Solar Pumping

[GKman]

I need to pump water from a stream to a pond. The lift is about 12 feet. I saw a credible youtube video of a Rule 4000 bilge pump supplied with 400 watts of solar panels. He's using no controller to prevent low voltage to the pump. Have a hunch they are operating manually, switch on when the sun shines. I can find a million controllers that charge batteries and have a low voltage cutoff but I don't want/need batteries. I'm needing a relay or equal that closes when the solar panel output is adequate to run the pump and opens when it drops below a certain level. Perhaps 28V on, 22 V off. Is there a name for such a device that I can search for?

I'm sure a simple circuit would do it but it seems my electronic designs usually end up with problems that I can't solve.

[chipmaker4130]

Unless you need a specific flow, why not just direct-wire the pump to the panel and take what you get. We run a number of radiator fans at work directly from a 400W panel in that manner and it works fine. I also have a solar water heater setup at home that runs the pump in the same way. If you have insufficient sunlight you simply don't get much flow.

I might add that our panels are 36V and we run 3 12V motors in series. For a year or so we ran only two motors in series and that worked fine too, no damage to the motors.

[1-800miner]

I have a Chinese 12v diaphragm pump ( cost about 100$ and running three years trouble free) wired direct to panels.
Low voltage has not hurt it. It pumps about ten feet but could go higher with more panels. Pumps when the sun shines and quits at dark.
I pump to a tank with the overflow plumbed back to the well. Tank then distributes it to the animals and garden.
Works so well that I forget about it.
I just looked at ebay and they are down to 65$. Why do they drop the price after I buy one?

I forgot to say: It is powered by two sets of Harbor Freight panels. (six total)

[mattthegamer463]

Do you have 400 watts of solar panels already? The cost of 400W of panels would be a non-start for me.

I would do a minimal quantity of cells, which charge a lead acid battery. Then use a programmable controller to monitor the battery voltage, when the battery goes up to 13.5V, a relay will turn on the pump and pump water until the battery voltage drops to 11.5V. Then it would spend some hours/days to recharge, and do it again. Possibly to make it run more regularly, run the motor a fixed time and not fully deplete the battery each time, so it can cycle faster.

[J Tiers]

Not sure what the issue with the drop-out is. In general the pumps will stand the stall current, because it is low. Solar cells do not put put voltage, they put out current based on the solar input. The voltage is dependent on the load, up to the max the panels can do. So if there is too little sun, the current is low, and will not damage the pump.

If you use a relay, odds are it will be clicking itself to death because the voltage will rise, relay close, voltage drops below the relay voltage, relay opens, and that cycle repeats until the cells are putting out sufficient current, or the relay has failed. You would be making a "buzzer".

There is NO reason for the battery system. You will pay as much for sensible sized batteries and controls as for the panels. The batteries will spend enough time discharged that they will be fairly quickly degraded, and need replaced.

[chipmaker4130]

. . .Solar cells do not put put voltage, they put out current. . .

That's part of the story. No voltage=no current. The 36V I noted above is what those panels can maintain with the rated 400W load in direct sunlight. It is a helpful spec when designing a system, especially here in the desert where full sun is the norm.

BTW, you don't have to get all techy on me to prove your point. Just let it go.... if you can.

[J Tiers]

.....

BTW, you don't have to get all techy on me to prove your point. Just let it go.... if you can.

Dude... The answer had info for 3 different people.... take a chill pill.

[GKman]

Great guys,
1. I've found odds and ends of solar panels on craigslist for less than $1.00/watt. One vendor for $135/235W.

2. A buzzer? That's why I specified an spread between on and off but if three of you guys say I don't need it then I don't need it. Wish other forums had credible members like HSM.

3. It always sounds to me like somebody repealed Ohms Law when I hear about devices producing current instead of voltage but once again I just can accept it being that way if I read it here. Would like to hear an explanation though.

Time to go buy some panels and a pump. Thanks again. I'll let you know how it works.

[chipmaker4130]

Dude... The answer had info for 3 different people.... take a chill pill.

