VA vs. Watts

[drbond24]

Not really - it is still not wrong. I don't like that the phrasing looses the phase angle information. Complex power keeps this information intact. I am absolutely clear that me not liking it doesn't make it wrong. I'd have left it right there had charlie and rattus not jumped on me. The idea that power and energy are not vectors doesn't set well with me. This insistance on dwelling on 'apparent power' instead of 'complex power' is a bit baffling.

Ok, that's good. I completely understand your reasons for not liking it and they are valid. The reason I don't have a problem with it is because of the answer I have for the question you asked:

Why would one purposely ignore the phase angle information?

Because this was a simplified answer to get the general idea across to a non-engineering person. If the original discussion had included complex numbers and phase angles instead of beer and foam, it wouldn't have been understood and the whole purpose would have been defeated. (edit: I should have clarified non-electrical engineering person. I'm assuming an electrical engineer wouldn't have asked that question, because they would already know everything like I do. )

I likely would not have said anything had not several posters landed on Besoeker for differing with charlie.

Just to be clear, if you think I fit into the group this was not my intention. Someone posted that a response to the OP was incorrect, I disagreed, and so I posted why. It went on from there, but it had nothing to do with the specific people involved. Charlie b isn't always right and this is the first time I've disagreed with Besoeker as far as I can remember. I wasn't 'landing on Besoeker' for disagreeing with charlie b, I was just correcting something that I thought was wrong, just like Besoeker was. I just happen to disagree with him this time. If charlie b posts something that I disagree with, I assure you I will insert my opinion there as well.

Rick did a fine job covering most all of these points in his last post.

I agree. A very good post from Rick.

So we have power that is wattless, energy that is pointless, Dr Bond is groundless, and the thread is unstitched. Sounds great - we have all done our jobs.

I just want to clarify at this point, since you are at least the 2nd person that has done that, that I am not a Dr. in any shape or form. Those just happen to be my initials. David R. Bond = drbond. 24 was the number on my jersey when I played church league basketball in high school.

 

[markstg]

So is it Beer Time Yet

 

[Cold Fusion]

---Just to be clear, if you think I fit into the group (landing on B) this was not my intention. ---

Well, David R, I didn't think that

---I just want to clarify at this point, since you are at least the 2nd person that has done that, that I am not a Dr. in any shape or form. ---

I was just following their lead. I thought it was kind of cool, as in a compliment - like, "Bond, James Bond". I can see where one could wear the 'funny' off of it pretty fast.

So is it Beer Time Yet

Not for another five hours for me. I'm susposed to be working - not doing this.

cf

 

[drbond24]

I was just following their lead. I thought it was kind of cool, as in a compliment - like, "Bond, James Bond". I can see where one could wear the 'funny' off of it pretty fast.

Oh, I don't mind at all, I just didn't want to be misrepresenting myself as a Ph.D. or something. I ain't that smart.

Actually, there are several people that call me 'Doc' because of my initials and because I had DR BOND on my license plate for a while because I thought it was funny.

Yeah, I've heard the "Bond, James Bond" thing a few times. :roll: Everybody that does it seems to think that no one else would have ever thought of that. The only time I use it is to help people with spelling my name. I must talk funny (well, I am from WV), because I've got everything from Bone to Vaughn after people hear me say my name. I usually say "David Bond, that's Bond like James Bond." They always get it then. :wink:

 

[LarryFine]

So is it Beer Time Yet

In three minutes.

 

[LarryFine]

Yeah, I've heard the "Bond, James Bond" thing a few times. :roll: Everybody that does it seems to think that no one else would have ever thought of that.

You think you have it bad. grin

 

[drbond24]

I'm susposed to be working - not doing this.

This should have gone on the bumper sticker!

Mike Holt's Forum - We're all supposed to be working, but...here we are!

 

[Besoeker]

All you did was repeat what charlie b has already agreed with; a watt and a joule per second are equal. Nowhere in the quotes you posted does it say "A watt is defined as one joule per second."

Definitions of watt on the Web:
a unit of power equal to 1 joule per second[/quote]
Is that not unequivocal?

Even in your definition of the joule, it says a joule is defined using newtons and meters, but then it says that a joule per second is equal to a watt. It never associates a watt or a J/s as being the definition of the other. They are just equal.
First, it wasn't my definition of a Joule.
Then you state that "they are just unequal" having previously endorsed Charlie's point that "a watt and a joule per second are equal".

