Very Basic Help Required

[Goingupltd]

Hi guys,

I am interested in learning more about the theory of electricity, and have been looking online for info, but there is one thing that I just cannot get past:

If the voltage (240v) is used to push the current, and the current is amps, and the power is watts, how is the wattage regulated??

That is to say, everything in the home uses 240v, but they all require different power, 60W, or 500W etc, so how is the wattage going to them changed?? A fuse doesn't reduce the wattage right?

So, if something requires 300Watts, and it is getting that from a 240 supply, how come the same supply powers a 60 watt light bulb without blowing it?
Does this make sense because its confusing me.

Thank you for any help, really appreciated

 

[timo1]

The easiest way I can explain it without confusing myself...each circuit is regulated by a fuse for example a socket circuit at 30amps. each electrical item will only pull or use what it needs to operate through the socket (for example a kettle), and is limited to usually 13amps by the plug top. a lighting circuit is usually 6 amps but a lightbulb will only pull the energy it needs. the fuse in the fusebox will trip in the event of a fault - for example if a fan or motor was faulty and pulling too much current. The power is always available depending what you plug in, but a well designed system will mean that the fuse in the fuseboard will protect the cable and blow or trip - for example if you plugged a cooker into a lighting circuit - cooker needing 13amps for example, on a 6 amp circuit (lighting circuit) the fuse will give way therefore protecting the cable (Smaller amp circuits are wired in thinner cable than larger circuits)

 

[malcolmsanford]

Magic ................son

Not to go into in depth theory but basically your 240 volt, by the way is now 230volt, is resisted by a resistance, this resistance as an ohmeric value, Depending on your ohmeric value that is what determines your power or watts.

so if you have a 300ohm value you will have approx 176 watts of power, and 3000ohms will give you 1.76 watts of power

As a formula it would be E2/P to prove it so 230X230/176 = 300 ohm approx

 

[Silly Sausage]

and my attempt to explain...!


Lights, washing machines, TVs etc are commonly known as the 'Load'.
Every load has a resistance, R, measured in ohms.
Taking the voltage as fixed, a load draws a current, I =V/R Amps (from Ohm's Law V = I * R)
Power, P = V*I Watts
So Power is the amount of energy a load consumes (every second) due to its Resistance and the applied voltage.

Hope that helps you a bit!

 

[Goingupltd]

The easiest way I can explain it without confusing myself...each circuit is regulated by a fuse for example a socket circuit at 30amps. each electrical item will only pull or use what it needs to operate through the socket (for example a kettle), and is limited to usually 13amps by the plug top. a lighting circuit is usually 6 amps but a lightbulb will only pull the energy it needs. the fuse in the fusebox will trip in the event of a fault - for example if a fan or motor was faulty and pulling too much current. The power is always available depending what you plug in, but a well designed system will mean that the fuse in the fuseboard will protect the cable and blow or trip - for example if you plugged a cooker into a lighting circuit - cooker needing 13amps for example, on a 6 amp circuit (lighting circuit) the fuse will give way therefore protecting the cable (Smaller amp circuits are wired in thinner cable than larger circuits)

Thanks for replying so quickly.
So, do I have this right..... It is the appliance that actually takes the wattage required that it needs, it is not pushed to it. For example like sucking on a straw when you drink. I mean, the appliance actually only takes what it needs, and the fuse in the line or plug is just in case the appliance develops a fault and tries to take more than it should???

 

[TaffyDuck]

as timo says the best way to think about it is that an appliance will only allow the amount of power to flow through it that it needs. Power (Watts) = Volts x Amps. So a kettle rated at 3000 watts would work out like this 3000 = 240v x Amps. Therefore 3000/240 = 12.5 Amps. That is the maximum that the kettle can draw due to the resistance to the flow of electricity within the kettle ( known as resistance). As Volts = Amps x Resistance we can see that 240v = 12.5 x the resistance or put another way 240/12.5 = 19.2 ohms of resistance.

