Use of the solar panel charger’s surplus energy
I have built the solar panel battery shunt regulator described in this thread. The way I use it is not so urban or sexy. I have a summer cottage in southern Finland. The cottage has a WC and all the sewage water from it goes to a container, which must be emptied at least once a year. In order to reduce its load I have built a separate dry toilet. Those, as some of you may know, can create a bad smell, if you do not ventilate them well. In order to reduce the risk of smell I have started to construct a solar panel-driven ventilator, which starts to run as soon as I open the lid of the toilet seat.
In summer time in southern Finland the sun is about 18 to 20 hours above the horizon. However, because the solar panel will be in a fixed position, the maximum power will be got only in the middle of the day, and at that time on a sunny day there probably will be a surplus of energy (the panel produces 12 V 5 W maximum). The surplus could be used for extra ventilation
Following the outlines discussed on this thread I have built a controller described in the adjoined schematics. As a shunt I used a low-power P-FET BSS92 with a load resistor of 150 Ohms. This resistor restricts the charger’s maximal shunt current to about 100 mA. When the voltage at the drain pin of the FET raises to the up-going threshold voltage (about 10 V, the shunt current is then about 66 mA) of CD40106 Schmitt trigger inverter 1, the capacitor at inverter 2 is discharged, inverter 2 output goes high and the transistor BC337 conducts. Now the fan (from a computer power supply) will run as long as the voltage at the input of inverter 1 is above the down-going threshold voltage (about 5 V). When the voltage goes under the low-threshold, the fan continues to run for the delay time determined by the RC-combination at inverter 2 input. The fan can be started and the delay activated manually any time by opening the toilette seat lid (which closes a normally open door switch). The power for the ventilator comes directly from the lead acid battery, which means that the fan always runs at full power. This can reduce the battery voltage, if the solar panel cannot deliver enough current to compensate it (the fan takes about 120 mA). As soon as the battery voltage is reduced, the FET is closed. The fan still runs for the delay period and then shuts down. Now, if the sun still shines, the battery voltage starts to rise, and when it is fully loaded, the FET will be activated and the cycle starts again.
One problem is that the total current consumption does not reach 300 mA, which maximum value is given in the specs of the solar panel. The fact that there is the ON- delay and that the fan always runs at full power may solve the problem. The shunt current can be increased by reducing the value of R1, but then a bigger portion of the energy will be wasted. The optimal resistor value can only roughly be estimated without knowing the real current production of the panel and frequency of the use of the toilet.
I appreciate all improvements and hints you could give to me. I am a hobbyist with no training in electronics. I have got all my knowledge by reading forums like this. I have not tested the circuit, since it still is a dark and cloudy winter here.
I have built the solar panel battery shunt regulator described in this thread. The way I use it is not so urban or sexy. I have a summer cottage in southern Finland. The cottage has a WC and all the sewage water from it goes to a container, which must be emptied at least once a year. In order to reduce its load I have built a separate dry toilet. Those, as some of you may know, can create a bad smell, if you do not ventilate them well. In order to reduce the risk of smell I have started to construct a solar panel-driven ventilator, which starts to run as soon as I open the lid of the toilet seat.
In summer time in southern Finland the sun is about 18 to 20 hours above the horizon. However, because the solar panel will be in a fixed position, the maximum power will be got only in the middle of the day, and at that time on a sunny day there probably will be a surplus of energy (the panel produces 12 V 5 W maximum). The surplus could be used for extra ventilation
Following the outlines discussed on this thread I have built a controller described in the adjoined schematics. As a shunt I used a low-power P-FET BSS92 with a load resistor of 150 Ohms. This resistor restricts the charger’s maximal shunt current to about 100 mA. When the voltage at the drain pin of the FET raises to the up-going threshold voltage (about 10 V, the shunt current is then about 66 mA) of CD40106 Schmitt trigger inverter 1, the capacitor at inverter 2 is discharged, inverter 2 output goes high and the transistor BC337 conducts. Now the fan (from a computer power supply) will run as long as the voltage at the input of inverter 1 is above the down-going threshold voltage (about 5 V). When the voltage goes under the low-threshold, the fan continues to run for the delay time determined by the RC-combination at inverter 2 input. The fan can be started and the delay activated manually any time by opening the toilette seat lid (which closes a normally open door switch). The power for the ventilator comes directly from the lead acid battery, which means that the fan always runs at full power. This can reduce the battery voltage, if the solar panel cannot deliver enough current to compensate it (the fan takes about 120 mA). As soon as the battery voltage is reduced, the FET is closed. The fan still runs for the delay period and then shuts down. Now, if the sun still shines, the battery voltage starts to rise, and when it is fully loaded, the FET will be activated and the cycle starts again.
One problem is that the total current consumption does not reach 300 mA, which maximum value is given in the specs of the solar panel. The fact that there is the ON- delay and that the fan always runs at full power may solve the problem. The shunt current can be increased by reducing the value of R1, but then a bigger portion of the energy will be wasted. The optimal resistor value can only roughly be estimated without knowing the real current production of the panel and frequency of the use of the toilet.
I appreciate all improvements and hints you could give to me. I am a hobbyist with no training in electronics. I have got all my knowledge by reading forums like this. I have not tested the circuit, since it still is a dark and cloudy winter here.