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Home > Archive > Electrical Engineering > July 2006 > The Kill A Watt meter is such an amazing instrument
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The Kill A Watt meter is such an amazing instrument
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| itsme.ultimate@gmail.com 2006-07-23, 9:25 am |
| I have a Kill A Watt AC power meter and this thing is such an amazing
instrument for the price.
Picture a load like this:
http://img305.imageshack.us/img305/...pboard02uk0.png
>From left to right,
a motor, a TV and a floor lamp using a half wave rectifier to dim. I
was surprised that the Kill A Watt was able to correctly measure a
combination of load like this that present difficulty even for a true
RMS meter. The motor draws a current with cos phi shift, the TV with
harmonics and the half wave rectified floor lamp pulls a DC bias.
Standard AC true RMS meter will not accurately measure this, because it
ignores the DC contents introduced by the half wave rectifier load. To
accurately measure a load like this, you have to measure the true RMS
AC current, then the DC current and calculate the total RMS(total RMS
amp= DC equivalent ampere to make the wiring heat up the same) current
by sqrt (ACA^2 + DCA ^2) or use a meter with "AC + DC true RMS"
capability. The total RMS "AC + DC RMS" is only found on very high
end multimeters and is can only be found on hall-effect type clamp
meter (the current transformer type transduce the DC content). My Kill
A Watt appears to take the total RMS into account and reads within in a
few percents of AC + DC RMS reading on a Fluke 189(which can't even
measure power, yet cost about ten times as much as this gadget)
Now, to be a power meter, it has to be able to measure power. The
custom DSP combines the voltage and current to calculate the true
power and gives a direct reading of watts and power factor.
Although the accuracy is likely not as good as an analog
integrator/multipler type power analyzer that cost a grand or two and I
don't know this gadget's sampling rate or bandwidth but the functions
are more or less identical.
Anyways, I find it amazing how they can build an instrument with this
level of functionality for thirty dollars using a custom DSP.
| |
| Salmon Egg 2006-07-23, 1:25 pm |
| On 7/23/06 6:20 AM, in article
1153660824.549100.86840@b28g2000cwb.googlegroups.com,
"itsme.ultimate@gmail.com" <itsme.ultimate@gmail.com> wrote:
> I have a Kill A Watt AC power meter and this thing is such an amazing
> instrument for the price.
>
> Picture a load like this:
> http://img305.imageshack.us/img305/...pboard02uk0.png
>
> a motor, a TV and a floor lamp using a half wave rectifier to dim. I
> was surprised that the Kill A Watt was able to correctly measure a
> combination of load like this that present difficulty even for a true
> RMS meter. The motor draws a current with cos phi shift, the TV with
> harmonics and the half wave rectified floor lamp pulls a DC bias.
>
> Standard AC true RMS meter will not accurately measure this, because it
> ignores the DC contents introduced by the half wave rectifier load. To
> accurately measure a load like this, you have to measure the true RMS
> AC current, then the DC current and calculate the total RMS(total RMS
> amp= DC equivalent ampere to make the wiring heat up the same) current
> by sqrt (ACA^2 + DCA ^2) or use a meter with "AC + DC true RMS"
> capability. The total RMS "AC + DC RMS" is only found on very high
> end multimeters and is can only be found on hall-effect type clamp
> meter (the current transformer type transduce the DC content). My Kill
> A Watt appears to take the total RMS into account and reads within in a
> few percents of AC + DC RMS reading on a Fluke 189(which can't even
> measure power, yet cost about ten times as much as this gadget)
>
> Now, to be a power meter, it has to be able to measure power. The
> custom DSP combines the voltage and current to calculate the true
> power and gives a direct reading of watts and power factor.
>
> Although the accuracy is likely not as good as an analog
> integrator/multipler type power analyzer that cost a grand or two and I
> don't know this gadget's sampling rate or bandwidth but the functions
> are more or less identical.
