Please help my understanding!!

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Of electrics that is! I just bought some mains voltage halogen downlighters for installation in my house shortly. A colleague has bought some 12 volt halogen downlighters and insists that they are more economical to run. I appreciate that the 12v bulbs may last longer, but can someone show me the maths as to why they would be more efficient to run? I thought that for a given wattage the voltage may be lower but the ampage higher, so no net difference. Anyway I appreciate that my understanding here is somewhat lacking as I couldn't really explain to my colleague why he was wrong (if he is!)

Thanks a lot

JD
 
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Don't know mate. The bulbs themselves are pretty similar. Transformer losses?

Could help you with the fact that there was nothing wrong with intelligence reports by our security services regarding the consequences of starting a war in Iraq. Only with how this information was used (ignored) by politicians.
 
He is wrong - watts are watts, and that's what the electricity company charge you for. A 50W 12V bulb needs as much power from the mains as a 50W 240V bulb. In fact, because of losses in the transformer, it needs slightly more power.

He is right - if you consider all of the running costs, not just electricity. In general 12V bulbs last longer than 240V ones, and in general they cost less to buy, although both types of bulb cover a spread of lifetimes and prices, and, of course, they overlap. And in any event, I suggest that if you are concerned about the actual differences you probably shouldn't be using halogen lighting at all.... Finally, there's the less obvious running cost of 12V systems - replacement transformers. The cheap electronic ones that you get with kits from the sheds are unreliable, and frequently fail. The proper design is 1 good quality transformer per lamp, but then this all costs more, which leads on to TCO.

He might be right, he might be wrong. When you get to TCO (Total Cost of Ownership), it's even less clear, because the capital cost of a 12V system is higher - you have to buy the transformers, and cables on the 12V side cost more than those in a mains system, as they need to be thicker. Obviously the effect on TCO depends on over what time you write those costs down.

Summary. It is difficult without knowing more about the comparative capital costs, and how long you each plan to keep the lights before changing them for something else to be sure which will be the cheaper system to run, and even then it'd only be a probability. I do know that analyses like these are like rearranging the deck chairs on the Titanic - both systems cost a lot to run, and the marginal differences are insignificant.

Personally I'd always go for mains - cheaper and easier to install, less to go wrong, easier to dim and better future-proofing; LED lamps are getting better all the time, and if you wanted those you could just swap them straight in, whereas your colleague would have to change his whole system.
 
Thanks Ban.

He is wrong - watts are watts, and that's what the electricity company charge you for. A 50W 12V bulb needs as much power from the mains as a 50W 240V bulb. In fact, because of losses in the transformer, it needs slightly more power

Thought so, good to know my understanding isn't too far off the mark!
There's a lot of misinformation given out on this point, when I bought low voltage downlighters for my last house I was told by the lighting shop that they wouldn't use as much leccy as the mains voltage ones!

Personally I'd always go for mains - cheaper and easier to install, less to go wrong, easier to dim and better future-proofing; LED lamps are getting better all the time, and if you wanted those you could just swap them straight in, whereas your colleague would have to change his whole system
Yeah me too, which is why I'm sitting here building up the enthusiasm to fit 24 HI-LITE 50W GU10's. Must say they look the biz tho' and managed to get a good price from a small lighting supplier, so very pleased overall.

Am I right is saying there aren't any 50W LED's available at the moment?

Thanks again

JD
 
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ban-all-sheds said:
He is wrong - watts are watts, and that's what the electricity company charge you for. A 50W 12V bulb needs as much power from the mains as a 50W 240V bulb. In fact, because of losses in the transformer, it needs slightly more power.

Now I know I'm gonna look stupid here, and the camera never lies!! but Watts = V(volts) * I(amps) ?

the transformer transforms 240v (230v really) to 12v a 20:1 ratio

Assuming (big assumption) that the transformer is 100% efficient doesn't this mean that the load on the supply side is 20x less?? So in other words, a 50w 12v bulb supplied by a 240v to 12v transformer would only draw 2.5 watts on the 240v side????

Now I assume this because I thought I'd been told that you could have loads of 12v halogens on a lighting circuit!!

I don't know why I am posting this, simply opening myself up to ridicule. :oops:
 
Your logic is wrong. The load is the same, the current is what is less.

The power supplied is the same, the current on the supply side is 20 times less because the voltage is 20 time more:

Power at 12V = 50 W, so current in low voltage circuit is 50/12 = 4.2 Amps

In the high voltage circuit, the current is 50/240 = 0.21 Amps
 
dmccormick said:
Your logic is wrong. The load is the same, the current is what is less.

The power supplied is the same, the current on the supply side is 20 times less because the voltage is 20 time more:

Power at 12V = 50 W, so current in low voltage circuit is 50/12 = 4.2 Amps

In the high voltage circuit, the current is 50/240 = 0.21 Amps

Thanks, I understand now :oops: why is it the more I think I know, the more I realise I know practically nothing. Perhaps I should steer clear of DIY, I think I'm getting dangerously incompetent !!
 
