Why has DIYNOT got a electrics forum?

[Igorian]

this is one of the reasons i dont even venture to electrics, i went there with a question a long time back and got the responce the original poster is talking of "what the hell are you touching it for,leave it alone,Your stupid, pay me all your money attitude". i agree electric can kill and if you drink enough paint that will also kill you and if you fall down a hole or off a roof that might kill you. You could even get run over at the builders merchants, so theres plenty of ways of dying (wether you knew the time place and whatever lol).should this thread still be in general chat?when does the thread get moved to electrics?

It's general electrics, so belongs in both.

 

[empip]

Guess who 'wired' the Aardman Animations warehouse

.. Blame the dog.
pro or diy ?

 

[oilman]

Actually, on the secondary, the current is quite low, so it hurts, but you generally live (and hopefully don't do it again )

It isn't if you want the same power out of it. W=EI, so if you half the volts you need to double the current.

But you haven't halved the volts, you've induced (correct usage ) a voltage many times that of the primary, and so current will be less (cos u can't get more power out than you put in). It's the primary that has high current, but at low voltage (12). The primary also has a low resistance, in the region of 1-2 ohms. The secondary uses thousands of turns of very thin wire resulting in a high resistance (thousands of ohms).

Sorry, I've confused things here. I did not realise you were talking about car electrics, I was thinking of isolating transformers used on construction sites.

Softus, I still maintain it's not current but power that does the damage. The burning is caused by heating and heat is power. Where people try to isolate volts or amps as the culprit there is a lack of understanding that it is the product of the two (integrated over time) that does the damage.

(Time for a water analogy)

water at 1000psi is not a problem if it's contained, nor is very high flow rates (like the Amazon) but where the 1000psi powers flow down say a 25mm pipe you can use it for quarrying rock.

 

[Big_Spark]

My, I have missed a lot of goings on here. I have 3 points:

Sorry to throw a spanner in the works so late in the game, but voltage is not a hazard in itself, nor is current. Many of us have had a belt from a car ignition system. Give or take 45,000 volts, which will give rise to quite a few amps. The killer is power or more specifically Wh, since this is the energy. Alright, you might be able to stop a heart, or muck-up it's function with a very small amount of energy, but then cell destruction can be achieved with 10mW.

As for Bright-spark's authoritarian idea of stopping people doing diy electrics, who the hell does he think he is? IF YOU WANT TO STOP PEOPLE BEING KILLED, FIRST STOP GEORGE BUSH DOING ANYTHING AS DEATH SEEMS TO BE HIS TRADE, AND SECOND LOOK AT ROAD DEATHS. AM I GETTING THROUGH? Just don't tell ME I can't do my own wiring. I am confident from what you have written here I know more than you.

115V will not give rise to twice the current in a circuit that 230V will. It's just that you need twice the current to achieve the same power output.

Total ballony...every single part of it...it shows that you understand VERY little about electricity. Power is simply the measurement of energy used as Joules (Energy) per second. 1 Joule per second = 1 Watt (P = j/t). However the same can be said for current which is coulombs (Charge) per second. 1 coulomb per second = 1 ampere (I = Q/t)

Now in metallic conductors, the positive flow of charge is fixed, it is the negative charge which moves. This is because electrons have a negative charge, and an electric charge is the product of the flow of electrons from point A to point B. Since a coulomb is approximately equal to 6.24×10E18 elementary charges, one ampere is equivalent to 6.24×10E18 elementary charges, such as electrons, moving through a surface in one second. However a more accurate quantity for the ampere can be defined as exactly 6.241 509 629 152 65×10E18 elementary charges per second.

Now with regards your comments more specifically, Current flowing through the body is more important than voltage when it comes to the actual hazard to human health. The amount of current depends on the voltage, skin resistance and the current capacity of the voltage source..in the home this will be the circuit your attached to...Power is a constant regardless of voltage, so your assertion regarding power would mean that even 1V would be dangerous as it would have the same power...do you see the flaw in your comment...although I appreciate why you may think along those lines.

Oilman, you THINK you know, and that is what makes people like you potentially dangerous, however as I have not seen any of your handywork I would not comment on whether your competent..technical knowledge is not a measure of competence.....
Perhaps you might like to read my reply to your question instead of jumping in and posting before reading my reply.

 

[pickles]

What the f$%K u all going on about in here. This is supposed to be general chat, not degree level electricity with added abuse go and have a lie down for gods sake

What kind of degree did you take pickles, if you think that i=V/R is so difficult?

A law degree

 

[Softus]

Softus, I still maintain it's not current but power that does the damage. The burning is caused by heating and heat is power. Where people try to isolate volts or amps as the culprit there is a lack of understanding that it is the product of the two (integrated over time) that does the damage.

I think this might be one of those where we just agree to disagree, but here's my take on it, in case we can converge opinions.

Burning caused by heat - I agree. Heat is power - don't agree, but I see where you're coming from. In rudimentary physics terms, heat is simply energy, whereas power is a measurement of work done, or energy given out per unit of time.

So, we could measure the power being applied to a human body resulting from contact with electricity, and this could usefully indicate the heat energy transferred, but the medical understanding, as described to me, is that the current is the important attribute because it alone causes the tissues to heat up.

Intuitively this is right to me, and I can give you an example - not proof, just an example.

For the sake of argument, let's say that 1.2 Amps, at 240 volts, when sustained for 36 seconds, is enough to cause fatal injuries.

