I don't Understand electricity ... ._.

[Evann]

So it's all about Volts and Ampere...

 

If you want to charge your notebook, you put your charging unit in the socket, and everything is fine. The Volts get transformed to like.. 20V (normal Notebook).

All fine with that.

 

Now at work i saw a fucking 120mm FAN beeing directly plugged into the socket, with around 230V. - That anyhow blew my knowledge of electricity a little..

 

How does that even work? Would't that thing just catch fire?

If it works, why don't we just charge our notebooks or whatever directly with 200+V (lol)

So.. apparently it works, but what are the pros and cons of using high, instead of low Voltage.

 

With my Highschool knowledge of Physics (already some years ago) i could only think of R(resistance) = V*I² - so the higher your Volts, the lower your Ampere, the lower your resistance...

 

 

Thx for answers, and sorry for my bad expression, english isn't my native language.

 

 

[Glenwing]

14 minutes ago, Evann said:

So it's all about Volts and Ampere...

 

If you want to charge your notebook, you put your charging unit in the socket, and everything is fine. The Volts get transformed to like.. 20V (normal Notebook).

All fine with that.

 

Now at work i saw a fucking 120mm FAN beeing directly plugged into the socket, with around 230V. - That anyhow blew my knowledge of electricity a little..

 

How does that even work? Would't that thing just catch fire?

If it works, why don't we just charge our notebooks or whatever directly with 200+V (lol)

So.. apparently it works, but what are the pros and cons of using high, instead of low Voltage.

 

With my Highschool knowledge of Physics (already some years ago) i could only think of R(resistance) = V*I² - so the higher your Volts, the lower your Ampere, the lower your resistance...

 

 

Thx for answers, and sorry for my bad expression, english isn't my native language.

 

 

Well first, computers need to be charged or powered with DC, so power from the wall (AC) will need to be converted either way, it doesn't matter what the voltage is.

 

I think you've got your formulas mixed up a little too

 

V = I * R. With a given resistance, higher voltage will be able to overcome the resistance more effectively, and so will produce higher current.

P = I * V. Power, in Watts, is current * voltage.

 

But since V = I * R, just replace V in the equation for power:

P = I * (I * R), or P = I²R

 

With P = I * V, if you double the voltage (and use a material with double the resistance so the current won't change), you double the total power being transferred. If instead the voltage is kept the same but the current is doubled (by using a material with half as much resistance) then the total power will also be doubled. If you do both (by simply doubling the voltage and not changing the resistance of the material, so the current will also double), the total power will be quadrupled.

[Evann]

7 minutes ago, Glenwing said:

Well first, computers need to be charged or powered with DC, so power from the wall (AC) will need to be converted either way, it doesn't matter what the voltage is.

 

I think you've got your formulas mixed up a little too

 

V = I * R. With a given resistance, higher voltage will be able to overcome the resistance more effectively, and so will produce higher current.

P = I * V. Power, in Watts, is current * voltage

 

But since V = I * R, just replace V in the equation for power:

P = I * (I * R), or P = I²R

I screwed up, now i remember.. ^^ - Thx a lot !

[Johannes_Lazor]

Depending on the fan it can work, Using a 12v DC fan it will die, thats for sure. However, if the fan is rated for AC and 230 volts it is just fine.
The primary problem with plugging you notebook directly into the socket is the AC, It burns through DC electronics like a hot knife through butter. Stepping down the voltage from 230 volts to 20 volts is not very efficient unless you use the AC with a transformer and convert it to DC( the powerbrick). You could just put a resistor with a cooler on it along with an powerful diod and capacitor to step down the voltage but that way all the 210volts which are excess would have to be converted into heat(That is the way mosfets work, but DC to DC)

[Hogger]

I find it's easier to learn hands on... Try jabbing a fork into a wall outlet, that'll give you a pretty good example of electricity ?

[annoyingmoments]

25 minutes ago, Glenwing said:

Well first, computers need to be charged or powered with DC, so power from the wall (AC) will need to be converted either way, it doesn't matter what the voltage is.