Hey Edward, more in your line ... What do you call a guy who owns and runs a bank ? ;)
Edit :- Only joking !! The man who never made a mistake never really tried anything new !! :)
 
There are no 50W led lamps at present. If there were, they would probably put out as much light as a garden floodlight.

That is just a guess without looking up any of the figures. LED produce light very much more efficienlt than ordinary bulbs, so the amount of light per watt of energy input is much greater. Trouble is that LEDs are rather small. Typical current for 1 LED might be 30mA at 1.5V which is 50mW. So a 50W bulb would need 1000 LEDs. Those in focus have about 10. I was surprised to see them there. Curent LED replacement bulbs have yet to get a good reputation.
 
We've got used to wattage as being a good indicator of light output... but it ain't.

A five-foot fluorescent consumes around the same power (in Watts) as a 60W tungsten lamp, but puts out much more light. A modern, compact fluorescent lamp of only 11W is about as bright (eventually) as an older 60W. Bring LED's into the equation and it gets more confusing still - as Damocles has said an LED lamp that consumes 50W would have you sitting there like a rabbit in the headlights; pinned to the back of your armchair by sheer light power!!!

Maybe we need to start talking in terms of candela, lumens, lux and luminous efficacy... but then we'd get all sorts of people in a lather about inverse squares, cosines and spectral light quality. Fun, isn't it?
 
Personally I'd always go for mains - cheaper and easier to install, less to go wrong, easier to dim and better future-proofing; LED lamps are getting better all the time, and if you wanted those you could just swap them straight in, whereas your colleague would have to change his whole system

Hmm.

Mains voltage are still awkward to dim in that you need a dimmer rated approx twice the wattage to be dimmed.

And here is a tale to beware: MK dimmers no longer have fuses, so if you get a kit from a shed and the lamps have no fuses inside, then it will toast the dimmer.....

Also, watt for watt, Mains Voltage are less "lumenous" (if you know what I mean!) than SELV. IE they have less light output than their equivalent. This may well mean fitting extra.
 
I thought the extra brightness of low voltage unit was due to the dichroic reflectors which are a more efficient design, and also direct less of the heat with the light. Is it true to say that mains GU10 units do not have dichroic reflectors, and if not, why not? As for mains vs low voltage, surely the main reason for fitting LV is for additional safety, for example, in bathrooms. Personally, I've bought GU10s for my kitchen and run LV in my bathroom.

I asked a question in another thread as well, that if the power of the bulb is the important factor rather than the voltage when considering dimmers, surely using LV units does not improve the situation when you have to run many lamps from one dimmer?
 
phykell said:
I thought the extra brightness of low voltage unit was due to the dichroic reflectors which are a more efficient design, and also direct less of the heat with the light. Is it true to say that mains GU10 units do not have dichroic reflectors, and if not, why not?

Some GU10 lamps are dichroic, but you have to be careful.

There are 2 common types of mains halogen lamp bases, GZ10 and GU10.

gu10bn6.jpg
gz10rv0.jpg


GZ10 lamps are the dichroic (cool beam) type, where a lot of heat comes out of the back, and GU10s have internal reflectors (the lamps are also known as PARxx - Parabolic Aluminium Reflector) where the heat comes out forwards.

If you look you'll see that you can put a GU10 lamp in a GZ10 fitting, but not the other way around. This was done so that you couldn't put a dichroic lamp into a luminaire designed for PAR lamps, as the rearward-reflected heat would damage it.

Well guess what - people have now started making dichroic GU10s :rolleyes:

If a luminaire has a GU10 base, then unless the instructions explicitly say otherwise, you must only use PAR GU10s in it, not dichroic.
 
Am I right is saying there aren't any 50W LED's available at the moment?

Thanks again

JD

..Well this is a bit off topic but regarding higher output led lighting in general I have a 13.5 watt consumption led outdoor floodlight (240 volt) it's equivilent to about 150 watts generally & makes for some very good lighting inside or out (handy in my loft etc as I've yet to mount it)
its got as I recall around 160 leds in the aluminium cased head unit which pivots like a regular outdoor security light.
Having spoken to another supplier of the same product they do a 12 volt version
+ a lower & a higher output 45watt consumption equivilent to around 500 watt security light.
my new light (yet to appear) will be a 12 volt version to which I'm intending to power via solar for my garden / pergola without attracting mosquito's & gnats / midges.
when I pull my finger out & get it sorted I'll post back here!
so far the one i'm using is worth every penny in terms of feeling smug & slightly greener.
fantastic site wish I'd found it years ago!
cheers
 
Hi MR GUS

Where did you get the 13.5 watt consumption led outdoor floodlight (240 volt) :?:

Thanks

Atty
 

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