Solar Water Heating Pump Controller
Solar Water Heating Pump Controller
Build an electronic pump controller for a solar water heating system
water | solar | electronicsAny
solar water heating system
(DIY or otherwise) with a
pump must have an electronic controller of some sort if everything is to run optimally.
Solar Water Heating Controller
This
controller detects the temperature of the
solar panel as well as that of the
tank which stores the heated water. Whenever the solar panel is hotter than the stored water, the pump should run to send hot water from the panel into the hot water tank. However, when the stored water is hotter than the solar panel, the pump (pictured below) should be off since the stored water would otherwise be cooled by the panel.
Since this is a very simple concept, it is possible for anyone to build their own
solar water heating pump controller relatively easily, and very cheaply.
12V 5 Watt pumps are available which can be powered directly by similarly rated
PV Solar Panels providing completely
renewable energy water heating.
Solar Water Heating System Pump Controller Circuit
The
circuit diagram displayed above is from the
Silicon Chip Online article entitled
Pump Controller for Solar Water System. (Click on the circuit diagram to view a larger printable version).
This very simple circuit is made up of just a few components. Key are the two
temperature sensors (LM335Z) which are used to measure the temperatures of the
solar panel and the
water tank, and the
comparator chip (LM393) which compares the two temperature readings. An STP60NE06
mosfet (a type of
transistor) is used to turn on the pump when triggered by the output from the comparator.
When the temperature of
Sensor 1 (solar panel) is higher than the temperature of
Sensor 2 (water tank), the
12V solar water pump is activated pumping hot water from the solar panel to the water tank as desired. When the temperature of the water tank is higher than that of the solar panel (for example at night) the pump is off.
LM335Z Temperature Sensors
The
LM335Z temperature sensor (
LM335Z Datasheet PDF available here) will accurately
measure temperatures between -40 and 100 degrees Celcius.
The voltage measured between the ground and the positive terminals of the
LM335Z increases at
10mV per °C. Since
absolute zero is -273°C, at 0°C, the voltage measured at 0°C is
2.73V
. At room temperature the voltage will be 273 + 20 = 2.93 Volts etc.
Since every sensor is slightly different, the circuit includes a couple of 10k
variable resistors which can be used to set the voltage output of the two sensors used so that they give exactly the same reading when they are at the same temperature.
Since the sensors are accurate to within
1°C, the variable resistors (trimpots) can be left out to simplify the circuit as shown above. Put the sensor with the
higher output voltage at a particular temperature as
Sensor 2 so that if both sensors are at the
same temperature, the pump will be off.
Sensor 1 should be stuck against the copper pipe as it leaves the
solar panel, and
Sensor 2 should be connected to the outside of the hot water tank underneath the insulation. In this way the two sensors will measure the temperature of the water pretty accurately without getting themselves wet. (
Note that water + sensor = broken sensor)
NEW LM335Z Precision Temperature Sensors are now available in the
REUK Shop.
Putting the Controller Together
Pictured below is the complete circuit put together for testing on
prototyping breadboard
.
For testing purposes the two
temperature sensors have been placed side by side on the breadboard, and a
12V LED Spotlight Bulb is used instead of the
hot water pump.
Since the
two temperature sensors are at the same temperature the pump is off. The
1 MOhm 10 MOhm resistor across legs 1 and 3 of the comparator chip provides
12mV of hysteresis - i.e. the readings from
Sensor 1 and
Sensor 2 have to differ by at least 12mV (1.2°C) for the output from the
comparator chip to be changed.
When
Sensor 1 (solar panel) is warmed up slightly by the heat of a finger, the light bulb used in this prototype turns on as it should.
Modifying the Pump Controller Circuit for 240 VAC pump
If the hot water pump is a 220-240 Volt AC model (or 120 VAC for US visitors), then this same circuit can still be used by using a
12V relay (and diode) in place of the 12V pump in the circuit. When the temperature of the
solar panel sensor is higher than that of the
hot water tank, the relay will be triggered supplying electricity (from an external 240 Volt AC source) to the
hot water pump.
Buying a Complete Solar Contoller or its Components
NEW We are now supplying complete solar pump controllers in the
REUK Shop. Click here to find out more about our
Solar Pump Controller Circuit (pictured at top of this page) offer.
If you are interested in building your own
pump controller and you need to buy some or all of the necessary components,
contact us and we will put together a package for you from the
REUK Shop.
Article Last Modified: 11:33, 9th Jul 2007
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