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Posted by Johnny B Good on July 1, 2008, 10:37 am
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> On Tue, 1 Jul 2008 02:51:50 +0100, Johnny B Good
> >
> >> I would like to know how much my various appliances are consuming.
> >> Where can I get a device (for the UK) that will measure the energy
> >> consumed by individual devices?
> >
> >> I have looked at things like "Brennstuhl Wattage and current meter
> >> PM 230" and the "Kill-A-Watt", but they look rather cheap, and I'm
> >> not convinced they will accurately measure loads with unusual
> >> waveforms (my computer for one thing).
> >
> >> Any better suggestions?
> >
> >> Tom
> >
> > You're quite right to be suspicious of such meters (that's not to say
> >such digital technology can't provide accurate fractional wattage
> >readiings with extremely distorted waveforms, I'm just saying such
> >accuracy can't be done on the cheap).
> Actually, such accuracy CAN be done on the cheap and the Kill-A-Watt does it
> quite nicely.
> I own several (originally 10, minus whatever have been lost here and there).
> At one time had 10 of 'em hooked in a series daisychain along with a
> GE analog
> "1/4% accuracy class" lab wattmeter and a NIST traceable GE watt-hour
> transfer
> standard meter.
> All 10 instrument read within a digit of one another and they all
> agreed with
> the traceable instruments to within my ability to read them. The
> first meter
> in the chain did read 1 watt higher which accounted for the burden of the
> other 9 plus the losses in the short cords connecting them together.
> It is pretty evident from looking at the internal construction that each
> device is flashed with its own calibration factors during manufacture. That
> means that the current shunt and voltage divider resistors don't have to be
> accurate, just stable. That they are.
That's interesting. Did any of your test loads include the 1 to 15 watt
range? What sort of test loads did you test with (less than unity PF or
narrow conduction angle loadings and so on)?
> OTOH, the very much higher priced Watts Up instrument is garbage once the
> power factor drops much below unity. Price is no indication of quality with
> such instruments.
That's true (FSVO).
> No experience with that Brennstuhl Wattage instrument so I'll not comment.
Same here, but I have to confess that the 20 dollar Kill-A-Watt meter
sounds like the yank equivilent to the £9.99 plug in digital watt meters
available over here in the UK (and Europe since the stores involved are
Aldi, Lidl and Netto), so I rather assumed they'd suffer the same
shortcomings with sub 40 watt loads noted by most owners of such
devices.
The one such meter I have is a DEM1379 and it can be totally misleading
with 11 watt loads and less. Since it can't display fractions of a watt,
it's totally unsuitable for checking the standby power of most wall
warts, particularly the smpsu based designs where it can be as low as
200mW.
--
Regards, John.
Please remove the "ohggcyht" before replying.
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