EL wrote:


Paul Furman wrote:

...transformer for my low volt
garden lighting. Here's what I learned:

The small (size of a pack of cigarretes) $25 12v transformer is an
ELECTRIC transformer that must be
mounted indoors and is easily damaged by moisture, the large (size of
a shoebox) $100 12v transformer is a MAGNETIC transformer suitable for
mounting outdoors and
more weather resistant.

All 60 Hz transformers are magnetic.


What does 60 Hz mean? Both types are 60 Hz.

I got my info from chatting with the manufacturer's tech support guy on
the phone. (small electronic transformer) American-De Rosa Lamparts.



The reason the small one blew my breaker is because the small wires go
to the 120v
wall plug & the fat wires go to the 12v lighting. The smaller voltage is
more sensitive to voltage drop thus the larger wires. The 120v leads
were really skimpy, less than most electric appliances.

The lower voltage (12 volt) wires are larger diameter because they have
higher current in them than the 120 volt wires. Almost 10 times as much
current.


They said the power usage when the transformer is plugged in is
trivial so it's not really necessary to switch the 12v side.

Not necessarily true for inexpensive transformers. Feel the case when
it has been plugged in for a while with no load and see if it's warm. If
it is the current isn't trivial. Most inexpensive transformers will
have fairly high magnetizing currents. This is largely reactive
current, but it's still current and is still going to result in core
losses and resistive losses in the winding...all these losses are real
and cause heating.


Maybe he exaggerated. Its running with a load and just slightly warm
now. The magnetic one gets more warm with no load. So is the electric
one a poorer quality? Wastes energy, dies younger?



Having a too-small transformer isn't a big problem, no loss of efficiency

Not true.


?


but if you only have say 10 watts of lights on a 150w

transformer it might provide irregular supply

No.


?