it does not make sense at all. (perhaps I missed something?) \$\endgroup\$
    – Giedrius
    May 26, 2016 at 10:36
  • \$\begingroup\$ There is no specific 'tolerance' - the current rating is exact given a specific type of current (RMS), specific test conditions (especially ambient temperature) and so on. In reality the safe max number might be much lower or slightly higher if the conditions are different or if you care more or less about reliability than the engineers who designed the transformer. To measure the AC current heating effect you need a true RMS ammeter or similar instrument- a regular multimeter will generally give deceptively low numbers in real electronic circuits. \$\endgroup\$
    – Spehro Pefhany
    May 26, 2016 at 11:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.