calculating power

[bernardgreen]

It is hard to credit, but what really amazes me is that people who claim to be, or think they could become, electricians can have any difficulty with it.

Wire 1 the red one from lamp terminal 2 to switch terminal L1
Wire 2 the black one from lamp terminal 3 to switch terminal Com
etc etc etc

Wiring by numbers as per a set of diagrams is enough to connect the wires into the right places to make the system work.

There seems to be many ( too many) "electricians" who believe that limited knowledge is more than adequate to be an electrician.

 

[spark13]

oh my lord this has become a joke .listen i can do ohms law my question was based around the lights being on 12v transformers and basically just making sure my sums were correct which is all i was doing just making sure !
wat i will say is that certain people on this forum seem to think it is a place were they can come and plant some kind of AUTHORITY on the forum and really puts people off this place these people need to remember to treat people and there inquiries with respect and really get down off their pedastal, its too easy to be rude and flippant behind a keyboard and you just get the impression that if these certain people talked to you in the street like they do on here sometimes they would run a mile at the first sign of confrontation people probably know who i am talking about and stand by and let these people treat people badly ! after all they are probably only like this on here coz they get treated the same way at home off the mrs

 

[holmslaw]

..

 

[spark13]

thanks for that . that was my point in posting in the first place because 1000w of the load are on 12v and i wanted to make sure i was getting confused myself!!!!

 

[spark13]

ha ha oh dear somebody else got confused

 

[davelx]

liampope:

1300 watt divide 230 = 5.7A

1300 watt divide 240 = 5.41A

the more voltage with the same current is LESS amps as there are more volts to divide the amps by!

I suggest you read that again "...the same current is less amps..."!!!!

I am at loss to understand why so many people think that with domestic electrical heating and lighting appliances the power drawn is constant regardless of the supply voltage. To achieve that requires an active, ie, electronically controlled, switching, power supply, as are used in induction hobs, computers, and other domestic electronics. They could, and in some cases are, also used in more sophisticated electronically controlled heating or lighting devices (including some electronic 12V halogen lighting supplies), but in the main, when we are talking about normal, resistive, heating/lighting loads powered directly from the mains feed or via a normal mains transformer, then the current drawn is directly proportional to the applied voltage.

That type of relationship is expressed by a formula of the form A=KB+C, where K is a constant and C is a fixed (offset) value In this case, A = voltage, B= current, C=0 (ie. if there are no volts applied there is no current) and the CONSTANT K, is the resistance. This gives us Ohms Law directly: V=IR.

Resistive loads have a fixed resistance (ignoring temperature effects). So if you change the voltage, the current changes in direct proportion. Double the voltage and you double the current, which gives you 4 times the power.

If anyone can't see why that is, then try a few examples and, as an exercise, see if you can derive the equations for determining power given the resistance and one only of applied voltage or current flowing for a purely resistive load (let's keep it simple)

 

[PrenticeBoyofDerry]

Could I also mention to OP that 100w lamps have now been discontinued and the calcs can be made using 60w ones. which will have an effect on is calcs.

 

[TicklyT]

Just to throw a spanner in the works......

Most electronic 'transformers' used for ELV lighting are more akin to SMPSs, capable of delivering a stable output over a range of input voltages, so the simple model of a fixed resistance load goes out the window.

Bearing this in mind, the current drawn WILL increase as the input voltage decreases, the control mechanism adjusts it's swithcing times to compensate for the supply voltage reduction. That's something a 'proper' transformer with it's fixed primary : secondary ratio can't do.

The POWER becomes the constant, not the resistance - 1000 Watts worth of ELV lamps requires 4.167 Amps at 240 Volts

At 230 Volts, the electronic 'transformers' will draw 4.348 Amps, and still deliver 1000 Watts.

Where the fixed resistance model does work, such as conventional GLS lamps, or wire wound transformers rated at 1000 Watts at 240V, they would draw 3.993 Amps, only delivering 918.4 Watts at 230 Volts

 

[flameport]

Either way, the two main points are:

The 6A circuit is already loaded to the maximum

20 x 50w halogen lamps in a kitchen is a grossly inefficient use of electricity and the best option would be to remove them and fit some proper lighting instead.

 

[spark13]

the kitchen is on its own circuit and 19 lights on that circuit not 20 19x50 =950 w 950/230 just over 4 amps still good debate !!!!!!!!!!!

 

[bhm1712]

i meant the same wattage not current.

my mistake,

I = P/E



there fore, at 240 volts the circuit will have a slightly less overall current than if it were 230.

 

[Spark123]

But not if the load is resistive

 

[securespark]

Well, I think the circuit is grossly overloaded already.

Those lamps at 12V will be drawing in excess of 79A.

At that rate, you should have each fitting on its own 6A breaker.

To make switching a little easier, you could pair them up & fit a 10A breaker for each pair.

 

[Spark123]

 

[spark13]