recently I purchased a new to market plug in device that measures & displays current drawn, Watts, voltage, power factor etc

Modern switch mode power supplies include power factor correction and run at power factors around 90-95%. What's the plug-in power monitoring device as it sounds like it is not accurately measuring the RMS current and hence giving a false measurement of both current and power factor (either that or its trying to measure the inrush current also which would screw up its peak reading of current power factor due to the charging capacitors inside the TV). 50% power factor, I don't think so unless the appliance power factor correction circuitry is damaged (or missing).

http://en.wikipedia.org/wiki/Switched-mode_power_supply

Try measuring a working appliance with a switch mode power supply (such as a computer) to get a base line measurement between your ac current meter and your new plug-in power monitoring device.

GA

If the SMPS is NOT Power Factor corrected (most Chinese imports) then the meter may be smoothing out the current - possibly using a peak detector, to display it.

These current peaks should have an RMS rule applied. There are many incorrect ways to measure and calculate the current that would work fine on normal resistive loads and loads with PF near 1.

Hi NK,

Can you tell me the name of the item or the site or shop you bought it from?

Take care.

The device is made by Arlec- a quality maker of electrical goods in Oz- it is intended to allow the home user to calculate the cost of whatever appliance is plugged in. It is brand new. I also bought a brand new dmm with ac current after results noted - results exactly same. Ran a dryer on setup- 100 pf- amps agreed- yes tested on Teac (chinese made) set-also tested on Akai ctv(Samsung made) with series reg p/s same thing- except pf now 75%- but still device displaying amps about double of what really drawn according to dmm- so is consensus device is unreliable & should be ignored or returned for refund?.

How is the 'How to" page.

Please veiw and let me know what you think?

