measuring ac wattage from ampere

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.

Reply to
suraj joneja
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Do you have any test equipment?

If so, what do you have?
Reply to
John Fields

suraj joneja:

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

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.

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Saluti
Reply to
F. Bertolazzi

"suraj joneja"

** With a wattmeter.
** Wrong.

Go look up the actual definition.

.... Phil

Reply to
Phil Allison

By measuring volage,current and cosine.

Reply to
Sjouke Burry

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..

Reply to
Jamie

..........

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?
Reply to
Pimpom

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...

Reply to
Jamie

Pimpom:

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.

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Saluti
Reply to
F. Bertolazzi

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

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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:

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

Many thanks.

Reply to
suraj joneja

suraj joneja:

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

Sure. But it will cost you a bit.

And cheaper.

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

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

Reply to
F. Bertolazzi

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.

Reply to
suraj joneja

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.

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.
Reply to
Pimpom

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.

Reply to
whit3rd

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

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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
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Reply to
John Fields

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that must be some laptop, 220watt supply ?

Reply to
Jamie

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A negative cosine?

Tricky! ;)
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Reply to
John Fields

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! ;)

Reply to
Jamie

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?

Reply to
whit3rd

"suraj joneja"

** Nothing you can do about that.

** Not true.

** Can you read at all ???

** PF is what you find when you know both the VA and true power.
** A wattmeter is the ONLY device that can do it.

Stop being a stubborn shit and take the advice.

.... Phil

Reply to
Phil Allison

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