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Hi All,

I have a problem -- output voltage of 230V - 9V transformer is not 9V,
but around 14V!

A couple days ago I have bought a small 230V to 9V transformer, it
looks like this:
http://www.inetcat.org/stuff/transfo...ransformer.jpg.

The transformer is a part of a power supply module, it is followed by
7805 regulator. After I have assembled the circuit I have noticed that
7805 is running hotter than I expected. Soon I have found the problem
-- the output voltage of the transformed is much higher that 9V,
around 13V.

Today I went to the shop again and bought another one. Similar effect:

http://www.inetcat.org/stuff/transfo...mer-output.jpg.

A little black box on the top is the transformer. White wires go to a
wall socket, 230V AC. Two multimeters measure AC voltages, left -- on
the primary windings, right -- on the secondary one.

Why a voltage on the secondary winding is 14.4V? The multimeters are
ok, I can swap them and get the same readings. Am I lucky enough to get
two faulty transformers? It is theoretically possible, both are likely
to come from the same batch. I fail to see what else can be wrong...

I am thinking about go back to the shop and complain, but would like to
hear somebody else's opinion first. Would anyone please care to
comment? Am I missing something about AC transformers labeling?

Please help.

Kind regards,
Alex

What is the voltage at rated load current? It appears that you are looking
at the open circuit voltage. Under load this will drop.

--

Don Kelly @shawcross.ca
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