Yeah. Its Monday, I'm ornery, and I was egging you on. Looks like 1/3 of an answer isn't sufficient:

Great guys,
. . . It always sounds to me like somebody repealed Ohms Law when I hear about devices producing current instead of voltage but once again I just can accept it being that way if I read it here. Would like to hear an explanation though. . .

[J Tiers]

......

3. It always sounds to me like somebody repealed Ohms Law when I hear about devices producing current instead of voltage but once again I just can accept it being that way if I read it here. Would like to hear an explanation though.

No laws repealed....

The panel produces an amount of current that depends on how much light hits it.* It DOES have a max voltage that it can produce.

So, Ohms law is very very active in the matter.... the panel can produce, say, 2 amps with the light that hits it, and is a nominal 18V panel. So.... if the load (pump, light, whatever) draws LESS than 2A at 18V, the panel will put out at least the 18V. Usually somewhat more, depending on the cells.

If the load draws 3A at 18V (and acts like a resistor), then its resistance is about 6 ohms, and the 2A available will produce a 12V output.

The whole point of saying it produces current and not voltage is that with a motor, the difference is important.

If you have a 12V motor that draws one ampere, and a big 12V battery to run it.... then if it is running right, it draws 1 Ampere (1A). But if you stall that motor, it may draw 5 or 6 amperes, maybe more, because the 12V is "fixed", the battery will supply 12 V at a lot more than 1A of current. That will probably burn up the motor.

If you have that same motor, and a power supply that produces a max of just over 1A, and no more voltage than 12V, then the motor will run fine. But if you stall the motor, you do NOT get a lot more current as you did with the battery. Instead, you still get the 1A, but the motor "acts like" a heavier load, so the voltage applied to the motor will drop. That means the motor will NOT be burned up if you stall it.

Not only that, but as the light decreases, the available current drops also. The motor will run slower, and finally stall, but it is at a low current, less than the normal current, so the motor should be OK, even without sny air being blown through it.

So a set of solar panels that are reasonably matched to the motor current requirements will not burn up the motor.

* techie explanation... Light is "photons", and each one that hits the panel produces some amount of electron flow (current) in the panel (that may not be 1 electron for 1 photon). The more light, the more photons, and the more current that is available. Each cell can only produce a certain maximum voltage, so a panel has a lot of cells in series to produce a higher voltage. Most common cell types produce about 0.4 V.

[A.K. Boomer]

Can't beat "direct drive" for it's simplicity and maintenance free, I went through the same process when building insulated duct work in my attic to pump air from the solar porch into the back of the house - one solar panel that doubles as a awning powers my fan,
I used a brushed motorhome squirrel cage at first - lasted for a few years but the armature did go through hell in those borderline current phases, it shot craps last year

not i have two electronic brushless fans and they do not seem to mind the idle times - they either start up or don't work and there's no in between,,,
they made it through their first year anyways and are dirt cheap so no worries...

[GKman]

Thank you Mr Tiers,
Will try to keep eye on ball.

[danlb]

Jerry, the rest of us really are not interested in how you justify the statement "Solar cells do not put put voltage, they put out current based on the solar input". You only THINK that you were expounding on the point for the benefit of "three different people". Those three apparently already had working systems.

The statement that a device supplies current, but not voltage is sure to be controversial and adds no value to the thread. It would be much easier if you just stopped using that phrase (you've used it before, also with great debate) and instead used some other phrase that does not contradict what we are taught in school. Then you would not need to type 9 paragraphs to justify it.

Besides, isn't the proper concept that the device is current limited based on amount of energy that hits the panel?

[GKman]

Another credible youtube video of a TOYOTA PRIUS Inverter Coolant Water Pump, running off a solar panel. About 2A at 12v. don't know if it will produce the 12' of head I need but sure is moving some water. Maybe two in series electrically from a 24v solar panel and in piping (6' Lift each) for $110. Looks like it would be rated for continuous use in a worse environment than I need. Or perhaps there there would be another automotive water pump that would utilize more of the output of one or 2 24v 235 watt rated solar panels? And yes I know the 235 is at noon on the equator at 10,000 feet elevation.

[gambler]

https://www.carparts.com/details/Vol...E&gclsrc=aw.ds vw and audi use these