As mentioned in another post we want to convert the 50W halogen bulbs in our
house to LEDs. We would like to use 12V bulbs but the electrician says that
would require a transformer for each bulb. It was my expectation a
transformer would be needed only for each circuit. Which is the case?
BOTH can be true. There are 12 volt "track lights" that use a single
transformer, and there are under-counter accent lights that share a
single transformrt - but MOST 12 volt lighting fixtures have separate
transformers for each - 120 watts at 12 volts is 10 amps, at 120
volts, it is only 1 amp, so running low voltage wiring requires
heavier wiring -
I have not researched the LEDs that much, but looks like for the same
ammount of light the LEDs only take about 5 to 10 times less power. That
would reduce the 12 volt current to not too much more than the 120 volt
halogen bulbs. Now if the 12 volt bulbs were the regular filiment bulbs it
would take lots more current and larger wire.
I was not comparing LED to Incandescent - I was only comparing 12v to
If he's using LEDs, the 12 volt still requires heavier wiring than the
120 volt - regardless..
For instance I have 7 120 volt 15 watt LED mini-floods on a track
light system.. That's 115 watts. Very close to 1 amp. If they were 12
volt, that would be 11.5 amps.
Now this track WAS designed for 560 watts of Halogen 120 volt lamps -
but that is still only about 4.65 amps.. Not smart to hook a 12 volt
power supply to it and install 12 volt LEDS.
No, they are not meaningless because if I connected the track light
system I currently have to a 12 volt supply and installed 12 volt
LEDs, I would be overloading the track system by almost 300%, Thatt's
using the efficient LEDs instead of the inefficient Halogens - on 12
volts. instead of 120.
And if I used 12 volts DC, the 15 amp rated 120 volt AC switch would
be overloaded as well.
On 12/05/2013 07:27 PM, email@example.com wrote:
You said your system can provide 560 watts at 120 volts (i.e. 4.65 amps
by your calculations); 4.65 amps at 12 volts is 56 watts. 56 watts of
LED lighting is roughly the equivalent of 450 watts of halogens (see,
: 4 watts of LED comparable to 32 watt MR16 ). Thus, I strongly suspect
you could get the same brightness at 12V using LED that you could get
with 120V halogen, all without overloading the wiring.
That's why I gave the link -- to establish the approximate equivalency
of light output. The rest has to do with the current carrying capacity
of the track light hardware rather than the ability to produce light.
That's not what I said though. I replaced the 7 120 volt 80 watt
halogens with 7 120 volt LEDs, which draw less than the halogens - but
if I installed the same output leds as 12 volts they WOULD have
overloaded the fixture. The lamps I have installed give me roughly
the same light intensity as the old Halogens did - just judging by
I don't know of any overriding electrical code that would require that --
once you get into the realm of low-voltage wiring it is the wild wild west.
If the electrician has code concerns, ask him (or her) to show you the
applicable page in the code book and go from there. The big things I'd
worry about is the wire gauge if the lamps are a long way from the supply
and whether the supply is UL (or CSA) approved. It is dead easy to find
150W supplies that are approved and they aren't too expensive. 150W of
high-efficiency LEDs is a _bunch_ of light. You should note that getting
into dimming of LEDs is a whole different thing that dimming regular lamps
and totally different rules apply; most switching supplies won't allow it
and you may need to resort to PWM dimming via an external module.
Personally, I have a lot of 50W and 60W halogen lamps in my house (14 in
one room alone) and prefer the light they produce over any present-day LEDs
I've seen. I guess that won't be true forever but for now I'll just put up
with the heat and pay the extra bit on the electric bill and be happy with
the easy dimmability.
What is the advantage of 12 volt bulbs especially if you want to put them
into your existing light bulb sockets that are powered with 120 volts?
12 volts bulbs, of course, require 12 volts and that would have to be
provided somehow either via a transformer (there are small electronic
transformers) for each bulb or one transformer for each multi-bulb fixture.
Switching your whole lighting system to 12 volt bulbs would likely require
rewiring -- or at least major changes to the system including figuring out
how and where to install the transformers.
Since your power rates are high, you might consider a solar panel system
with battery storage so you could take your lighting "off grid". Then a 12
volt system and 12 volt LED lighting would make sense, but the initial cost
would be higher and it would take time to pay off via energy savings.
I think one would work. I don't have any idea of your led. My 12 volt
constant current converters work on AC or dc, any polarity. Your
requirements are totally unknown without circuit details and specific Parts
Do you care about efficiency?
If you do, make sure that's in your specification.
I've been collecting led lights and transformers
at garage sales.
When I decided to hook 'em up I was very disappointed.
The leds were 3W. The wall-wart transformer dissipates 1.7W
with the lamp off.
And I did say watts, real power.
If your lights are on all the time, that's only 50% excess.
If they're off most of the time, it's a BIG excess.
In theory, one transformer would do.
But you gotta ask the electrical inspector what the code
says about it in your jurisdiction. Rewiring is a pita.
They might not let you put 12V on the normal house wiring.
The wire doesn't care, but the next owner of the house might.
Might be cheaper overall to use 120VAC leds.
They come in a variety of bases.
On Wednesday, December 4, 2013 2:12:55 PM UTC-5, Gary wrote:
You can't find an led bulb that would go into the existing 120vac base?
Transformers are pretty inefficient as compared to alternatives these days. Plus they are not dimmable. The chopped ac overheats them.
You are talking about switching power supply. I saw big 12V output
x-formers made for 12V application. My idea would be just put in LEDs
made for 120V ordinary screw in sockets. I have a few in my house, New
ones are pretty good with some choices. Earlier ones did not last long.
But current ones seems OK. But still price should come down more.
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