Thanks! The little wall box is cold when it's not carrying a load. The
big one stays rather warm. It seems there must be some difference in
design the way they described it and given the huge difference in size.

Chris Lewis wrote:
According to Paul Furman :

Mmmm there must be some distinction. Can you clarify? All I get is that
my info was wrong but I don't know anything further.



What is the significance of a hertz?


Not much here.


What is the difference between the large and small transformers?
Solid state?


These are not solid state devices.

Transformers are transformers, big or small. They're stacks of iron
plates with wire wrapped around them, and they're all relying on "magnetic"
induction to transform power from one voltage to another. That's what the
definition of a transformer _is_ (at least within this context).

The only differences between a small interior "wall cube" transformer and
a large exterior-rated transformer is that the former is smaller than the
latter, and the latter is rated for out doors. Also, the former will
_generally_ not be as robust as the latter - mass production/engineering
shortcuts/cost tuning etc. etc. etc.


How closely should the wattage match? I may have several fixtures on one
transformer and switch them separately. Is it necessary to have a bunch
of 60w transformers switched on the 120v side?


A "perfect" transformer consumes _no_ power when there's no load being drawn,
and runs perfectly cold even under full load, so the transformer wattage is
irrelevant as long as you have enough.

But nothing is ever perfect.

All things being equal, then, the more excess wattage capacity in the
transformer, the more power you waste. But the effect is usually fairly
small. And between small mass-produced wall cube transformers, and larger
LV lighting purposed transformers, there's bound to be an efficiency
difference.

The main issue simply is ensuring that the power transformer has enough
power for the load, and preferably a bit extra. That 60W transformer
driving exactly 60W worth of lightbulbs is, when compared to a 90W
transformer driving 60W of lightbulbs:

(a) going to run a lot hotter
(b) probably have a shorter lifespan
(c) be FAR more likely to trip its integral breaker due to
power glitches/spikes/manufacturing tolerances and other
things.

Should you switch the 12V or the 120V? Well, it's probably better to switch
the 120V AS LONG AS you leave the bulbs on for hours at a time. A bit less
energy wasted in heating the transformer when there's no lights on, but there's
on/off stress on the transformer as well as the bulbs. However, in most
cases LV lighting switching (eg: motion or light detectors) are almost always
on the 12V side - less on/off stress on the transformer.

Tradeoffs all over the place, depending on individual units, installations
and usage habits, so it's impossible to tell ahead of time exactly which one
is "better".

The only definitive things you should keep in mind is: choose good quality
units, and make sure you have 10-50% more capacity in the transformer than you
need right away. Besides, it makes it easier to add a few lights later.