 

I think you've got your formulas mixed up a little too

 

V = I * R. With a given resistance, higher voltage will be able to overcome the resistance more effectively, and so will produce higher current.

P = I * V. Power, in Watts, is current * voltage.

 

But since V = I * R, just replace V in the equation for power:

P = I * (I * R), or P = I²R

 

With P = I * V, if you double the voltage (and use a material with double the resistance so the current won't change), you double the total power being transferred. If instead the voltage is kept the same but the current is doubled (by using a material with half as much resistance) then the total power will also be doubled. If you do both (by simply doubling the voltage and not changing the resistance of the material, so the current will also double), the total power will be quadrupled.

Ehm, is it not U [Voltage V] =  I [Current A] * R [Resistance R]?

Therefore the formula for electrical power would be

 

P=U * I

or P= I² * R

or P= U² / R 

 

Anyways, as Glenwig already mentioned you get 230 V aC in the European Electric Power grid form the AC plug in the wall, then theres usually a transformator which has coils in it, which due some other formuals I forgot, transform the 230 Volts for example into 12 V. It has something to do how many layers of copper wires are used.

 

The first coil would have 230 layers for 230 V so if the other coil has 10 "layers" your output is 23 V on the other side of the transformer. As it it still AC current you need a diode or another device called a rectifier to get an DC output for IT equipment or fans. And a rectifier to get 12 Volts DC.

 

Nevertheless there are AC motors which are also used in industrial fans, as they are plug and play and have a bigger electrical power (i.e for air ventilation in montage halls or something or to cool things like electric welding machines)

 

 

EDIT: A higher rated voltage will lead to a higher electrical power due to above formulas, 12 V motors are good for fans in low voltage machines, where the risk of an electric shock can be minimised.

 

There are three protection classes with different levels of protection.

 

1. Protection by protective conductor

2. Protection by reinforced insulation

3. Protection by low voltage (50V AC/ 120 V DC)

 

The third point is the safest, but with limited voltage devices can not output a higher power. Imagine a hybrid bus in mass transit with only 12 V, it is not possible, so we use 700V instead as this high voltage leads to a higher power.

 

 

Edited May 18, 2016 by annoyingmoments
Added some further explanation

[annoyingmoments]

11 minutes ago, Hogger said:

I find it's easier to learn hands on... Try jabbing a fork into a wall outlet, that'll give you a pretty good example of electricity ?

Well I would not suggest that, as you never know if there is a Residual Current Device that protects your power plug. Especially as I heard that in the USA you do not really need a training of 3.5 years to become an electrician.

 

NEVER PUT SOMETHING INTO WALL PLUGS

[Evann]

12 minutes ago, annoyingmoments said:

The third point is the safest, but with limited voltage devices can not output a higher power. Imagine a hybrid bus in mass transit with only 12 V, it is not possible, so we use 700V instead as this high voltage leads to a higher power.

 

Can't we just take some kind of magic material and force like 500A with 12V? Theoraticly that thing would melt.. but in theory there is no limit, is there?

What is the Limit of current you can fire on a 12V "string"?

[annoyingmoments]

12 minutes ago, Evann said:

Can't we just take some kind of magic material and force like 500A with 12V? Theoraticly that thing would melt.. but in theory there is no limit, is there?

What is the Limit of current you can fire on a 12V "string"?

Ehm now you got me

It depends on the specific conductive characteristic of the conductive material (copper, gold, tin) and the cross section of the conductor. There are specified industrial norms but atm I am to lazy to get the book out of my bag...

 

If the cross section of the conductor is big enough the only restriction on the maximum current is the resistance. Sure if you push 500 Ampere current on an LED with 20mA, then this thing will burn and sometimes you can even see a little "explosion" with sparks and smoke

 

U= R * I

12V = R * 500A

R = 0,024 Ohm

 

It is possible to use voltage of 12 V and a current of 500A. Every variable (U, R, I) is depending on the other two. If you had a resistacne of 0 Ohm or next to 0 Ohm (infinte small) you get a short circuit and you see sparks. Usually there should be a safety switch, circuit breaker or fuse or how you call them in English, to avoid damage on the conductors in your house or electrical circuit.

