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Wall Plug watts/current measure

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bowlesj

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Hi, is there something I can buy to plug into a house wall socket which will measure the watts and/or current being drawn by a fair bit of equipment using that one plug. So far I just try it and everything seems okay so I assume I won't have a problem.

Thanks, John
 

Hi,

Yes, some-one showed me a plug with an LCD screen that at least measures the watts a device is consuming, as they had to hunt down something using a lot of electricity in their home. I don't know the brand, but there is something you can plug into a house wall socket. Maybe try searching for "power consumption monitoring for home use"

Online shop, one of first links found: Plug-In Power and Energy Monitor

Whether these devices are truly accurate would be for a "break-down" type video/article to ascertain, I assume they are, the neighbours, which was inexpensive, seemed fairly accurate.
 


Thanks guys. Sounds good. I just put it into my todo list. I just checked and 73 have viewed this thread within a few hours so it seems your answers will help a lot of people. John
 

My electrical utility company (the government) wanted to avoid expanding the grid so they gave away solar garden lights, compact fluorescent light bulbs, LED Christmas tree lights and 2 weeks free borrowing of a power meter available from libraries.
 

Its well worth doing.

I more than HALVED my overall power consumption by replacing a few lurking energy vampires that I never suspected.

Biggest energy suckers were my ancient refrigerator and CRT computer monitor.
Some real surprises were mains powered wall clocks, now replaced with battery wall clocks. LED lights everywhere followed, plus a few other minor things.

One interesting thing was my garage door opener. There was this huge 24v transformer for the motor that ran constantly with no load, but it still drew a continuous 80mA (19 watts = 0.46 Kwh per day).
What I did was fit a dc wall pack to power just the radio receiver only. When I wanted to operate the door, a relay in the primary of the big transformer supplied power to the rest of the circuit.
No load standby power went from 80mA down to 7mA.

The cost of an (almost new) refrigerator, and LCD monitor and LED lights and everything else will be repaid in about two years of electricity savings.

Anyhow its all jolly good fun, and rather an interesting challenge.
 

Hi,

One interesting thing was my garage door opener. There was this huge 24v transformer for the motor that ran constantly with no load, but it still drew a continuous 80mA (19 watts = 0.46 Kwh per day).
Click to expand...

There are some good energy meters, and there are many energy meters that are quite useless.

Here we have the example with the transformer. 80mA of no load current will never give 19W. It gives 19VA.
Energy meters (from the electrical company...and at least in Europe) don't count Amperes and they don't count VA.
They count energy, which is Watts x time.

A no load transformer has low cos(phi), so with 80mA (19VA) it has maybe only 3W of real power.

Back to the energy meters:
Good ones will take power factor into account.
Power factor depends on cos(phi) and current waveform (and voltage waveform, which typically is fairly good sine waveform)

You can make a simple test:
Use a 1.5uF capacitor.
(Mind that it should be AC rated and rated to withstand mains voltage. SAFETY: Mind to discharge it with a resistor immediately after use)
With 230V and 50Hz it should draw about 108mA.
Your meter should show 108mA, 24.8VA, cos(phi) near zero, Watt near zero (maybe 1W of internal capacitor loss and measurement error).
The energy meter must not increase kWh.

Klaus
 

The energy meter I have measures volts and amps and (real resistive watts) not Va, and also power factor. If you want Va's you have to do the multiplication yourself.

I was using it to reduce the power to the heating element in my tumble dryer which was a bit much for my prototype 2Kw inverter, when there are other loads running as well. When my big inverter is completed I will put it back to original.

My energy meter said the original element power was 2Kw which was about right as it was indicating just over 8 amps at roughly 240 volts.

By placing a bunch of capacitors which added up to around 110uF in series with the heating element, I reduced the heater power to roughly an indicated 1Kw, at from memory about an 0.8 power factor. The current measured as five amps. All these figures are from memory, but this inexpensive power meter has turned out to be a rather neat thing to have.

Another nice feature, is a peak hold for maximum and peak minimum measured current.
Its great for recording inrush currents into refrigerators, air conditioners, or washing machines.
Vital information for not smoking an underpowered inverter.
 

Hi,

the new values make sense.
* 8A (ohmic) @ 240V makes 1.92kW and 30 Ohms
* 110uF @ 50Hz make 28.9 Ohms (cpacitive)
* both in series make 41.6 Ohms (complex)
* creating a current of 5.76A (complex)
* 5.76A at 30 Ohms generate 996W real power

Klaus
 

Yes I did all this only about three weeks ago, so its all reasonably fresh in my memory.
I did write it all down, but once it was working I trashed the sheet of paper.
So I can only remember rough rounded numbers not precise numbers.
It has turned out to be a good solution to the problem.
Other initial ideas were fitting a diode, or phase control, but my inverter might not have liked either.

The garage door opener project goes back about three years, and I still have the sheet of paper, but cannot now remember if the 80mA was just measured current, it probably was. In which case you are quite correct about it being 19Va (not 19 watts). That transformer still ran pretty darned hot with no load which is not a good sign.

I went around the entire house and measured everything just as an ac current draw.
I probably should have measured true watts, but I achieved what I set out to do in vastly reducing my daily power consumption.

It was all a prelude to eventually going solar as a retirement project, which is very slowly coming.
 

Hi,

You talk about an inverter.

It surely is possible that it limits on VA (current) than on Watts.

Klaus
 

Not this one.
Its bi directional, can feed reactive power back into the dc bus so its very happy with low power factors.
Remember your idea a while back about a multi stepped inverter ?
Its one of those. And its proved itself to be pretty tough little beast.

It has survived things that would have easily killed a PWM inverter.
 

Hi,

too bad that I was too late with my idea with the multi stepped inverter.

***
To OP:

If you need more detailed (in time, in voltage, in current) information about your load then..

I´ve just finished to develop a high precision and very fast metering USB device.
It measures up to 400V AC RMS with a precision of about +/- 5mV. Precise up to the 30th overtone. And this every 20ms. (could be even faster, with sliding window, optionally)
RMS current, DC current, RMS voltage, DC voltage, true power. Very low output signal ripple.
It is used for precision load measurements, mains voltage research, as reference meter or to be used in voltage regulation loops.

For example: It can measure inrush current of transformers and the resulting DC component during the first full waves.
It can measure the dirt thats been caused by coffee machines or printers - even in shutdown...Very interesting.

But not a cheap one...

Klaus
 

There is still a place for low cost relatively accurate instruments that can be very useful in a practical way.

Sometimes only the very best laboratory grade test instruments will do, but for home use, just being able to measure things at all is a huge advantage.
 

Warpspeed said:
Sometimes only the very best laboratory grade test instruments will do, but for home use, just being able to measure things at all is a huge advantage.
Click to expand...

I am sure you will recall the old household watt-hour meters.

It had a wheel (loaded by a magnet) and one voltage coil and one current coil. The rotation of the wheel (5000-10000 rotations== 1Watt-hour) was shown on a mechanical counter.

This lousy device ruled the market for more than 7-8 decades. Modern meters are particularly cheap and accurate. I still do not know how much my desktop and the fridge are consuming.
 

Its a funny thing, but many household appliances draw huge power but only for a minute or two each usage, such as microwave ovens and electric kettles, the total power consumed over 24 hours may not be as much as you might expect.

Something fairly innocuous that draws only a very few watts but continuously day and night might really surprise you. Its the small stuff that runs all the time where you can usually make the biggest energy reductions.
 

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