EEVblog 1446 - Analog Watt Hour Meters are AMAZING!

Analog Watt Hour energy meters are fascinating! How they work, teardown, and experiments.

Thanks to Max Button for sending this in to the mailbag.

00:00 - Watt Hour Energy Meters
02:11 - Teardown
05:13 - What's to stop it taking off?
06:40 - Does it work? Testing with a load.
07:24 - Can you get free electicity with a neodymium magnet?
08:14 - Timelapse of no load creepage
08:49 - Anti creep holes
10:45 - When this baby hits 88 MPH you're gonna see some serious spin!
11:38 - Inside the voltage and current coils and how they work
14:39 - DaveCAD magnetic flux vector edition
19:06 - Theory of Operation
24:00 - Design Bonus - Jewel bearings
25:07 - Design Bonus - Magnetic temperature compensation
26:58 - Design Bonus - Full load compensation
27:40 - Design Bonus - Dimples

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#ElectronicsCreators #Teardown

[flymypg]

We got the basics of this in the first year of university Physics classes, then revisited it two years later to solve the full set of field equations for both ideal and real materials, and then measure the difference in the lab to get the right values in the model for the real materials and see the affect of mechanical design choices. The hardest part, by far, was summing the effects of all the fields in the disc and the topology (shape) of the induced currents.

We also had to allow for the thermodynamics. A factor in the size and design of the disc is to dissipate heat, particularly to minimize peak local heating during high loads, and to have consistent behavior during the full range of environmental conditions. Aluminum is chosen for the disc because it has a good balance between conductivity and heat transfer while also minimizing angular inertia. Iron alloys could not be used because they could be magnetized (though we did not consider austenitic stainless steels). A copper alloy could work, but the disc mechanical design would need to be very different, with affects that would ripple through to the rest of the meter design.

[rwbishop]

Out of passing interest... eons ago, a friend lived in a large apartment complex. All the electric meters were on on a wall in the laundry room... there must have been 50 or more. He was doing laundry one day, & out of mere curiosity found his meter & noticed it rotating quite fast... then noted it speeding/slowing in time various laundry machines cycling on/off! Cheesed him off... but to be sure he ran & turned off his main breaker, & returned to find the same! He called & reported to his DWP; and they were there seemingly within minutes. It seems the landlord had jumpers behind that wall & rotated the laundry and common areas to different meters on a regular basis. He said it turned into a colossal legal S storm that lasted about a year.

[danmenes]

I think the grid pattern of divots in the rotor is intended to make the rotor acceptably flat. When you stamp sheet metal, it often won't come out flat if you just smash it between two flat dies. The blank was almost flat to begin with, so the tiny amount it moves during stamping isn't enough to overcome the metal's elastic limit. When the press opens, the stamping springs back to it's original almost-but-not-quite flat shape.

But if you make little divots everywhere, you stretch the metal much more. By exceeding the metal's elastic limit, you convince it to take on the shape of the flat dies.

[mikefochtman]

You have to remember that V x I x COS(theta) on the disc creates a TORQUE, not an RPM. That means once the friction is overcome, it would go faster and faster. Those permanent magnets provide a drag proportional to the speed of the disc. Without the drag magnets it just won't record watt-hours. When you add drag proportional to speed, and TORQUE proportional to Watts, you get Watt-Hour.

[VincentGroenewold]

I love the mechanical solutions of the time just before the digital age, they are so incredibly clever always.

[TheSpud]

That style of plug in meter base can actually have the meter installed rotated 90deg, when in this arrangement none of the electrical connections are made and the meter is just acting as a cover for the bare terminals.
This function is used when the electricity company wants to disconnect supply from a property without removing the meter from site as the meter is tied to the address. It is used mainly when disconnecting people for non payment or when a rental property is unoccupied for an extended period and has the advantage that the meter can have the seals fitted to prevent the customer from tampering with the disconnection.
Source - former metering tech

[electronicsNmore]

Years ago I had a bundle of wires inside a conduit and needed to figure out which of the 20 or so wires was connected to a particular branch circuit. I made sure every appliance was turned off, then connected a hair dryer on high to the branch circuit I was trying to identify. I then held a 1" x 3/4" neodymium magnet close to the wire bundle and spread the wires apart. It was very easy to identify the correct wire, the magnet was vibrating in my hand just like you showed in the video. A very useful method.