[Evann]

9 minutes ago, annoyingmoments said:

you get a short circuit and you see sparks. Usually there should be a safety switch, circuit breaker or fuse or how you call them in English.

isn't that exactly what happens when you turn on to many devices at once (let's say in an household)? The Resistance gets lower (why actually? o__O), due to that there is to much Ampere in the wire, then the fuse kicks out.

 

don't want to annoy you with to many dumb Questions ... Thank you the great answers. LTT still best Forum around ^^.

[annoyingmoments]

29 minutes ago, Evann said:

isn't that exactly what happens when you turn on to many devices at once (let's say in an household)? The Resistance gets lower (why actually? o__O), due to that there is to much Ampere in the wire, then the fuse kicks out.

 

don't want to annoy you with to many dumb Questions ... Thank you the great answers. LTT still best Forum around ^^.

There are no dumb questions, well at least not really. It is a good repetition for me either.

 

If the fuse kicks out, lets say if you turn on the light and at the same time you start your vacuum cleaner, then the fuse got the "signal" to shut down the power because it might took to much current (in the EU mostly max. 16A for single a single phase conductor), if it is more than 16A the fuse kicks in to prevent damage on the conductor.

 

The resistance gets either lower or higher depending on the conductors specification. For example Wolfram wires in a light bulb are PTC-Thermistors (Positive Temperature Coefficient Thermistor), therefore they take more power in the moment of turning them on, because PTC means that the material is a better conductor if its cold. On the other site you have NTC (Negative) which are better conductors if they are warm. Now as a normal user you never know which conductors are used.

 

If you now turn on the light bulb, the resistance is still low, so the current has no resistance in form of atoms and it just "shoots" through the pipe (your conducting wire).

Remember U = R * I ? So the resistance is low but the voltage is the same, always around 230 Volts, the only variable that can be changed is the current (I). Especially motors like in vacuum cleaners do need a high starting current to get into movement, therefore the fuse securing your wall plug is kicking out.

 

Then again due to the restriction on at least in Germany maximumum voltages of 230V and 16 Ampere per wall plug, you have P=U*I -> P=230V*16A=3680 Watts of maximum power per wall plug are allowed. Now you never know if the wires are somewhere connected to each other in your house so one fuse might be securing for some reason 10 wall power plugs and if you have a TV there (200W), two PCs there (lets say 2*500W), and a 2000W vacuum cleaner in another room and a refigerator with 200 W in the kitchen and a 2000W washing machine in the basement and for some reason all are secured on the same fuse, you try to "extract"  5400W in total which is too much.

 

This means according to  (P=U*I) 5400W=230V*I -> I = 23.5 A are needed to power all the things. The fuse kicks out. To avoid such mess it is better to secure every room and its  power plugs on their own and since 2006 even with a necessary Residual Current Device, but this is another topic on how to secure power plugs.. Before I forget: sometimes you see a switch for the light and under it in the wall a power plug, so they often are connected to the same phase conductor which leads easily to kick the fuse out if the light is on and you take too much current at once.

[xentropa]

2 hours ago, Evann said:

So.. apparently it works, but what are the pros and cons of using high, instead of low Voltage.

 

With my Highschool knowledge of Physics (already some years ago) i could only think of R(resistance) = V*I² - so the higher your Volts, the lower your Ampere, the lower your resistance...

 

 

Thx for answers, and sorry for my bad expression, english isn't my native language.

 

 

I'll answer this part,

 

Consider the following example

 

Power = Volts (V) times current (I).

 

There is a motor that 

 

a) uses 240 volts and 1 amp

b) uses 12 volts and 20 amps

 

They are both USING 240 watts but here are some differences.

 

Heating loss is = I^2R.  For motor b, energy is lost to heat and is less efficient since current (I) is 20 times larger.

