Arfa Daily wrote:

"Michael A. Terrell" wrote in message
m...

"Dave Plowman (News)" wrote:

In article ,
Ardent wrote:
Someone plugged my Dream machine (rated 110 VAC) into a 220 VAC outlet
and the transformer primary got trashed. Since I will be living here
for a while I thought of getting a transformer made here locally (very
cheap, honest).

I'm willing to bet it's rather more than just the transformer. Copper
takes time to melt while solid state destructs near instantly.


You are ignoring core saturation. That limits the maximum voltage on
the secondary. I have replaced several 120 VAC transformers that opened
when plugged into 240 VAC and had no problems with the electronics. You
aren't always lucky, but if it is a typical cheap as possible
transformer it will die first.



I reckon you've been lucky then Michael. Living here in a 240v country, I
see several pieces of kit a year that have either come over from the states
with their owners to live here, or have been brought back here by UK holiday
makers, picking up that 'deal of the century' at Walmart. Almost always,
although agreed not *always* always, in my experience, the damage which
ensues from plugging these 120v transformer based items into 240v line
power, is not limited to just the transformer primary winding failing.

However, I have seen more than a few which have had a perfectly conventional
glass fuse in the primary, which has failed violently, but has managed to
protect both the transformer, and the following circuitry ...


You also have the problem of 50 Hz, vs 60 Hz, which requires a larger
core, and makes it easier to saturate a transformer made for the North
America markets. If the primary is impedance limited, it allows the core
to heat quite a bit before the primary winding opens. If the DC supply
is close to the upper limit on the semiconductors, or electrolytics, it
does a lot of damage before it opens. That was why we tested a lot of
parameters on iron core transformers.

It was even worse when we moved to SMPS. We went through a dozen
suppliers before we found one that met our EMI requirements. the rest
either radiated too much noise, or had noise on the DC rails, and it was
within one of the IF frequencies. All SMPS had to be tested for over
current shutdown, and even then we had one fail in a radio during burn
in. It didn't shut down, and it destroyed a new $20,000 radio a customer
was waiting for.


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