"Jeff Thies"
Phil Allison wrote:
"robb"


Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram)
he

http://www.flickr.com/photos/bbqboye...7626457562742/

http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring of
the
115V leads going into the transformer, and of course the 115V circuit is
open (again).


** From the damage to the tranny visible in the photos - the primary has
developed an internal short ( due to insulation failure) and since there
is
no fuse link in series, the resulting current was high enough to make an
exposed wire leading to the terminals explode.

An internal short could develop due to heat alone because of an overload
on
the tranny - but this requires a fault to exist on the secondary side
which
seems not to be the case.

High voltage spikes on the primary could also cause insulation failure
leading to the damage seen in the pics - lightning does this sort of
thing.
So also could back emfs from the blower fan if the is a bad connection in
the AC supply feed.

I suggest you provide the next replacement for that vulnerable tranny
with
some "protection" - firstly an in-line fuse of say 1/4 amp AND a
capacitor wired across the primary of say 1uF rated for continuous use
across the AC supply.

If there is an overload on the tranny, the fuse will blow.

The 1uF capacitor should suppress spike voltages enough to save the
tranny
from harm.

1 uF sounds a little high.


** No it ain't.


I would think .01 uF at 400V would be a better bet.

** Think again.

Or an MOV (metal oxide varistor) or three (across the line and then from
each side to ground).

** Bad idea.

I don't think this is a voltage spike problem though. Voltage spikes take
out other components first.

** Not on the AC supply they don't.


...... Phil