On Apr 12, 8:49*pm, (Don Klipstein) wrote:
In article , Dave M wrote:
Don Klipstein wrote:
In article , Tony Miklos wrote:

Yes, the thread got too long. *If you saw the photo, and know the
primary went open on 3 transformers, it sure looks like a problem on
the primary side. *If the load was too much, those wires on the
secondary side would most likely have been at the very least
discolored from the heat.

*This makes me think the most likely causes a

* * Improperly connecting the transformer (such as using only 1 of
*the 2 primaries of a 120/240V dual primary transformer)

* * DC flowing through the secondary. *That can occur if the tranny's
*load has a fullwave rectifier with one diode open. *If the fullwave
*rectifier has discrete diodes or a dual diode, the problem may be a
*bad solder joint at one of the diodes.

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. *True, it's
unidirectional current, but it's an intermittent current, not constant DC.
If your statement were true, then half-wave rectifiers wouldn't be feasible.

* A unidirectional pulsing waveform has a DC component.

* That analyzes to a sum of DC, fundamental frequency AC, and AC at
harmonic frequencies. *The average as averaged over a whole cycle is the
DC component.

* It is fairly well known that a transformer driving a halfwave rectified
load can run into core saturation problems from the DC component in the
unidirectionally pulsing current waveform.

--
*- Don Klipstein )- Hide quoted text -

- Show quoted text -

Interesting theory. One helpful piece of info which it's quite
amazing we
still don't have is what the currents are on both sides of the
transformer.
For saturation to occur I would think the transformer would have to
be close
to fully loaded. Which it could be, given the trends to lower cost,
cheaper
components, etc.