Abstract:
A protection system for an electric generator includes a fluid sensor to measure a fluid level in a fuel tank, an indicator lamp to display the fluid level, a timer to measure a time interval beginning in response to a low fuel signal from the fluid sensor and a low fuel switch to shut off the electric generator at the end of the time interval.

Description:
FIELD OF THE INVENTION 
   This invention relates to electric generators and more particularly to protection systems for electric generators. 
   BACKGROUND 
   Small-scale electric generation, such as backup, standby and emergency generators, are used in many locations. The electric generators must be maintained by an operator to monitor fuel, oil and temperature levels. In some cases, alarms might alert the operator that the electric generator might be running low on fuel. However, by the time the operator becomes aware of the low fuel condition, the electric generator could run out of fuel before fuel supplies are replenished and/or may not be able to safely shut-down electrical loads before a power system disruption. 
   Fuel level detectors for warning an individual of a low fuel supply are well known. For example, a Hara, U.S. Pat. No. 4,175,435 discloses a liquid level detection device. As disclosed a liquid level detection device comprises an annular float adapted to float constantly on the surface of a body of liquid subjected to level detection, a barrel passing through the float to guide the motion of the float, permanent magnets disposed in the float and a magnetically operable lead switch disposed in the barrel permits the detection of the liquid level. The device works on the principle that the lead switch is magnetically turned into it&#39;s on state at the time that the float while in motion reaches the position at which the barrel incorporates the switch. 
   A more recent patent of Wickman et al., U.S. Pat. No. 6,253,742 discloses a method for controlling the operation of a fuel system that uses a lift pump. The system uses a lift pump to transfer fuel from a remote tank to a vapor separator tank. Only one level sensor is provided in the vapor separator tank and an engine control unit monitors the total fuel usage subsequent to the most recent filling of the tank. When the fuel usage indicates that the fuel level in the vapor separator tank has reached a predetermined lower level, a lift pump is activated to draw fuel from a remote tank and provide that fuel to the vapor separator tank. 
   Notwithstanding the above, it is presently believed that there is a need and a potential commercial market for a protection system for an electric generator in accordance with the present invention. There should be a demand for such systems for use with electrical generators to protect the generators from running out of fuel and shutting down prematurely. 
   SUMMARY 
   In essence, a protection system for an electric generator includes a fluid sensor to measure a fluid level in a fuel tank, an indicator lamp to display the fluid level, a timer to measure a time interval beginning in response to a low fuel signal from the fluid sensor and a low fuel switch to shut off the electric generator at the end of the time interval. 
   Embodiments of the invention may include one or more of the following features. For example, the fluid sensor may include a float, a conductor block, a rod to attach the float to the conductor block and spring contacts to contact the conductor block thereby causing an electric current to illuminate an indicator lamp. 
   As another feature, an isolation wall may have a port that receives the rod and that separates the spring contacts from the volume of the fuel tank. 
   The indicator lamp may also include a green lamp to indicate a nearly full fluid level, a yellow lamp to indicate an approximately half full fluid level and a red lamp to indicate an almost empty fluid level. The green, yellow and red lamps may be green, yellow and red LEDs, respectively. 
   The timer may also include a clock that measures a time interval and an output circuit that issues a shut-off signal at the end of the timer interval. 
   The protection system may also include an audible alarm to indicate a low liquid level in the fuel tanks. 
   A battery may provide backup electric power for the protection system to operate the indicator lamp, alarm, fuel sensor, timer and switches. In addition, a solar cell and a battery charger can be used to recharge the battery. 
   Additional protection features include a thermal sensor and a high temperature switch to shut of the electric generator in response to a high temperature signal from a thermal sensor. 
   The fuel tank may also be supplemented by a reserve fuel tank and a pump to transfer fluid from the reserve fuel tank to the fuel tank. The pump transfers the fuel to the fuel tank in response to the low fuel signal from the fluid sensor. 