Plug-In Electricity Consumption Monitor
	Ideal to find the electricity consumption and running costs of: - Fridges and Freezers - Computers and all associated peripherals - Standby Costs of TV, DVD, computer, stereo, video, chargers etc - Washing Machines - Find the cost of your 30, 40, 60 degree wash - Dehumidifiers & Air Con units - Pond pumps, Swimming pool pumps (if they have a plug) - Televisions - CRT, LCD or Plasma - Anything that plugs into a wall socket ! Simply plug this monitor into the wall then plug the item into the monitor and you'll see exactly how much electricity it consumes. Once you have this figure it's easy to work out the running cost. Be prepared for some surprises! All the functions and how to use the monitor are described in detail below Our Price: £17.95 inc VAT (£19.95 inc UK Delivery)
What will this monitor tell you and how do you use it ? Take a closer look at the display Mode 1 - Volts Simply push the 'Volt' button to see the voltage of the supply. In the average house it will show around 240v, if you have 3 phase it'll show around 230v. Mode 2 - Amps Push the 'Amp' button to see the number of Amps being drawn. Handy to check what fuse rating a plug should have! Mode 3 - Watts Push the 'Watt' button and you'll see the number of watts currently being consumed. In this example 2438 watts are being used, a value you might see if you measured a kettle. A 60W light bulb would show around 60 watts. Use this mode to measure household items on standby. We found the following in our house: 13 watts - Sky+ on standby 9 watts - DVD Player on standby 9 watts - Lounge Stereo on standby 9 watts - Kitchen TV on standby 7 watts - VCR on standby 2 watts - Lounge TV on standby Also use this mode to measure the consumption of things such as: 196 watts - Complete Computer System - Flat out processing video footage 138 watts - Complete Computer System - Just Reading Emails 90 watts - Lounge TV 70 watts - Pond pump and filter 53 watts - Cold Air Fan set to 'Fast' 5 watts - TV Arial Booster 3 watts - Radio Alarm Clock 2 watts - Telephone Base Station 2 watts - Mobile Phone Charger 1 watt - iPod charger Mode 4 - Hz Push the 'Hz' button to see the frequency of your supply. A normal UK reading is around 50 Hz. Mode 5 - kWh (KiloWatt Hours) used Push the 'KWH' button and you'll see the number of kWh's consumed since the monitor was last reset. kWh is short for KiloWatt Hour and often abbreviated to just 'unit'. Your electricity bill will tell you your 'Cost per Unit'. In this example, 3.69 kWh's have been used since the monitor was last reset. For someone who pays 20p per unit, the cost of the electricity would be 20 x 3.69 = 74 pence. Typically you would use this mode for 2 types of test: 1) Calculate the cost for a particular task As an example, say you wanted to find out how much the electricity costs to do a 60 degree wash. Reset the monitor by switching it off and on. Push the KWH button and you'll see 0.00 showing. Plug the washing machine into the monitor and start the 60 degree wash. If you were to watch the kWh display you would see the 0.00 start ticking up slowly as the electricity gets consumed. Anytime after the wash has finished you can take a look at the monitor and you will see a value that will probably be around 0.5 kWh. This means you have used half a unit of electricity (half a kWh). You can look up the cost per unit on your electricity bill and work out the cost of the wash. e.g. half a unit at 20p per unit = 10p to do a 60 degrees wash. While the wash is running you can change mode to Watts, Amps or any other and the kWh counter will still keep counting correctly. 2) Calculate daily running costs of fridges / freezers etc Reset the monitor then plug in your fridge, freezer, dehumidifier, pond pump, electric blanket, air conditioner, computer, printer, monitor, television etc. Let it run for 24 hours then take the reading from the monitor. From the kWh's used reading it's easy to work out the running costs per day, week, month & year. Mode 6 - Hours When you are in the 'KWH' display, push the 'Hour' button and you'll see how many hours ago the monitor was last reset. Great if you forget what time of day you started a 24hr test. In this example, the monitor was reset 10 Hours 28 minutes ago. Mode 7 - PF Power Factor For advanced use. When you are in the 'Hz' display, push the 'PF' button you'll see the Power Factor. Read about Power Factor on the Wikipedia Mode 8 - VA For advanced use. When you are in the 'Watt' display, push the 'VA' button you'll see the Amps multiplied by the Voltage. VoltAmps are Amps x Voltage Watts are Amps x Voltage x Power Factor This monitor is included in some of our Electricity Monitor Packs. Our Price: £17.95 inc VAT (£19.95 inc UK Delivery) Why choose this monitor ? The first monitor we picked for this website had it's faults and we received complaints, so we set out to find the best plug-in electricity monitor on the market to replace it. We purchased 6 different makes, compared them all and chose this one because we think it's the best. Some monitors don't read below 10 watts and are useless for measuring standby costs. This monitor has the easiest to read display. Some monitors don't display 'Watts' correctly (they display VoltAmps and leave you to manually multiply their value by the Power Factor to give the real Watts reading!). This monior does all that for you. This monitor has buttons marked Volt, Amp, Watt, Hz & kWh (see picture below), each reading is just a single button push away. Other monitors have a 'Mode' button which cycles through the various readings and can get frustrating at times. Some monitors have the display below the plug so the wire gets in the way. Simplicity is the key. This is the easiest monitor to use, there isn't even any setup to do. When it arrives in the post just open the box and it's ready to use. This monitor doesn't have batteries so in a years time you won't find yourself searching around to find some LR44 button cells. This monitor was the most expensive of the 6 we tested but as we wanted the best model available we chose it. At the time of writing this, our price for this monitor is £10 cheaper than on our suppliers website. We know this monitor won't disappoint you. Our Price: £17.95 inc VAT (£19.95 inc UK Delivery) View all Electricity Monitors

Hi Neil,

I have a Kill-a-Watt (brand) unit that sounds similar to yours. It reads amps, watts, watt-hours, etc correctly. It is described as true RMS as most AC meters should be. A simple test would be to use the unit to measure a standard resistive load, such as a 100 watt light bulb. Here, where we use 120 VAC, I'd expect to see about .8 amps. I imagine you use 220 V or some such, but you can do the math. See which of your meters gives you the correct reading.

Actually, on rereading your post -- it sounds like maybe you have done the equivalent of that? when you say "results exactly same" do you mean that the two meters read the same under the same condition? Or do you mean that the results were the same as previous results, in other words, that one meter shows double the reading of the other?

