Information: solar powered drip irrigation system
This is information rather than a question. I built a drip irrigation system that operates with a small 12V pump, which is connected to a solar charger and battery. The system has been very troublesome, so I am posting some info about my tribulations in case it is helpful to anybody else.
The system consists of:
* 12V 14.7 litres per minute, 40 psi pump (cheap pump, you can get them online for well under $100)
* 12V gel cel battery (now 26 AH, but started with 12 AH)
* 40 watt solar panel (but started with 8 watt)
* Solar battery charger / controller (now 30A, started with 10A)
* 100 drip points over about 500m total length
* About 6 m rise to highest drip point (but some are about 2 m lower than the pump - it's hilly territory)
The good news is that the system is "just right" when it works, providing good flow at all points around the garden, and pump able to pressurise the full run in about 7 minutes.
Problems I have encountered after one year of use:
* The pump! They are incredibly unreliable. The main problem is the pressure switch - they seem to have a mean time between failure of about 5 hours. There are many online vendors selling what appears to be the same pump, just with different labels. They are all made in China. I have bought three pumps and two additional pressure switches so far. Probably because the systems cycles on and off quite quickly, the mechanical pressure switches just can't take it and fail. The switch can be bypassed so the pump just runs continuously, but that sucks a lot of power and can also burst connections on the irrigation pipe. My summer project is to build my own controller so I don't have to use the pump's own pressure switch.
* Gel cel. They have high "internal resistance", which means the voltage drops quite quickly when they are heavily loaded. They bounce back again, but the temporary low voltage can be seen as "discharged" by the controller and it shuts the system off. I have more than doubled the battery size and that seems to have fixed the problem. The pump has a nominal current of 7.5A but it is much higher when the pressure builds up, especially if I have bypassed the pressure switch.
* Battery charger / controller. Not really a problem, I just chose one that was too light. It had a max load of 10A I found the pump often sucks more current than that. It was sensing an "overload" and shutting down. The new 30A unit is OK. They are really cheap anyway.
* Solar panel. Again not really a problem, but I have found that I want to run the system more often and for longer than I can manage with the original 8 watt panel. The new battery and solar panel setup should be good for about one hour run time per day, but I'll have more data on that by the end of summer. The pump has never been reliable enough to get a "normal" month of operation.
* Add a pressure accumulator to even out the pump cycles (slow down the on/off cycling)
* Build my own pump controller!