Voltage ratings on power transformers

[dmills]

Actually, the really funky bit is that core flux actually drops somewhat as you increase the load, worst case for the magnetics is a lightly loaded transformer!

But yea, 2:1 will saturate almost any mains iron.

Regards, Dan.

[Robert Kesh]

Originally Posted by Elvee

A way to picture it is to imagine the primary is in parallel with a varistor having an AC rating similar to the mains voltage.
Whether you draw current or not changes nothing: the varistor will conduct when its voltage is exceeded.
The non-linear behavior of the varistor is similar to that of the core (actually there is an integral difference between the two, but let's not obscure the picture)

Yes, thanks. I now get that there comes a point where you can no longer control primary current from the secondary load.

[DF96]

Originally Posted by Robert Kesh

Current was what I thought, which is why I wondered if running well under current would make it all roses. But I guess not.

The current which matters is the magnetising current. This is only a small part of the primary current in a loaded transformer, but is the entire primary current in an unloaded transformer. Adding a load can improve things, as it causes a voltage drop in the primary winding resistance so the primary sees a smaller effective input voltage.