In the interest of fuel saving could there be any saving in having a 12v lighting circuit? Using maybe one or two larger transformers and the equivalent of a mains lighting circuit or would the cost not be justifiable? This being in addition to the normal mains circuit.
On a similar topic because transformers become warm, is there significant electricity use when on standby?
PhilC
Energy consumption is a function of wattage, not voltage alone.
As a very simple rule-of-thumb, lighting level is a function of bulb wattage - a 40w bulb is much dimmer than a 100w bulb.
I'm sure the theorists will be popping up to argue over those points, but they're close enough for the purposes of your question.
Whilst 12v halogen bulbs can appear to give a relatively higher light output than 230v bulbs, they tend to be fairly directional, so you'd have to rethink your overall lighting scheme to give good lighting levels, and probably use more 12v bulbs.
Transformers have two losses, iron and copper. The iron losses are incurred in magnetising the core of the transformer - they happen just by switching on the transformer. In addition, when you put a transfomer on load, the windings actually incur some losses.
Ask yourself, if there was some merit in your suggestion/question, whole-building lv lighting circuits would be commonplace.
No! Just change to a cheaper gas and electricity supplier to save money. You can save a lot more for electricity by looking at costs per unit. I changd over and have now got a cheaper unit price and no standing charge. For gas I pay less than half of what british gas want, and no standing charge. Why pay more than you need to?
Possibly, but 12V is the wrong voltage. The most efficient 100W filament lamp will be designed for 55V operation, so if you were going to design a circuit for efficient filament lighting, it would likely be at least 55V. I²R losses in the copper will be very much higher than for mains lamps, and when you factor in that and the consequential cost of thicker conductors, you would probably go for a higher voltage.
In the US, a range of 85V filament lamps was produced. These included a diode in the lamp base so they could be run from 120V mains supply (RMS voltage of half-wave rectified 120VAC is 85V). These were more efficient than the same power rated 120V filament lamps, because they are nearer to the optimum filament lamp operating voltage.
However, this is all rather academic now. No one who is concerned with lighting energy efficiency will be using filament lamps any more.
Transformers aren't generally left on with no load. Actually, electronic ones often won't work below a certain minimum load.
Agreed and using CFLs.
Do you really mean "no standing charge" or a tarrif that says it has "no standing charge" but the first X units cost more than those after? Curiously the price difference between the two rates times the number of units at the higher rate equals the standing charge...
There are tarrifs that truely have no standing charge and have a single rate for all units. Equipower and Equigas I know of, there may be others. Very handy if you have a low usage. However if you always use enough units to pay all the hidden standing charge you'll probaly be better off looking at standing charge tarrifs with a single, lower, per unit cost.
12v halogens are more efficient than mains halogens, but 240v CFLs are much more effieicnt than either, and 12v CFLs cost more and are a bit less efficient than 240. So no, theres nothing to gain.
CFl or linear fl are the energy saving options.
There would be savings if you had a LV system that you could plug small appliances into, to replace wall warts, but the savings would be too small to be worth installing a system for.
NT
12v halogens are more efficient than mains halogens, but 12v CFLs are much more effieicnt than either, and 12v CFLs cost more and are a bit less efficient than 240. So no, theres nothing to gain.
CFl or linear fl are the energy saving options.
There would be savings if you had a LV system that you could plug small appliances into, to replace wall warts, but the savings would be too small to be worth installing a system for.
NT
Ther could be in that the bulbs last longer and give more light as tehy run hooter, for a given power.
However you have also identified that there will be losses associated with the transformers, and the wiring losses will likeley be greater, and the currents will necessitate a lot of thick cable, and the switches would need uprating to deal with the currents.
Which is why we run 240v lighting circuits and switches, and use local transformers for 12v lighting.
Since these are mostly spot lights, the advantages are lessened by the smaller illumminated foot print. I guess you COULD use car headlamp bulbs...
relatively short lamp life though
NT
I don't think so. Not comppared with a normal incandescent bulb anyway.
Something like 250 hours. (Some of the boy-racer high temperature ones are much less.) At 12V, they would last longer than at the battery charging voltage they are designed for, of course.
Someone did the calcs in this newsgroup a while ago, regarding how much power the average wallwart consumed while left plugged in - can't remember the figure but a few quid per annum IIRC?
I've mused about this myself; not particularly in connection with lighting, but because of the huge number of wall-warts which you now see festooned around most houses these days; the majority of which get left plugged in and switched on when not in use. All LV appliances have different requirements of course, but wouldn't it be better if there was a standard LV circuit(s) wired into houses, with uniform wall-mounted sockets, which all manufacturers of electronic appliances could design their kit around?
Without even trying, I can think of 25 wallwarts in my house, most of which stay plugged in 24/7 despite my nagging! and this list is certainly not exhaustive:
Mobile phones (x4) Printer Router Monitor PC speakers Kids games/toys (x6) Playstation Ipod basestation AA battery charger DECT phones (x3) Power tool chargers (x3) Clock Laptop ...
David
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