[net.consumers] Power meters

sasaki@harvard.ARPA (Marty Sasaki) (03/21/85)

I'm looking for a gadget to plug into the wall that will tell me how much
power an appliance, lamp, etc. is consuming. My electric bill has recently
increased and I would like to find out where the power is going.
-- 
----------------
  Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}
  Havard University Science Center	phone: 617-495-1270
  One Oxford Street
  Cambridge, MA 02138

paul@dual.UUCP (Baker) (03/25/85)

> I'm looking for a gadget to plug into the wall that will tell me how much
> power an appliance, lamp, etc. is consuming. My electric bill has recently
> increased and I would like to find out where the power is going.
> -- 
> ----------------
>   Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}
>   Havard University Science Center	phone: 617-495-1270
>   One Oxford Street
>   Cambridge, MA 02138

I simply can't believe that someone from the scientific section of
one of the U.S.A's supposedly leading universities doesn't know the
answer to this.  Someone midway through high school physics should
be able to answer this.  On the other hand perhaps education in the
U.S. really as bad as Raygun says it is if we have science
undergraduates or possibly graduates who don't that AMMETERS exist.

Paul Wilcox-Baker.

jeff@rtech.ARPA (Jeff Lichtman) (03/26/85)

> > I'm looking for a gadget to plug into the wall that will tell me how much
> > power an appliance, lamp, etc. is consuming. My electric bill has recently
> > increased and I would like to find out where the power is going.
> > -- 
> > ----------------
> >   Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}
> >   Havard University Science Center	phone: 617-495-1270
> >   One Oxford Street
> >   Cambridge, MA 02138
> 
> I simply can't believe that someone from the scientific section of
> one of the U.S.A's supposedly leading universities doesn't know the
> answer to this.  Someone midway through high school physics should
> be able to answer this.  On the other hand perhaps education in the
> U.S. really as bad as Raygun says it is if we have science
> undergraduates or possibly graduates who don't that AMMETERS exist.
> 
> Paul Wilcox-Baker.

Before you insult somebody because of his "ignorance", you should be sure that
you are not ignorant yourself.  An ammeter won't work to measure AC power, even
with constant voltage.  This is because AC power equals RMS voltage times
RMS current times the cosine of the phase angle between them.

Power meters do exist.  I'm not sure where to get them, though.
-- 
Jeff Lichtman at rtech (Relational Technology, Inc.)
aka Swazoo Koolak

sasaki@harvard.ARPA (Marty Sasaki) (03/26/85)

> > I'm looking for a gadget to plug into the wall that will tell me how much
> > power an appliance, lamp, etc. is consuming. My electric bill has recently
> > increased and I would like to find out where the power is going.
> 
> ...  On the other hand perhaps education in the
> U.S. really as bad as Raygun says it is if we have science
> undergraduates or possibly graduates who don't that AMMETERS exist.
> 
> Paul Wilcox-Baker.

To top it off, I went to MIT and majored in computer science in the
Department of Electrical Engineering and Computer Science.

Yes, I know about AMMETERS and VOLTMETERS and own a few as well. I even
know how to do the measurements. But this doesn't help me with my
problem. When the motor is running on my 'frige, I can measure it's
power consumption, but this doesn't tell me how often, and for how long
the 'frige has been running.

I would like to plug the gadget in and find out that the 'frige used N
kilo-watt hours during the week.
-- 
----------------
  Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}
  Havard University Science Center	phone: 617-495-1270
  One Oxford Street
  Cambridge, MA 02138

rfg@hound.UUCP (R.GRANTGES) (03/26/85)

[]
I simply can't believe that we have pseudo college graduates on this
net so stupid they think that AMMETERS measure power.

