12 volt lighting transformer tips

[Paul Furman]

I had some trouble with setting up a 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.

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.

They said the power usage when the transformer is plugged in is trivial so it's not really necessary to switch the 12v side. The small electronic type does not have a delayed startup like the large magnetic one so you could switch the 120v side if you want to save a tiny bit more energy and don't mind operating everything on one switch.

Having a too-small transformer isn't a big problem, no loss of efficiency but if you only have say 10 watts of lights on a 150w transformer it might provide irregular supply however they said a 40w draw on a 150w transformer was no problem.

Just thought y'all might find this helpful.

[jim]

Thanks Paul, good to get the imput, never know when it will be needed...

[EL]

All 60 Hz transformers are magnetic.

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.

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.

The small

Not true. but if you only have say 10 watts of lights on a 150w

No. however they said a 40w

Boden

[Paul Furman]

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.

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?

?

?

[EL]

60 Hz is the abbreviation for 60 Hertz (formerly 60 cycles per second) the frequency at which the voltage alternates polarity. Magnetics are electric.

Both are electric. Nothing you've said indicates the quality of the unit. The distinction between "magnetic" and "electric" is not there. By definition a transformer is magnetic. It is also electric. Energy from one port is coupled to the other by means of a magnetic field. The heating of the larger transformer under no-load conditions is because of the magnetizing current. This heating is frequently significant in a cheap, not necessarily inexpensive, transformer.

[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?

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

How closely should the wattage match? I may have several fixtures >

[Chris Lewis]

According to Paul Furman :

Not much here.

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.

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.

[Paul Furman]

[EL]

Hertz, a proper noun, is the SI (International System of Units) unit for frequency named for Heinrich Rudolf Hertz.

The difference is the size, and possibly the amount of power that can be handled by one vs. the other. There is no such thing as a sold state transformer. Look at a dictionary for the definition of the word "transformer."

The "wattage" specified on a transformer is the maximum that can be handled. Lower loads are no problem.

I may have several fixtures on one

No.