I don't want to make this acrimonious.
It's by and large a polite forum.
I just don't think some of the points made by you and Charle really hold water.

 

[drbond24]

Is that not unequivocal?

All I can do here is repeat what I've already said. The definition says they are equal. It does not say "A watt is defined as a joule per second." There is a difference.

First, it wasn't my definition of a Joule.

Yes, I realize you didn't write it. It was yours in that you posted it.

Then you state that "they are just unequal" having previously endorsed Charlie's point that "a watt and a joule per second are equal".

I said they are equal, charlie b said they are equal, and all of the definitions you posted said they are equal. In fact, I don't think anyone has disagreed so far that they are equal. What I'm saying is that "a watt is equal to a joule/second" and "a watt is defined as a joule/second" are two very different things.

I did not post that "they are just unequal."

The trouble started when we said a volt-amp is equal to a joule/second and a volt-amp reactive is equal to a joule/second.

I don't want to make this acrimonious. It's by and large a polite forum.

I agree, and I'm glad this thread hasn't gone there.

I just don't think some of the points made by you and Charle really hold water.

Why? Unless I missed something, you have yet to explain your position. You have stated over and over that you don't agree, but I haven't heard a good reason from you why. I'm all for a good debate, but it isn't much of a debate without you giving some reasoning behind your position.

Us: Blah blah blah.
Besoeker: I disagree.
Us: Blabbity blah blabbity blah.
Besoeker: I disagree.
Us: Bippity Boppity Boo.
CF: Blah blah is right but I'm with Besoeker anyway.
Besoeker: I disagree.

(That was just an attempt at humor, not intended as an insult to anyone.)

I'm not trying to be rude or disrespectful in any way here, I'd just like to hear a more thorough explanation of your position. You came the closest to explaining yourself back in post 17, and you almost did it again in post 44 before you went back to telling us that a VA and a Watt are not the same thing. We know that, and we never said that. What started all of this is the response to the OP that said VA and VAr could be described in Joules per second. You say post 44 that the dimentional analysis is not disputed, so I don't understand where you're coming from. Telling me that a watt is a joule per second over and over again isn't helping; I already know that. Tell me why a volt-amp ISN'T a joule per second.

 

[mikehughes8]

I have heard that for all intents and purposes, VA and watts are the same.

Is this true? Does anyone have a good explination of the difference?

They are the same if P.F. is at unity.

 

[Rick Christopherson]

You came the closest to explaining yourself back in post 17, and you almost did it again in post 44 before you went back to telling us that a VA and a Watt are not the same thing.

Thank you Dr. Bond grin for pointing this out, because this makes it clear where/how the discussion went south.

The dimensional analysis is not disputed.
One Volt times one Amp is one Watt. Provided they occur at the same time.
It works for instantaneous and steady state values. For time varying or periodic waveforms the instaneous values of current and voltage give Watts.
For an alternating circuit, displace the current and voltage by a quarter of a cycle and you still have VA but no W.
They are not the same units.

Besoeker, the sentences I highlighted from your post #44 are not correct. You have confused the difference between units of measure and their usage. As has already been stated (or maybe not) VA = j/s = Watts. They are all the same units of measure.

Real Power, Reactive Power, Total Power can all be expresses in Watts, joules/second, or VA, because all of those units of measure are Equal. There is no difference between any of them except in how we have chosen to utilize them.

We Invented the units "VA" simply to distinguish total power answers from real power answers. We arbitrarily assigned Watts to represent real power, and VA to represent total power. This is no different than using knots to distinguish speed at sea versus mph on land.

Maybe this will help make more sense: It is incorrect to say that you convert KVA to KW by applying the powerfactor. The proper way of stating this is that you convert total power to real power by applying the powerfactor. You are not converting the units, you are converting the function.

 

[iMuse97]

Thank you Dr. Bond grin for pointing this out, because this makes it clear where/how the discussion went south.

Besoeker, the sentences I highlighted from your post #44 are not correct. You have confused the difference between units of measure and their usage. As has already been stated (or maybe not) VA = j/s = Watts. They are all the same units of measure.

Real Power, Reactive Power, Total Power can all be expresses in Watts, joules/second, or VA, because all of those units of measure are Equal. There is no difference between any of them except in how we have chosen to utilize them.

We Invented the units "VA" simply to distinguish total power answers from real power answers. We arbitrarily assigned Watts to represent real power, and VA to represent total power. This is no different than using knots to distinguish speed at sea versus mph on land.

