LowTech Controller for a Direct Solar Heating Floor System With Drain-back

The heating system is quite simple and very efficient. It is made of underfloor heating pipes in a concrete slab (4m x 5m), a circulation pump, two solar water panels and a tank.

The tank is a sand filter for swimming pool salvaged from the local rubbish dump...

We decided to use a drain back system after viewing the excellent video of Ben Gravely "The advantages of Drain Back Solar Hot Water System".

The project itself is the controller of the circulation pump. A "solarimeter" drives a relay which powers the pump.

1 photovoltaic panel 12V 2W

1 junction box (Gewiss GW44026) 150x110x70mm

1 industrial green signal light 22mm 230VAC

1 knob switch 3 position self-blocking 2NO 22mm 230VAC (XB2-ED33)

1 ammeter 0-100mA

1 relay FINDER 9V(or 12V) 40.61

1 varistor 07D391K

1 diode 1N4007

1 LED 1W batwing type (optional)

2 PCB terminal block 5.08mm pitch 3 ways

1 PCB terminal block 5.08mm pitch 2 ways

1 PCB header and 1 PCB connector 5.08mm pitch 3 ways

1 PCB header and 1 PCB connector 5.08mm pitch 2 ways

1 PCB

Once you get all the components and the board, you can solder everything on the board. Be careful with the diode and the LED which are polarized. Begin with the lower components (LED and diode) and finish with the higher (relay).

There is a low voltage side of the board and a high voltage side (at the bottom).

There are 2 holes of 22m and something special for the ammeter. We used Fusion360 to draw the dxf file for our 40W laser cutter.

We put the switch on the left and the lamp on the right. The ammeter is at the top of the cover. Tighten everything carefully.

Use some soft wire (0.75mm2) to connect the ammeter and the "auto" switch to the 2 pins header in the low voltage side of the PCB. The ammeter is polarized, test it with a small battery to find the + and the -.

Use some soft wire (0.75mm2) to connect the lamp and the "on" switch to the 3 pins header in the low voltage side of the PCB.

Install the 4 screws and slide the PCB, then tighten the screws.

The power cord is connected to the central block and the pump on the right block.

The PV panel is connected to the block with 2 pins on the left side. Again it is polarized, use a Voltmeter or try...

Normally, when the switch is on the middle position, the pump is off.

When the switch is on the position "ON", the pump is working and the lamp is ON.

When the switch is on the position "OFF" and if it is sunny then the LED is giving light, the ammeter shows some current and the pump is working. The lamp is also ON.