>
> Anyways, I find it amazing how they can build an instrument with this
> level of functionality for thirty dollars using a custom DSP.
>
It is not amazing at all. The kind of KWHR meter used by electric companies
is excellent for measuring true power. It really multiplies power and
current and then integrates that. The theoretical basis is that individual
harmonic currents contribute power only when driven by that harmonic's
voltage. Transformers cannot provide a zero-frequency voltage to drive a
zero frequency current. These meters are now available as surplus for 5 or
10 dollars.
Please give a better description of your Kill A Watt meter.
Bill
-- Ferme le Bush
| |
| operator jay 2006-07-23, 5:25 pm |
|
"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C0E900B5.34502%salmonegg@sbcglobal.net...
> On 7/23/06 6:20 AM, in article
> 1153660824.549100.86840@b28g2000cwb.googlegroups.com,
> "itsme.ultimate@gmail.com" <itsme.ultimate@gmail.com> wrote:
>
>
> It is not amazing at all. The kind of KWHR meter used by electric
companies
> is excellent for measuring true power. It really multiplies power and
> current and then integrates that. The theoretical basis is that individual
> harmonic currents contribute power only when driven by that harmonic's
> voltage. Transformers cannot provide a zero-frequency voltage to drive a
> zero frequency current. These meters are now available as surplus for 5 or
> 10 dollars.
>
> Please give a better description of your Kill A Watt meter.
>
> Bill
> -- Ferme le Bush
>
>
It multiplies _what_ and current?
| |
| Salmon Egg 2006-07-24, 3:25 am |
| On 7/23/06 11:41 AM, in article SpPwg.81323$nJ2.33302@newsfe15.lga,
"operator jay" <none@none.none> wrote:
>
> It multiplies _what_ and current?
You caught me red handed. That should have read:
[color=darkred]
-- Ferme le Bush
| |
| itsme.ultimate@gmail.com 2006-07-24, 3:25 am |
| Salmon Egg wrote:
> It is not amazing at all. The kind of KWHR meter used by electric companies
> is excellent for measuring true power. It really multiplies power and
> current and then integrates that. The theoretical basis is that individual
> harmonic currents contribute power only when driven by that harmonic's
> voltage. Transformers cannot provide a zero-frequency voltage to drive a
> zero frequency current. These meters are now available as surplus for 5 or
> 10 dollars.
SURPLUS. You obviously can't compare surplus to a new item. Maybe
it's available where you are but not available everywhere.
Does the meter you say support direct read out of V, A, watt, PF rather
than just cumulative kWh? Revenue grade electric meters are not cheap
brand new.
> Please give a better description of your Kill A Watt meter.
http://www.p3international.com/prod...0/P4400-CE.html
| |
| Salmon Egg 2006-07-24, 9:25 am |
| On 7/23/06 10:14 PM, in article
1153718083.478820.132690@b28g2000cwb.googlegroups.com,
"itsme.ultimate@gmail.com" <itsme.ultimate@gmail.com> wrote:
> SURPLUS. You obviously can't compare surplus to a new item. Maybe
> it's available where you are but not available everywhere.
>
> Does the meter you say support direct read out of V, A, watt, PF rather
> than just cumulative kWh? Revenue grade electric meters are not cheap
> brand new.
These are KWHR meters. They have been replaced by meters with more
electronics--probably for remote sensing. They will handle harmonics and
power factor just fine.
They are available at swap meets. In particular, try the TRW (now Northrup
Grumman) in Redondo Beach.
Bill
-- Ferme le Bush
| |
|
| I was kind of trying to get a ballpark figure to get a UPS for my two
computers. I hit a page today that showed me my first look of the Kill
A Watt meter. It looks pretty slick. The page is not selling the
device and it also has a 0$ solution to finding the output of a single
device. It is not rocket surgery but it does seem engenius. I am an
electrician and this never occurred to me.
