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How to make solar pump run intermittently ?  RSS feed

Posts: 533
Location: South Tenerife, Canary Islands (Spain)
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Setting up a misting system for cuttings. Objectives are cheap, simple, effective.

I plan to use a $10 solar fountain to mist a bed containing sand over gravel. The water drains thru the bed by gravity into a reservoir where the solar fountain pump is. The pump runs continuously while the sun shines (all day everyday here, not worried about cloudy days). But I want it to mist intermittently so the cuttings get a chance to dry off between mistings.

Is there a REALLY SIMPLE circuit or device I can put between the solar panel and the pump to make it run intermittently? I know I can buy timers but I want to make numerous misting beds and keep costs and complexity to absolute minimum. 10 seconds on, 50 seconds off would be great, but I'm sure a number of other variations would work well.
Posts: 1129
Location: Big Island, Hawaii (2300' elevation, 60" avg. annual rainfall, temp range 55-80 degrees F)
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I talked to a guy who came up with a solution, but it was with with normal grid electricity. If you're willing to figure it out, I'm sure you could adapt the idea to solar.

He said he used some sort of solenoid that he had rigged to a horizontal flapper . The idea was that the moisture would build up on the flapper. When it was heavy enough it would droop down, make or break some sort of connection and thus trigger the switch on the power to the pump. That turned the pump off. When the moisture evaporated off, thus making the flapper lighter, it would trigger the switch to turn the pump back on.

I've never tried this, so I can't tell you exactly how to rig it. But I thought it was a great, simple solution geared directly to the amount of moisture on the plants.
Posts: 598
Location: Victoria BC
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Huh, that's a really interesting solution that you describe, Su Ba.

For an electronic solution, you're looking for a cycle timer. I see prebuilt adjustable ones on ebay for a few bucks.

If you want to DIY, you might be able to do it with a 555 timer circuit in astable mode controlling a relay, which would be really basic. I'm not totally sure the frequency could be set low enough for this use...

A PIC controlling a relay could take care of it, but it's been a decade since I played with that stuff, details have definitely flown the coop.
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