Small solar plant irrigation system.

[stillhanginginthere]

Hi, looking for some advice please. I would like to use the following without a controller or battery. Will use a timer. This is just to pump water at specified times to plants growing in pots.
The solar panel is a Model SGP-5W-18. Polycrystalline. Peak power 5wp. Power tolerance +/- 3%. Open circuit voltage 21.9v. Maximum power voltage 17.6v. Short circuit current 0.31. Maximum power current 0.2 8. Maximum system voltage 600v DC. Size 185x250x15mm.

The pump is Anself model DC30A. Brushless DC. Hmax 350cm. Qmax 260 L/H. Input DC 12v/5w.
Any advice as to whether this is feasible would be greatly appreciated.
Thanks

 

[SeaGal]

Sounds like an interesting project

Obviously it won't work if there not enough luminescence to generate the required power to turn the motor - but then, I am guessing you will only need to irrigate when it is pretty bright.

If I was attempting this project I would find a suitable buck converter to generate the 12V required output. I'm no expert in BLDC motors, but I suspect they might need a bit more current to start-up, so I'd connect a largish electrolytic capacitor across the buck's output to be able to deliver any initial surge current needed - maybe something like a 3300uF or 4700uF

The buck will reduce voltage from the 15-22v generated by the panel to the 12V required (and increase current), but will lose a bit of power in the conversion process - around 5-10%.

The question will be whether the motor _needs_ all the 5W to run - if so, as your panel will only produce 5W in perfect ideal conditions and you will lose a bit in the conversion, then most of the time you won't have 5W to run the motor - maybe just 3W to 4W with UK sunshine levels.

If so, then it may be necessary to run the motor at a lower voltage (if that is possible - maybe someone else with more experience with BLDC motors might chip in) - this will also allow the buck to deliver more current. So, I'd choose an adjustable buck converter rather than a fixed one to give you more options to play with.

If you have a bench power supply it would make sense to test the motor under different voltage / current options to see how it runs.

If the motor won't run with only a 3W-ish supply you would need to increase the solar panel size and/or put two of them in parallel.

Do let us know how it goes - will be interesting to follow

 

[wpns]

How often do you want the pump to run (only when there's sunlight?), and how many peak hours do you get in your location. With a 12V battery charger and below a certain number of runtime minutes, it'll probably work, but it feels undersized to me.