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 Post subject: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Fri Nov 13, 2009 12:13 pm 
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Found an AC 220V alternativeto North-American Kill-a-Watt on e-bay. It's a reworked original Kill-a-Watt actually. With the UK BS1363 socket :) Need to mount a Schuko one there, if you live in Germany e.g.

Image

Any thoughts? There are not so many good power meters with 220V input.

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PostPosted: Fri Nov 13, 2009 3:42 pm 
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I just got something by random from a local store. What's the difference?

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PostPosted: Sat Nov 14, 2009 5:33 am 
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lm wrote:
I just got something by random from a local store. What's the difference?

It depends on the model, and can be not so accurate with readings when it comes to real use. Look here for some links. Also useful information is left here, at electrodacus thread.

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PostPosted: Sun Jan 31, 2010 8:08 am 
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I picked up a load of meters from Wilkinson for £2.00 each. They do not seem to be amazingly accurate but are within about 10% of what I would expect, some within 5%.

I posted in the thread Ksanderash linked to. I am going to open some of them up and look for ways to make them more accurate.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Sun Jan 31, 2010 9:36 am 
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Ksanderash wrote:
Image

I have one of these units. They are available in the UK from Maplin and I got mine on a special offer at £12.49.

Not sure on accuracy but the readings don't show much fluctuation with variation normally being 1W over time on the same load. It works well and has a kWh function which counts use over time. I've not used this function on a computer but it's been useful before on domestic applicances for counting cost over time and making a case for replacement based upon energy saving.

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PostPosted: Sun Jan 31, 2010 10:04 am 
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i got one of them from maplin for £12 also, dont know about the accuracy, but it seems to output what was expected when i have checked :)

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Wed Jan 26, 2011 3:39 am 
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After a year :shock: I finally got mine :D

Has arrived for £15 from Amazon, and it can be found also on Ebay. It is completely the same device, from Maplin (hm, their server doesn't respond...) Had to pay some extra money to transfer purchase to Eastern Europe, but the device deserve the pay. Nothern American Kill-a-Watt (and this adapted euro-clone) is still the best power meter on mass market!

What is inside:

Image

And some pics on how I made it Schuko compliant, lol :lol: It's just a little dumb box now, with some hanged wires

Image

Image

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Wed Jan 26, 2011 9:48 am 
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Anyone in the UK should check Robert Dyas shops. They have them for £5 in the clearance section at the moment.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Jan 27, 2011 9:09 am 
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Sometimes you can't plug this thing into overpopulated socket set, or can't rich its buttons, or see screen readings, so I desided to attach a power cord to it. And a socket on cord for the output too, cause I couldn't find a small Schuko socket to integrate it into the case.

Image

...

MoJo wrote:
Anyone in the UK should check Robert Dyas shops. They have them for £5 in the clearance section at the moment.

Lucky you! :D

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Jan 27, 2011 9:29 am 
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Why is it that the UK versions need batteries? The Japanese and US versions are powered from the mains which seems obvious. It must have something to do with safety.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Jan 27, 2011 12:12 pm 
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MoJo wrote:
Why is it that the UK versions need batteries? The Japanese and US versions are powered from the mains which seems obvious. It must have something to do with safety.

Batteries? I did hear nothing about this. But there is a lot of room inside, as you can see. They could make much smaller device, but didn't, maybe because the battery supplying option.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Fri Jan 28, 2011 2:35 pm 
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Quote:
Anyone in the UK should check Robert Dyas shops. They have them for £5 in the clearance section at the moment.


MoJo, I couldn't find this on Robert Dyas online, is this clearance offer just in-store?

cheers :)


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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Sat Jan 29, 2011 4:27 am 
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In store only I think. It depends on the store too, some have them for £6 and some for £5. The Southampton store has then for £5 on the basement floor.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 1:59 am 
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An article describing how to recalibrate the meter to measure small quantities of current, e.g. ten times lower. The meter's maximum admissable load rate decreases proportionally, but that's still bearable issue.

It's Brennenstuhl' PM230 on the photo, but Kill-a-Watt has the similar element (current sense bridge)
Image

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 3:49 am 
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What is the upper current capacity of the 220-240v meter? The appearance of electric cars may make these meters much more common.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 4:33 am 
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I have an NZR Standby-Energy-Monitor SEM 16+ which was pretty expensive (559 SEK = ~87$) and the specifications says 16A. I recommend this meter btw, it's very accurate on low loads. It is expensive though..

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 4:54 am 
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PM230 should be avoided, apparently. A normal meter measures starting at 1W (albeit with quite an error). Max 3680W (16A).
MoJo wrote:
...batteries?

Only for moments when the meter is not plugged in. For clock, settings (like kWh price), results.


Last edited by Klusu on Wed Mar 16, 2011 1:45 pm, edited 1 time in total.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 5:01 am 
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NeilBlanchard
It is limited by socket rating, i.e. 16A

Sense module of Kill-A-Watt EZ (pretty much alike with Maplin device):
Image

Klusu
Yep. For those who count up kW/h and economizes with the help of power meter.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 10:14 am 
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Klusu wrote:
PM230 should be avoided, apparently. A normal meter measures below 1W. Max 3680W (16A).
MoJo wrote:
...batteries?

