20 Jan
2002
20 Jan
'02
11:38 a.m.
On Sun, 20 Jan 2002, Tothwolf wrote:
On Sun, 20 Jan 2002, Tony Duell wrote:
If you want to rewind it just for nostalgia sake, fine. However, a bit
of rustling around in some of the thrift stores would likely turn up a
wall wart with the proper connector and a 9VAC output. I think I saw
one today when looking for a 6VDC one.
- don
And sometimes the primary is designed to be the
thermal fuse. If it
overheats, the insulation melts, you get shorted turns, and it either
melts the wire or blows the current-operated fuse. Apparently the
former (wire that's designed to melt after the insulation has melted)
actually meets most safety approvals, and it's the intended failure
mode of most cheap wall-warts over here. Is it any wonder I can't
stand the darn things?
The 9V AC wall-warts that are sold with USRobotics/3Com modems are made
this way. I had one spontaneously fail, and could find no problems with
the modem it had powered. The wall-wart had an open primary, so I
disassembled it. Inside, I found the core's plastic bobbin was melted.
While removing the primary windings, I found damage to the enamel wire
that indicated that the wire had been wound too tightly when the core was
manufactured. It appears that a few layers of the primary winding were
shorted out from the factory. What seems to have happened, is that the
remaining primary windings were over voltage, and eventually the heat that
it produced damaged both the plastic bobbin and the wire's enamel
insulation.
USRobotics/3Com still would not send a replacement unit free of change,
even tho this one was clearly factory defective. They want $15 plus
shipping for these pieces of junk.
I've been considering rewinding this particular transformer, just for
practice (I haven't rebuilt one in awhile). I've not yet decided if it's
worth possibly wasting some enamel wire on. I think I'd want to replace
the plastic bobbin if I do decide to rewind this transformer.
-Toth