measuring ac wattage from ampere

[suraj joneja]

Hi

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage? On the
net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage. How do I do
that?

Many thanks.
Suraj.

 

[John Fields]

On Fri, 22 Oct 2010 23:25:57 -0700 (PDT), suraj joneja
<suraj.joneja@gmail.com> wrote:

Hi

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage? On the
net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage. How do I do
that?

---
Do you have any test equipment?

If so, what do you have?

---
JF

 

[F. Bertolazzi]

suraj joneja:

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage?

Which sort of device is it? What you mean by "rating"?
The one of the equipment or of its fuse?

On the net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage. How do I do
that?

If the device is resistive (lamp, kettle, anything that does not have a
motor or a switching power supply non properly power factor corrected)
current and tension are in phase, so you can measure the current with a
cheap tester and use Ohm's law.

By the way, are you sure the power there is 220V?
In Europe it has been recentlt and silently brought to 230V.

--
Saluti

 

[Phil Allison]

"suraj joneja"

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage?

** With a wattmeter.

On the
net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage.

** Wrong.

Go look up the actual definition.



..... Phil

 

[Sjouke Burry]

suraj joneja wrote:

Hi

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage? On the
net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage. How do I do
that?

Many thanks.
Suraj.
By measuring volage,current and cosine.

 

[Jamie]

suraj joneja wrote:

Hi

I am in india where the AC mains supply is 220 v 50hz. Now I have a
device which has a rating of 1 amp. How do measure its wattage? On the
net I read that one has to consider the power factor which is the
cosine of the angle between the current and the voltage. How do I do
that?

Many thanks.
Suraj.

A device or a power supply that plugs into the wall that has this rating?

If it's a power adapter that is giving you this rating ? that indicates
the given max handling power, not necessarily the power being demanded
from it..

But in cases of max handling, it would be 220 watts. Basically..

You see, there are things that need to be considered, like Apparent
power and real power.. VA etc.. which can be calculated from the PF
(Power factor)... So, with out knowing some more about what this
device is... It's just a ball park figure..


Jamie..

 

[Pimpom]

F. Bertolazzi wrote:

suraj joneja:

I am in india where the AC mains supply is 220 v 50hz. Now I
have a
device which has a rating of 1 amp. How do measure its
wattage?

....<snip>.......

By the way, are you sure the power there is 220V?
In Europe it has been recentlt and silently brought to 230V.

I'm in India and AFAIK, the standard domestic supply has been
230V for at least a few decades. However, it's not unusual to see
220V or even 240V on labels and nameplates. A few have 250V
printed on them.

Between the early 80s and early 90s, I acted as a sort of
unofficial consultant to my state's power department. The
engineers and technicians were uncertain as to what voltage they
should supply. For reasons not clear even to the Chief Engineer,
they'd had a vague tradition of making their 3-phase supplies
415V and distribute the single-phase domestic supplies from that.
I advised them to try to keep it at 230V single phase or 400V
phase-to-phase.

I didn't know that Europe had changed to 230V. It used to be
240V, didn't it?

 

[Jamie]

Pimpom wrote:

F. Bertolazzi wrote:

suraj joneja:


I am in india where the AC mains supply is 220 v 50hz. Now I
have a
device which has a rating of 1 amp. How do measure its
wattage?

...<snip>.......

By the way, are you sure the power there is 220V?
In Europe it has been recentlt and silently brought to 230V.


I'm in India and AFAIK, the standard domestic supply has been
230V for at least a few decades. However, it's not unusual to see
220V or even 240V on labels and nameplates. A few have 250V
printed on them.

Between the early 80s and early 90s, I acted as a sort of
unofficial consultant to my state's power department. The
engineers and technicians were uncertain as to what voltage they
should supply. For reasons not clear even to the Chief Engineer,
they'd had a vague tradition of making their 3-phase supplies
415V and distribute the single-phase domestic supplies from that.
I advised them to try to keep it at 230V single phase or 400V
phase-to-phase.

I didn't know that Europe had changed to 230V. It used to be
240V, didn't it?


Here in the states. We use the 220,230 and 240 range and all it

really means is, 220 being the lowest, 230 at mid point and 240 at
the high end..
Devices come label depending on when they were made.. but these
days, most devices label the mid point (230). that does not mean,
that is what you get at your service.. It could be any where from
220..240.. and some times even a little higher depending on what type
of xformer they used from the source they connected it too!
Delta, WYE etc...

P.S.
Last time I knew,100 and 200 volts was common in area's like
Japan./.. Which is why you see export equipment with transformers
able to bump the voltage up just a little for these area's. In
area's where the voltage is already up there, some idiots like to
use that little bump to push their tube heaters up, plate voltage, etc...

