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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
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More
Watt Hour Meter Circuits |
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Watt-Hour Meter
designed by David Johnson, P.E. |
| Have you ever wondered
how much power your house or apartment is using? Most watt-hour meters are
like the one shown below. Some newer ones have a digital display but there
millions of these older models still in use. |
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Note the Kh 7.2 number on the tag in the photo
above. This says that the wheel takes 3600/72 or 50 seconds to make a
complete rotation, when the house is drawing one kilowatt of power. Using
a stopwatch, you can measure how much power your house is drawing from the
utility grid. First, measure the time (T) it takes for the wheel to make
one rotation. Take that number and insert it into the equation below.
Power = 3600/72 X 1/T
As an example, suppose you measured 7.5 seconds
for the wheel to make one rotation. Then, using the equation, you would be
drawing 6.7 kilowatts of power.
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Tapping into the guts of a
watt-hour meter to remotely record the energy use is dangerous and
illegal. But, there is a way to monitor power consumption without
making any electrical contact with the meter or any other electrical
wiring. Note the black band on the wheel. I think it would be
possible to use a visible red LED and a PIN photo diode to detect this
back band and measure the time for each wheel rotation. Using an RF
transmitter, that information could then be sent to a matching RF receiver
mounted somewhere inside the house.
A microprocessor or even a computer could then keep track of the time for
each rotation and the number of rotations. The processor could use
the information to display the kilowatts of power being used and the total
kilowatt-hours of energy consumed for any given time.
This might make a nice hobby project. |
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Click on Drawing Below to view PDF version of Schematic |
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paste schematic here & Link to PDF |
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