30 sec-3 min (water) pump timer relay (schematic)
A very simple circuit with which you can use a 12 V (1-3 Amp) immersed water pump (used in automotive/caravans) to pump out a water tank for (say) 30 seconds up to 3 minutes. Of course: the pump may not run dry, use/select a proper time (!) to prevent overheating/damage to the water pump. When the pump runs dry it can get too hot, it is often cooled by the water flow. The whole circuit is connected to the grid, in the Netherlands 230 V - 50 Hz, other grid values and transformers will work too, though the transformer must be adapted to e.g. 110 V etc mains. The very good property is that it takes NO current when it is not in use, so an environmental-responsible circuit in terms of energy consumption. By the way: Use good quality timing capacitors. Best is to take the working voltage high, so a 100 uF - 200 V cap works better than a 100 V - 24 V cap. Anyway, this is no guarantee so you have to do some experiments with the timing capacitors. By the way: it always works, also with low quality capacitors, so don't worry. More electronics in my books on the Lulu website, author Ko Tilman.
