How many milliamps in 1 amp?

joshm_2

Zahc wrote:

Geez, I thought I was a geek; I'm saving this thread to show the beloved to prove that I'm only a pretend geek!!
Very informative though.

P= VR, everyone knows that. V=IR, so........

Oh never mind:rotfl:

Zahc

P=I^2 R for what it's worth...

moonrakerz

Fifer wrote:

U is archaic.

Archaic - that's the word I was looking for !

GabbaGabbaHey

moonrakerz wrote:

To be really pedantic, although the domestic mains voltage in the UK is referred to as 230 VAC, it is, in fact, and has been for many, many years 240 VAC. Most of Europe uses 230, because previously they used 115. The EU in its infinite wisdom decided that everyone should use the same voltage, and that would be 230. For the UK to change its supply to 230 would have cost billions, so the change was accomplished by changing the tolerances. So even though the voltage was actually still 240 you could call it 230 - aren't these politicians wonderful !!

My understanding is that this was done to harmonise with those parts of Europe which use 220V. By calling it 230V +/-10%, both 220V and 240V supplies are within tolerence.

There are very few devices which are that voltage sensitive. Anything which needs to use the mains supply as a reference (e.g., record decks) tends to use the frequency, which is pretty much guaranteed to be 50Hz over a 24 hour (I think) period.

steady__eddie

"which is pretty much guaranteed to be 50Hz over a 24 hour (I think) period."

50 cycles over a 24 hour period works out at just over 2 cycles an hour.
That's just over a tandem in my books.

Need_More_Money_2

moonrakerz wrote:

The SI symbol (the universally accepted symbol) for voltage is V; U is VERY, VERY rarely used, this post was the first time I've seen it mentioned in about 40 years ! A more commonly used, albeit still rarely, alternative is E. A known voltage is always referred to as V: eg 240V NOT 240U.

Likewise the SI symbol for current is A, although I is sometimes used as an alternative in a general sense as you have used it above, ie: as an indeterminate quantity. A current of 6 amps is always referred to as 6A, NOT 6I.

I think there is some confusion between SI units and symbols used in equations

The SI unit is the Volt and the standard abreviation is V. In equations it is usual to use V to indicate voltage. Sometimes E is used (Electromotive Force). I've never seen U used.
However, although the SI unit for current is the Ampere and this is abreviated as A, in equations it is usual to indicate current as I. Hence

Power = VI

(In answer to the OP - milli always means a thousandth)

bingo_bango

OMG :eek:

Is TV that bad tonight then?????

I thought I was bad sitting reading through the raw data files on a fried HDD.

DrBenway

Toxteth_OGrady wrote:

How many millipedes in a centipede?

:rotfl:

:cool:

TOG

[MYRIAPODOLOGY LESSON]

For what it is worth no centipede, ([LATIN LESSON]Centum meaning hundred, ped meaning foot[/LATIN LESSON]) ever has one hundred legs or feet:shocked: . They always come with an odd number of pairs of legs or feet. So you can have 98 or 102 but not 100.

[/MYRIAPODOLOGY LESSON]

bearing

Did you know that Kirchoff's Voltage Law states that the sum of the voltage drops around any closed loop in a network must equal zero. And that his Current Law states that at every node, the sum of all currents entering a node must equal zero.

Obviously this has no bearing on the original question, just thought I'd enter the Geekhood.

stevemcol

Just to out geek the geeks, power isn't strictly volts x amps.
It's volts x amps x power factor.

Power factor is the cosine of the phase difference between the voltage and current waveforms.

fairenoughclough

For those of you interested in Kirchoff, from Wikipedia.




Gustav Robert Kirchhoff (March 12, 1824 – October 17, 1887), a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects. He coined the term "black body" radiation in 1862, and two sets of independent concepts in both circuit theory and thermal emission are named "Kirchhoff's laws" after him.
Gustav Kirchhoff was born in Königsberg, East Prussia (now Kaliningrad, Russia), the son of Friedrich Kirchhoff, a lawyer, and Johanna Henriette Wittke. He graduated from the Albertus University of Königsberg (now Kaliningrad) in 1847 and married Clara Richelot, the daughter of his mathematics professor Friedrich Richelot. In the same year, they moved to Berlin, where he stayed until he received a professorship at Breslau (now Wroclaw).
Kirchhoff formulated his circuit laws, which are now ubiquitous in electrical engineering, in 1845, while still a student. He proposed his law of thermal radiation in 1859, and gave a proof in 1861. At Breslau, he collaborated in spectroscopic work with Robert Bunsen, he was a co-discoverer of caesium and rubidium in 1861 while studying the chemical composition of the Sun via its spectral signature.
In 1862 he was awarded the Rumford Medal for his researches on the fixed lines of the solar spectrum, and on the inversion of the bright lines in the spectra of artificial light.
He contributed greatly to the field of spectroscopy by formalizing three laws that describe the spectral composition of light emitted by incandescent objects, building substantially on the discoveries of David Alter and Anders Jonas Angstrom (see also: spectrum analysis)
Kirchhoff's Three Laws of Spectroscopy:

1. A hot solid object produces light with a continuous spectrum.
2. A hot tenuous gas produces light with spectral lines at discrete wavelengths (i.e. specific colors) which depend on the energy levels of the atoms in the gas. (See also: emission spectrum)
3. A hot solid object surrounded by a cool tenuous gas (i.e. cooler than the hot object) produces light with an almost continuous spectrum which has gaps at discrete wavelengths depending on the energy levels of the atoms in the gas. (See also: absorption spectrum)

The existence of these discrete lines was later explained by the Bohr model, which helped lead to the development of quantum mechanics.


And I'm pretty sure that in an ac circuit Power Factor has an effect.

Any queries to stevemcol.