Maybe this will help make more sense: It is incorrect to say that you convert KVA to KW by applying the powerfactor. The proper way of stating this is that you convert total power to real power by applying the powerfactor. You are not converting the units, you are converting the function.

Thank you RC. I've been following this thread with some interest. Thanks to all who've contributed, so far. And for continuing to pursue the discussion to a resolution.

 

[resistance]

Very informative!!!

 

[Besoeker]

No, apparent power is defined as the product of two magnitudes, therefore there are no phase angles involved. It is not inherently complex.

Yes. Two scalar magnitudes.

 

[Besoeker]

Besoeker, the sentences I highlighted from your post #44 are not correct. You have confused the difference between units of measure and their usage. As has already been stated (or maybe not) VA = j/s = Watts. They are all the same units of measure.

Not so. In an alternating current circuit, it is only in the quite specifiic case of unity power factor where VA = W

Real Power, Reactive Power, Total Power can all be expresses in Watts, joules/second, or VA, because all of those units of measure are Equal. There is no difference between any of them except in how we have chosen to utilize them.

The very reason we need them is because they are not the same. For example, you specify PFC by the kVAr, not by the kW. And transformers in kVA, not kW.

We Invented the units "VA" simply to distinguish total power answers from real power answers. We arbitrarily assigned Watts to represent real power, and VA to represent total power.

There isn't a lot arbitary about it. Power is rate of doing work. The Watt is a measure of power - a rate of doing work. The VA isn't.

This is no different than using knots to distinguish speed at sea versus mph on land.

But they are still both measures of speed and you can convert one to the other (30knots is about 35 mph). You can't do that with W and VA so the analogy isn't applicable.

 

[charlie b]

Power is rate of doing work. The Watt is a measure of power - a rate of doing work. The VA isn't.

That is where you have it wrong. Power is not the rate of doing work. Power is the rate of using, or supplying energy.

Under certain circumstances, the "Work-Energy Theorem" will declare the two to have equal values. But nothing, nothing defines power and the rate of doing work as being identical. It is no different than my earlier assertion that power and joules per second are equal, but not identical.

 

[Besoeker]

That is where you have it wrong. Power is not the rate of doing work. Power is the rate of using, or supplying energy.

For a balanced system, production and consumption match.

 

[Besoeker]

That is where you have it wrong. Power is not the rate of doing work. Power is the rate of using, or supplying energy.

Slightly more seriously....
Work and energy are equivalent units.
Thus, the rate of doing work is equivalent to the rate of using, or supplying energy.

 

[Rick Christopherson]

Not so. In an alternating current circuit, it is only in the quite specifiic case of unity power factor where VA = W

NO! The units are Identical. They are Equal. They are Interchangeable!!!!!

As I already told you, you are confusing units with function.

Your profile says you are an engineer, so I am going to give you an engineering assignment. PROVE that the units are not the same. Blow the cobwebs off your old text books where these terms were first defined to you many years ago......trust me, I already did this before I made my last posting.

The very reason we need them is because they are not the same.

No! The reason we need them is because the functions are different, but the units are the same. We created these separate units to avoid confusion, but those units do not define the function.

The most telltale flaw in your argument is that you did not respond to any of the concepts I presented in posting #99. Your silence on this posting is quite surprising, but your absence from the discussion was also very revealing. My follow-up statements are all predicated on the information presented in this posting, so if you are going to attempt to contradict the follow-up information, then you need to contradict what I wrote in Posting #99.

As an engineer, you have forgotten where these equations came from, and are only remembering the short-cut equations. These short-cut equations are extremely useful, but when you forget where they came from, then you also forget Why they came about. Your error is that you falsely assumed that the concepts you start with are the base-concepts, and have forgotten that there is a much deeper level of equations that originally lead to them.

So to reiterate, your engineering assignment is to prove that the units of VA, j/s, and Watts are not equivalent, equal, and fully interchangeable aside from the fact that we have "Chosen" them to be used for different functions. You must show how these units differ.

You will be graded on a pass/fail basis, so it is recommended that you at least don't fail. Since I already know the answer, your only hope for passing is to flip-flop your position.

 

[Cold Fusion]

---So to reiterate, your engineering assignment is to prove that the units of VA, j/s, and Watts are not equivalent, equal, and fully interchangeable aside from the fact that we have "Chosen" them to be used for different functions. ---.

Rick -
Did you forget "vars" in this list? Or did you leave them out on purpose?

cf