   In another general aspect, the protection system for an electric generator includes a float to measure a fluid level in a fuel tank, a conductor block, an arm to attach the float to the conductor block and spring contacts to contact the conductor block, a set of indicator green, yellow and red LED lamps receiving signals from the fluid sensor to indicate a high fluid level, a half full fluid level and a nearly empty fluid level, respectively, a timer to measure a time interval beginning in response to a low fuel signal from the fluid sensor, a low fuel switch to shut off the electric generator at the end of the time interval and an audible alarm to indicate a nearly empty fluid level. The protection systems in accordance with the present invention may include any of the above features. 
   In another general aspect, a method of protecting an electric generator from a low fuel condition includes sensing a fluid level in a fuel tank of the electric generator, measuring a time interval beginning in response to a sensed low fluid level and shutting off the electric generator at the end of the measured time interval. 
   The method may include any of the above or following features. For example, the method may include displaying the fluid level. 
   The invention will now be described in connection with the accompanying drawings wherein like reference numerals have been used to designate like parts. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an electric generator with a protection system; 
       FIG. 2  is cross-section view of a fuel tank with a fuel level sensor; 
       FIG. 3  is a warning light panel; 
       FIG. 4  is a schematic diagram of a generator protection circuit; 
       FIG. 5  is a cross-section view of a reserve fuel tank; 
       FIG. 6  is a block diagram of a protection system; 
       FIG. 7  is a block diagram of a solar powered motor; 
       FIG. 8  is a block diagram of a heat alarm circuit; 
       FIG. 9  is a schematic diagram of a heat lamp circuit and a heat alarm circuit; 
       FIG. 10  a lamp circuit to indicate whether the generator is working; 
       FIG. 11  is a diagram of a portable display screen; 
       FIG. 12  is a lamp circuit connected to the main generator; 
       FIG. 13  is a diagram of a fabric window screen; 
       FIG. 14  is a window screen installed in a tent; 
       FIG. 15  is a block diagram of an electrical distribution system; and 
       FIG. 16  is a portable display panel. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , an electric generator with a protection system in accordance with the present invention includes an electric generator  101  with a fuel tank (not shown) that incorporates a float switch  102 . The float switch  102  provides information about the amount of fuel in the fuel tank to a fuel level gauge or display  104  and to a relay  106 . 
   The relay  106  is operable to trigger a timer  108  which can issue a shut-off signal to the electric generator  101 . The relay  106  also triggers an audible alarm  110  which notifies an operator of a low fuel condition. The alarm  110  is connected to a battery and battery charger which is provided with an electrical charge via a solar cell  114 . 
   Referring to  FIG. 2 , the float switch  102  is located in the fuel tank  202 . The float switch includes a float  204 , a rod or pipe  206 , and a conductor block  208 . The conductor block  208  moves up and down inside a housing  210  which encloses pairs of electrical spring contacts  212 . The position of the conductor block  208  varies depending on the fuel level  214  causing the conductor block to complete an electrical connection through a pair of the spring contacts  212 . Each pair of spring contacts is connected to a lamp or light emitting diode (LED) which is lit to indicate the amount of fuel left in the tank  202 . 
   Fuel can be added to the fuel tank  202  through a filling port  216  at the top of the fuel tank  202 . A first fuel line  218  feeds a fuel pump  220  which pumps fuel through a second fuel line  222  to the electric generator  101 . 
     FIG. 3  shows a fuel warning indicator which includes a series of green, yellow and red LEDs  302 . As the fuel level gets lower the green and then the yellow LEDs are extinguished and the red LEDs are illuminated. 
     FIG. 4  illustrates an electrical schematic diagram of the protection circuit. Each pair of spring contacts  212  is connected in series with green, yellow and red LEDs  302 , respectively, and current limiting resistors  402 . 
   The relay  106  is also actuated when the fuel level is low. When the relay  106  is actuated, the electrical circuit is completed so that the solar/generator charged battery  404  energizes the audible alarm  110 . The relay also provides power to a transistor  406  which sends a signal to initiate the counter in the timer circuit. A current limiting resistor  408  reduces the input current to the base of the transistor  406  and a capacitor  58  reduces rapid voltage fluctuations. 
