Low Voltage Lighting

Need to light a display in a dark room with less-than-full brightness lights
(ie, "mood" lighting). Would like to use small spots, but these are mostly
quartz-halogen bulbs. To my understanding, QH bulbs must be run at full
brightness, otherwise the filiments fail to "redeposit" properly.

Also, dimming LV lighting is not straight forward (out of the box; I know
anything can be done with custom controls...)

This leaves mineature incandescant spots. Wiring is a pain (mains voltage,
conduit, code requirements, etc.), but if all else fails, I'll do this using
a dimmer.

Suggestions?

Thanks,

 

No problems running LV halogens at levels down to 20% or so as long as you
occaisionally run them at 100% to 'clean up' the deposited tungsten from the
capsule wall.
I use inductive rated dimmers with wirewound transformers throught out my
house with LV with no lamplife issues at all. In fact I think that lamplife
has actually been improved.
You can bounce queries like this on sci.engr.lighting NG.
regards,
JB

 

These are mains voltage-rated dimmers controlling the 120 vac input to the
step-down wirewound transformers?

Can you provide a reference to such a dimmer & said transfomrers?

Thanks, I will.

 

--Snip--

So what is the difference between a regular incandescent dimmer and a
magnetic (or electronic) LV dimmer?
At one time I had heard that the inc. dimmers put out a small DC offset
which would than be fed to the transformer in the light fixture. Is that
really the case, and is it really that bad? (bad, but how bad?)

 

I wonder if this would help at all. Just a thought; I've never used
them.

http://tinyurl.com/xj46

 

If you looking for mood lighting consider switching the lights at full
bright in several stages. A dimmer accepts the full load and only passes on
the level you set. Using a 100 watt base and you set it for 50 % or 50 watts
then your burning off 50 watts in heat. Not exactly efficient. I know it
means more wiring but if you think about it you might decide that it is a
better way to go.
Just a wild thought from the cheap seats

 

"DaveC" wrote ...

Some people put in multiple switched circuits so you can control
the number of lights that are burning (and thus, the "mood")
without any tricky equipment. Sort of a room-level equivalent
of those "3-way" bulbs.

 

Nope.
Modern semiconductor based dimmers (99% of those sold now) are around 95%
or so efficient.
They basically are on-off switches that switches on at varying points in
each cycle.

I would be really, really surprised if you can even buy resistive dimmers
(which even then are not quite that bad) nowadays as it's cheaper to
make the semiconductor based ones rather than a high power resistor.

 

I don't understand what you said. What are you using to switch lights at full
bright in stages? Do you mean use several lights and turn on combinations of
them? Or switches with resistors in stead of a dimmer?

Please clarify.

Thanks,

 

SQLit wrote:
||
|| If you looking for mood lighting consider switching the lights at
|| full bright in several stages. A dimmer accepts the full load and
|| only passes on the level you set. Using a 100 watt base and you set
|| it for 50 % or 50 watts then your burning off 50 watts in heat. Not
|| exactly efficient. I know it means more wiring but if you think
|| about it you might decide that it is a better way to go.
|| Just a wild thought from the cheap seats

You're wrong, to have half power you will need V_half_power=0.707V_full, the
resistor would only need to dissipate 0.293Vfull at 0.707*Ifull=20.7W if the
lamp had 100W. This assumption is for pure resistive and linear loads.
In reality an incandescent bulb will reduce the heat and its resistance, so
you need a little less voltage and more current for this, but the resistor
will not need to dissipate more than 25W when the bulb puts out 50W. Got it?

 

not a big problem: turn them up full every once in a while.

also not a problem: use a dimmer rated for LV. Lutron and others sell them.
They cost more partly because they are only available on the high price trim
lines. People who buy those trim lines are paying extra anyway. When I
opened a LV dimmer up (a few years ago) the only differnce I saw compared to
the standard dimmer was a snubber (RC network). You could modify it yourself
but I wouldn't. Pay the extra ten bucks and let Lutron oir whoever bear any
liability. BTW: if you use an electronic "transformer" (not magnetic, more
like a buck SMPS) then be sure the dimmer is rated to work with *that*.

Either way you have code requirements: you'll be runing line voltage to the
dimmer.