 

The high voltage motor is more efficient but more dangerous.  High voltage means more likelihood to overcome resistance and if mishandled, 240 volts can kill people.  I am sure you can kill yourself with 12V though that would take some serious effort.  I have never heard of anyone dying to 12V electrocution.

 

Generally power lines are high voltage (up to 700,000 V) in the USA, but they are held on high pylons and kept far away from people to prevent death.  These power lines can send electricity long distances without losing heat in the wires.  To distribute this 700,000V to people's homes, there is a machine called a transformer.  A transformer changes voltage and amps but power remains the same.  So the 700,000V on the power lines is converted to 120 or 240 in your house.  If your house sockets ran 700,000 volts, it would kill anyone that came within 1 meter of it.

[annoyingmoments]

43 minutes ago, xentropa said:

The high voltage motor is more efficient but more dangerous.  High voltage means more likelihood to overcome resistance and if mishandled, 240 volts can kill people.  I am sure you can kill yourself with 12V though that would take some serious effort.  I have never heard of anyone dying to 12V electrocution.

As you seem to be from the US of A, do you have the same 3 protection classes with 1. protective conductor, 2. reinforced insulation and 3.protective low voltage (50 VAC / 120 VDC for humans and 25 VAC / 60 VDC for animals?). As long as you do not have to wear a cardiac pacemaker, 12 V are completly safe. Of course only if the transformer is galvanic insulated, so the high voltage is strictly seperated from the safety low voltage circuit.

 

I completly forgot about the efficency thing tbh, plus English is not my native language, so it was kind of hard to even think about it.

[Evann]

1 hour ago, xentropa said:

a) uses 240 volts and 1 amp

b) uses 12 volts and 20 amps

 

They are both USING 240 watts but here are some differences.

 

Heating loss is = I^2R.  For motor b, energy is lost to heat and is less efficient since current (I) is 20 times larger.

i'm dumb i know, but i still dont really get it.

 

earlier we said U = R*I . Therefore we can say R = U/I.

 

let's say motor:

 

a) 240volts @ 2 amps --> R = 240/2 --> R= 120 Ohm

 

then u said I^2R - 2A^240Ohm = lot of heating loss.

 

 

b) 12volts @ 40 amps --> R = 12/40 --> R= 0.3 Ohm

 

I^2R - 40A^0.6Ohm = way less heat loss.

 

[Ivo]

9 minutes ago, Evann said:

i'm dumb i know, but i still dont really get it.

 

earlier we said U = R*I . Therefore we can say R = U/I.

 

let's say motor:

 

a) 240volts @ 2 amps --> R = 240/2 --> R= 120 Ohm

 

then u said I^2R - 2A^240Ohm = lot of heating loss.

 

 

b) 12volts @ 40 amps --> R = 12/40 --> R= 0.3 Ohm

 

I^2R - 40A^0.6Ohm = way less heat loss.

 

Your reasoning is good, less resistance = less heat, you misunderstood the math a little, its I (squared [I^2]) times resistance (R), not I times 2xR

[Glenwing]

On 5/18/2016 at 5:14 AM, Evann said:

Can't we just take some kind of magic material and force like 500A with 12V? Theoraticly that thing would melt.. but in theory there is no limit, is there?

What is the Limit of current you can fire on a 12V "string"?

Yes, you could, and some systems are designed like this. Car batteries for example operate at 12 V, but deliver several hundred or even 1000+ amps very briefly to crank the engine. Since they only operate at 12 V DC though, you are completely safe from electrocution if you were to touch the terminals of the battery with your hands. Through the low resistance of the car's electrical system, the battery might be able to generate huge amounts of current, but such a low voltage won't send more than a few milliamps through something with high resistance to DC like your body, so touching the terminals of a car battery is totally safe (although there are other dangers besides electrocution associated with something that can deliver that much current, like if there is a direct short with something metal like a tool).

 

But resistance is higher over a longer wire distance as well as through thinner wire, which is why jump-start cables for your car should not be any longer than necessary, and cheaper thin cables often won't work, because the resistance of long wires or thin wires is higher, and at 12 V they may not allow enough current to jump start cars, especially larger ones like trucks. So, if you wanted to design something to carry power over a much longer distance than the internal systems of a car, for example power lines, and you wanted them to operate at 12 V so they would be completely safe, you would need either impossibly thick wires, or you need to find a material that is basically a room-temperature superconductor (ultra-low resistance), which if you can find a material like that, there is a Nobel prize waiting for you. This is why power lines operate at tens or hundreds of thousands volts, even though this poses significant danger of electrocution to people (among other reasons, such as efficiency/losses at low voltages).

On 5/18/2016 at 5:37 AM, Evann said:

isn't that exactly what happens when you turn on to many devices at once (let's say in an household)? The Resistance gets lower (why actually? o__O), due to that there is to much Ampere in the wire, then the fuse kicks out.

 

don't want to annoy you with to many dumb Questions ... Thank you the great answers. LTT still best Forum around ^^.

If you plug in a device to an outlet, you are creating a connection between the positive and negative terminals of the outlet, so current can return to ground (which it will do since ground is at a lower voltage than the power line). But in doing so, the electricity must flow through the device in order to get from the positive terminal of the outlet to the ground terminal. The device will have some components inside with some certain resistance, electricity passing through the resistance will dissipate power (in Watts) and that is utilized by the device for operation.

 

The rate at which electricity returns to ground (the current) depends on the resistance of the device, through the formula V = I * R. Voltage is held constant at 120 V (or 230 V in Europe), so if resistance (R) of the device is lower, the current (I) generated will be higher, because the two numbers multiplied together still need to be equal to 120 or 230. So, a device provides a path to ground, a certain amount of electricity will flow through that path depending on the resistance of the device.

 

If you attach another device to another outlet, you are providing a second path for electricity to return to ground. Electricity will also flow through that path, and power that device, in addition to flowing through the other path. Again, voltage is still held constant on the power line at 120 V, so some certain current will flow through the second device to ground, depending on the resistance of the device.

 

So, the total effect is that more current is flowing. Even though you have more devices, so more total resistance being connected, the results depend on how you connect them. If you connect multiple resistors in a row, the resistance stacks up and the total current will be less. But if each resistor provides a separate path to ground, each path can carry an additional amount of current without affecting the current flowing through the other resistors. The more you connect, the more total current will flow.

 

In a physics class, this would be studied as "connecting resistors in parallel". The formula for the "effective" resistance of multiple resistors in parallel (like if you just looked at the total current going into the house and came up with one big "resistance" figure for the entire house) is

 

R_effective = 1 / (1/R₁ + 1/R₂ + 1/R₃ + ...)

 

And indeed, if you do a little algebra you can prove that the total "effective" resistance of multiple resistors in parallel will always be lower than any individual resistor in the circuit, so with more devices connected, the resistance of "the house" will be lower and more current will flow through the house. Which makes sense; with more resistors creating more paths, more total current will be flowing than there would be if that one resistor was the only path to ground.

 

On 5/18/2016 at 8:41 AM, Evann said:

i'm dumb i know, but i still dont really get it.

 

earlier we said U = R*I . Therefore we can say R = U/I.

 

let's say motor:

 

a) 240volts @ 2 amps --> R = 240/2 --> R= 120 Ohm

 

then u said I^2R - 2A^240Ohm = lot of heating loss.

 

 

b) 12volts @ 40 amps --> R = 12/40 --> R= 0.3 Ohm

 

I^2R - 40A^0.6Ohm = way less heat loss.

 

Heat is a form of power, so that can be expressed in Watts, and also can be determined from the power equation, P = I * V.

