low voltage light calculations!!!!!!!

30 Mar 2003
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United Kingdom
was just doing abit of basic mathematics.....

for low voltage lights (assuming 50w halogen bulbs and 12v transformer)
P=IV so I=P/V..... so I=50/12= 4.16A per light fitting

for mains voltage lights (assuming 50w halogen bulbs)
P=IV so I=P/V..... so I=50/240 = 0.208A per light fitting !!!!!!!!!

The mains voltage downlights are alot less in current consumption so why the hell do we spend time and hassle and expense to fit LV transformers?
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You've missed atrick.

For the 12v example, you need to look at the current on the 230v side - that is what you pay the electricity company for.

Even with transformer losses (not much) the current on the 230v side of the transformer will be about the same (0.2A).


12v is EXTRA low voltage.
ok so then why the need to go down the route of ELV?.... is the brilliance of light much more on the ELV route?
Fashion and manufacturers persuading you to buy expensive things you don't need - capitalism.
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read on the net earlier it was to do with the brilliance of light as compared to mains halogen downlight. mind u elecronic transformers are cheap as chips nowadays. costing anything from £2-£3.
I was thinking more of downlights in general rather than ELV v LV.

Although that's still £2 or £3 + fitting x number x rooms.
Just a thought before I give up - after all it's your house.

Are you confused between ELV (or low voltage as most people and shops call them) and Low Energy lamps. These are still expensive to buy but cheaper to run?
The Extra Low Voltage transformer not a simple transformer but is an inverter. This ensures as long as no silly dimming units have been fitted that the element and envelope is right temperature for correct colour and long life. The inverter compensates for any volt drop in the mains low voltage supply.

Where the voltage from the mains is steady then using the GU10 low voltage lamps instead of the MR16 extra low voltage lamp is likely cheaper and just as effective. But where the voltage is not as stable then the MR16 type has the edge.

The other consideration is the types available. The angle of the beam from a MR16 bulb varies far more than that from the GU10 type so where a pin point of light is wanted (and unless a pin point is wanted why use spot lamps) the MR16 can be selected to give it to closer tolerances. However the GU10 also comes with the very wide spread of the cold cathode florescent lamp which are not available for MR16.

The reflectors is another thing. With the GU10 and GZ10 a GU10 will fit in a GZ10 holder but a GZ10 will not fit in a GU10 holder so with Dichroic lamps (GZ10) they can't be fitted into holders which are recessed so unsuitable for Dichroic lamps. But with the MR16 lamps there is no such safe guard and Dichroic lamps can be in error fitted into recessed lighting with the associated fire risk.

The inverters used with the MR16 lamps are often fitted far too far away from the lamp and often also overloaded where wrong size lamps are used. With lamps ranging from 10W to 75W and many angles it is so easy to replace with wrong one.

But while looking for angles I found this advert for a Dichroic Lamp where the picture clearly shows a GU10 base with the taper so it should not be a Dichroic Lamp. So it seems some manufacturers are breaking the rules?
no i'm talking about the Low Voltage downlight MR16 (which u call ELV) not the low energy lights. hope this clarifies things.
The main reason 12 volt lighting came into fashion for house lighting is that a 12 volt lamp filament can be much shorter than a 230 volt filament. This allows for more compact lamps which allows for more compact fittings. And it is easier to create fashionable spot light fittings when the filament is small.

Also in shop display cabinets where items needed to have the spot light on them 12 volts had the additional benefit of near zero risk of electric shock.

That lead to the open wire suspended spot light system being sold as fashionable for "upmarket" domestic use.

And why sell a single low profit ordinary fitting when instead you can sell (mostly to the dim witted ) several bright torches with higher profits.

There are a few other less significant reasons.
The first extra low voltage lamps I used were for traffic lights and projectors. In both cases they were as "bernardgreen" rightly points out to get a more compact element which could be better focused. The envelopes were small quartz units which ran at a very high temperature and some means of retaining the very hot parts was required.

The spot lamp has the retaining part built in saving the need to put a glass in front to stop the extremely hot bits setting things alight. It also saves the problem with grease causing lamps to fail not touching lamps with ones fingers is a problem.

The MR16 is a very popular base and although there are other bases most designed for house hold use have two pins which right from the early days have seemed to cause problems with the traffic lights it seemed every 5 bulbs the holder needed to be changed. Sorry to say little has improved and still with the extra low voltage lamp the holders seem to fail.

As we move away from the two pins most of the lamps seem to be designed for the auto-mobile. Although these look similar they are very different. Unlike the domestic lamp which run on just under 12 volt the car type has to be able to work on the output from a 12 volt lead acid battery and it's charging arrangement. So these run from 11.5 volt up to 14.8 volt (Charging voltage with three stage charger). In fact old RB108 regulators were set at 16 volt open circuit so the bulb could get even a higher voltage at times.

There have been problems using 12 volt spot lamps in caravans and boats the problem is although they look the same they are not as although called 12v they are not.

I realise that people think 12 volt is "Low Voltage" but the labels "Low Voltage" and "Extra Low Voltage" are defined in BS7671:2008 as below:-

Voltage bands
Band I
Band I covers:
- installations where protection against electric shock is provided under certain conditions by the value of voltage:
- installations where the voltage is limited for operational reasons (e.g. telecommunications, signalling, bell, control and alarm installations).
Extra-low voltage (ELV) Will normally fall within voltage Band I.
Band II
Band II contains the voltages for supplies to household and most commercial and industrial installations.
Low voltage (LV) will normally fall within voltage Band II.
NOTE: Band II voltages do not exceed 1000 V a.c. rms or 1500 V d.c.
Voltage, nominal. Voltage by which an installation (or part of an installation) is designated. The following ranges
of nominal voltage (rms values for a.c.) are defined:
- Extra-low. Not exceeding 50 V a.c. or 120 V ripple-free d.c., whether between conductors or to Earth.
- Low. Exceeding extra-low voltage but not exceeding 1000 V a.c. or 1500 V d.c. between conductors, or 600 V a.c. or 900 V d.c. between conductors and Earth.
- High. Normally exceeding low - voltage.
NOTE: The actual voltage of the installation may differ from the nominal value by a quantity within normal tolerances.
Voltage, reduced (see Reduced low voltage system).

Reduced low voltage system. A system in which the nominal line to line voltage does not exceed 110 volts and the nominal line to Earth voltage does not exceed 63.5 volts.

However much one would like to re-name the voltage bands it is not going to happen. 230vac as used in our homes is "Low Voltage".

Years ago we had a rubber sheaved twin core cable that we could screw a lamp holder to giving us light where it was needed. However this cable and lamp holder were banned and so an alternative method of providing light where required was needed. Two systems replaced the old.
1) The lighting track
2) The extra low voltage lamp. These could be suspended from two discrete wires and provide light where required without the need for insulation on the wires. In the main these were developed for the window dressing so the items on display could be lit.

Again "bernardgreen" has rightly said this system then spread into the home I remember in late 1960's going to Habitat to buy these new age lighting units. Can't believe 30 years latter they are still being fitted.
"ericmark".... what have u been smokin?.... talk about going off on a tangent!..... you've just bored the pants out of me!....lol.....i think u need to get out abit more mate!

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