You haven't described your room in any detail but if you're trying to
minimize the amount of line voltage wiring try looking at cable lighting
systems: 2 bare wires are suspended across a space and driven by a remote
tranformer. The bare wires carry only 12 volts. The fixtures hang across the
bare wires.
Another possibility: use a LV landscaping lighting system. Or, adapt a LV
landscaping system into a cable system. All of these systems can be dimmed
(see above).

Bob

 

Some architectural installs are programmed to go full up early in the
morning for bulb clean up and helps the cleaners sweep up.

Its not custom , just a more slightly more specialised dimmer, the magic
words are `inductive` or ` hard fired`and dimmer, people in the U.S. like
Leviton and Lutron make them, sure there are few more wallet friendly
manufacturers too.Try searching `wall plate inductive dimmer ` or similar.

Line voltage MR16s are getting neater, low voltage does not mean low
current, if you use inductive transformers the cable thickness is big
between that and the light, inductives are fine for wire and rail lights
where the conductor is big and RFI concerns rule.Otherwise electronic
transformers are just the thing.

Down to a faintly glowing wire if you want.

Personal and anecdotal evidence is that the soft start of dimmers lengthens
lamp life.

More common than you might imagine, dont try and use dimmers that miss out
the magic inductive. Transformer and dimmer may suffer.

The easisest an usually cheapest way after cable costs are considered is to
take mains as close to LV lights and then use an Electronic Transformer
near the light or cluster of lights.These will dim on low cost standard
dimmers, making choice of face plate usually a bit wider as well.
Shop around this was p1 on google for 120V dimmable electronic transformer;

http://www.ylighting.com/transformers.html

Hi from sci.engr.lighting, only helps if server accepts growing cross post
list ;-)

Adam

 

I use a halogen torchiere as my main light in my office. It has a dimmer
built in; I haven't taken it apart, so I don't know how it dims, but I do
run it at about 20% full brightness most of the time, and don't have any
problems with bulb life.

It runs off of mains.

 

Bob,
Look at the bulb (when it's off!). I just replaced one in a similar lamp that
was always run at low settings. The glass gets blackened from the deposits
that don't get back to the filiment.

Dave

 

So, to summarize:
1) Full mains V, wired to standard dimmer (rated for electronic xfmr), wired
to electronic xfmr, wired to LV lamps.

2) Full mains V, wired to LV dimmer, wired to LV lamps.

Do I have these options right?

Other suggestions?

Thanks,

 

nope.

I don't know of any LV dimmer. That is, there is no such beast (besides
designing your own) that is a dimmer and a transformer in one. (even if you
design your own, I think you would have a code issue trying to run mains and
LV wires in the same J box) So, 2 is not an option. Maybe you misunderstood
what I meant by a LV landscaping system: they have a tranformer (often in an
outdoor rated enclosure), some LV fixtures, and some wire suitable for
running LV outside (buried or on the surface).

Bob

 

Are electronic transformers supplied only by electronics houses? This isn't
something I can find at the local electrician's supply house, is it?

Thanks,

 

Bob wrote:
||
|| I don't know of any LV dimmer. That is, there is no such beast
|| (besides designing your own) that is a dimmer and a transformer in
|| one. (even if you design your own, I think you would have a code
|| issue trying to run mains and LV wires in the same J box) So, 2 is
|| not an option. Maybe you misunderstood what I meant by a LV
|| landscaping system: they have a tranformer (often in an outdoor
|| rated enclosure), some LV fixtures, and some wire suitable for
|| running LV outside (buried or on the surface).
||
|| Bob

This transformer w built in dimmer I found at this (popular) German
Electronic Parts vendor.
http://www1.int.conrad.com/scripts/...UID=AB8CB23C95B0380EE10000000A010251&x=46&y=4

 

sci.engr.lighting has dropped back off the crosspost , so for
sci.electronics.xx

Electronuic transfomers are very common in the U.K. and cam see no reason
why any *good* U.S. electrical supply house would not have them available
off the shelf.

Adam

 

A simple a regular incandescent dimmer when connected to highly
inductive loads can have two side-effects:
1. The dimmer might not be too accurate on the accuracy of the
dimming agle both half half cycles of mains power. This can cause
some DC component to be generated ot the output power. This
DC component will heat up tranformer and can even cause
it to saturate (saturation leads to lots of heating and
can cause transformer failure).
2. The dimmer might not triger the controlling triacs always
reliably with highly inductive load. This can cause that
on soem dimmer settings the light could be unusable,
can flicker etc.