-- 

"It's the thought, if any, that counts!"  Dick Grantges  hound!rfg

ned@brl-tgr.ARPA (Raymond Prenatt ) (03/26/85)

In article <973@dual.UUCP> paul@dual.UUCP (Baker) writes:
>> I'm looking for a gadget to plug into the wall that will tell me how much
>> power an appliance, lamp, etc. is consuming. My electric bill has recently
>> increased and I would like to find out where the power is going.
>> -- 
>> ----------------
>>   Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}
>>   Havard University Science Center	phone: 617-495-1270
>>   One Oxford Street
>>   Cambridge, MA 02138
>
>I simply can't believe that someone from the scientific section of
>one of the U.S.A's supposedly leading universities doesn't know the
>answer to this.  Someone midway through high school physics should
>be able to answer this.  On the other hand perhaps education in the
>U.S. really as bad as Raygun says it is if we have science
>undergraduates or possibly graduates who don't that AMMETERS exist.
>
>Paul Wilcox-Baker.

----------------------------------------------------------------------

What you see above is an example of the kind of snotty, condescending,
insulting response that, I think, we see all too frequently on the net.
It harks back to the early days of microcomputing when it used to be
considered *cute* to have the computer respond with insults when the
user made an error.  Of course, this sort of childishness predates the
computer by millennia.  You know.  A kid's just gotten some new learning
and suddenly everyone who doesn't know something that he knows is somehow
*stupid*, or at least *ignorant*.  I guess I sorta went through that stage
myself back in grade school, and maybe a little even into high school.  It's
amazing how getting smacked in the mouth a few times (literally as well as
figuratively) encourages behavior modification.  I do think that most of us,
at we grow up, soon realize how really sophomoric such talk sounds.  It really
IS less a reflection on the person we're putting down than it is on
ourselves.  I've found that one thing that often really helps in overcoming
such an attitude is to concentrate on the many, many things that other
people know about THEIR fields, or talents or skills that they have in THEIR
areas of interest that I lack.  (Maybe I'm not interested in acquiring them
either, but that's beside the point.)

My apologies, Paul.  I'm sure that you're a fine person in many respects.
It's just that this has been building up in me for some time; I needed to get
it off my chest and you just happened to provide the last straw.

                                                          =Ned=

halle@hou2b.UUCP (J.HALLE) (03/26/85)

While it may be true that many on the net incorrectly think that an ammeter
measures power, an ammeter can be used to determine energy usage.
Power equals voltage times current.  Energy equals power times time.
V can be measured with a voltmeter elsewhere on the line with nominal
error, or can be estimated well enough at 110VAC.  An induction ammeter
(clip-on type) will measure the current.  (RMS or peak, depending on the meter)
A watch measures time.  Use all of these to estimate the consumption of a
particular appliance.  Or get a wattmeter.

hood@homxa.UUCP (Ron Hood) (03/26/85)

Actually, power is the vector product of voltage and current.
A third variable is required in the cases where the voltage and
current are not in phase, giving the following formula:

	Power = Volts X Amps X Power Factor

For most household loads (lights, heaters, small motors) the power
factor is 1 and can be ingnored.

This brings up a question.  Do the meters used by the power companies
measure the total power used (volts X amps X power factor X time) or
just the total voltamps used (volts X amps X time)?  It seems I remember
something about devices which "fool" the power company meters into
reading less power than was actually used.  If the meters are based
on voltamps rather than power, all it would take is a large inductor
to shift the power factor and reduce your power bill.  Hmmmmmmm.

			Ron

paul@dual.UUCP (Baker) (03/26/85)

> 
> Before you insult somebody because of his "ignorance", you should be sure that
> you are not ignorant yourself. An ammeter won't work to measure AC power, even
> with constant voltage.  This is because AC power equals RMS voltage times
> RMS current times the cosine of the phase angle between them.

