AC DC Differential Controller
The AC/DC differential controller is designed to optimize the solar heat gain from a collector and also provide continuous monitoring of both collector and storage temperature. The illustration to the left shows the collector temperature on the top monitor to be 115.1* F. The bottom storage tank temperature monitor reads 99* F.
To power a DC pump with a PV power supply the user will install a jumper between pin 2 and 3 to bring DC power to the relay. If an AC pump is regulated a small 12VDC Wall Wart DC adaptor is used to supply DC current to the controller. In other words the AC DC controller may be used to regulate either an AC or DC pump. If a PV power supply is used a battery backup is required to stabilize the voltage under variable light conditions.
The relay is guaranteed to handle up to 300 watts of power and it has been tested on 500 Watt loads.
The differential on temperature is preset at about 18* F, ideal for solar collectors that can reach stagnation temperatures over 250* F in bright sunlight if no water is circulated. The differential off adjustment is made by the user and it has a range of about 15* F. The best differential off adjustment is normally between 2 and 5 degrees F.
The temperature probes are made from LM34 temperature sensors that have a direct relation between voltage output and temperperature. The storage probe is normally taped to return pipe between the tank and the pump. The collector probe is taped to the output pipe of the collector about 3" from the collector body and the supply voltage to the probes comes from a 5 Volt regulator on the controller. This is done to protect the controller in case the probe wires are shorted.
As you can see the basic differential controller is fairly easy to connect to either an AC or DC pump, but if you're looking for a fully enclosed, very attractive basic controller specially modified for a PV system look no further. The basic controller illustrated below comes fully assembled in a rugged but attractive package. Notice that all the components are fully enclosed and the differential control is clearly marked. The pump may be turned on manually or it may be controlled with the included sensors. Click on the above illustration for more information.
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