Ohms Law and low voltage

[Monkeyblaine]

How come Ohms law doesn't apply when talking about low voltage downlights. i.e 50w divided by 12V = 4.16A so thats obviously wrong. I think Im getting a bit confused.

 

[WPD Lad]

Ohms law always applies

 

[WPD Lad]

Lower the voltage the higher the current, that's why electric is transported at thousands of volts over long distances!

 

[Sparky Ninja]

havn't you noticed that the ELV cables are usually larger?

 

[Knobhead]

If you manage to prove Ohm’s law wrong, can I be your agent? I’ll only want 15% of the fortune you’ll make.

(Discounting supper cooled conductors).

 

[Richard Burns]

How come Ohms law doesn't apply when talking about low voltage downlights. i.e 50w divided by 12V = 4.16A so thats obviously wrong. I think Im getting a bit confused.

A 50W 12V lamp will be drawing 4.17A through the ELV cables and then on the other side of the transformer (ignoring transformer losses), 230V using 50W will be drawing 0.22A on the LV side.
Try a clamp meter on the ELV cable to a downlight and measure the current.

 

[telectrix]

think the OP is confused by not converting the current to the primary 230V and thus thinking 1 50watt lamp will draw 4+ amps from the 230V supply.

 

[D80]

Have been asked several times by customers How much am I saving by having 12v 50W lamps instead of 50W mains - if anything it will be costing more due to the transformer losses, but 50W is 50W.

 

[Monkeyblaine]

Clears it up. Didn't think about the transformer. Thanks a lot.

 

[Knobhead]

It’s raised a question for me. Why the hell are they so popular?

It’s been bugging me for a while, (since I joined this board). They don’t make economic sense.

Is it just kudos on the part on the customer giving bragging rights, (we’ve got these new low voltage lamps in our kitchen, etc). Or marketing gobbledygook by the manufacturers.

As D80 says 50W is 50W + losses. So for 50W with transformer losses of say 1.5% (generous) you use 50.75W.

I thought we were supposed to be GREEN.

If I’m wrong please correct me.

 

[Richard Burns]

It’s raised a question for me. Why the hell are they so popular?

It’s been bugging me for a while, (since I joined this board). They don’t make economic sense.

Is it just kudos on the part on the customer giving bragging rights, (we’ve got these new low voltage lamps in our kitchen, etc). Or marketing gobbledygook by the manufacturers.

As D80 says 50W is 50W + losses. So for 50W with transformer losses of say 1.5% (generous) you use 50.75W.

I thought we were supposed to be GREEN.

If I’m wrong please correct me.

Probably should not get into this one!:38:
You are not wrong, in my opinion.
But they are so safe because they are separated 12V (with 230V just next door, lots more connections and a transformer to go wrong).
The lamps have thicker filaments so they won't break so easily (depends only on lamp quality)
The light quality from 12V is so much better (barely noticeable)
12V can go in a bathroom safely (so can 230V, OK maybe more flexibility with separated 12V)
So for an additional cost, with additional components, additional energy losses, more space required in ceiling for transformer they are so much better.
Someone else will probably cut me down, oh well!:74:

 

[Knobhead]

So that’s why they’re so popular.
More things to go wrong = more call outs to lighting faults!

 

[Geordie Spark]

My mate has just built himself an extension on his house to make a kitchen / diner.

He's wanting to put 20+ of these damn' downlighters in it !!! :hanged:

 

[Rockingit]

My mate has just built himself an extension on his house to make a kitchen / diner.

He's wanting to put 20+ of these damn' downlighters in it !!! :hanged:

LED and he'll be alright.