[GreenKeys] Another idea for a loop supply transformer

[Douglas W. Jones]

On Mar 11, 2008, at 10:04 AM, gil smith wrote:

> I use an isolation transformer with 115 output, and dual primaries
> for 115 or 230 input.  Wired with primaries in parallel you get
> about 160VDC supply (after rectifier/filter).

Eek!  Don't do this!  Wiring primaries or secondaries in parallel
when they're wound for different voltages is not, in general, a good
idea.

The 115 volt primary is trying to induce 230 volts on the 230 volt
primary, but it's connected to 115 volts.  As a result, you get
current flowing the wrong way in that primary.  In the worst case,
it's resistive limited, and you get a very hot transformer.  If you're
lucky (apparently you were), the high current saturates part of the
magnetic circuit, and you just get lower coupling from input to output.

		Doug Jones
		jones at cs.uiowa.edu