Differential thermostatic
control is the best way to insure a net heat gain from the sun. Some controllers
not only regulate heat flow but they also monitor collector and storage
temperatures. Some controllers use multiple relays that control pumps and
electronic valves… AND some controllers use separate controls for both the
differential on and differential off settings. All of these things are fine…
BUT remember the most important job of any solar controller involves the
activation of a pump when heat is available for collection. For this reason I
have developed a rugged basic differential controllers that respond to solar
heat availability.
Conventional on demand
heaters rely on the convenience of fossil fuel energy concentrates. Only one
temperature sensor is needed to activate the combustion process within a
furnace. Solar heating systems are a bit more complicated. They rely on the
intermittent nature of sunlight and two temperature sensors.
The solar heat available for
collection is the driving force behind the differential controller. Metering the
actual collector and storage temperatures can be interesting but it’s not an
essential part of the heat collection process.
The AC/DC
Differential Controller is sometimes called a solar controller because it controls
the heat flow from a solar collector. It will turn an AC or DC pump on and off
to maximize solar heat gain from a solar collector with a minimum expenditure of
electrical power. An AC pump may be regulated with this controller by using a tiny 12 VDC wall transformer
instead of a PV power supply for the controller. A simple jumper wire between terminal
2 and 3 changes the AC pump differential controller into a DC pump differential
controller so the AC/DC controller can be used to drive either an AC or DC
pumps... It's rugged and dependable and it consumes less than one watt per hour yet it
can drive pumps that consume up to 300 Watts per hour.. Two temperature
monitors continuously monitor and display both collector and storage temperatures.
A differential potentiometer is used to adjust the temperature at which the pump
turns off.
This
is a basic differential controller with most of the components enclosed. There
are two indicator lamps. One turns on when the pump is activated and the other
one glows in proportion to the heat that's available.
Pins 1 and 2 are used to connect the relay to the
pump. Pins 3 and 4 are used to connect either a PV supply or a Wall Wart 12VDC
supply. The last three pins are used to connect thermistor probes to the
enclosed differential controller.
Remember the main function of a
differential controller involves the regulation of a circulator pump based on
the temperature difference between the heat collector area and the heat storage
area. Heat is monitored with a single LED that glows in proportion to that heat
availability.
.This Basic Differential Controller is
identical to the one above in every way except that it's not enclosed. It's
available as a kit for $65 and it comes fully assembled with a set of probes for
$85.
The relay can handle up to 300 watts of power and
it may be used to regulate either AC or DC pumps.
The differential pot adjustment is used to strike
a balance between heat gain and energy conservation.
Polarity protection is also included incase the user
mistakenly reverses the power supply.
This is a tough little differential controller
designed to simplify the the hook up connections as well as the differential
settings.
I also have a few controller kits left that only
use one LED to indicate when the pump is on
Differential thermostatic
control is the best way to insure a net heat gain from the sun. Some controllers
not only regulate heat flow but they also monitor collector and storage
temperatures. Some controllers use multiple relays that control pumps and
electronic valves… AND some controllers use separate controls for both the
differential on and differential off settings. All of these things are fine…
BUT remember the most important job of any solar controller involves the
activation of a pump when heat is available for collection. For this reason I
have developed a rugged basic differential controllers that respond to solar
heat availability. 