Have a good day...

 

[F. Bertolazzi]

Pimpom:

I didn't know that Europe had changed to 230V. It used to be
240V, didn't it?

In Italy it was 220 volts. I said "recently" because no news ever appeared
about this. Well, at least it was not reported on the TV news.

--
Saluti

 

[F. Bertolazzi]

suraj joneja:

Now I believe one can calculate the wattage VA* PF. So I believe it
will come out to be 220w . Ok. But I take the point that that is the
peak onsumption. Ok. Now to add more to the confusion is what is
written on the power supply that the input voltage range is 110-250v !

And there is also written that it draws 1A? I don't think so.

Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best?

Sure. But it will cost you a bit.

I don't have an AC ammeter but it will be easier for me to
buy one than a wattmeter.

And cheaper.

Can you please look at this product listing:
http://cgi.ebay.in/Digital-Clamp-Meter-1000Amps-AC-Large-LCD-Model-DT266-/170545323898?pt=LH_DefaultDomain_203&hash=item27b54b1f7a#ht_4146wt_836

Probably your laptop consumes around 0,1A, so there's no way you can use
that.

One more ques, with this clampmeter can I measure the current without
breaking the circuit?

Yes, bur it measures currents 10.000 times bigger than the one you are
interested in.

 

[suraj joneja]

Sorry for being vague. The 'device' is a charger for a laptop. I
belive it is A switching power supply. I read on a site that smps have
a power factor approaching unity. Also something similar was written
on this site http://www.powerstream.com/VA-Watts.htm

Now I believe one can calculate the wattage VA* PF. So I believe it
will come out to be 220w . Ok. But I take the point that that is the
peak onsumption. Ok. Now to add more to the confusion is what is
written on the power supply that the input voltage range is 110-250v !
Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best? I don't have an AC ammeter but it will be easier for me to
buy one than a wattmeter. If I can sure that either I can measure the
pf or approximate it...I can go in for the ammeter.

Can you please look at this product listing:
http://cgi.ebay.in/Digital-Clamp-Meter-1000Amps-AC-Large-LCD-Model-DT266-/170545323898?pt=LH_DefaultDomain_203&hash=item27b54b1f7a#ht_4146wt_836


One more ques, with this clampmeter can I measure the current without
breaking the circuit?

Many thanks.

 

[Pimpom]

Jamie wrote:

Pimpom wrote:

F. Bertolazzi wrote:

suraj joneja:


I am in india where the AC mains supply is 220 v 50hz. Now I
have a
device which has a rating of 1 amp. How do measure its
wattage?

...<snip>.......

By the way, are you sure the power there is 220V?
In Europe it has been recentlt and silently brought to 230V.


I'm in India and AFAIK, the standard domestic supply has been
230V for at least a few decades. However, it's not unusual to
see
220V or even 240V on labels and nameplates. A few have 250V
printed on them.

Between the early 80s and early 90s, I acted as a sort of
unofficial consultant to my state's power department. The
engineers and technicians were uncertain as to what voltage
they
should supply. For reasons not clear even to the Chief
Engineer,
they'd had a vague tradition of making their 3-phase supplies
415V and distribute the single-phase domestic supplies from
that.
I advised them to try to keep it at 230V single phase or 400V
phase-to-phase.

I didn't know that Europe had changed to 230V. It used to be
240V, didn't it?


Here in the states. We use the 220,230 and 240 range and all it
really means is, 220 being the lowest, 230 at mid point and 240
at
the high end..
Devices come label depending on when they were made.. but
these
days, most devices label the mid point (230). that does not
mean,
that is what you get at your service.. It could be any where
from
220..240.. and some times even a little higher depending on
what
type of xformer they used from the source they connected it
too!
Delta, WYE etc...

I remember reading a long time ago about a nation-wide survey of
domestic supplies in India. The average came out as 230V - no
doubt rounded off - and this has been pretty much accepted as the
standard. I'm not sure if there was a formal directive though.

P.S.
Last time I knew,100 and 200 volts was common in area's like
Japan./.. Which is why you see export equipment with
transformers
able to bump the voltage up just a little for these area's. In
area's where the voltage is already up there, some idiots like
to
use that little bump to push their tube heaters up, plate
voltage,
etc...
I remember such products well, especially Japanese imports. They

used to have a recessed voltage selector switch with values like
100, 110, 120, 200, 220, 240V. The power supply situation was so
bad then that some people used them at the 120V position at
night. Sometimes they forgot to change them back during the day
and fried the product.

