LV lamp wattage

[jonathan.hancock]

Hi. Does anyone know if a 50W LV lamp with electronic transformer current is calculated the same as a regular 50W bulb? ie 50W/240V = 0.2A and 50W/12V = 4.1A. Which, if any, calculation do you use? Thanks.

[ban-all-sheds]

It is always I=P/V

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[jonathan.hancock]

ban-all-sheds wrote:

It is always I=P/V

ok. But do you take the voltage to be 12v or 240v?

[ban-all-sheds]

What is the voltage rating of the bulb?

__________________
I mustn't warn people that the "experts" on the plumbing forum can't be trusted to tell the truth.

[jonathan.hancock]

12V

[ban-all-sheds]

There you go then - use 12V.

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I mustn't warn people that the "experts" on the plumbing forum can't be trusted to tell the truth.

[jonathan.hancock]

I am a little confused. 50W at 12V is 4A per lamp. So you are suggesting that 4 lamps will take 16A. That can't be right. The circuit is only rated at 6A.

One of the electronic transofrmer manufactures states that the input current is approximatelt 20 times less than the output current. So the i/p current for a 50W bulb would be 0.2A which sound a bit more like it. Any thoughts?

[Adam_151]

The power is always the same, 50W (ignoring inefficenies atm)

current = power / voltage (form P=IV)

so if you work out 50 / 12 that gives just over 4A, this however is on the secondary side of the transformer, make sure your cable is rated accordingly.

if you work it out for the primary side of the transformer, the voltage is 230, so that is 50/230 which gives 0.20.

Just remember that power (the wattage) is what stays the same both side of the transformer, not current

EDIT: the reason Iout = Iin x20 is becuase Vout(12V) = Vin(230)/20 (it doesn't work perfectly, becuase we do calculations with 230, when in actual fact tha volatge will more likely be nearer 240, and as everything is relatd by P=IV, and P is constant...

[jonathan.hancock]

Thanks Adam 151. That makes sence now.

[plugwash]

ban-all-sheds wrote:

It is always I=P/V

for lighting that is pretty damn close to true and it seems most sparkys assume that to be true all the time. However be warned that in an ac system it is not true in general.

[backtothebeer]

[quote="Adam_151"]The power is always the same, 50W (ignoring inefficenies atm)

Hello All,

My electician insists that a 50w Halogen Dichoric GU5.3 12V bulb for a ceiling downlight does not actually use 50w of mains electricity.

Do they use 50w - e.g. 10 of them would be 500 watts and for cost of electricity to me I take that as half a KWh ?

thanks

[Steve]

backtothebeer wrote:

Do they use 50w - e.g. 10 of them would be 500 watts and for cost of electricity to me I take that as half a KWh ? thanks

Yes. 500w is 500w whatever the voltage. The amount of power is the same.

Approx. 42 amps at 12V, and 2.1 amps at 230V.

[Pens]

backtothebeer wrote:

My electician insists that a 50w Halogen Dichoric GU5.3 12V bulb for a ceiling downlight does not actually use 50w of mains electricity

You might be getting confused between wattage and light output. As Crafty said, 500watts of energy is 500watt of energy whichever way to cut it. However, that is the energy rating of the lamp, not its light output which is measured in lumens.

For example, a 35watt florie will use around 35watts of energy, (a bit more with internal losses) however, the light output will be a lot higher than an equivalent filament lamp.

The same applies to halogen lighting, the lumens/watt of energy used is higher than the lumens/watt of tungsten lighting which may be what your sparks was trying to say

[Adam_151]

This is an old thread, you'd have been better off starting a new one, but anyway, seeing as I'm a regular in this forum, I'm still here

backtothebeer wrote:

My electician insists that a 50w Halogen Dichoric GU5.3 12V bulb for a ceiling downlight does not actually use 50w of mains electricity.

unless he is being predantic about it because it doesn't actually use any electricity straight from the mains , then he is wrong, watts are a measure of the rate of transfer of energy, that means for the transformer to be supplying the lamp with 50w, it must be drawing 50w from the mains (unless its magicing energy out of thin air )

The only slight exception (well not really, but if you interpret the labeling wrong...) to this rule are energy efficeient lamps, they are generally sold on what wattage normal lamp they give out equivelent light to, but take less power to do so (again, no magic, they just dont create anywhere as near as much heat) and typically one equiv. to 60w takes 12w. Anyway thats a side point

Sadly the occasional electrician doesn't seem to get this (Probably spent his time at college smoking and swapping porno mags at the back of the room )

Quote:

Do they use 50w - e.g. 10 of them would be 500 watts and for cost of electricity to me I take that as half a KWh?

Yes, that is correct, ten 50w lamps will take 500w, which is half a kilowatt, which means that have them on for an hour and you'll clock up half a Kwh on your meter


Hope that answers your question, though I seem to have digressed a little

[backtothebeer]

Thanks for the replies,

I was concerned that each light would consume 50w

The sparky said that as they are 12v, due to the step down process they don't actually use 50w.

the actual bulb is

http://81.29.94.80/sourceandselect/Applications/catalog/search/KeywordSearchFrameset.asp?Keyword=LV50MF