   Referring to  FIG. 5 , in the event that the fuel runs out suddenly, a reserve tank  502  that can be installed in a vehicle is used to provide additional fuel. The tank  502  has a fuel line  504  connected to a pump  506  which pumps fuel through a filler hose  508 . The pump is operated by an operation switch  510  which provides power to the pump  506  from the car battery. An aluminum bracket  512  is used to install the tank  502  in the car and maintains the tank in a fixed position to prevent it from tipping or spilling. 
   Referring to  FIG. 6 , the protection system may have more than one relay to protect the electric generator from malfunctioning. In addition to providing power to the relay  106  that triggers the fuel alarm  110 , the solar cell  114  and battery  112  may power a heat alarm  602  that is triggered by a relay  604  to warn the operator of a potential overheating problem. In addition, a heat timer  606 , which is triggered by another relay  608 , may issue a shut-down signal to the electric generator after a short time delay if the high heat condition is not alleviated. Referring to  FIG. 7 , is a solar cell  702  that is connected to a switch is used to drive a small motor  706  of a fan  708 . 
     FIG. 8  shows a more detailed view of the heat alarm with a relay  802  which is connected to a timer  804  which is in turn connected to a lamp  806 . Source  1   808  refers to the energy provided from an electric generator. Source  2   810  refers to the electric power available from the charged battery. A second relay is connected to a heat alarm which in turn is connected to lamps  816  and a speaker  818 . When the generator is switched off, the circuit is powered by the charged battery. 
     FIG. 9  is a schematic diagram of a heat lamp circuit  902  and a heat alarm circuit  904 . The heat lamp circuit is designed to extinguish a lamp  910  after the generator cools off. Source  1   906  refers to a 9 volt, 0.5 ampere power supply and source  2   908  is a 9 volt, 3 ampere power supply. L 1   910  is a lamp connected to a transistor  912  in the heat lamp circuit  902 . C 1   914  and R 1   916  are a capacitor and resistor, respectively, that are connected to the base of the transistor  912 . Relay  1   918  switches off the timer after one second if the generator shuts off. 
   Transistors  920  are used in the heat alarm circuit  904  to actuate a speaker  922  and a warning lamp  924 , in what is referred to as a “bi-stable” circuit. Capacitors C 3   926  and C 2   928  and resistors R 3   930  and R 2   932  bias the transistors  920  at a determined voltage and current level. SC 1   934  is a solar cell that maintains a charge on a 6 volt, 3 ampere battery. S 1  is an on/off electrical switch. 
   Referring to  FIG. 10 , a lamp  1002  on the portable screen is used to indicate whether the generator  1004  is working. The portable screen,  FIG. 16  can be connected by cable or wireless connection so that it can be seen from inside a building or other structure. A switch  1006  connects the generator  1004  to the lamp circuit. The switch  1006  is also connected to a base  1008 , motor  1010  and small generator  1012 . 
     FIG. 11  shows a portable display screen  1  from the back with a motor  2  and a handle  4  used to start the motor. 
     FIG. 12  is a circuit connected to the main generator. A switch on the portable screen is used to switch the main generator on. The switch  1202  provides power to a lamp  1204  and a motor  1206  to indicate whether the generator is working. 
     FIG. 13  is a block diagram of a screen for a window installed in a tent or other structure to use direct solar warming without the use of electric energy. It can be made of plastic or heat-resistant nylon and can allow passage of hot air and fine dust. 
     FIG. 14  shows the window screen  1402  that can be installed in a window  1404  of tent  1403  or other building structure with a roof  1405 . 
     FIG. 15  is a diagram of an electric distribution system which includes 240 volt electric distribution sources  1502 . A switch  1506  connects the 240 volt distribution source  1502  to an electric converter  1508 . The converter  1508  provides a low voltage of between 1.5 to 12 volts to an electric distribution panel  1510 . The distribution panel  1510  distributes the low voltage power to the electric devices in the main tank  1512 , tent  1514  and petrol tank  1516  and to the relays  1518 ,  1520 . 
     FIG. 16  is a display panel with status indicators that include a tent lamp  1602 , heat lamp  1604 , petrol level speaker  1606  and motor  1608 . 
   While the invention has been described in connection with its preferred embodiments, it should be recognized that changes and modifications may be made therein without departing from the scope of the appended claims.