solar watering system

I proposed a solar powered watering system for the plants to water them daily from the water butts by the greenhouse. As with all my projects, this has been work in progress for a long time now, but I have picked it up again with the intention of completion! View of the control box with the lid off showing all the major system components. Pumps go on the base, control and battery on the
solar watering system - schematic

lid (in case of leaks the electronics don`t get flooded) Main control PCB top side showing switching FETs (top left), control and timing (left) and power filtering / switching (bottom right). Top left is a not yet implemented MPPT controller circuit. Main control PCB bottom side. Power supply connections made with tinned copper wire, other connections made with enamelled copper wire (transformer wire). Note D2PAK transistor for switching the power rail. The control panel end that will be visible in the greenhouse. Dial of timing pot marked in 0. 5l increments to 2l. Force watering button and power switch. LED indicators to show which pump is active and if the control circuit is powered. At the other end of the case, a 15-way D-type connector forms the connection to the alarm clock. 3. 5mm stereo jack sockets form the connection to all 8 soil moisture sensors as well as the solar panel. Some kind of low power water pump is required so I picked up a couple of generic windscreen washer pumps from eBay (much cheaper than Halfrauds ). These are 12V rated, but judging by the power consumption they are not designed for continuous operaton. To decide how big the battery needed to be, I needed to characterise the pumps performance. To do this I pumped a pint of water between two milk bottles, varied the voltage and measured the time taken for the transfer. Measurements are in the below table. This is better shown in this graph below...

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