This is strictly speaking true. However

1) Most devices are designed to have a power factor close to one.  In
   this case the power consumed does equal scalar voltage times scalar
   current.  For example flourescent lamps have a capacitor solely for
   power factor correction.
2) Domestic electricity meters measure scalar voltage times current and
   the person in question was interested in optimizing for minimum
   electricity bill and not particularly for minimum power.
> 
> Power meters do exist.  I'm not sure where to get them, though.
>
Paul Wilcox-Baker.

crandell@ut-sally.UUCP (Jim Crandell) (03/26/85)

> Power meters do exist.  I'm not sure where to get them, though.

Try Fort Knox.
-- 

    Jim Crandell, C. S. Dept., The University of Texas at Austin
               {ihnp4,seismo,ctvax}!ut-sally!crandell

zben@umd5.UUCP (03/27/85)

Its a little more difficult than it seems, due to a concept usually called
POWER FACTOR.  This measures the fact that your load seldom acts like a
simple resistor, but more often has a reactive component.  Simply put, your
load is going to look a little bit like a capacitor or an inductor, this
depends on the load.  Motors and power transformer driven gear looks like
an inductor, florescent lights look like a capacitor.

This phenomenon causes the current sine wave to get out of phase to the
voltage sine wave.  Thus an instantanious product of voltage and current
will tend to read LESS than the actual power drawn.

The little box with the spinning wheel outside your house is specially
designed to cope with this (somehow?!) and is uncheap because of it.
-- 
Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA

snafu@ihlpm.UUCP (wallis) (03/27/85)

> 
> I simply can't believe that someone from the scientific section of
> one of the U.S.A's supposedly leading universities doesn't know the
> answer to this.  Someone midway through high school physics should
> be able to answer this.  On the other hand perhaps education in the
> U.S. really as bad as Raygun says it is if we have science
> undergraduates or possibly graduates who don't that AMMETERS exist.
> 
> Paul Wilcox-Baker.

Actually, an ammeter won't give you an accurate
measure of the amount of power used by an AC
appliance.  Ammeters are calibrated for DC
operation.  An AC powermeter (which is a
combination of an ammeter and a voltmeter) must be
used to measure AC power usage. They are neither
as inexpensive nor as easy to use as an ammeter
(i.e. Radio Shack does not sell them).




                              Dave Wallis
                           ihnp4!ihlpm!snafu
                       AT&T Network Systems, Inc.
                            (312) 510-6238

louie@umd5.UUCP (03/27/85)

In the September, 1984 issue of BYTE, Steve Ciarcia's column entitled
"Ciarcia's Circuit Cellar: Build the AC Power Monitor" may give you some
ideas.  He hacked over a power strip to insert a shunt, and produced a
circuit that would give your computer a 100ms pulse for every 
kilowatt-second of power that was consumed.
-- 
Louis A. Mamakos WA3YMH   University of Maryland, Computer Science Center
 Internet: louie@umd5.arpa
 UUCP: {seismo!umcp-cs, ihnp4!rlgvax}!cvl!umd5!louie

stadlin@hou2h.UUCP (Art Stadlin) (03/27/85)

>> I'm looking for a gadget to plug into the wall that will tell me how much
>> power an appliance, lamp, etc. is consuming. My electric bill has. . .
>>   Marty Sasaki
>>   Havard University Science Center	

> I simply can't believe that someone from the scientific section of
> one of the U.S.A's supposedly leading universities doesn't know the
> answer to this.  Someone midway through high school physics should
> be able to answer this.  On the other hand perhaps education in the
> U.S. really as bad as Raygun says it is if we have science
> undergraduates or possibly graduates who don't that AMMETERS exist.
> Paul Wilcox-Baker.

I simply cannot understand why anyone would lash out so vociferously
to such an innocent net posting.  Marty asked a good question.  If I knew
where to buy a simple, ready-to-install, power measuring gadget,
I'm sure I'd pick up a few.

I'm convinced that you missed the point, which is why net traffic
picked up considerably with discussions of power factors, current meters,
RMS values, energy, and other high school physics topics.

But none of the peripheral discussion answered the original question:
----->>>  Does anyone know of an off-the-shelf, inexpensive, modular,
          household, AC power meter that can be installed without tools?
-- 
  \\\
   \\\\                                  Art Stadlin
    \\\\\\________!{akgua,ihnp4,houxm}!hou2h!stadlin

dsi@unccvax.UUCP (Dataspan Inc) (03/27/85)

      You've been watching too many "Death Valley Days" reruns (or whatever). An
ammeter in and of itself is generally worthless at AC. Many household loads are
NOT generally resistive; perhaps if this gentleman had an unaccountable increase
in energy consumption where there was large inductive machinery, it might even be
USEFUL to know the power factor on individual devices......

       In all seriousness, I think the gentleman was making a request for a 
specific, inexpensive device, not a lambasting as to his scientific credentials.
Ever try to measure the power consumption on dynamic RAM with your typical garden-variety Weston ammeter? How do you know the power is flowing towards the generator or the load ? Is your 60 hz sinusoidal (not at the output of a Solatron)???Not every measurement problem can be reduced to high school physics.

'Nuff said. Pfft.
dya

jeff@rtech.ARPA (Jeff Lichtman) (03/27/85)

> > ... AC power equals RMS voltage times
> > RMS current times the cosine of the phase angle between them.
> 
> This is strictly speaking true. However
> 
> 1) Most devices are designed to have a power factor close to one.  In
>    this case the power consumed does equal scalar voltage times scalar
>    current.  For example flourescent lamps have a capacitor solely for
>    power factor correction.

Motors running with a load on them can have power factors close to one,
but when the load decreases the power factor decreases and gets close to
zero.  For example, the power factor of a refrigerator motor is close to
one when the motor is starting, and much lower when it is running normally.

> 2) Domestic electricity meters measure scalar voltage times current and
>    the person in question was interested in optimizing for minimum
>    electricity bill and not particularly for minimum power.
> Paul Wilcox-Baker.

Domestic electricity meters *do* measure true energy.  They will even run
backwards if there is a net outflow of energy.  My father, who has
a graduate engineering degree, assures me that this is true.
-- 
Jeff Lichtman at rtech (Relational Technology, Inc.)
aka Swazoo Koolak

dr@ski.UUCP (David Robins) (03/27/85)

> > Power meters do exist.  I'm not sure where to get them, though.
> 
> Try Fort Knox.
> -- 
> 
>     Jim Crandell, C. S. Dept., The University of Texas at Austin
>                {ihnp4,seismo,ctvax}!ut-sally!crandell

Note:  The power company offers an energy rebate on power meters installed
in the home, for monitoring consumption.  I assume they can point one to
a suitable source, if they don't sell them.  Probably, you can also find,
through surplus dealers, watt-hour meters of the type installed in the 
incoming power feed to your house.  They don't read in small number of
units.
-- 
David Robins, M.D.; Smith-Kettlewell Institute of Visual Sciences
2232 Webster St; San Francisco CA 94115
415/561-1705
			{ucbvax,dual,sun}!twg!ski!dr
			dual!ptsfa!ski!dr

rkd@ccice5.UUCP (R. K. Downes) (03/28/85)

> I'm looking for a gadget to plug into the wall that will tell me how much
> power an appliance, lamp, etc. is consuming. My electric bill has recently
> increased and I would like to find out where the power is going.
> -- 
> ----------------
>   Marty Sasaki				net:   sasaki@harvard.{arpa,uucp}

I have used the following equipment for this purpose:

Item	Brand		Model #	Description		Price
----	-----		-------	-----------------------	-----
1.)	SIMPSON		230-3	AC Volt-Amp-Wattmeter	$160

2.)	TIF Instruments	2000A Wattprobe			$180?

Item 1 is a in-circuit type meter, and via pushbuttons, displays
volts, amps, or watts via a analog meter.

Item 2 is a clamp-on/clip on type meter, which dispays watts to
a digital readout.
-- 

	Ray Downes
	Computer Consoles Inc.
	ccice5:rkd (CCI Central Engineering systems only)

jans@mako.UUCP (Jan Steinman) (04/02/85)

In article <267@rtech.ARPA> jeff@rtech.ARPA (Jeff Lichtman) writes:
>Domestic electricity meters *do* measure true energy.  They will even run
>backwards if there is a net outflow of energy.

It's a well-known fact in the alternative power community that you can hook
your windplant/hydroplant/whatever to the load side of your power meter, spin
it backwards, and sell the utility energy.  (Saves capital equipment costs for
the storage subsystem!)  Recent court decisions have strengthened the right of
small power generators to force-sell to the utilities, but the generator is
required to notify the utility, and the utility may install a dual meter
system, one for retail rate (consumer-used power) and one for wholesale rate
(consumer-produced power).
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::

crandell@ut-sally.UUCP (Jim Crandell) (04/02/85)

Okay, I readily concede that mentioning common sense on USENET borders
shamefully on the oxymoronic, but I'd like to suggest something on this
subject.  The cheapest device you can find for measuring the cost of
operating an appliance -- and that IS the bottom line here, isn't it? --
is so because you don't have to buy it.  You already have it.  It is
(TA-DA!) the exact same device the electric utility company uses for the
same purpose.  Now, there is one catch for some users: if the meter is
mounted about four feet above eye level (I've seen that done) then the
activity may prove sufficiently unenjoyable to motivate one to seek
another method.  But anyway, remember the little wheel someone mentioned?
If you get close enough to the meter, viewing it from slightly above its
level, you'll see inside it a thin metal disk a few inches in diameter.
This disk is (at least in some models) the armature of the motor in the
device that does the actual measuring; the theory is that the speed of the
motor is directly proportional to the average power over some relatively
short interval, and the speed is reduced by gears to drive the indicators.
Now the nice feature for our purposes is that the disk is always marked
in such a way that its orientation is visually evident at least most of
the time.  Marking schemes vary, but one feature that seems to have been
universally adopted is the big black blob (actually, sometimes its a very
neat stripe) at one point near the edge, so you can always count whole
revolutions, at the very least.  (Okay, it isn't always black, either.)
The motor is usually designed so that one of its revolutions represents
some nice round fraction of a Watt-hour, but the exact fraction varies
by model, so you 'll have to figure out what it is (I've long suspected
that there's a universal marking scheme on kWH meters which encodes the
value but I've never tried to discover it).  The ``calibration'' procedure
is quite straightforward, but you may choose to perform it under conditions
of daylight and agreeable exterior atmospherics.  As simply as possible,
you disconnect (unplug or turn off) EVERYTHING connected to your power
lines, if possible.  Don't worry about the contents of the fridge -- it
won't be off long enough to matter.  Occasionally there's a load which
really can't be easily turned off, such as a doorbell transformer, al-
though you can switch off everything at the breaker panel.  (If you can't,
and if you rent, complain to your landlord at once!)  Leave one circuit
on, and connect to it only a lamp containing a standard 100-Watt bulb.
Of course, you can go get a 144-ohm, 1% wire-wound resistor if you feel
that you really must, but we don't really need that kind of precision
here.  After all, we're looking for relative measurements, aren't we?
The rest is pretty obvious: the revolution period under this load (call
it T) represents 100 Watts; we then disconnect the lamp and connect
instead the device whose consumption is in question, and if it spins the
disk once in time X, then the device is partaking of just about 100*T/X
joules every second, or at least that's the way the electric company's
reasoning goes.

> Domestic electricity meters *do* measure true energy.  They will even run
> backwards if there is a net outflow of energy.

True in most cases today.  Surely by now everyone's at least heard how
various sleazy characters have contrived to rip off the electric companies.
NO, I am not recommending or condoning such practices!  They are illegal,
and for very good reason.  But in some areas, sad to say, there are old-
style noninstantaneous-integrating meters still in use.  However, measuring
the power consumption of each appliance on the same instrument the utility
company uses to bill you guarantees that you correctly attribute to each
item its real share of the bill, assuming you really know how many hours
each month each one is using power.

If on the other hand, what you really wanted to do was to check the
calibration on your service kWh meter, then of course, none of the fore-
going would be of much concern to you.
-- 

    Jim Crandell, C. S. Dept., The University of Texas at Austin
               {ihnp4,seismo,ctvax}!ut-sally!crandell

john@x.UUCP (John Woods) (04/04/85)

> Domestic electricity meters *do* measure true energy.  They will even run
> backwards if there is a net outflow of energy.  My father, who has
> a graduate engineering degree, assures me that this is true.
> -- 
Alas, no longer:  this was fixed long ago.  I am told that the birth of
particle physics had something to do with it:  the cyclotron at MIT would
brown out all of Cambridge when it charged up, and then send that current
back into the power grid when the magnets discharged.  The local power company
got upset at having MIT brown out Cambridge "for just pennies a day!" :-)...
Hence, they started putting ratchets into modern meters to prevent the wheel
from turning backwards.

On the other hand, it has the flavor of an apocryphal story.  Maybe I should
borrow a 5KW gasoline generator and test it out...
-- 
John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101
...!decvax!frog!john, ...!mit-eddie!jfw, jfw%mit-ccc@MIT-XX.ARPA

You can't spell "vile" without "vi".

doug@terak.UUCP (Doug Pardee) (04/05/85)

> It's a well-known fact in the alternative power community that you can hook
> your windplant/hydroplant/whatever to the load side of your power meter, spin
> it backwards, and sell the utility energy.

This gives the impression that there's "nothing to it" to sell energy
to the local utility.  Not quite the case, since the power you supply
must be properly balanced and phased with the distribution grid.

A local housing developer is doing the paperwork prior to building an
entire solar-powered subdivision which will (he says) have the ability
to be a "negative consumer" at times.  He's been running a prototype
solar house for a few years.

I'm curious what this practice does to the "peak versus average"
demand problem which the utilities claim is the ?real? culprit in
our utility bills.  I'd think it would make matters worse.
-- 
Doug Pardee -- Terak Corp. -- !{hao,ihnp4,decvax}!noao!terak!doug

rjk@mgweed.UUCP (Randy King) (04/07/85)

<><><>

RATS!  I saw this device about a year ago in one of those energy mags,
but I don't remember it,  It does exist, and has a 2" wide chart recorder
built in.  I have also seen one that beeps at you from your fuse box if
you exceed a pre-set power level.  Don't know if it compensated for PF.

						Randy King
						AT&T-CP@MG
						ihnp4!mgweed!rjk

moroney@jon.DEC (Mike Moroney) (04/08/85)

>> Domestic electricity meters *do* measure true energy.  They will even run
>> backwards if there is a net outflow of energy.  My father, who has
>> a graduate engineering degree, assures me that this is true.

>Alas, no longer:  this was fixed long ago.  I am told that the birth of
>particle physics had something to do with it:  the cyclotron at MIT would
>brown out all of Cambridge when it charged up, and then send that current
>back into the power grid when the magnets discharged.  The local power company
>got upset at having MIT brown out Cambridge "for just pennies a day!" :-)...
>Hence, they started putting ratchets into modern meters to prevent the wheel
>from turning backwards.

Not true. (At least not any more)  There is a fairly recent law stating the
electric utility HAS to purchase excess power from their customers.  No
changes had to be done by the utility to meet this law since standard electric
meters do spin backwards.  My old high school installed a wind generator
and the meter to the school building did spin backwards during windy nights
when the building lights were mostly off.

"There's a madness to my method."			Mike Moroney
						..decwrl!rhea!jon!moroney