You can, but if you have to ask how I would not recommend it for you.
this post was submitted on 13 Feb 2024
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This.
The theory beside measuring power with a multimeter you way even have done it in high school usinq a 12V power supply and a small resistor/motor. Fun exercise and you may even loop on the whole high school physics curriculum with electricity --> power --> force --> work --> Energy and efficiency calculation.
However, unlike the 12 V you work on at school the domestic 230V can kill you (same for US 110V). I don't see a safe way to use a regular multimeter to measure a current in these voltage range. If you know what you do, you'll build a dedicaced/enclosed set up. If you don't buy a watt meter at the hardwarc store, it'll be safer and cheaper than a DIY one
depends on you multimeter. but an eaiser option would be to get something like a kill-o-watt meter and plug it between the power source and the TV
Depending on how well-provisioned your local community library is, a Kill-o-Watt may be something you can borrow for this exact task!
This is tricky, as power is calculated as voltage x current. Measuring (or knowing) voltage is usually pretty straightforward. But accurately measuring current requires setting up the circuit so it flows through the multimeter (while set to whatever current measurement mode it has - usually "Amps A/C", or similar). However, this method isn't safe, or practical, for non-electricians to measure A/C appliances.
As someone else mentioned, you could buy a multimeter that has an "amp clamp" - effectively a non-contact way of measuring current. BUT, you need to be aware...
A typical appliance's cable will have both active and neutral wires inside the outer layer of insulation. Current flows through a circuit - up one wire and down the other, if you will. So an amp clamp can only measure the current on one of those wires. If you were to measure both at once (ie. clamp the whole cable), the readings in each direction will cancel each other out. You'll measure zero net current. The only way is to cut the outer insulation and clamp a single wire inside.
I would absolutely NOT recommend this for an A/C appliance. The possibility of accidentally cutting through the insulation of one of the inner wires, combined with the possible death of the person handling it afterwards, should make this a non-starter.
Your safest options for ANY A/C powered appliance are to either:
- rely on the manufacturer's label; or
- buy a smart plug that measures the current for you.
There's many, many brands for the latter available, and most are really quite affordable.
Edit: as another commenter said, you could possibly buy a short extension lead that splits the wires out for you, but now you're buying a non-standard extension lead and (possibly) a new multimeter, all to validate what's on the appliance's label.
A $20 smart plug with current measurement will still be your cheapest and safest option.
If you're the kind of person who doesn't know how to do this, you probably don't have a true RMS meter and getting any kind of accurate reading is probably a no go.
Also something like a TV has a highly variable power draw, so a measurement of power over a longer time is probably more useful than a momentary snapshot. This is why most energy rating have something like kwh per year for some kind of defined typical usage.
For all the reasons others have already stated, what you want is a Kill A Watt instead of a multimeter or another thing to buy. Plug this thing into the wall and then plug your appliances etc into the meter and leave it for a week. I will record total power draw over the duration so you can see exactly how much power is being used under normal operating conditions. With a little bit of math you can compare kilowatt hours consumed with your power company costs and figure out how much money it cost to use TV's etc per hour.
You can, but one of those wall plug-in power meters are recommended for your use case.
I have one that looks like this, there are many clones that will do just fine, which gives W, A or V and you can even put a price per kWh to have it give you the cost of running.
product image
Just a heads up OP worth checking your state, country or councils government websites that note about electricity. Some of them give free power/watt checkers to help people reduce their electricity usage.
You will need a multimeter that measures amperage.
Watts = Voltage × Amperage
I suggest using a non-contact meter like this Fluke multimeter.
Even this probably won't result work though because you need to put the clamp around only one wire, not the entire power cable that has live, neutral, ground.
You can get a short extension that breaks the wires out individually.
Usually to use an amp meter like that, you also need one of these: https://a.co/d/d7qb5pj
But for $12 you can buy a plug with a screen that will record power usage, which would be even easier and cheaper. https://a.co/d/bj4U2hA
If your meter can measure AC millivolts, use a shunt. You'll have to build a special cable from an extension cord. Cut either the live or neutral wire, insert a shunt, which is a resistor with a very low resistance (typically milliohms), then provide some taps at either end of the shunt. Make it all electrically safe. You don't want to do the 50/60 Hz Shuffle.
Plug in the extension cord, plug your TV into the extension cord, then measure the AC voltage across the shunt while the TV is operating and apply I=E/R. Now you know the current in the circuit. Measure the wall outlet voltage and use P=IE to determine the power. The measurement is accurate when the power factor of the device being tested is close to 1.
But honestly, plug-in consumer-level power meters like the Kill-A-Watt are MUCH safer to use, relatively inexpensive, and work for appliances with power factors that are not 1 (like motors). They read out voltage, wattage, and energy usage (KWh).
Yes, but differentiating between actual power and apparent power will be difficult without building a rather complex circuit. A dedicated power meter will tell you, as well as computing the power factor. On the flip side, a TV's switching power suppy should have a good power factor, so apparent power (AC amps * RMS volts) is close to actual power.
Not easily. Power is a function of current, which requires your multimeter to be in series with the load.
Hilariously enough, I now use my portable power station(like these https://www.techradar.com/best/portable-power-stations) to do this kind of testing. It has a watts output on the front panel, so I can just plug something in and see how much it draws.
Another free way of doing this is to use the power meter outside your home.
- turn everything using power off
- verify by ensuring the power meter is no longer moving; no electricity consumed
- record current reading
- turn on tv for some period of time
- record new reading
Calculate usage as difference of the readings divided by how long you ran the tv for.
You can, but you would be better off buying something like this:
Upgraded Watt Power Meter Plug Home Electrical Usage Monitor Consumption, Energy Voltage Amps Kill Tester with Backlight, Overload Protection, 7 Modes Display https://a.co/d/bj4U2hA
Measuring watts with a multimeter:
Lol, that video shows you how to measure voltage, then multiply by current to calculate power. It totally skips over measuring current.