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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, June 01, 2021 03:06 PM
Hobby Circuits List
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More
Watt Hour Meter Circuits |
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Watt-Hour Meter -
12/26/1998
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
are 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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