[conspire] check out AC power (Watt)meter (What's Your Watt?/...) from library

[Tony Godshall]

I certainly concur that the display does not have much resolution and
thus cannot properly measure the instantaneous power use of cell phone
chargers, led lights, etc.  It's also a poor measure of average
electric use of a refrigerator, a heater, anything with a thermostat,
anything that turns on and off.  And that includes a computer, which
can turn fan on and off, hard drive on and off, cpu clock up and down,
even shut down and fire up cpus as load requires.

However I've been able to get values that seemed credible to me by
measuring the total kwh over enough time, and then dividing by the
number of hours, both figures being readily available from the
kill-a-wat, which costs, IIRC, $20 or so at Fry's.  Don't spend the
extra money on the "easier to use" model- it's pointlessly dumbed
down.

At that price, it's good thing to have around.

Turns out that fancy German fridge with the dual variable speed
compressors will pay for itself.  Eventually.  Mostly what we like
about it is that it is counter depth and narrow and tall.  And has no
ice-maker to break.


On Wed, Mar 18, 2015 at 10:11 AM, Ross Bernheim <rossbernheim at gmail.com> wrote:
>
> One thing to remember about the Kill A Watt and similar consumer power/watt meters
> is that they are meant for lights and appliances and while they will easily measure
> a refrigerator or 100W light bulb, they are not accurate at low power levels.
>
> The accuracy at low levels, typically below seven watts is not terribly useful. As
> we move to LED light bulbs that only draw a few watts and very low power
> computers with solid state drives these meters may give inaccurate results.
>
> One suggestion is to use a multi-outlet power strip and pair the device you want
> to check with another device such as a light bulb that is a constant load above
> ten watts so that you can accurately measure it then add the load you want to
> test and measure the increased load accurately.
>
> All test equipment has limitations and you need to know what they are so
> you can assure the accuracy of your measurements.
>
> Ross
>
>
>
>
>> On Mar 18, 2015, at 3:44 AM, Nick Moffitt <nick at zork.net> wrote:
>>
>> Michael Paoli:
>>> One can check out AC power Wattmeter (What's Your Watt?) from
>>> library.
>>
>> These devices are really useful for installations where you have a lot
>> of devices running.  You can accurately measure median loads, sample and
>> get a rolling average, and take note of peak load (typically on startup
>> for devices that have spinning rust).
>>
>> It's also amazing to look at two identical pieces of hardware and notice
>> that they have dramatically different power loads. Often you can trace
>> that to software load differences, and make adjustments as necessary.
>>
>> But of course the best reason is for energy savings and capacity
>> planning.  You can work out that your mains bus can handle N servers at
>> normal load, and N/4 at peak load, or what have you.  Then you know to
>> only start up a quarter of your systems at any one time, and stagger
>> boots (or just increase capacity to cover full synchronised peak load).
>>
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Best Regards.
This is unedited.
This message came out of me
via a suboptimal keyboard.