So as you can see the higher the resistance the less electricity can flow through the appliance, therefore the less power is consumed.

 

[Goingupltd]

and my attempt to explain...!


Lights, washing machines, TVs etc are commonly known as the 'Load'.
Every load has a resistance, R, measured in ohms.
Taking the voltage as fixed, a load draws a current, I =V/R Amps (from Ohm's Law V = I * R)
Power, P = V*I Watts
So Power is the amount of energy a load consumes (every second) due to its Resistance and the applied voltage.

Hope that helps you a bit!

Thanks Archy, see my reply to Timo....is that about right?

Malcolm - Your just trying to confuse me again!!!! Ha ha

 

[Harry Worth]

Simplifying here but the parameter that controls the watts is the resistance of the device. Volts pushes the current through the item and resistance opposes it.

There are two formula that explain what's happening - Ohms law which gives V = I x R and Power is V x I.

So in your example for an item rated at 60W. 60W = V x I therefore rearranging. I = 60W/230 = 0.26A. from Ohms law and rearranging the equation R = V/I = 230/0.26 = 884 Ohms. For your 500W example I = 500/230 = 2.17A and R = 230/2.17 = 106 Ohms. So really, the lower the resistance the more current is used and the higher the power of the device. This a simplification but it gives you an idea of what's going on. (before someone mentions impedance)

 

[malcolmsanford]

Lol I'm trying to confuse you....................my way you don't need to do 2 calculations ie trying to power/resistance ratio by finding the current.

Simple straight forward voltage squared/ reistance (ohms) to find power (watts)
Voltage squared/power to find ohm

Yes very complicated .........................but we won't go down the road of really these are all DC calculations, that will complicate things

 

[Goingupltd]

Thanks guys, you have all helped me a lot to understand it. I think my main problem with getting my head round it was thinking that the 240v supply was giving the power to the device, but it is the device taking the power from the supply and the device itself which has the resistance internally to regulate the wattage its using.

Thanks again, really appreciate it

 

[Silly Sausage]

my reply to Timo....is that about right?

Yes, the Wattage listed on an item tells you how much power it uses.

 

[TaffyDuck]

Lol I'm trying to confuse you....................my way you don't need to do 2 calculations ie trying to power/resistance ratio by finding the current.

Simple straight forward voltage squared/ reistance (ohms) to find power (watts)
Voltage squared/power to find ohm

Yes very complicated .........................but we won't go down the road of really these are all DC calculations, that will complicate things

Pleeeeeeeease don`t :smart:

 

[Napoleon]

Resistance is the element you're missing. Resistance to the flow of current.

You can regard every outlet (bulb, kettle, washing machine) as a load. Every load has a resistance. This resistance dictates the current flow & the power output of the load.
Everything we do concerns creating the situation where the given fixed voltage can safely allow sufficient current to flow for the given load to function.

But as you may have spotted there will be better explainations than you'll get here.
Have a read about it & come back with any further questions.

 

[D Skelton]

Thanks guys, you have all helped me a lot to understand it. I think my main problem with getting my head round it was thinking that the 240v supply was giving the power to the device, but it is the device taking the power from the supply and the device itself which has the resistance internally to regulate the wattage its using.

Thanks again, really appreciate it

Voltage doesn't push the current so to speak. It allows the current to flow.

Think of voltage as your arm and current as a ball. The higher you lift your arm, the more potential energy is stored within the ball. When dropped from a higher height, the ball will discharge more potential energy than if it was dropped lower down. ie, the ball will reach a higher speed and hit the ground harder.

The higher the voltage, the more potential for current to flow.

If you take this view of voltage, then it becomes easier to understand how appliances, and the resistance they apply to that flow of current, will draw only the current they need as opposed to having it pushed through them.

 

[telectrix]

and there was i, thinking for all these years that it was the voltage that pushed the electron fairies to work harder, and the resistance was the thickness of the mud they had to wade through