 

[John Fields]

On Sat, 23 Oct 2010 10:50:57 -0700 (PDT), suraj joneja
<suraj.joneja@gmail.com> wrote:

On Oct 23, 9:58 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:
suraj joneja:

Now I believe one can calculate the wattage VA* PF. So I believe it
will come out to be 220w .  Ok. But I take the point that that is the
peak onsumption. Ok. Now to add more to the confusion is what is
written on the power supply that the input voltage range is 110-250v !

And there is also written that it draws 1A? I don't think so.

Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best?

Sure. But it will cost you a bit.

I don't have an AC ammeter but it will be easier for me to
buy one than a wattmeter.

And cheaper.

Can you please look at this product listing:
http://cgi.ebay.in/Digital-Clamp-Meter-1000Amps-AC-Large-LCD-Model-DT...

Probably your laptop consumes around 0,1A, so there's no way you can use
that.

One more ques, with this clampmeter can I measure the current without
breaking the circuit?

Yes, bur it measures currents 10.000 times bigger than the one you are
interested in.

Thanks. Please don't doubt! I checked again! Its the power supply for
a large screen toshiba laptop. But I guess that the one amp rating
must be for 110v?

No, the one ampere is undoubtedly what the output of the supply is
capable of delivering continuously, so to get the power delivered from
the supply you multiply the power supply output voltage (essentially
your laptop's battery voltage) times one ampere.

If the supply's input range is 110 to 250 then it's a "universal"
switching supply and the input current will depend on its efficiency
and how much power is being deilvered to the load, your laptop.

for instance, let's say the supply is 80% efficient, that its output
is 12VDC, and that it's delivering 1A into the load.

The power out, then, will be:

P = IE = 1A * 12V = 12 watts.

Now, since the supply is only 80% efficient it'll be taking:

Pout
Pin = ------ = 15.0 watts
0.85

from the mains and dissipating 3 watts as heat.

If you're in India and your mains voltage is 240V, then the current
the supply will draw from the mains will be:

P 15W
I = --- = ------- ~ 0.0625 ampere ~ 63 milliamperes.
E 240V

I checked on youtube and saW "kill a watt". Just the thing I need but
its expensive and in the USA.

---
If you're going to be measuring the real power consumption of "many
other devices" then you'd be well advised to get a power meter of some
kind which would allow you to read real power as well as power factor
or phase angle voltage and current.
---

What if I get an in range ammeter?

---
Not knowing whether your supply (or many of the "many other devices")
is power factor controlled, all the ammeter is going to allow you to
figure out is Volt-Amperes into the AC side of the supply and watts
into the load.

Also, If I were you I'd be very, very, careful working around 240V
mains, and never work alone, since it seems you're new at this game
and death likes newbies.

BTW, is your supply an AC to DC converter or just a transformer, and
what else is written on it?

---
JF

 

[Jamie]

suraj joneja wrote:

Sorry for being vague. The 'device' is a charger for a laptop. I
belive it is A switching power supply. I read on a site that smps have
a power factor approaching unity. Also something similar was written
on this site http://www.powerstream.com/VA-Watts.htm

Now I believe one can calculate the wattage VA* PF. So I believe it
will come out to be 220w . Ok. But I take the point that that is the
peak onsumption. Ok. Now to add more to the confusion is what is
written on the power supply that the input voltage range is 110-250v !
Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best? I don't have an AC ammeter but it will be easier for me to
buy one than a wattmeter. If I can sure that either I can measure the
pf or approximate it...I can go in for the ammeter.

Can you please look at this product listing:
http://cgi.ebay.in/Digital-Clamp-Meter-1000Amps-AC-Large-LCD-Model-DT266-/170545323898?pt=LH_DefaultDomain_203&hash=item27b54b1f7a#ht_4146wt_836


One more ques, with this clampmeter can I measure the current without
breaking the circuit?

Many thanks.
that must be some laptop, 220watt supply ?

 

[John Fields]

On Sat, 23 Oct 2010 12:07:58 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Oct 23, 10:50 am, suraj joneja <suraj.jon...@gmail.com> wrote:
On Oct 23, 9:58 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

Now I believe one can calculate the wattage VA* PF.

I checked on youtube and saW "kill a watt". Just the thing I need but
its expensive and in the USA.

What if I get an in range ammeter?

As you know by now, the ammeter measures one of three items, A.
Your AC mains might be constant enough to just plug in the V number,
for a rough calculation. The 'power factor', though, is only known
to be 'the cosine of...' and can be any number in the range of
+1, -1.

---
A negative cosine?

Tricky!
---

With ammeter only, you can establish an upper limit
of how much power is drawn (the upper limit is achieved if the
power factor is +1).

---
No, you can't.

