mA/VA ??

[EddieCurrent]

Hello,

mA/VA, Does anybody know of any internet sites where I can find out more information please ?
It is probably 'rating' I should know, but to be honest don't !!
VoltAmp ????? what's all that about ??? !!!!!!

Thank you.

 

[Maxxy]

Is the question to do with earth leakage?

Im thinking volt amp = volt x amp = power

so 0.1 ma earth leakage per voltamp aka 0.1ma earth leakage per watt?

 

[davelx]

VA - product of Voltage and Current - which is only the same as power if the voltage and current are in phase, which only happens with purely resistive loads:

http://en.wikipedia.org/wiki/Power_factor

 

[rlc]

...take a look at http://www.pcguide.com/ref/power/ext/basics_Power.htm

it tells you all about 'apparent power', 'true power' etc....enjoy!

~rlc

 

[EddieCurrent]

Thanks for the replies, I will go have a read up, and no doubt be back later when I get to scratching my head !

Maxxy, I just want to understand the whole 'concept' and know when it is applicable, or when I would ever have to use the info, (maybe I will come across earth leakage in my reading), thanks.

Thanks again all.

 

[ricicle]

As has been stated above VA is the apparent power (the product of voltage and current) usually stated for a non-resistive load (voltage and current waveforms not in unison)

mA stands for milliamps obviously used for low current ratings such as earth leakage and electronics

 

[sm1thson]

When VA is used on a transformer i had assumed it was due to the fact that it doesnt actually consume power (other than a small percentage): so for example a power supply for supplying 5v 1A would say 5VA as it would be incorrect to say 5W as it does not consume 5W. -is this true in the case of a transformer? or does it say 5VA purely because it's inductive?

 

[ricicle]

VA rating on a transfomer is stating the maximum apparent power that it can handle.An inductive load, for example, will draw more current than it needs for its true power due to its magnetic properties.
This 'extra' current will be drawn through the transformer and will still contribute to the I²R (heat) losses in the windings so has to be accounted for especially on power transfomers that have no power factor correction
(power factor is the relationship between true power and apparent power and is expressed as a number between 0 and 1)

example (230V only)

500W motor 0.7 power factor

500w resistive load would draw 2.17A

500w/0.7 = 714.3VA 714.3/230 = 3.1A

In the inductive circuit the apparent power will always be greater than the true power

Hope this helps

 

[sm1thson]

Yep. I get it now thanks

 

[Taylortwocities]

Blimey! AC theory 101

Takes me back.....

TTC