 

Since V = I * R, you can use (I * R) instead of V in the power equation:

P = I * V is equivalent to:

P = I * (I * R), or

P = I * I * R, or

P = I² * R

 

Which is not the same as P = I^2R

 

With P = I² * R:

2A² * 120 Ω = 4 * 120 = 480 W

 

40A² * 0.3 Ω = 1600 * 0.3 = 480 W

 

So, everything checks out

 

This confusion, by the way, is why everyone here really should take advantage of the superscript/subscript formatting buttons built into the forum rather than the up-arrow (^) symbol:

 

[Evann]

46 minutes ago, Glenwing said:

So, everything checks out

Wow... thanks so much for all the effort. 

[ThomasD]

10 hours ago, Evann said:

...

Now at work i saw a fucking 120mm FAN beeing directly plugged into the socket, with around 230V. - That anyhow blew my knowledge of electricity a little..

...

120 mm case fans do not have a connector that is suitable plugging into any wall socket anywhere in the world.  So that was not an ordinary case fan.  I suspect that it had a small switch mode power supply as part of the attached plug to convert the wall AC into a usable DC voltage.

 

https://en.wikipedia.org/wiki/Switched-mode_power_supply

[Johannes_Lazor]

18 hours ago, annoyingmoments said:

Well I would not suggest that, as you never know if there is a Residual Current Device that protects your power plug. Especially as I heard that in the USA you do not really need a training of 3.5 years to become an electrician.

 

NEVER PUT SOMETHING INTO WALL PLUGS

When i was 7 i took two wires and put them on my tounge, I thought it would tickle since i already did it with 9 volt batteries.. I had to go to speech therapy later :P, But look at me now! Now i am an Electrician x D

[You_are_a_cunt]

you spelled electrocity wrong

[annoyingmoments]

4 hours ago, Johannes_Lazor said:

When i was 7 i took two wires and put them on my tounge, I thought it would tickle since i already did it with 9 volt batteries.. I had to go to speech therapy later :P, But look at me now! Now i am an Electrician x D

Maye the "spirit" of electricity came into to you, when all of this happened

 

 

Lucky, that things went quite okay, I guess?

[Johannes_Lazor]

17 minutes ago, annoyingmoments said:

Maye the "spirit" of electricity came into to you, when all of this happened

 

 

Lucky, that things went quite okay, I guess?

Yup, Everything went just fine, The best way to learn is to fail as i have shown time and time again 

[annoyingmoments]

37 minutes ago, Johannes_Lazor said:

Yup, Everything went just fine, The best way to learn is to fail as i have shown time and time again 

May I ask you something?

 

Your signature says that you need to study, therefore attend uni to become an Electrician?

 

So you are then allowed to wire houses and stuff? Or more like planning electrical systems as an engineer?

[Johannes_Lazor]

31 minutes ago, annoyingmoments said:

May I ask you something?

 

Your signature says that you need to study, therefore attend uni to become an Electrician?

 

So you are then allowed to wire houses and stuff? Or more like planning electrical systems as an engineer?

Im on an practical education, Half of all days which i study are on real jobs, I have stacked up about 800 hours of work during the 3 years i have studied. I am allowed to wire houses and such, But a full-paid electrician has to give the go-ahed to power everything up. The people i work with trust me enough so they just say "Sure, power it up" at this point. Most of what i do is wiring stuff, but i also do some planning and such. The boss at the place i "work" says im better than some of the guys who have been working for him 1-3 years

[annoyingmoments]

2 minutes ago, Johannes_Lazor said:

Im on an practical education, Half of all days which i study are on real jobs, I have stacked up about 800 hours of work during the 3 years i have studied. I am allowed to wire houses and such, But a full-paid electrician has to give the go-ahed to power everything up. The people i work with trust me enough so they just say "Sure, power it up" at this point. Most of what i do is wiring stuff, but i also do some planning and such. The boss at the place i "work" says im better than some of the guys who have been working for him 1-3 years

Okay, thanks!

I thought it is more like the German "Ausbildung" where you have a contract with a company, which pays you in order to make a professional out of you and where you have to attend a school which is teaching you the theory.

 

Alright then, I guess I am done on this thread.