Solar Water Heating Pump Controller
Solar Water Heating Pump Controller
Build an electronic pump controller for a solar water heating systemwater | solar | electronics
Any solar water heating system
(DIY or otherwise) with a
must have an electronic controller of some sort if everything is to run optimally.
Solar Water Heating 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
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
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.
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
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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