Electicity monitor (N Power)

[DerbyBorn]

I have a monitor that I had from N Power about 4 years ago, Never really used it until now. Last night I was trying to get my residual consumption to zero but didn't want to turn off any circuits due to the odd timer that would need resetting. I was unable to get it below 130 watts - which seems a bit high for the alarm clock, microwave and a couple of phone base units.

I need to repeat the exercise, but I wondered if these things perhaps get unreliable at the lower end of the readings due to induction or something. It has a detector clamped around the incoming live lead to the meter.

[philipuk]

Count the meter light flashes/rotations over a period of time. That will give you a definitive answer.

Philip

[Bob Minchin]

Those simple monitors cannot make allowance for power factor and so can only read correctly on pure resistive loads. None of the things you mention are that sort of load. You need a proper RMS power meter to get any sensible readings

[cl]

It would be simpler to watch how fast the meter was counting, they nearly always have a fraction of kwh digit which you can see changing even at quite low consumption levels.

I really don't understand what extra information a (fairly crude) power meter adds.

[Brian Gaff]

And besides, the items together could well be that high when taken together. I've had chordless phones that use half of that, rather inefficient if you ask me. Brian

[Andy Burns]

Bet that kept your lugholes warm!

[harryagain]

Any device that takes account of Power Factor must also measure the voltage as well as current. Ergo, no simple clip on device can be accurate. Even at unity power factor because the voltage is not constant, that is another inaccuracy. (It's only measuring the current, voltage is assumed.) RMS has nothing to do with it.

[dennis]

You don't have to stand next to the meter.

If you have a smart meter the displays can be accurate even with odd power factors.

[Dave Liquorice]

At low levels to get a reliable reading takes quite a while.

One of our meters is 1000 flash/kWhr or so at 1 kW that's 1 flash every (60 * 60)/1000 seconds = 3.6 seconds. At 100 W that's a flash every

36 seconds. It'll take a good five minutes of meter watching to get a reliable reading.

They maybe crude but ours matches the meter readings fairly well, I have taken a bit of trouble to get the current transformer carefully installed around the live tails though. I certainly don't trust the low end measuring but overall it's not bad.

The instantaneous reading is handy and if the data is logged and plotted can show how much energy could be considered wasted from some appliances. Like the "keep warm" feature of a kettle or how much the coffee machine hotplate is taking.

[DerbyBorn]

"Dave Liquorice" wrote in news: [e-mail]:

What can you recommend about placing the thing on the meter tail?

[Dave Liquorice]

May well vary from clamp to clamp. I find that with the (large) CurrentCost clamp the most consistent (I hesitate to use the word "accurate") readings are with the tail passing cleanly through at 90 deg to the clamp with a couple of straight inches of tail either side. The tail being close to the hinge of the clamp. But the most important thing is to make sure they are fixed relative to each other, any movement or change of position will affect the reading. Don't just clip it round the tail and let it dangle and be free to move.