If the readings are different on a steady state resistive load, then one or the other is incorrect. If the readings are the same on a resistive load but not on an inductive load, then one meter is faulty if they are both advertised as true RMS. With a switch mode power supply, the load the meter sees is not a sine wave, so perhaps inadequate sample rate will figure into the displayed readings?

But in any case, if they do not read the same on a resistive load, then one is definitely bad.

It seems i should have true rms meters both- well -I ain't!. Yes both describe accurately on resistive load ie dryer - it seems to me maker Arlec is putting onto the market a device not rms- but intended use is for consumers to test their consumer equipment for running cost etc- & consumer equipment could be res-ind- or comb. I will send Arlec email querying- cheers all.

Nowhere in my experience have i heard or read that ac amps are different- I have never heard of an rms ac current meter to differentiate between resistive inductive or comb- ac amps is ac amps!-eg- a moving iron meter will display ac or dc amps -or is this device a rms ammeter?. Certainly I know about voltage measurement & how a rms is needed to measure other than sine accurately. So if rms correction is needed- the formula is approx 10/7. This doesn't answer the power factor anomaly. It seems to me the Arlec meter is using algorithm to present what it sees is the cost incurred by a less than satisfactory pf.

Hi NK,

Just a small point...........

These Digital 'plug and display' meters, may not display 'rms' as that, in most cases, is not what the product in designed to do.

Must people would not know the meaning of 'rms' anyway. Which is why it is an 'idiot proof' plug and play? And of course no insult meant here, just me trying as best I can to describe what I mean! OK?

It certainly sounds like you know what to look for, but you are not using a moving coil type meter, so what you have, may not be as versatile as a moving coil meter?

Just one other point. It would be helpful if you could use a more descriptive vocabulary, IE:

You use "true rms meters both- well -I ain't!" .........................as the full explanation to a request.

A better description in a longer sentence, rather than details of the company and device, may be of more help to us? Just Just a thought.

Take care.

Hello NK,

If you will allow me to add my 5¢ worth here..............

I have read the 'specs' on some of these plug in Power Monitors and, they are no more than ± 2% on any measurement or type of use.

As I understand it, according to 'Ohms Law' anything connected permanently or temporarily by a plug to a circuit, will only draw and use the power it needs and no more.

Bearing this Law in mind, are you able to test it out on a 100W bulb as advised by 'Blink'? Or perhaps try it in a friend's home and see the results. As I say above, according to Ohms Law if a 2Kw Kettle is connected, it will draw (or use if you like) 2Kw of power for as long as it is connected. So saying your sockets are said to be using about ~twice the equivalent power of any single item, hardly makes sense.

It could make sense (perhaps), if your home was wired incorrectly, with a huge earth or (Ground) connection and loss that way, or, if your home was maybe connected to your neighbour's by your electrical supply............. But then Ohms Law would still apply!

Now this may sound stupid, but are you getting mixed up and measuring Watts rather the Kilowatts perhaps? Or getting mW confused with Watts? I am just trying to understand the reasons why you have the measurements you do, that's all.

Has anyone you know got a similar power tester, or do you have the type of power tester that has two separate nodes or prongs? If so use this and it should give correct measurements. The advantage of using an Ohmmeter with an Analogue needle scale, is you can see if the measurement varies over time, pulses etc.

Do you have any 'spare wire or 'tails' which could be sending power anywhere else?

Take care and please keep in touch. But you have to do the checks as listed by others and me above and check you are reading it correctly.

Red face time- I honestly had never realised that a true rms ammeter is needed to measure ac current where other than a sinewave is involved. I plugged in my true rms dmm on ac current & reading agreed with the Arlec device- so I have learnt something at least- on reflection it makes sense of course- & the Arlec device is going to be a worthy addition to my test gear- a true rms device & far cheaper than a true rms dmm!. I would like to thank respondents who led me collectively to my own iggerance!.

Hi NK,

A nicely written post my friend.

This site is so diverse I think most Members learn something, it is kind of the premise of the site?

Take care.