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1. Remote water level sensing
Homepower was approached to find out if there was a way of controlling the level of water behind
a small dam to within one inch. The requirement was for a wireless communication system
which would sense the water level and control a servo operated valve feeding a water
turbine. The idea was to minimize the amount of water going over the spill-way, and thus
maximize the water available for the turbine.
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As more water flowed into the dam, the system would sense the level change and
transmit this change in conditions to the servo operated valve. This would then open a
small amount, consuming more water and reducing the water level. Timers controlled the run time of the servo to minimize overshoot and frequent corrections.
The level data was transmitted 3 Km on a 900 MHz spread spectrum radio link. There were no existing communication lines between the dam and the turbine, and the cost to install
wires would have been prohibitive.
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2. Remote water tank level meter and alarm
Many isolated communities, farms or camps rely on water storage tanks. In most cases it is desirable to know the level of the water in these tanks, but in most cases the storage tank is at a high point and not readily accessible for inspection.
The meter described here uses a single paired wire to carry level data from a submerged transducer to a small display unit. Water level is continually monitored and displayed in 1/10 of a foot resolution on the display unit which is conveniently mounted in-doors. High and low set points can be adjusted to sound an internal alarm at any user selected point over the range of the transducer, typically 0 to 17 feet. Alarm muting is provided by means of a front mounted switch. A yellow LED lights when the switch is set to mute, to remind the user the alarm is disabled.
The transducer signal can be transmitted on any 2 conductor wire for distances of up to 2000 feet, depending on wire gauge. The signal wire provides both power to the transducer, as well as the return path for the signal.
An additional output is provided which can activate a small relay in an alarm condition to key a radio transmitter, sound an additional alarm or control a strobe light.
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3. Frequency / Voltage alarm
Remote sites are often powered by diesel or gas generators. In some situations, small hydro
supplies the electrical needs. What ever the source, 'home made' power is usually more prone to fluctuations
than is grid supplied juice. For this reason, it is important to monitor the condition
of the line and take action if the quality of the generated electricity falls out of
acceptable limits.
A system which monitors both the line voltage and frequency was developed for just such
applications. A small transformer supplies the unit with 12 volt AC at the line frequency.
The voltage is compared to an internal reference with a window comparator. Both high and
low limits are user selectable, generally set to +/- 5 volts of nominal.
The frequency is handled in a similar manner. The limits are set to +/- 5 hz of 60 hertz.
This will give adequate protection, while still allowing for short term droop in the
generated frequency.
If either the voltage or frequency goes out of spec, an alarm indicator LED operates. As
well, a separate delay setting determines the time before an internal relay opens which
can be wired to an auto shut off on the engine or hydro turbine.
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4. Water level measurement RTU. One of four remotes measuring small creek flows.
This is part of a system of four remote terminals units, RTU's, used to measure water the level in various creeks for hydro power potential. Each RTU transmits to a central base station, where the data is stored in a laptop computer and also sent out onto the internet by FTP client software and posted to a web site. Updates can be set from daily to hourly.
Each RTU is battery powered by eight D cell alkaline batteries and solar charging is not used in this case due to the lack of sunlight. Also, with periodic transmissions and no receiver power draw, battery life should be over one year. Pictured is one of the antennas on a tree, the open RTU and the probes and cables. These are protected in flexible conduit to reduce the risk of animal bites damaging the cables.
This was custom built for the client. Other similar systems available if you have a need.
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5. Solar Powered Outdoor Wireless Network Cameras:
This stand alone, internet linked camera monitors the intake of an hydro electric penstock and water supply. The tower is mounted on an 8 foot deep by 4 foot diameter holding tank from which the pipeline exits. In addition to monitoring the water intake, the telematary package also monitors the water level in the tank and radios the level data to the power house. Low water level will set off an alarm. The package is powered by a 20 watt BP module, charging a 12 amp hour gel cell. An internal controller can be set to transmit pictures at any desired time interval. Pictures can be sent via ftp and or email. An access point or router serves as the receiving terminal. Long range, outdoor 'Tranzio brand' radios are used. Protocol is 802.11G.
Complete made up packages are available from us here. Email to info@homepower.ca for more information. Different sized modules are also available depending on the solar influx. Yagi or dish or flat panel antennas available from 6 to 30 dB gain. See the Solar page for more products.
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6.Wireless remote control
This controller was developed for the owner of a small island who wanted a way to remotely
control an electrically operated winch. The winch would lower a rail mounted flat car over which he would maneuver his boat. The winch would then haul the flat car out of the water.
The controller served as an interface between an existing low power radio link and the motor controller. Provision was made for forward, reverse, pause and disable. The control functions were written in code and stored in an eprom based micro controller. Opto isolation provided the interface to 120 volt triacs, which controlled the motor.
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7. Data Logging
This water level information will determine the amount of water that has passed through the weir at the time of reading. Generally, some percentage of the total flow is used for power production, the rest is left to preserve the aquatic environment. When entered into the power formulas, total gross power can be calculated from the water used and the available elevation change.
Data loggers also find uses in recording temperatures, voltages, wind velocities, lake levels, and current draw. Other applications are possible as long as the parameter being measured can be converted in to a voltage or a current signal. Loggers supplied by RPT are designed for out door use in harsh contitions.
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8. Constant current 50 mA nicad charger
Most portable electronic devices use nicad batteries as a power source. Often these devices
have battery packs in the 9.6 to 10.8 volt range, requiring an AC powered charger to deliver the 50 mA required to do a slow charge. A problem arises when operating remotely, where to plug the charger in. Nicads are best charged with a constant current source, for a specific time.
Sometimes it is possible to connect the nicad pack to a car battery, but this always requires the use of current limiting resistors, and a meter to get the correct value. Conventional 3 terminal regulators require up to several volts to operate in a limiting mode, and often this does not leave enough head room to drive the 50 mA to the nicads.
A simple solution is to use a series pass transistor set to limit the current to 50 mA regardless of the input voltage. As well, the voltage drop across the transistor is in the range of 0.2 volts, enabling a 10.8 volt nicad battery to receive a full charge from a 12.0 volt car battery. In addition, the current limiting charger can be connected directly to a solar panel of any amperage and up to 20 volts open circuit, and it will still deliver a regulated 50 mA. Note however, the output voltage will be very close to that of the input source, so don't connect sensitive electronics directly to the current limiting charger.
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Contact Information:
Phone: 604-465-0927
Email:
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