DIYbanter - View Single Post - Blew another damn transformer on my Trane XB80

Don Klipstein

In , wrote:
On 13 Apr 2011 09:57:33 +1000, "Phil Allison" wrote:

"Dave M"

That's not true. an open rectifier does not allow DC current to flow
through the secondary. It's just 1/2 of the power line cycle. During the
opposite half of the cycle, no current flows in the secondary.

** So the average value is non zero and that means there is a DC component
to the current.

True, it's unidirectional current, but it's an intermittent current, not
constant DC.

** It will show a nice, steady reading on a DC current meter.

The interesting thing is how there is no corresponding DC component in the
primary current.

.... Phil

Unless the half wave rectifier is on the PRIMARY side.

There won't be a rectifier feeding the primary of a transformer with DC.
A transformer does not pass DC from one winding to another the way it does
with AC.

Changing AC that transformers work with to DC that electronics work with
has to occur downstream of the transformer.

I don't see any evidence of that on any of the diagrams I saw, but is
there something else on this furnace circuit? By code there cannot be
- but we don't know know this to be the case - or what is on the
circuit if there is.

I have yet to look at these diagrams, but is the circuit board
powered by this tranny shown to "board level" as opposed to "component
level"? If so, then the board can have, probably does have, a rectifier
not shown in the diagram.
--
- Don Klipstein )