I am searching for a way to determine the inductance of a transformer, either primary or secondary. Example: I have a isolation transformer that can carry
1000VA 115(primary) to 230(secondary) VAC.
Which means that the transformer is capable of delivering 4.3Amp RMS at 230V.
Is there a way that I can determine what is the inductance of the secondary of that transformer. I looked at the other question posted,
titled: "How can I calculate the inductance of the primary of a transformer given a specific load on the secondary"
The answers given are a bit off subject and do not supply an adequate answer.
Thank you for your help.

  • \$\begingroup\$ an ideal transformer has infinite inductance, so it can't be done. \$\endgroup\$
    – Jasen
    Apr 8 '17 at 3:56

There is no way from those figures to calculate any accurate estimate. The inductance of a transformer can range over one, or possibly even two orders of magnitude, and you still end up with a viable transformer.

However, you could make some assumptions to put some bounds on what it could be.

It's a fair assumption that the magnetising current will be somewhere between 0.1% (for an instrument grade high mu toroidal core) and 30% (for a fan-blown designed-down-to-minimum-cost operates-at-full-load-only microwave oven transformer) of the rated load current, with the few percent region being reasonable for middling transformers.

So if we guess at 100mA magnetising current with respect to our 4.3A rated 230v winding, the impedance is 2300johms, which at 50Hz is 2300/2pif = 7H, give or take a factor of 3, or 10.

Of course if you actually measure the magnetising current, you don't need such loose assumptions.

  • \$\begingroup\$ According to your calculations if I measured the magnetizing current I would be able to come up with a fairly good approximation, is it? So, when you talk about magnetizing current do you mean the AC RMS current circulating in the coil while noting is connected on the output ? Which means if I connect my digital meter in series, set on AC current, and come up with a reading of 100mA AC RMS, that would indicate a 7H inductor ? \$\endgroup\$ Apr 8 '17 at 19:16
  • \$\begingroup\$ Correct, if you're at 50Hz, it would be slightly different at 60Hz, \$\endgroup\$
    – Neil_UK
    Apr 9 '17 at 5:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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