Low Voltage Lighting – Master Xfmr
I really like the 3″ halogen fixtures that use the MR bulbs and are usually LV. We might have 3 or 4 cable light runs and 4 or 5 other areas that will use that lighting in cans in our new home.
Figuring big, say 1200 watts per zone, that makes for nearly 10k watts – perhaps it would be better to base it on (8) 15A single pole CBs in the pane, each serving it’s own light circuit – 14.4kWatts.
In either case, I was wondering if it makes sense, in new contruction, to home run the light runs into a main enclosure served with one large transformer – 10-15 kVA or so. I am picturing something like an enclosed transformer feeding it’s own sub-panel. That would give each circuit it’s own CB, but it would be only have 12 or 24 Vac on the bus and headed out to the lights.
The house is not that big – worst case, I’d say we’d be 150′ of 12 or 14 AWG wire (one-way) from the location of this “LV subpanel” to the fixture.
Anybody see a problem with this? I can think of some potentials – transformer hum, this thing might weight 100#, voltage drop to consider.
The hum would be in the basement, the weight is not a big deal (until I have to replace it!), I could use one that has 16/32 secondary rather than 12/24.. . .
I am concerned about mouting 8 small transformers throughout the home and still having easy access for replacement. These things get hot, too and I’d feel better having them in a steel box on a concrete wall then hidden in a wood framed wall.
Like I said – anyone have thoughts on this? I am meeting with a lighting person soon, but I thought I’d ask around here first. Perhaps this has been tackled in a commercial install in a boutique or office somewhere.
Adventures in Home Building
An online journal covering the preparation and construction of our new home.
Edited 4/21/2006 4:04 pm by jhausch
Replies
We use the Juno cans with integral transformers, undercab fixtures by Kichler (xenon bulbs only, please) with same, and only do xformers for the cove light strips. We do strip lighting at 24V, not 12.
Prima Lighting makes little mini-cans that are fabulous, available with integral xformers. Great for those special little niches.
For dimming, we prefer a master dimmer with scene settings, and for that, prefer the Lutron Grafik Eye packages.
Having always built with the xformer requirements on the mainfloors only, we find ways to put the xformers immediately below in unfinished space in the basement level, or in closets.
Edited 4/21/2006 5:22 pm ET by Gene_Davis
LV cans........... come with their own transformer built-in and everything
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'Wer ist jetzt der Idiot?'
well, your close on the weight, eg: a 5KVA weighs about 100#,
and for your example of 10 -15 KVA, your secondary amps will be more like ...for the smaller transformer......
between 833amps @12 volts to 312 amps at 32 volts
and the larger transformer, which BTW I don't think exists
to be .....1250 amps @12 volts -------468 amps @ 32 volts...
which would require those 8 breakers to be sized quite large, along with a 50 -75 amp 220 primary
At any rate, your transformer, depending on what type you buy should be run 24 hrs a day regardless of any lighting load, just idling and buzzing ..... staying warm and dry....
......... and spinning the meter
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'Wer ist jetzt der Idiot?'
Edited 4/21/2006 10:11 pm by maddog3
I suppose that's another reason why they want those smaller transformers closer to the lamps. Oh well, thought I'd throw the idea out there.
Thanks.
http://jhausch.blogspot.comAdventures in Home BuildingAn online journal covering the preparation and construction of our new home.
10 kW for 12V lamps? Miller probably makes a welder that can meet your requirements...
Or you could use fixtures with local step-down xformers as others suggested. Much safer and more reliable.
.......:>).
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'Wer ist jetzt der Idiot?'