Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Reexamination Certificate
1999-05-18
2002-02-26
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
C307S113000, C251S129040
Reexamination Certificate
active
06351366
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to controllers, and more particularly to an improved battery powered programmable controller having extended battery life for controlling distant switches such as irrigation valve solenoids.
FIELD OF THE INVENTION
Programmable irrigation valve controllers are well known in the art. Such controllers are used to open and close irrigation valves by providing electric current to solenoids located in close proximity to the valves. Relatively large electric currents are required to activate and deactivate such solenoids. Providing this required electricity is a simple matter if an external power source is readily available, such as a power line. However, in many commercial agricultural and horticultural situations, controllers must be located at remote field locations where it is impossible or impractical to run a power line or otherwise provide an external power source. In some situations, the valves may be in even more remote locations that are themselves hundreds or even thousands of feet from the controller. Thus, insufficient voltage or current at the both the controller and at the valves is a common problem, especially where long distances or multiple valves are involved. Although some battery powered irrigation controllers have been developed they do not properly address these situations.
A significant limitation of existing battery powered irrigation controllers is battery life. Two voltage levels are generally required by such controllers: a law voltage level (which can be supplied by batteries, e.g. 3.5 volts) to operate the programming circuitry, and a higher voltage level (which can be supplied by a second set of batteries, e.g. 9 volts) to provide the necessary electrical impulses to operate the valve solenoids. The batteries on most existing battery powered controllers must be changed every few weeks or months, making them inconvenient to maintain and potentially unreliable to depend on for controlling irrigation cycles. At least one controller has addressed the problem of conserving the low voltage batteries used to operate the computing circuitry. In U.S. Pat. No. 4,423,484 to Hamilton, the microcomputer is turned off between cycles thereby conserving the low voltage batteries. However, the Hamilton controller does not address conservation of the higher voltage batteries used to operate the solenoids.
It is typical for an irrigation controller to use charging capacitors to operate the valve latching solenoids. These are generally large capacitors of 1000 micro farads or more. Most controllers (including Hamilton) maintain these capacitors in a charged condition, ready for immediate discharge to the solenoid upon receipt of a signal from the microprocessor (see e.g. U.S. Pat. No. 4,718,454 to Appleby). In addition, in most controllers these capacitors have an uninterrupted connection back to the high voltage (e.g. 9, 12, 18 or more volts) batteries from which they are charged. Both of these situations reduce the life of the high voltage batteries, and give rise to other potential problems with the controller.
It is known that all charged capacitors leak over time. This places a constant drain on the high voltage batteries to which they are connected. Such leakage significantly increases with temperature increases. Thus, a fully charged capacitor in a controller located in the middle of an unshaded field during the hot summer months can rapidly deplete the high voltage batteries, even when not in use. The larger the capacitor, the larger the leakage current. Also the higher the ambient temperature, the higher the leakage. This leakage is very significant and could be as much as hundreds of microamps. The leakage causes the capacitor to draw on the battery power supply in order to stay fully charged, thereby wasting energy and leading to the frequent need to change batteries without even any solenoid operation. Preventing this leakage would conserve the life of the high voltage batteries.
Battery operated controllers such as Hamilton use the high voltage batteries for operating both the solenoids and the electronics. Since most low power circuits operate from 3 to 5 volts DC, the high voltage batteries must be reduced and regulated, thereby wasting a considerable amount of energy.
In all controllers, the large capacitors are fully discharged in order to operate the valve solenoids. The capacitors are then recharged from the high voltage batteries. At the instant the discharge occurs, current may also be drawn directly from the high voltage batteries themselves, resulting in unnecessary depletion of the high voltage batteries.
Reliable operation of water valve solenoids is essential to ensure that water is regularly delivered to plants. Typical irrigation systems are designed to use 24 volts of alternating current (AC) to activate and control electric solenoids. However, AC powered irrigation systems suffer from several drawbacks. First, AC voltage drops over long runs of wire such that reliable voltage delivery cannot be assured beyond a few thousand feet. Where multiple solenoids are operated by a single controller, long runs of parallel wires in close proximity to each other may result in capacitive coupling: leakage current and floating voltages induced by energized adjacent wires. This effect may cause unwanted valves to turn on, or fail to cause valves to turn off. Other problems with AC systems include potential burn out of solenoids close to the controller because of excessive primary voltage.
Irrigation valve controlling systems also generally suffer from susceptibility to lightning, and power outages. A lightning strike on a valve in the field can couple onto the buried wires and run back to the controller with devastating results. A power outage can interrupt irrigation cycles potentially inducing stress to vegetation.
A conventional solution to the problem of AC voltage drops over long runs of wire is to provide thick, low-gauge solid wire (e.g. 8 gauge solid copper wire) which has a lower resistance factor than the thinner, higher-gauge wire. This solution provides a reliable method of controlling remote solenoids by decreasing voltage drops. However, the high cost of long runs of low-gauge wire becomes prohibitive, especially when several runs are required to operate several remote solenoids simultaneously. In addition, since the wires are carrying AC, the capacitative, coupling problem is still present.
Another proposed solution is to provide direct current (DC) voltage through long runs of copper wire to the solenoids, since DC systems do not suffer from the capacitive coupling problems of AC systems. However, when copper wires carry DC for long periods of time, the galvanic effect of the inductive field created by buried wires carrying the direct current causes the copper in the wires themselves to deteriorate over time, resulting in unreliability and eventually requiring replacement. For this reason, such DC systems are only used in short distance, above ground installations. These systems also suffer from the general problems presented by lightning strikes and power outages.
A third option is to provide a DC power source at the same remote location as the valve itself utilizing on-site batteries, solar power, or an on-site diesel generator. The disadvantage of this approach is the high cost of a self-contained remote system, and the problems of reliability in the event batteries or generator fail, or the weather is overcast for several days.
My 1994 patent (No. 5,347,421) addresses these problems to some extent by providing an AC power saving module in the form of a local circuit for energizing a solenoid. However, the circuits described in the '421 patent require a constant (albeit very low) current flow while the valve is open. The low AC current requirements of the '421 circuits allow much longer or thinner wire run; however, since the wires are carrying AC, the capacitative coupling problem is still present.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantage
Alexanian George
Carlson Eugene S.
Huynh Kim
Miller Mark D.
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