Low Voltage Lighting

[esp-protocol]

Surely as you double voltage you half the current.?

So if 12v=50w

then 24v=25w etc, etc,

and 240v = 2.5w

At 240V each unit draws 2.5W but i'll say 2.4 to make it easier to calculate

So if 240w AT 240V = 1 AMP

Then 2.4W AT 240V = 0.1A

So each 50W at 12V unit will require approx 0.1A of current from 240V

So that means you can fit upto 10 units, cus if each unit draws 0.1A of 240V, then 10 units would draw 1A.

Obviously the above is only approximate, so's to be safe i'd say no more than 9 units.

Dave, how did you get to 2.4 watts ??

Ok, look at your transformers closely for detail of the current they pull at full load, it's always printed on them. Go from there and it should be understandable.

Or use this.

Calculator

Thanks lugs but that calculator doesn't really answer the question....

Transformer states .26 amps on the secondary....

[esp-protocol]

Surely as you double voltage you half the current.?

So if 12v=50w

then 24v=25w etc, etc,

and 240v = 2.5w

At 240V each unit draws 2.5W but i'll say 2.4 to make it easier to calculate

So if 240w AT 240V = 1 AMP

Then 2.4W AT 240V = 0.1A

So each 50W at 12V unit will require approx 0.1A of current from 240V

So that means you can fit upto 10 units, cus if each unit draws 0.1A of 240V, then 10 units would draw 1A.

Obviously the above is only approximate, so's to be safe i'd say no more than 9 units.

Think your right except that 2.4W @ 12 volt (not 240) = .2 A which makes sense ....! I think.... therefore 10 units would = 2 amp at 240v ??

[luggsey]

Think your right except that 2.4W @ 12 volt (not 240) = .2 A which makes sense ....! I think.... therefore 10 units would = 2 amp at 240v ??

Transformer Spec

0.22A x 230v = 50.6 Watts

250 Watt dimmer, use 5 is too many, use 4 is ok, .

BTW you don't "have" to acknowledge the fact that I have tried to help you out. .

[Service Engineer]

So if 240w AT 240V = 1 AMP

Then 2.4W AT 240V = 0.1A

Calculated that wrong I'm tired

how did you get to 2.4 watts

50w at 12v = just over 4 amps at 12v

4 amps at 12v = 2 amps at 24v = 1 amp at 48v = 0.5amp at 96v = 0.25amps at 192v

if 2 amps at 24v then that's 0.2 amps at 240v

240v/0.2A = 48Watts so each unit draws 1/5 of the switches capacity.

So that means you can use 5 units.

[esp-protocol]

Transformer Spec

Well that seems to concur..... approx .2 amps at 240v per fitting therefore 5 lamps would draw 1 amp (ish), 10 lamps 2 amps (ish).

Top man...... my new kitchen lighting scheme and dimmer switch salute you.

You will find your reward in heaven......

Thanks men

[luggsey]

Well that seems to concur..... approx .2 amps at 240v per fitting therefore 5 lamps would draw 1 amp (ish), 10 lamps 2 amps (ish).

Top man...... my new kitchen lighting scheme and dimmer switch salute you.

You will find your reward in heaven......

Thanks men

Ok so you answers to my posts appeared some time after my following posts making me think I was being ignored!

Dave what's going on when I see the most recent postings but not older ones???

[Service Engineer]

Dave what's going on when I see the most recent postings but not older ones???

I have no idea.?

[luggsey]

I have no idea.?

That's two of us then! I am using the view new posts button, could that somehow be the cause?

[breff]

Even if you use 4 lamps totalling 200w and account for some losses, you are still talking around 16 amps being pulled through the switch which I can't believe !!

Where's Lurch when you need him ?????!!!!!!!

You are switching the 240v though not the 12v, 250w@240v= 250/240 amps or 1.04 amps.

As luggsey says though there will be some loss with the transformers so go for 4.

[uski]

Hi folks,

I just wanted to let you know that in an AC current circuit, the law P = UxI is not always true. Well, not always *exactly* true

There are 3 "types" of power:

- Active power

- Reactive power

- Apparent power

This is because in an AC circuit, capacitibr and inductive load make the current lag or be in advance compared to the volts. If the current is not synchronized with the voltage, electricity is not used efficiently.

This is measured by the Power Factor. Generally, it is considered to be good when it is between 0.95 and 1 (you can see it on the specs on the transformer: it's 0.99 for this one).

In the case of this transformer, and generally in all the circuits we deal with (alarm systems, access control, ...), this is no big deal because the equipment we use all have a power factor very near to 1.

But if you deal with motors, a lot (I mean a huge amount) of fluorescent lamps, or big industrial machines, there can be a problem and corrective measures may need to be taken.

If you look at recent PC power supplies, sometimes you can read "active PFC" which means that they have a circuit to correct the power factor (an active circuit i.e. not only an inductor or a capacitor, but a full electronic circuit that is as efficient as possible)

For more info, Instead of reexplkaining something badly when it's done correctly somewhere else, I prefer to redirect you to the following pages rather than continuing the explanation myself:

http://www.energy-in-motion.com/PFC.html (explained informally)

http://en.wikipedia.org/wiki/Power_factor (explained with the maths)

uski