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Coin-Operated Electricity

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
8,096
Location
Kamloops, BC, Canada
Here in North America we don't really expect that the electricity coming into our homes to be a serious expense. For one it has at times been considered "too cheap to meter". While that may not really be the case we do take for granted that when we open an account with the regional electric company other than a certification that the installation complies with code they will install the meter, seal the box and then we start receiving the bill every month/quarter. If we stop paying the bill, eventually they remove the meter which effectively cuts off the electricity and the account remains in bad standing until the outstanding payment is resolved. In other regions of the world however this isn't as simple. Some conditions might instead require that electricity be paid for BEFORE it is used. It could be in residences where the occupant turnaround happens more often than the bill is sent out and the consumption fee is not included in the bill (cabin rentals for example) or where the tenants might not be entirely trusted to pay on time...if at all. This can be their idea of energy management as it can force people to better recognize phantom power consumption which over time adds up or it can supplement other provisions that allow a building owner to have one meter issued by the electric company and every suite pays for what they use separately. In modern times these meters use electronic key, chip or card systems to apply credit to a meter but previous to this and even in some situations today they also had meters that let you pay by coin.

Returning back to North America, that I can find my provincial electric company has never offered prepayment as an option. Historically it seems prepayment in residential addresses was not ever really popular, presumably because again, the cost of electricity is/was cheaper. The only examples of meters that operated domestically on 120/240v 60hz service date back as far as the 1900's and 1910's.

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These meters are quite rare, often selling for large amounts as antiques. Travelling only to the other side of the planet however such mechanical meters are still in use in the United Kingdom and thus can still be found used for as little as $40cad.

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These two meters cost me no more than $120CAD after shipping. Both are manufactured by Smith Meters Ltd. One of them has been refurbished recently enough to have the website for electricmeters.co.uk, who as of this article do not sell these meters new anymore, but will service and refurbish them.
Let's dig into one.

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The meter keeps everything behind special screws designed to be locked by feeding a piece of wire through them and applying a lead seal to prevent tampering. Under the base of the meter are the four main terminals that are the line and load points of the meter. In the UK this method of wiring is still allowed but here in North America meters can now only be fed through conduit and dedicated meter boxes.

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The mechanical component that accepts the coins is quite simple for how it works. If it's thin enough to fit in the slot it will, but it has to be large enough in diameter to press down a spring-loaded arm which extends a little finger and allows a gear set in the back of the cavity to be turned. Exactly how far that gear can turn is determined by the rotary orientation of the coin acceptor in the recess and an indexing pin. The more the gear is allowed to turn, the more Kilowatt-Hours the meter is credited up to. It also advances a counter that indicates how many coins have been inserted and how many units of energy have currently been paid for. On the first coin it also loads the contact release spring so that when you run out of credit there is a kinetic force available to open the contacts again. While the mechanism has no complicated method to verify what you inserted is the correct denomination coin...or a coin at all....this relies on whoever empties the coin box. The moment they see things like washers or under-sized coins, you're busted.

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The electricity metering side is exactly the same as any other mechanical KwH meter. A metallic disc has on one half a smaller winding that acts as the voltage field coil. On the other half a much larger coil is the main load coil. As the load through that winding increases the metal disc spins and sets in motion a very large and very complicated arrangement of gears and dials that display a running log of all power used through the meter.

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The prepayment portion of the meter simply taps into these gears so that as you add credit it can accurately subtract from it. You might of noticed on the credit dial and the scale on the coin acceptor it has two rates available. A screw switches between the two available rates and also adds or removes an additional ratio transmission so that the meter continues to remain accurate.

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Here is the main contact assembly for the credit system. The contacts and the wiring on this meter are rated for up to 40 Amps. Interestingly the rubber insluation on the wire has begin to degrade, causing the metal around it to corrode.
In addition to the main contacts there is a smaller secondary contact to which I don't fully understand its purpose. My thought is it is for arc control when the contact opens during very high loads and the meter running out of credit.

So now that I've explained a bit how it works, where they are typically found and what is inside it also made sense that I should try it for myself. This imposed a serious challenge that cannot be easily resolved.
Part of what makes this kind of metering accurate is the line frequency which is typically kept within .5hz at all times. The UK and almost every other country that uses 220v service also generates 50hz power. With only a few exceptions the rest of the world generates 60hz power. That difference means that on my bench this meter should operate faster, if I used it on 220/240v (it's weird here. You can really see our single-phase power as anywhere between 220 and 240v and split-phase as anywhere between 110 and 120v but regardless...) I however will test this on 120v.

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Using a Kill-a-watt meter and a resistive load (a space heater) my results were....strange.
The smallest unit of measurement on the meter is 1/10 KwH. This is the tiny red indicator.

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With that in mind, every time the Kill-a-watt logs 0.1 KwH the dial will increase by one. After one full rotation it would be 1KwH and so on. What I saw however was that for every Kilowatt-Hour I was only behind by about 0.1 to 0.08KwH. Strange.
Well, while that means the meter will never be accurate here it DOES mean that it's accurate enough to use it as a novelty item on both 240v and 120v electronics and circuits. Pranks, EV chargers, heaters, lawn mowers...anything really. If you don't entirely mind the meter drifting off you can still use it for coin-op. I'll probably keep one of these meters on the demo stand as you see here. With very little adjusting it now accepts Canadian quarters. Now to figure out a better way to wire it into boxes of modern Canadian electrical code.....
 
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I recall this being mentioned on old episodes of "Steptoe and Son". Seems that it would be simple to bridge, given the wire hookup. I wonder if strong rare-earth magnet would retard the spinning wheel...
 
The magnet was a common trick on the mechanical meters, but the meter readfers were on to it.
Prepay electricity in New Zealand, when I was involved, used a "smart card" which could be topped up.
It used a citrix server and took less than a minute to update the card. As technology "improved" the running costs exceeded the electricity billed, but regulations dictate it must be available.
I think it is all now done with cellular connected smart meters.
 
I remember those from when i was a Kid, My parents called them 'Money Box', They were always feeding it, And when it was full, Trying to get someone from the electric company to come out and empty it was a real pain sometimes, Back then we rented our TV and had to feed that with coins as well.
 
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