[jpsimas]

The amount of accumulated knowledge built into these things is quite amazing

[donob]

Hi Dave .. you did an excellent job explaining all this. Back in the 80s I spent over 10yrs working for a power company calibrating single & 3 phase meters and troubleshooting meter problems. People used to drill holes through the case and poke a bit of wire into the brake magnet (and of course remove it before the meter reader was due) and play around trying to slow them down with an external magnet. Our own experiments with external magnets showed that you are just as likely to speed the meter up ... This particular meter like most later ones has magnetic suspension usng the two repulsion magnets at the bottom combined with an upper and lower centering guide needle .. We typically tested meter calibration at both unity and .5 PF (Cos 60), the power factor adjust is the 2 copper vanes on the rotatable shaft. Full load adj usually involves movement of the brake magnet but this later L&G appears to be using a different form of brake magnet adjustment

[byronwatkins]

Faraday's law: The induced emf in the disk and the induced eddy current in the disk is proportional to the flux rate of change. The torque on the disk is proportional to the eddy current times the instantaneous magnetic field. When voltage is maximum (positive or negative), it provides a background magnetic field centered on the coil assembly so that the offset eddy current induced by the rapidly changing current is attracted or repelled. When the current is maximum (positive or negative), it provides a background magnetic field offset from the center that attracts or repels the centered eddy current generated by the quickly changing voltage. All four torques are in the same direction. Torque provides angular acceleration except that the permanent magnets' eddy currents provide opposite torque proportional to disk speed. Together the disk's speed is in equilibrium at some speed proportional to the IV's torque... proportional to power. The counter integrates the disk's speed (power) wrt time to yield Watt-hours. Very sharp spikes are filtered out by the disk's inertia.

[chelstonthomas]

I worked on meters for 4 years, and that was the most concise lecture I have yet seen.

[pednn]

3 Phase meters are interesting too, they just have 3 of those disks on the same spindle. Being connected on one spindle it will measure true resulting power. These measure true power regeardless of the noise on the powerlines due to switching powersupplies, led lamps and other odd consumers. Digital meters need all kinds of clever engineering to get the same accurate result. Those mechanical meters do not need any of it and are just accurate, even 50 year old ones.

[jg]

We had a mechanical meter for a little while with a solar system. The retailer's systems eventually managed to cope with negative electricity usage each month, although eventually they fitted a non smart digitial meter that only lasted a few months before they replaced it again with one with a radio. It was pretty fun to watch the mechanical meter on a bright day when someone was welding as it would be spinning moderately fast backwards, before spinning very fast forwards for a few seconds, then going back to its usual spinning backwards :).

[mikeselectricstuff]

I wonder if the dimples are to stop the disc warping over temperature changes, reducing surface stresses

[RODALCO]

The dimples on the disc can be scanned with a photo electric cell during calibration. It speeds up the testing process when a line of meters is on the test bench. The readers are mounted above the meter and read the 10 dimples as the reflect the light back from the opto LED in the photocel. So for each revolution of the disc, 10 pulses are 'generated'. The Landis & Gyr CL 147 has similar patterns on the disc, which was a predecessor of this meter, made in the UK.

[sefarkas]

The trick is to get an old low voltage/high current filament and wire the secondary across the meter, one lead on an AC outlet the other on the mains. Then put a Variac on the primary of the filament transformer. as you raise the Variac voltage the disc slows down and starts the disc running backward. This is of course purely theoretical and is for educational purposes only.

[Hasitier]

This was really fascinating. I always wondered how those old meters work. Thanks Dave for the great explanation. Please do more of those educational videos.

[tomwimmenhove]

The temperature compensation blew my fucking mind. It's amazing how much engineering goes into these simple-seeming little electromechanical devices.

[jamess]

Had a funny one for you.
Had an analogue meter on a remote site that was permanently shut down; site uses like $150/month in power. After the site was shut-down, 3 months went by, utility company swapped the utility meter, and then another billing cycle went by and they billed us $15, 000 because they thought the meter rolled over. What a great day at the office. 🤙

[patrickdaxboeck]

It feels nice when you compliment this precision product of my home country, Switzerland. The company name is spoken like „Landes and Ger“ as the „y“ is spoken like a „e“ in English or an short „i“ in Alemannic. Even in my current flat there are still Landis & Gyr devices at work. Indestructible and very reliable.