Volts, Amps, and VA....

[twocvbloke]

I have here 2 Motorola adaptors, one is 24v 4.8VA AC, the other is 12v 10.8VA DC.

 

Now, me and VA do not get on well, I always assumed that VA = Watts, but I think Gibbo informed me on here that it doesn't, soooo, I'd like to know how to translate the VA value into Amps and into Watts, cos to me, Amps is everything...

 

Though the 24v AC one I don't plan to use for anything other than my Motorola Overnight Charger base for my old phones, aminly cos it's AC, not DC, though that said, the 12v one, for the "Intellicharge XT" base, I'll probably not purloin for use on anything else cos it's needed for one of my 3 bases, but I would like to know the proper values anyway...

[dor]

As far as DC is concerned, VA & watts are effectively interchangable.

 

So, you 12V 10.8VA unit can give a current of 0.9 amps.

 

The AC one is probably much the same as far as VA = watts is concerned; it depends on the type of load. As far as your charger is concerned I would think it is happy to give 200ma, 0.2A.

 

Someone will now come along and give you pages of calculations to show how this is all theoretically wrong (or has he stopped posting here now?).

[Gibbo]

Let's "analogise"............

 

To water!

 

Volts is the pressure of the water. It's how hard it can be pushed. Put a pressure meter on the pipe connected to a tap that is turned off. Say you get 30PSI - that's the voltage.

 

Amps is the amount of water flowing when you turn the tap on. The more you turn it on, the more water flows, more amps. That's measured with an ammeter. Or flow meter for water.

 

However the water feed cannot provide the volts without limit when you turn the tap on. As you turn the tap on, the volts will drop slightly. Just as they would with a battery.

 

VA is the power, it's the pressure of the water multiplied by the volume flowing.

 

The difference between VA and watts isn't so easy to understand. It only applies in the case of AC. With DC, VA and watts is always the same.

 

For a full explanation of the difference between VA and watts on AC you could try this..............

 

http://www.smartgauge.co.uk/watts_1.html

 

Beware, it's quite heavy going even though I tried to write it in non technical language. I know supposedly qualified electronics and electrical engineers who still don't fully understand it. They can "do the math" to get the answers but they don't actually have a "feel" for what is going on. And to me, no matter how many sums one does, unless one has a "feel" for something then one simply doesn't understand it. You'd be better off understanding what is going on but unable to calculate it rather than vice versa. One can always look up how to calculate it. That's the easy bit. Actually understanding the process (not the sums) is the difficult part. This applies to almost the entire field of electronics and is why people can throw lots of maths at things and still get the worng answers

 

Gibbo

 

Someone will now come along and give you pages of calculations to show how this is all theoretically wrong (or has he stopped posting here now?).

 

I think he said he'd gone on holiday.

 

He'd have got the answers wrong by a factor of 10 anyway.

 

 

Gibbo

[mayalld]

I have here 2 Motorola adaptors, one is 24v 4.8VA AC, the other is 12v 10.8VA DC.

 

Now, me and VA do not get on well, I always assumed that VA = Watts, but I think Gibbo informed me on here that it doesn't, soooo, I'd like to know how to translate the VA value into Amps and into Watts, cos to me, Amps is everything...

 

Though the 24v AC one I don't plan to use for anything other than my Motorola Overnight Charger base for my old phones, aminly cos it's AC, not DC, though that said, the 12v one, for the "Intellicharge XT" base, I'll probably not purloin for use on anything else cos it's needed for one of my 3 bases, but I would like to know the proper values anyway...

 

VA is like watts, but different, because it incorporates a factor for inductive load.

 

For ampage calculations, you can regard them as if they were Watts. Indeed, they give a better view of the current than watts than does a value in watts for a partly inductive load.

[alan_fincher]

He'd have got the answers wrong by a factor of 10 anyway.

 

In my experience, to succeed you sometimes need to get your numbers wrong by more than a factor of 10!.

 

I used to often watch Dragons Den - people got torn to shreds by the Dragons if they felt their predictions were optimistic by a factor of 2 or 3.

 

Then the charming "Levi Roots", (real name, Keith, I believe!), came on looking for sponsorship for his "Reggae Reggae Sauce".

 

His numbers about his proposed manufacturing volumes got exposed to be out by a factor of one thousand!

 

I expected him to get torn limb from limb. What actually happened ? Two Dragons gave him his investment.

 

The product was taken up by Sainsbury's, (clever Sainsbury's !), and is now selling very well, along with a line of alternate Levi Roots products, I'm told.

 

So getting your numbers badly wrong doesn't have to be a disaster - perhaps holiday boy knows that ?

[carlt]

Let's "analogise"............

 

To water!

 

Volts is the pressure of the water. It's how hard it can be pushed. Put a pressure meter on the pipe connected to a tap that is turned off. Say you get 30PSI - that's the voltage.

 

Amps is the amount of water flowing when you turn the tap on. The more you turn it on, the more water flows, more amps. That's measured with an ammeter. Or flow meter for water.

 

However the water feed cannot provide the volts without limit when you turn the tap on. As you turn the tap on, the volts will drop slightly. Just as they would with a battery.

I thought water and electricity should never mix??

 

 

 

 

I think he said he'd gone on holiday.

 

He's got a static caravan, on a site in Mablethorpe.

 

If you pm him you can get a week, at mates rates.

[twocvbloke]

Let's "analogise"............

 

To water!

 

Volts is the pressure of the water. It's how hard it can be pushed. Put a pressure meter on the pipe connected to a tap that is turned off. Say you get 30PSI - that's the voltage.

 

Amps is the amount of water flowing when you turn the tap on. The more you turn it on, the more water flows, more amps. That's measured with an ammeter. Or flow meter for water.

