If I have 3 transformers (120V transformers) in series (on the input side) on a 240V circuit, will the transformers experience a voltage drop? If so, how much and will this affect the secondaries by the transformer equation?

  • \$\begingroup\$ Circuit schematic, details on transformers, details on loads? The primary impedance will depend on the secondary loads. \$\endgroup\$
    – Transistor
    Jan 18, 2016 at 7:22
  • \$\begingroup\$ Transformer primaries in series are a BAD idea especially if they might drive different loads : the lightest loaded one see most of the voltage, and potentially fails. See Andy's answer : this comment is here because +1 isn't enough. \$\endgroup\$
    – user16324
    Jan 18, 2016 at 11:44

1 Answer 1


Nope, this is under-constrained. You have not said the the transformers are identical and, because of this, the big problem is that putting the primaries in series does not mean equal distribution of voltage to each primary.

This immediately means one transformer might expect more core saturation than another and overheats and fails. And, all of this is before you analyse any effect due to secondary currents. If secondary currents are unequal then you have an even worsening scenario and you might expect a fire.

Don't do it - test the transformers first and ensure they are VA and primary magnetization current compatible. Then ensure that any secondary current is identical for each.

Even if you obtained three transformers that were of the same make and model, the primary magnetization inductance might vary quite a bit between them and this could cause one of them to exceed the 120V AC rating even though, on the face of it, you might expect all three to have 80V AC across the primaries.


Your Answer

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

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