The same amount of energy would be transferred by 0.012 Amps, at 2.4 Volts, over 360,000 seconds. So it should follow that the injuries would be same if I connected myself up to a torch battery (or similar) for just over 4 days (100 hours). But I'm as sure as I can be (without trying it) that I wouldn't be killed by the torch battery.

Does this make sense? Have I got my sums right?

water at 1000psi is not a problem if it's contained, nor is very high flow rates (like the Amazon) but where the 1000psi powers flow down say a 25mm pipe you can use it for quarrying rock.

Hmm. You're right, but I can't quite mould this inside my head so that it appears as an analogy. But I'll try again tomorrow.

 

[pickles]

it's old wimin arguing is what it is

...which, presumably, is why you've joined in.

Correct

 

[oilman]

...Power is a constant regardless of voltage, .....

The word ballony comes to mind..........or is this just another of your unintended/unexplained collections of words.

 

[Igorian]

My, I have missed a lot of goings on here. I have 3 points:

Sorry to throw a spanner in the works so late in the game, but voltage is not a hazard in itself, nor is current. Many of us have had a belt from a car ignition system. Give or take 45,000 volts, which will give rise to quite a few amps. The killer is power or more specifically Wh, since this is the energy. Alright, you might be able to stop a heart, or muck-up it's function with a very small amount of energy, but then cell destruction can be achieved with 10mW.

Actually, you were talking about car electrics, which is a step-up transformer as opposed to what you weren't talking about, which is a step-down transformer

The power thingy is a little misleading, cos as you already mentioned, to generate power, you need a voltage and current. However, power is just a derived figure, and a better formula to look at, which kind of backs up the Softus theory, is P=I^2R. You can clearly see that for a given resistance, as the current increases, so does the power. So you are both correct, from different points of view.

Power is also not a constant, regardless of voltage and can be derived as P = V^2/R. Dunno where you guys get all this stuff from

 

[oilman]

Softus, I see the point you are making. I need to be more careful/pedantic in my use of words. However this confusion does indicate that the body can survive electrical input provided the heat can be moved away fast enough, so it would be possible to have direct personal central heating.

 

[Big_Spark]

Oilman, if you think Power is not constant, then simply consider you PC power supply..

It is rated at say 300W for argument sake...but that 300W is the same at 230V and at the combined total of all the voltages that it produces to run your machine...

Example:

+12V = 14A = 168W
-12V = 2A = 24W
+5V = 10A = 50W
-5V = 2A = 10W
+3V = 15A = 45W
-3V = 1A = 3W

Total = 300W maximum power across the voltages..but at 230V it is still 300W but only 1.3A

If you doubt this, then I suggest you look it up.

 

[oilman]

Actually, you were talking about car electrics, which is a step-up transformer as opposed to what you weren't talking about, which is a step-down transformer

Oh, it's been a long day, can't be bothered now, time for bed. Goodnight.

 

[oilman]

Oilman, if you think Power is not constant, then simply consider you PC power supply..

.

Thank goodness I use a Mac.

 

[Softus]

What the f$%K u all going on about in here. This is supposed to be general chat, not degree level electricity with added abuse go and have a lie down for gods sake

What kind of degree did you take pickles, if you think that i=V/R is so difficult?

A law degree

I certainly have great respect for that achievement, but are you serious when you say that I=V/R is too technical?

In case the answer is yes, the favourite analogy is a hosepipe....

The pressure of water at one end of the pipe is analogous to the potential difference, measured in Volts.
The resistance of the hosepipe to water that is otherwise willing to flow inside it, is analogous to, well, er, resistance (measured in Ohms).
The flow of water along the hosepipe, when you open the tap, is analogous to current, measured in Amps.

So, if you have a long hosepipe, and a short one, and the two are identical bore and constriction, it follows that the resistance of the longer one is greater, and the effect on the flow is to reduce it.

This is basically it - the flow is determine by the pressure and the resistance. In a simple electrical conductor (e.g. a wire), the flow of current (Amps) is determined by the 'pressure' (potential difference, in Volts) between one end of the conductor and the other, and the electrical resistance of the wire.

Thanks to various scientists over the decades, we have a means of calculating the current, without measuring it, if we know the Volts and the Ohms for a given conductor.

I (current) = V (Volts) divided by R (resistance)

Lo and behold, I=V/R.

BTW, I is used for current because C got reserved for Coulombs, which is a measurement of charge (related to current, but I'm heading off track).

If you were winding us up, then you probably regard my explanation as patronising, in which case please accept my apologies - I'm just trying to help.

 

[Igorian]

Oilman, if you think Power is not constant, then simply consider you PC power supply..

It is rated at say 300W for argument sake...but that 300W is the same at 230V and at the combined total of all the voltages that it produces to run your machine...

Example:

+12V = 14A = 168W
-12V = 2A = 24W
+5V = 10A = 50W
-5V = 2A = 10W
+3V = 15A = 45W
-3V = 1A = 3W

Total = 300W maximum power across the voltages..but at 230V it is still 300W but only 1.3A

If you doubt this, then I suggest you look it up.

I edited my previous post because this example makes no sense. You are talking of the maximum power that can be achieved from the PSU and not the actual power, which would require knowledge of the load. Switched mode PSUs use current limiters to protect them. Ever seen one where the limiter fails?