 

However the water feed cannot provide the volts without limit when you turn the tap on. As you turn the tap on, the volts will drop slightly. Just as they would with a battery.

 

VA is the power, it's the pressure of the water multiplied by the volume flowing.

 

The difference between VA and watts isn't so easy to understand. It only applies in the case of AC. With DC, VA and watts is always the same.

 

For a full explanation of the difference between VA and watts on AC you could try this..............

 

http://www.smartgauge.co.uk/watts_1.html

 

Beware, it's quite heavy going even though I tried to write it in non technical language. I know supposedly qualified electronics and electrical engineers who still don't fully understand it. They can "do the math" to get the answers but they don't actually have a "feel" for what is going on. And to me, no matter how many sums one does, unless one has a "feel" for something then one simply doesn't understand it. You'd be better off understanding what is going on but unable to calculate it rather than vice versa. One can always look up how to calculate it. That's the easy bit. Actually understanding the process (not the sums) is the difficult part. This applies to almost the entire field of electronics and is why people can throw lots of maths at things and still get the worng answers

 

So, for DC, VA=Watts, that's good, though this PSU is rated way less than what I was thinking of using it for, but still, it's a phone charger for me ol' motorola smaller bricks (I'm not into the old breezeblocks, cos I can't use them as they're analogue!!!)...

 

As for the AC version of VA, erm, LEGGIT!!!!

[Gibbo]

So getting your numbers badly wrong doesn't have to be a disaster - perhaps holiday boy knows that ?

 

 

The difference is, Mr Sauce, when his errors were pointed out, said "Oh yeah, I bow to your superior knowledge experience", as opposed to "no they're not, no they're not, no they're not, I don't care how many people tell me I'm wrong and I don't care how many references you cite I still won't ever admit it".

 

 

Gibbo

 

He's got a static caravan, on a site in Mablethorpe.

 

Oh dear, aren't you already going to be sued for every last penny? What a brave man you are.

 

Gibbo

 

As for the AC version of VA, erm, LEGGIT!!!!

 

I know qualified engineers who still think that.

 

Gibbo

[bobtom]

Hi could you tell me where watts fits into the water analogy

[twocvbloke]

I know qualified engineers who still think that.

 

Gibbo

 

I'm not surprised!!!

[Gibbo]

Hi could you tell me where watts fits into the water analogy

 

Re-read the prvious posts.

 

VA and watts are a measurement of power. Power is the pressure of the water multiled by the volume flowing.

 

Gibbo

[Timleech]

Re-read the prvious posts.

 

VA and watts are a measurement of power. Power is the pressure of the water multiled by the volume flowing.

 

Gibbo

 

It might not help anyone understand, but.........

 

I have two 180 Amp welding sets, both run from the 240V single phase mains.

Both I expect to have similar 'efficiency' in terms of the amount of waste heat developed in the unit, so both will consume a similar number of Watts when running the same size of welding rod.

One is a big old oil-immersed transformer, it has to be plugged into a 32A supply with at least 6 sqmm cable to give useful results.

The other is a little inverter unit, I can run it all day on the end of a Caravan-type 2.5 sqmm extension cable.

That's because (someone please correct me if I'm wrong and there's more to it) the Power Factor for the oil-immersed unti is Cr*p, so it draws much more current (Amps) for the same output (Watts) because the Volts and Amps are out of phase with one another. The Watts (energy) are roughly the same, but the VA are much higher for the older unit.

 

Tim

[Gibbo]

That's because (someone please correct me if I'm wrong and there's more to it) the Power Factor for the oil-immersed unti is Cr*p, so it draws much more current (Amps) for the same output (Watts) because the Volts and Amps are out of phase with one another. The Watts (energy) are roughly the same, but the VA are much higher for the older unit.

 

Almost certainly correct. Also, the old one will pull power in brief pulses, so for the same average power, it has to pull great big pulses. The inverter one will pull the power continuously so the peaks that it pulls will be much smaller.

 

Gibbo

[PaulG]

 

So getting your numbers badly wrong doesn't have to be a disaster

 

Tell that to the guy(s) who did the sums for the imaging system for the Hubble Space Telescope.....

[The Meerkatat]

Tell that to the guy(s) who did the sums for the imaging system for the Hubble Space Telescope.....

 

 

Perhasp trying to keep it simple would be an advanatge

 

For Dc circuitary

 

Voltage=Current x Resistance . . . . . . . . . . .Power = Current x Voltage

 

Voltage = Volts (v)

Current = Amps (A)

Resistance = Ohms (Omega symbol)

Power = Watts (W)

 

 

Easy, so easy!!

[Gibbo]

Easy, so easy!!

 

But wrong because we're talking about AC!

 

Gibbo

Edited June 11, 2009 by Gibbo

[RLWP]

Hi could you tell me where watts fits into the water analogy

 

The first steam engines built by Watt were used for pumping water from mines.

 

Does that help?

 

Richard

[GeoffS]

Am I right in thinking then that, to stay with the water analogy, that with AC there would be a pulsed pushes of water rather like pumping up a tyre manually. The Watts are then calculated with an average of the 'pushes' which means the Watts are Volts x Amps x Pulse factor??

[WotEver]

Am I right in thinking then that, to stay with the water analogy, that with AC there would be a pulsed pushes of water rather like pumping up a tyre manually. The Watts are then calculated with an average of the 'pushes' which means the Watts are Volts x Amps x Pulse factor??

 

No.

 

Read Gibbo's description in the link he gave in his first post in this thread. It's V x A x POWER FACTOR which you'll only understand by reading his description.

 

T