With only an ammeter and voltmeter you never know whether you're
measuring Volt-Amperes or watts.

---
JF

 

[suraj joneja]

On Oct 23, 9:58 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

suraj joneja:

Now I believe one can calculate the wattage VA* PF. So I believe it
will come out to be 220w .  Ok. But I take the point that that is the
peak onsumption. Ok. Now to add more to the confusion is what is
written on the power supply that the input voltage range is 110-250v !

And there is also written that it draws 1A? I don't think so.

Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best?

Sure. But it will cost you a bit.

I don't have an AC ammeter but it will be easier for me to
buy one than a wattmeter.

And cheaper.

Can you please look at this product listing:
http://cgi.ebay.in/Digital-Clamp-Meter-1000Amps-AC-Large-LCD-Model-DT...

Probably your laptop consumes around 0,1A, so there's no way you can use
that.

One more ques, with this clampmeter can I measure the current without
breaking the circuit?

Yes, bur it measures currents 10.000 times bigger than the one you are
interested in.

Thanks. Please don't doubt! I checked again! Its the power supply for
a large screen toshiba laptop. But I guess that the one amp rating
must be for 110v?

I checked on youtube and saW "kill a watt". Just the thing I need but
its expensive and in the USA.

What if I get an in range ammeter?

Thanks.

 

[Jamie]

John Fields wrote:

On Sat, 23 Oct 2010 12:07:58 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:


On Oct 23, 10:50 am, suraj joneja <suraj.jon...@gmail.com> wrote:

On Oct 23, 9:58 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

Now I believe one can calculate the wattage VA* PF.

I checked on youtube and saW "kill a watt". Just the thing I need but
its expensive and in the USA.

What if I get an in range ammeter?

As you know by now, the ammeter measures one of three items, A.
Your AC mains might be constant enough to just plug in the V number,
for a rough calculation. The 'power factor', though, is only known
to be 'the cosine of...' and can be any number in the range of
+1, -1.


---
A negative cosine?

Tricky!
---

Two Atoms walking down the street talking;

A1. I think I lost an Electron?

A2. Are you sure ?

A1. Yes, I am positive..




Yes, I know, it's a bad one!

 

[whit3rd]

On Oct 23, 10:50 am, suraj joneja <suraj.jon...@gmail.com> wrote:

On Oct 23, 9:58 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

Now I believe one can calculate the wattage VA* PF.

I checked on youtube and saW "kill a watt". Just the thing I need but
its expensive and in the USA.

What if I get an in range ammeter?

As you know by now, the ammeter measures one of three items, A.
Your AC mains might be constant enough to just plug in the V number,
for a rough calculation. The 'power factor', though, is only known
to be 'the cosine of...' and can be any number in the range of
+1, -1. With ammeter only, you can establish an upper limit
of how much power is drawn (the upper limit is achieved if the
power factor is +1).

What you ask to measure, power, requires a power meter, i.e. the
Kill-a-watt, or that gizmo the power company has bolted to your house.
If it's important, turn off all the house circuit breakers and connect
only ONE circuit, with your unknown item plugged into it.

And, the number at any given time (this is a laptop power adapter?)
will
depend on the laptop power usage (is it charging the battery? Quick-
charging
a very low battery? Running a compute-intensive application using
multiple
cores? Sleeping with the display turned off?). There is NO
expectation that this number is a constant.

 

[Phil Allison]

"suraj joneja"

Sorry for being vague.

** Nothing you can do about that.

The 'device' is a charger for a laptop. I belive it is A switching
power supply. I read on a site that smps have a power factor
approaching unity.

** Not true.

Also something similar was written
on this site http://www.powerstream.com/VA-Watts.htm

** Can you read at all ???

Now I believe one can calculate the wattage VA* PF.

** PF is what you find when you know both the VA and true power.

Ok let me tell you that my real objective is to measure the real watts
being drawn by the device (and many other devices) . A wattmeter will
be best?

** A wattmeter is the ONLY device that can do it.

Stop being a stubborn shit and take the advice.


..... Phil

 

[whit3rd]

On Oct 23, 12:38 pm, John Fields <jfie...@austininstruments.com>
wrote:

On Sat, 23 Oct 2010 12:07:58 -0700 (PDT), whit3rd <whit...@gmail.com
wrote:

With ammeter only, you can establish an upper limit
of how much power is drawn (the upper limit is achieved if the
power factor is +1).

No, you can't.

With only an ammeter and voltmeter you never know whether you're
measuring Volt-Amperes or watts.

Huh? You can only measure Volt-Amperes that way (if you have
the Volt value from the utility standards). The Watts value cannot
exceed the VA value, can it?