Only for moments when the meter is not plugged in. For clock, settings (like kWh price), results.


No, they need them all the time to work. Without the batteries you get nothing at all on the display.

Image

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 12:55 pm 
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Strange. It must have something to do with cheapest possible.


Last edited by Klusu on Thu Feb 03, 2011 2:38 am, edited 1 time in total.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 01, 2011 1:53 pm 
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Thanks MoJo, presumably the pic is from Robert Dyas...

And I wonder how you decide to choose from the identical £6 or £5 one... :roll:


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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Wed Feb 02, 2011 12:46 am 
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leem wrote:
I wonder how you decide to choose from the identical £6 or £5 one... :roll:

...and what is inside. Is it Kill-A-Watt clone or not?

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Wed Feb 02, 2011 10:27 am 
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I don't know what is inside, I bought about ten for £1.80 each from Wilkinsons years back so never needed any more. The ones I have use fairly a standard power resistor and op-amp circuit, easy enough to interface.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Feb 03, 2011 6:18 am 
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There must be a specialized integrated circuit, not just op amps.
Here is my meter EL-EPM02HQ (a good one):
ImageImage


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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Mon Feb 14, 2011 2:20 pm 
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Ah, Maplin UK advertizes the original Prodigit device (manufacturer of P4400) -- I have just stumble upon Kill-A-Watt page at Wikipedia :)

Klusu
It seems that IC is ADE7755 over there on your photo. Nice one. Prodigit uses only PIC+OpAmp.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 15, 2011 10:16 am 
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Klusu wrote:
There must be a specialized integrated circuit, not just op amps.
Here is my meter EL-EPM02HQ (a good one):
ImageImage


It was a while ago when I opened it but basically there was an op-amp which did both current and voltage measurement outputs going into a chip-on-pcb blob which runs the display. I stuck a multimeter and then an oscilloscope on the op-amp and could take accurate measurements from it. Well, I say accurate, within 5% I think. I intend to hook an AVR up to the op-amp and let the PC monitor its own power usage, and will probably replace the resistor with one more suited to accurate measurement of <100W devices... Or maybe I should just do the whole thing from scratch.

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Tue Feb 15, 2011 2:21 pm 
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ADE pin No 2 is interesting. "The HPF should be enabled in power metering applications." Then some loads (like a simple half-wave regulator for a soldering iron) may be measured wrong.


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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Feb 17, 2011 4:22 pm 
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ADE7755 IC is also being used in no-name Chinese meters like this:

EU Advanced WATT Power Energy Voltage Meter Monitor. Inside:
Image

And this. Inside:
Image

I'm having some problems with PayPal (Republic of Moldova is out of service) so can't realy touch these devices :cry:

The PCB of Prodigit device (sorry for the quality, there is Atmel + op amp + LCD driver):
Image

Again my Prodigit with Schneider Schuko plug socket integrated:
Image Image

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Sat Feb 19, 2011 12:54 pm 
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Interesting! The ADE7755 outputs a square wave with frequency proportional to power consumption. Do the meters also show line voltage? In that case there must be other hardware measuring that.

In mine they used a dual op-amp. One to measures voltage by scaling approx ±600v to 0-5v, for more precisely 0-300v to 0-5v with the assumption that the negative part of the sine wave has the same amplitude at the positive part. The negative part is clamped. I bet that the input to the op-amp isn't full voltage though, more likely the output of a potential divider. I didn't check at the time.

The other one to measures current by scaling the voltage drop over the current sense resistor by some large factor I forgot. Frequency probably just uses a low logic level detector on the voltage output.

The ADE7755 provides some output isolation which is quite useful here. I bet the op-amp based ones have a high return rate.

At the moment I am trying to get a cheap analogue 'scope off eBay to do some mains work with. I don't want to risk my expensive digital one. In the UK the voltage is very stable, rarely deviating from 230V, so I may not bother measuring voltage at all. If you just assume that it is 230V RMS and a perfect sine wave (which over time it will be) then you only need to measure current and can use a hall effect sensor. I am thinking about doing a clock which uses mains frequency to keep time too because over a few hours it is extremely precise. Atmel have an app note where they connect an AVR pin to the mains via a 1M resistor and rely on the clamping diodes on the pin! It works but if how much do you trust that 1p resistor not to fail and pump 230v into your low voltage circuit?

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 Post subject: Re: 220V alternative to Kill-a-Watt Power Energy Meter
PostPosted: Thu Feb 24, 2011 6:45 am 
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MoJo
Can't put my hands on ADE7755 yet.

...

Oh, a banal idea came into my mind! Concerning under 1-1,5W load measure.

It seems that lower operating limit of such devices can be extended simply by adding a known extra load (small, 2-5W), by connect a 10 kOhm resistor e.g., and it will result in 2W positive offset to meter readings :P

Right?

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