12v lights ohms law

[peteludman]

am i being stupid ohms law sais that a 12 v light draws more current than a 240 v so 12v light is more exspensive to run?
feel stupid but can i have a answer

my brain has stopped working on this one

 

[adam.h]

Ideally a 50W light, at what ever voltage will use the same amount of power. The Lower the voltage the higher the current as stated by ohms law.

P= VI or I = P/V

So if you had
1. 50W at 12V and
2. 50W at 230V....

I (@12V) = 50/12 = 4.1A
I (@230V) = 50/230 = 0.22A

Personally, I can't see the benifits of low voltage ones. Mains ones you have less to go wrong with (no transformer needed) not to mention you will have reduced efficiency as the transformer itself will consume some power stepping down the voltage. Also with higher current, which at the end of the day is what kills you, they are not any safer.

 

[sparks1234]

Ideally a 50W light, at what ever voltage will use the same amount of power. The Lower the voltage the higher the current as stated by ohms law.

P= VI or I = P/V

So if you had
1. 50W at 12V and
2. 50W at 230V....

I (@12V) = 50/12 = 4.1A
I (@230V) = 50/230 = 0.22A

Personally, I can't see the benifits of low voltage ones. Mains ones you have less to go wrong with (no transformer needed) not to mention you will have reduced efficiency as the transformer itself will consume some power stepping down the voltage. Also with higher current, which at the end of the day is what kills you, they are not any safer.

Agree here, at the end of the day the little wheel in your meter will spin at about the same rate, as to low voltage against Gu10 lamps, the GU10 are not yet as white and bright as LV fittings so maybe thats why

 

[Mac]

am i being stupid ohms law sais that a 12 v light draws more current than a 240 v so 12v light is more exspensive to run?
feel stupid but can i have a answer

my brain has stopped working on this one

Your electric bill is measured in kilowatts/watts,not voltage or current.

 

[peteludman]

Your electric bill is measured in kilowatts/watts,not voltage or current.

so ,that wasnt the question

 

[Mac]

so ,that wasnt the question

am i being stupid ohms law sais that a 12 v light draws more current than a 240 v so 12v light is more exspensive to run? This is what you quoted.
Yes a 12 volt light does draw more current than a 240 volt light.Why is a 12 volt light more expensive to run than a 240 volt light

 

[peteludman]

ok but kw is watts w=powerp=VI ,i=p/v ,50/240=0.2A ,50/12=4.16 A so i looks like a 12 V light will draw more power so it will cost more the real question is is it going to cost less because its a transformer at 240 v down to 12 V i dont know it dose my head in.if so why have low voltage lighing i know it white not yellow like mains but cant you get a coloour 840 low energy for mains?help me i dose my head in if you have a good answer please explane in detail

 

[Mac]

ok but kw is watts w=powerp=VI ,i=p/v ,50/240=0.2A ,50/12=4.16 A so i looks like a 12 V light will draw more power so it will cost more the real question is is it going to cost less because its a transformer at 240 v down to 12 V i dont know it dose my head in.if so why have low voltage lighing i know it white not yellow like mains but cant you get a coloour 840 low energy for mains?help me i dose my head in if you have a good answer please explane in detail

This is all i could find mate.
Low Energy Stick Light Bulb CFL T 23W ES 840 6K Hr 23 Watt

 

[peteludman]

im still not any wizer
thank for trying mate

 

[NoSparks]

ok but kw is watts w=powerp=VI ,i=p/v ,50/240=0.2A ,50/12=4.16 A so i looks like a 12 V light will draw more power so it will cost more the real question is is it going to cost less because its a transformer at 240 v down to 12 V i dont know it dose my head in.if so why have low voltage lighing i know it white not yellow like mains but cant you get a coloour 840 low energy for mains?help me i dose my head in if you have a good answer please explane in detail

I think you fail to understand basic units, Voltage V it the force behind the elctrical energy. Amps I is the amount of electricity flowing in any circuit at any time. (We don't pay for Volts or Amps) The product of the two ( VI ) is the power (Watts) and multiplied by time (VI x time) is what we pay for, so if we take 50 watts for 1 hr we are using 50 watt hrs. (However a watt hour is very small, so a Unit is defined as 1000 watt hrs, otherwise known as a kilo watt hr, so 50 watts for 1 hr = 0.05 KWh or 0.05 Units and Units are what we see on our electricity bills).

Go back to your own example. In the equation VIt

after the transformer you have 12 volts * 4.1666 amps * 1 hr = 0.05 KWh or 0.05 units

before the transformer you have 240 volts * 0.208333 amps * 1hr = 0.05 KWh or 0.05 Units

or in current 230 volt systems

before the transformer you have 230 volts * 0.2173913 amps * 1hr = 0.05 KWh or 0.05 Units


this is in theory.


In practice the transformer will not be 100% efficient ie the input power will be slightly more than the output power (the difference is given off in the form of heat and maybe noise (hum)). But then two bulbs marked 50 Watts will not be 50 watts but slightly more or less. And as remarked above, different bulbs will run at different temperatures (whiteness) so the light given off (candle power or Lumins ) for the same amount of power will actually be different. And of course the bulb technology will affect its efficiency; tungsten, halogen, sodium, mercury ... but this of course is getting very far off the question!

 

[adam.h]

not to mention that with a transformer there will be more connections in the circuit which can also lead to deficiencies

All in all you are charge by how much power you use. 50W is 50W regardless of what voltage it uses. The lower the voltage the higher the current. Have a read up on ohm's law if you are still confused.