If I had to do many I would go for the 40$ solution but the 0$ option
is pretty slick IMO.
http://michaelbluejay.com/electricity/measure.html
itsme.ultimate@gmail.com wrote:
> I have a Kill A Watt AC power meter and this thing is such an amazing
> instrument for the price.
>
> Picture a load like this:
> http://img305.imageshack.us/img305/...pboard02uk0.png
>
> a motor, a TV and a floor lamp using a half wave rectifier to dim. I
> was surprised that the Kill A Watt was able to correctly measure a
> combination of load like this that present difficulty even for a true
> RMS meter. The motor draws a current with cos phi shift, the TV with
> harmonics and the half wave rectified floor lamp pulls a DC bias.
>
> Standard AC true RMS meter will not accurately measure this, because it
> ignores the DC contents introduced by the half wave rectifier load. To
> accurately measure a load like this, you have to measure the true RMS
> AC current, then the DC current and calculate the total RMS(total RMS
> amp= DC equivalent ampere to make the wiring heat up the same) current
> by sqrt (ACA^2 + DCA ^2) or use a meter with "AC + DC true RMS"
> capability. The total RMS "AC + DC RMS" is only found on very high
> end multimeters and is can only be found on hall-effect type clamp
> meter (the current transformer type transduce the DC content). My Kill
> A Watt appears to take the total RMS into account and reads within in a
> few percents of AC + DC RMS reading on a Fluke 189(which can't even
> measure power, yet cost about ten times as much as this gadget)
>
> Now, to be a power meter, it has to be able to measure power. The
> custom DSP combines the voltage and current to calculate the true
> power and gives a direct reading of watts and power factor.
>
> Although the accuracy is likely not as good as an analog
> integrator/multipler type power analyzer that cost a grand or two and I
> don't know this gadget's sampling rate or bandwidth but the functions
> are more or less identical.
>
> Anyways, I find it amazing how they can build an instrument with this
> level of functionality for thirty dollars using a custom DSP.
| |
| TimPerry 2006-07-26, 3:25 am |
| Salmon Egg wrote:
> On 7/23/06 11:41 AM, in article SpPwg.81323$nJ2.33302@newsfe15.lga,
> "operator jay" <none@none.none> wrote:
>
>
> You caught me red handed. That should have read:
>
>
>
> -- Ferme le Bush
i have one (a kill-o-watt). it would be more amazing (and useful to me) if
it were rated higher then 15 amps. 25 or 30 would be much nicer.
| |
| Salmon Egg 2006-07-26, 3:25 am |
| On 7/25/06 8:18 PM, in article
SLSdnUNe8ra-QlvZnZ2dnUVZ_vadnZ2d@adelphia.com, "TimPerry"
<timperry@noaspamadelphia.net> wrote:
> i have one (a kill-o-watt). it would be more amazing (and useful to me) if
> it were rated higher then 15 amps. 25 or 30 would be much nicer.
I have an old fashioned (circa 1950) wattmeter for 240/120V and a current
transformer bought at the TRW swapmeet. I was going to make up a breadboard
for measuring power consumption of various devices, but never got around to
it.
Bill
-- Ferme le Bush
| |
| John Gilmer 2006-07-28, 5:25 pm |
|
"TimPerry" <timperry@noaspamadelphia.net> wrote in message
news:SLSdnUNe8ra-QlvZnZ2dnUVZ_vadnZ2d@adelphia.com...
> Salmon Egg wrote:
>
> i have one (a kill-o-watt). it would be more amazing (and useful to me) if
> it were rated higher then 15 amps. 25 or 30 would be much nicer.
They don't cost much. Perhaps you can open one up and:
1) Put larger conductors in the main current carrying path.
2) If needed, cut the sensitivity of the current sensing circuit in half.
If there is a "core" with several turns, remove half of the turns. If
there is but a single turn maybe you can rewind the other half of the
"current transformer."
OR (getting tricky):
Get two IDENTICAL units and wire them in parallel.
>
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