Explanation

Instantaneous and average power calculated from AC voltage and current with a unity power factor ([FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=0, cos[FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=1)



Instantaneous and average power calculated from AC voltage and current with a zero power factor ([FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=90, cos[FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=0)



Instantaneous and average power calculated from AC voltage and current with a lagging power factor ([FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=45, cos[FONT=lucida console,andale mono,gulim,batang,simsun,simhei]φ[/FONT]=0.71)


In a purely resistive AC circuit, voltage and current waveforms are in step, changing polarity at the same instant in each cycle. Where reactive loads are present, such as with capacitors or inductors, energy storage in the loads result in a time difference between the current and voltage waveforms. Since this stored energy returns to the source and is not available to do work at the load, a circuit with a low power factor will have higher currents to transfer a given quantity of power than a circuit with a high power factor.
In phase - this is analogous to two athletes running around a race track at the same speed and direction, side by side. They pass a point on the track together (simultaneously). Out of phase - this is analogous to two athletes running around a race track at the same speed and direction but starting at different positions on the track. They pass a point at different instants in time. But the time difference (phase difference) between them is a constant - same for every pass since they are at the same speed and in the same direction. If they were at different speeds, this would be analogous to two waves of different frequencies. Then, the phase (angle) difference measurement would be meaningless and void.
Real power is the capacity of the circuit for performing work in a particular time. Due to reactive elements of the load, the apparent power, which is the product of the voltage and current in the circuit, will be equal to or greater than the real power. The reactive power is a measure of the stored energy that is reflected to the source during each alternating current cycle.
AC power flow has the three components: real power (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in reactive volt-amperes (VAr).
The power factor can be expressed as:
. In the case of a perfectly sinusoidal waveform, P, Q and S can be expressed as vectors that form a vector triangle such that:

If φ is the phase angle between the current and voltage, then the power factor is equal to , and:
By definition, the power factor is a dimensionless number between 0 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle.
The power factor is determined by the type of loads connected to the power system. These can be

• Resistive
• Inductive
• Capacitive

If a purely resistive load is connected to a power supply, current and voltage will change polarity in phase, the power factor will be unity (1), and the electrical energy flows in a single direction across the network in each cycle. Inductive loads such as transformers and motors (any type of wound coil) generate reactive power with current waveform lagging the voltage. Capacitive loads such as capacitor banks or buried cable generate reactive power with current phase leading the voltage. Both types of loads will absorb energy during part of the AC cycle, only to send this energy back to the source during the rest of the cycle.
For example, to get 1 kW of real power if the power factor is unity, 1 kVA of apparent power needs to be transferred (1 kW ÷ 1 = 1 kVA). At low values of power factor, more apparent power needs to be transferred to get the same real power. To get 1 kW of real power at 0.2 power factor 5 kVA of apparent power needs to be transferred (1 kW ÷ 0.2 = 5 kVA).
It is often possible to adjust the power factor of a system to very near unity. This practice is known as power factor correction and is achieved by switching in or out banks of inductors or capacitors. For example the inductive effect of motor loads may be offset by locally connected capacitors.
Energy losses in transmission lines increase with increasing current. Where a load has a power factor lower than 1, more current is required to deliver the same amount of useful energy. Power companies therefore require that customers, especially those with large loads, maintain the power factors of their respective loads within specified limits or be subject to additional charges. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.

URL="http://en.wikipedia.org/w/index.php?title=Power_factor&action=edit&section=2"][U][COLOR=#0000ff]edit[/COLOR][/U][/URL Non-sinusoidal components

In circuits having only sinusoidal currents and voltages, the power factor effect arises only from the difference in phase between the current and voltage. This is narrowly known as "displacement power factor". The concept can be generalized to a total, distortion, or true power factor where the apparent power includes all harmonic components. This is of importance in practical power systems which contain non-linear loads such as rectifiers, some forms of electric lighting, electric arc furnaces, welding equipment, switched-mode power supplies and other devices.
A particularly important example is the millions of personal computers that typically incorporate switched-mode power supplies (SMPS) with rated output power ranging from 150W to 500W. Historically, these very low cost power supplies incorporated a simple full wave rectifier that conducted only when the mains instantaneous voltage exceeded the voltage on the input capacitors. This leads to very high ratios of peak to average input current, which also lead to a low distortion power factor and potentially serious phase and neutral loading concerns.
Regulatory agencies such as the EC have set harmonic limits as a method of improving power factor. Declining component cost has hastened acceptance and implementation of two different methods. Normally, this is done by either adding a series inductor (so-called passive PFC) or the addition of a boost converter that forces a sinusoidal input (so-called active PFC). For example, SMPS with passive PFC can achieve power factor of about 0.7...0.75, SMPS with active PFC -- up to 0.99, while SMPS without any power factor correction has power factor of about 0.55...0.65 only.
To comply with current EU standard EN61000-3-2 all switched-mode power supplies with output power more than 75W must include at least passive PFC.
A typical multimeter will give incorrect results when attempting to measure the AC current drawn by a non-sinusoidal load and then calculate the power factor. A true RMS multimeter must be used to measure the actual RMS currents and voltages (and therefore apparent power). To measure the real power or reactive power, a wattmeter designed to properly work with non-sinusoidal currents must be used.

URL="http://en.wikipedia.org/w/index.php?title=Power_factor&action=edit&section=3"][U][COLOR=#0000ff]edit[/COLOR][/U][/URL Mnemonics

English-language power engineering students are advised to remember: "ELI the ICE man" - the voltage E leads the current I in an inductor L, the current leads the voltage in a capacitor C.
Or even shorter: CIVIL - in a Capacitor the I (current) leads V (Voltage), Voltage leads I (current) in an inductor L.



Hope that simplifies things a little.


:rolleyes: