# watt-hour meter

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For years I have used the watt-hour meter at the service entrance to
measure the rate of power consumption. I'd switch off all circuits
except a known load, such as incandescent bulbs or a water heater, then
time the on the meter disk to determine the constant in the relationship
between speed and watts.
Turning everything off requires resetting digital devices. If a year
later I wanted to check wattage and couldn't remember the constant, I'd
have to go through the procedure again. I couldn't be certain that my
test load was using exactly the watts I thought, and a constant found
for one watt-hour meter wouldn't necessarily apply to another.
Today I read that on most meters, Kh is the watt-hours per revolution.
(I wonder what Kh stands for.) Aha! You read the Kh, multiply by 3600,
and divide that constant by the seconds per revolution to get watts.
My Kh is marked 7.2. The time for 1/10 revolution was 41 seconds. That
came out to 63 Watts, right?
The house was running a computer in sleep mode, hooked up to an external
drive, an external modem, and a boom box. I switched that all off,
leaving only the power supply for the computer clock. There was a night
light. I switched it off. Otherwise, there was standby power for
furnace controller.
I timed the disk. Still 41 seconds. How could turning off my computer
equipment and the night light not have reduced power consumption? I
went out and timed it again. Still 41.
The third time, it had slowed way down. I don't know of anything in the
house that would have switched off since my last check.
Over the years I've seen that with other watt-hour meters. When a load
is turned on, there can be a long pause before the disk suddenly speeds
up. When the load is reduced nearly to zero, the disk may continue
spinning, then suddenly come nearly to a stop. What could account for
these delays in electromechanical watt-hour meters?
• posted
It is not really happening. The response of a watt-hour meter to changing load is instantaneous (OK, there is a finite delay, but you won't measure it with the naked eye).
Most watt-hour meter test equipment tests the meter by applying a known load and measuring the time for the disk to rotate.....one time! If the meter paused long enough for you to see it, it would fail the test.
The disk does not pause. You are seeing some other loads cycling. You used to be able to buy a desk lamp with a watt-hour meter and an incandescent light bulb. Turn on the bulb, meter spins immediately, turn off the bulb, meter stops. No pause.
Charles Perry P.E.
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Like Charles said, your typical watt-hour meter doesn't have such a delay. The inertia of the disk is so small that for all intents and purposes, they respond instantly to load changes.
Have you looked for some other cycling load? Perhaps a refrigerator?
daestrom
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I was sure it wasn't the refrigerator. Yesterday I had time to investigate further. I discovered a possibility: the air conditioner. It has a heater for the outside unit. I wonder: is there any harm in leaving it off for the winter? How long should it be allowed to warm up before I run the compressor next summer?
With only three breakers on, I got 135 Watts. Oh-oh, I'd left a fluorescent on in the bedroom, estimated at 100 Watts. I turned it off and got 35 Watts. I went through the house looking for circuits that were energized. All that seemed to be on were voltages for chips in the answering machine, the microwave, and the furnace. I unplugged the answering machine and the microwave. The meter disk didn't move in several minutes. I plugged them back in. The disk still didn't move in several minutes.
I guess those three devices didn't provide enough torque to get the disk moving. So far I haven't seen it move slower than 35 Watts, and I haven't been able to account for more than an estimated 15 watts.
• posted
Your furnace likely has a small transformer to step down to supply the thermostat and control relay. You also have a small transformer for your doorbell. These are both cheap units -lossy at no load- and if you have an electronic thermostat, there will be some more losses. This will chew up some of your 15 watts. Did you unplug any electric clocks, etc? Try opening your main breaker - shutting everything off- and see what happens. --
Don Kelly @shawcross.ca remove the X to answer ----------------------------
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The crankcase heater is important to prevent the refrigerant from dissolving into the oil. If it does, when you start the unit the oil will foam up and damage the compressor. I turn off the breaker in the fall each year and turn it on at least 24 hours before running the unit. (Crane manual says six hours, but what the heck...)
daestrom
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My only outlet-powered clocks are in the range, microwave, computer, and answering machine. The range breaker was off. I didn't try the doorbell to see if it was on a live circuit. The thermostat is mechanical, but the board in the furnace is digital.
The wheel could stop with the furnace, answering machine, microwave, and perhaps doorbell energized, or it could indicate 35 Watts, apparently with no additional load. I was unable to get it to turn between 0 and 35 Watts by disconnecting those small loads one by one.
If I knew more about shaded-pole motors, it might make sense to me.
D> > Your furnace likely has a small transformer to step down to supply the > thermostat and control relay. You also have a small transformer for your > doorbell. These are both cheap units -lossy at no load- and if you have an > electronic thermostat, there will be some more losses. This will chew up > some of your 15 watts. Did you unplug any electric clocks, etc? > Try opening your main breaker - shutting everything off- and see what > happens. -- > > Don Kelly @shawcross.ca > remove the X to answer > ----------------------------
> > daestrom wrote: > >>
• posted
Shouting ... SHUT OFF THE MAIN BREAKER, AS DON KELLY SAID.
Then report your findings. What you *think* is connected, and what is *actually* connected may differ. If the meter does not stop with the main off, you have a serious problem. The proper procdeure for shutting off the main is to first shut off all the other breakers, then the main. When restoring power, turn the main on first, then all the other breakers, one at a time.
For branch circuit testing to find out which circuit is causing the meter to run: (Shouting) TO DISCONNECT LOADS THAT MAY BE MAKING YOUR METER RUN, SHUT OFF THE BRANCH CIRCUIT BREAKERS.
Then report your findings. Unplugging some stuff and leaving other stuff plugged in tells you precisely ... nothing. You end up not knowing which "stuff" on which branch causes the meter to run. Do it right and you'll get it right. Ed
• posted
MAY I SHOUT, TOO?
I SHUT OFF THE MAIN SEVERAL DAYS AGO. NATURALLY, THE METER STOPPED.
AS I SAID, MY METER WILL ALSO STOP WHILE SUPPLYING POWER TO THE DC SUPPLIES OF AT LEAST THREE HOUSEHOLD DEVICES.
AS I SAID, THE ONLY BRANCHES I RUN ARE THE ONES WITH THE THREE DEVICES WHOSE COMBINED WATTAGE WON'T NECESSARILY TURN THE METER. SHOUTING IT MAKES ME FEEL THAT I KNOW EVERYTHING THERE IS TO KNOW!
WATT WILL I GET RIGHT? WATT'S THE SMALLEST WHATAGE YOUR METER WILL REGISTER?
• posted
Of course.
But you never told us that. So your shouting it now is unjustified. But the information is welcomed.
No, you didn't. You said the meter did not turn after you plugged them back in: "All that seemed to be on were voltages for chips in the answering machine, the microwave, and the furnace. I unplugged the answering machine and the microwave. The meter disk didn't move in several minutes. I plugged them back in. The disk still didn't move in several minutes.
I guess those three devices didn't provide enough torque to get the disk moving. So far I haven't seen it move slower than 35 Watts, and I haven't been able to account for more than an estimated 15 watts."
So again, your shouting is not justified.
Since the distinction between unplugging something that had been operating vs stopping the meter *by* unplugging escapes you: A device can draw power periodically and store it, stay operational off the stored energy for a period while not drawing any more, and then draw it again when the stored energy level needs to be replenished. Whether that is happening with your answering machine and microwave I cannot say - but the possibility exists. Your devices may have stored power while they were connected, and may not have used it up in the several minutes they were disconnected and the several minutes you monitored the meter after connecting them.
What will you get right is the answer to your mystery. Part of what puzzled you was why the meter was running when you thought it shouldn't. (It seems that part may be solved in your mind.) And part of what puzzles you is why the meter doesn't move when you think it should.
Finally, I apologize for shouting - not because I shouted, but because it apparently did not have the desired effect. It was for emphasis, to try to get you to think about the answers, rather than resisting them. All I see is that it made you angry - not the intended effect.
Good luck with your mystery. Ed
• posted
... : "All that seemed to be on were voltages for chips in the : answering machine, the microwave, and the furnace. I unplugged the : answering machine and the microwave. The meter disk didn't move in : several minutes. I plugged them back in. The disk still didn't move in : several minutes. : : I guess those three devices didn't provide enough torque to get the disk : moving. So far I haven't seen it move slower than 35 Watts, and I : haven't been able to account for more than an estimated 15 watts." ...
Jeez, guys: a nightlight and such isn't going to show any meter movement for a LONG time; probably days, certainly many hours! Think about it! Certainly you won't see anything in 'several minutes' as mentioned here! Oh, and the wheel will most likely turn - done it with vacation home with night lights; 3 of them; left on for a winter.
• posted
Well, a 7 watt nightlight on a meter with a Kh=7.2, should rotate the disk once in just under an hour. But I think there is a minimum friction where it just won't register. I think it was Charles that had a link to watt-hour-meter calibration spec.
Utility has to answer to the state's public service commission if too many of their meters register with *no* load, while if they don't register with a tiny load, they don't stand to lose very much (most utilities have a flat-rate for the first few kwh just for having service, so they get paid for those kwh even if the meter doesn't register them). So it wouldn't surprise me if there is a minimum load before the mechanical ones actually start to turn.
Wonder if the new electronic style are better? Seems an electronic integrator setup could probably be more accurate at tiny loads.
daestrom
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:
: > ... : > : "All that seemed to be on were voltages for chips in the : > : answering machine, the microwave, and the furnace. I unplugged : > the : > : answering machine and the microwave. The meter disk didn't : > move in : > : several minutes. I plugged them back in. The disk still : > didn't move in : > : several minutes. : > : : > : I guess those three devices didn't provide enough torque to get : > the disk : > : moving. So far I haven't seen it move slower than 35 Watts, : > and I : > : haven't been able to account for more than an estimated 15 : > watts." : > ... : > : > Jeez, guys: a nightlight and such isn't going to show any meter : > movement for a LONG time; probably days, certainly many hours! : > Think about it! Certainly you won't see anything in 'several : > minutes' as mentioned here! Oh, and the wheel will most likely : > turn - done it with vacation home with night lights; 3 of them; : > left on for a winter. : > : : Well, a 7 watt nightlight on a meter with a Kh=7.2, should rotate the disk : once in just under an hour. But I think there is a minimum friction where : it just won't register. I think it was Charles that had a link to : watt-hour-meter calibration spec.
Yeah, there does have to be a minimum friction, I'd have to agree. I guess I was reacting more to waiting a "few minutes" or whatever the phrase was. Also, everyone here says, and others seem to agree with, the fact that 1 revoution = 1 kWH but that's not true here in upstate NY. I don't recall the numbers anymore, but when I was using the spinning disk to measure power, my utility told me where to find the "multiplier" on the meter face to convert the number of revs/minute to kWH. I don't recall the number any longer, but two numbers are stuck in my head: 6.4 and 7.2. I do know the disk didn't indicate that one rev was a kWH though; it was far from it. They recently stuck us with one of the modem call-home types so I can't support my allegations anymore. I really dislike the new digital meters: There is zero way to guestimate ANY power usage unless it's a very high current or a long period of time. The lowest digit is a kWH; you'd think they'd have been down to tenths, at least, but I guess since they charge by even hours, they only have to display the even hour. Oh! A little sidelight here: When they went down the road here switching out the meters for the new digitals, you should have heard the complaining about the power company using THEIR phone lines to call in their meter readings, and how could they stop it, and what else was it telling them about their houses? . They just couldn't fathom that it didn't use the phone lines for that. : : Utility has to answer to the state's public service commission if too many : of their meters register with *no* load, while if they don't register with a : tiny load, they don't stand to lose very much (most utilities have a : flat-rate for the first few kwh just for having service, so they get paid : for those kwh even if the meter doesn't register them). So it wouldn't : surprise me if there is a minimum load before the mechanical ones actually : start to turn. : : Wonder if the new electronic style are better? Seems an electronic : integrator setup could probably be more accurate at tiny loads.
Interesting: I'll bet the new digitals don't have any trouble seeing six or seven watts. I wonder ... oh well, not worth any time or I'd go see what I could find out . Reminds me of the big scandals when the banks were caught rounding less than penny billing fields to their favor. e.g. if you owed \$100.032, you got charged \$100.04. And vice versa.
: daestrom : :
Cheers,
Pop
• posted
Do you remember when he posted it?
Did anyone in this thread say 1 revolution = 1 kWh? For decades, if I wanted to use a watt-hour meter to measure watts, I had to time the disk with a known load. At the start of this thread I said I'd just learned where the watt-hours per revolution is printed on a meter.
My disk turns 1000 times faster than yours: 1 revolution is 7.2 Wh. My disk is divided into 100 marks. In 5 minutes, a 7.2W nightlight should move the disk 8.3 marks.
• posted
I've found information on watt-hour meters. Speed is proportional to power because magnets cause retarding torque proportional to speed. Those magnets are adjusted to calibrate the meter at its rated load, typically 30 A.
Then they adjust some sort of compensation to calibrate it at 10% of its rated load. For me, that would be 720 W.
When that's done, it will read high at less than 10%. At 1% of its rated load it may read 100% high. What do you know? All my troubles have been below 72 W!
The disk has holes to stop it at very light loads. That way the customer won't see the disk keep turning after he turns off his main breaker, and the power company can keep claiming its meters are accurate.
That explains my two most recent obsevations: that a load of about 15 W reads 35, and that load won't start the disk moving.
So if I want to use the power-company meter to see how much power a small device uses, I should first turn on several lights so the total will be in the 700 W range.
• posted
: > : > "daestrom" wrote in message : > news:2b%hf.65715\$ snipped-for-privacy@twister.nyroc.rr.com... : > : : > : : > : Well, a 7 watt nightlight on a meter with a Kh=7.2, should : > rotate the disk : > : once in just under an hour. But I think there is a minimum : > friction where : > : it just won't register. I think it was Charles that had a link : > to : > : watt-hour-meter calibration spec. : : Do you remember when he posted it? : > : > Yeah, there does have to be a minimum friction, I'd have to : > agree. I guess I was reacting more to waiting a "few minutes" or : > whatever the phrase was. : > Also, everyone here says, and others seem to agree with, the : > fact that 1 revoution = 1 kWH : : Did anyone in this thread say 1 revolution = 1 kWh? For decades, if : I wanted to use a watt-hour meter to measure watts, I had to time : the disk with a known load. At the start of this thread I said I'd : just learned where the watt-hours per revolution is printed on a : meter. : : > but that's not true here in upstate : > NY. I don't recall the numbers anymore, but when I was using the : > spinning disk to measure power, my utility told me where to find : > the "multiplier" on the meter face to convert the number of : > revs/minute to kWH. I don't recall the number any longer, but : > two numbers are stuck in my head: 6.4 and 7.2. I do know the : > disk didn't indicate that one rev was a kWH though; it was far : > from it. : : My disk turns 1000 times faster than yours: 1 revolution is 7.2 Wh. : My disk is divided into 100 marks. In 5 minutes, a 7.2W nightlight : should move the disk 8.3 marks.
Interesting; and informative. Thanks for the education.
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Interesting: Did you find that online and can you post a URL?
Pop
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Here's where I found the explanation of inaccuracies:
Google took me there. I wasn't able to read about the second stage of calibration (at 10% load) because the text turned to gibberish as I scrolled.
Here's a page that says GE Watthour meters have the disk mounted by magnetic suspension to avoid friction. (That wouldn't eliminate worm-gear friction.)
Here's a 72-page manual on checking and calibrating watthour meters:
Adjusting braking magnets affects speed by the same percentage at all loads. When the magnets are adjusted to calibrate the meter at full load,friction would cause the meter to run slow at light loads.
A short-circuited coil overcomes friction by increasing the effect of the field from the potential coil on the disk. Its position can be adjusted to adjust its effect. Its effect on disk speed is inversely proportional to the load, so the coil has the effect of adding a certain number of watts to the load.
If my meter was calibrated with a light load of 750 W, maybe the torque adjustment to compensate for friction was equivalent to 20 W. At 15 W, it would take only 0.4 W to add that same torque. So my meter would read 34.6 W when the load was 15 W.
Disk creep can be up to 1 revolution per ten minutes and still meet calibration standards. With a Kh of 7.2, that's 43.2 watts, or 1 kWh/day.
A disk has holes that serve as parking brakes. When a hole is directly under the pole of the potential coil, torque will be reduced. If the disk was moving very slowly, it may stop. With a very light load, the disk should be timed for a complete revolution because the holes will cause the speed to vary.
That helps explain the lag I've noticed over the years. I used to live in a house where the meter and the breaker box were within arm's reach of the back door, so I could see the meter very quickly after switching breakers. If I switched everything off, the light-load coil would keep the disk turning until a hole came into position. If I switched on a 50-watt load, that might be just big enough to get the disk turning, but it might take a minute or so to move that first 1/4 of a mark, so that the hole was no longer interfering with torque.
• posted
Well, *I* didn't say it was 1kwh, and I see a couple of others that pointed out that the meter's Kh number tells you how many watt-hours per rev of the disk.
Yep, the number you want is shown as Kh=xx (mine used to be 7.2 before it was replaced with a digital one).
Here in upstate NY in Nimo(oops, National Grid) country, they've been moving to electronic meters. But the one I have has a small black 'dot' on the LCD readout that pulses with each watt-hour, to show you it's 'turning'.
Look underneath the digital readout for a small LCD 'spot'. When you have some loads running, it should blink on/off slowly, the speed tells you how fast the older 'disk' would have turned.
Funny, our meters (national grid in the CNY division) don't use phone lines. They are RF and the meter reader comes by once a month and simply drives up/down the street. His unit polls each meter and gets kwh reading and serial number while driving by at 10 mph. Still have a meter-reader, but one can cover the territory that used to take about eight.
Are you *sure* yours uses a phone line? I know some commercial installations in DTE country (lower Michigan) required a dedicated phone line, but those were 'open choice' commercial customers, where the non-utility supplier had to schedule power in 15 minute intervals and bill accordingly.
Who's your utility, maybe you can take the model no. off the meter and google it. That's what I did and found out all about it.
daestrom
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:
: > : > "daestrom" wrote in message : > news:2b%hf.65715\$ snipped-for-privacy@twister.nyroc.rr.com... : > :