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dmg
Posted: August 07, 2017 07:16 pm
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ookay, so it turns out i need some help.

My borther has a tiny tiny electric pump pumping water from a small creek on his ranch stuff.
It does not need a lot of power, only 100 watt.

The problem is it needs to run 24/7 for reasons i fail to understand or would like to understand.
So over a month it does consume a hefty amount, and they have no option of grid tie solar solution.


How would it be possible to power the thing from solar, and if that is not available resort to grid ?
He has a small UPS that sortha manages to power the thing for a short time if power goes out.
The UPS consist of a battery charger , a battery, and a real sine wave inverter.
The pump runs from the inverter, there is no cut out to grid driectly.

How could i connect a solar panel and make sure the solar panel is utilised at its maximum, and if say.. the sun sets, then just have the grid supply the power ?
i was thinking of having more than one battery, one allways running the pump via the inverter, one on the battery charger, and one charged by the solar panel...
and then say.. at a fixed time intervallum a circuit should swap them around , the one that ran the pump till then would be connected to the solar panel, the one that was connected to the solar panel would be connected to the charger (so if it managed to top off then it should take no further charging, if it did not manage then the charger would top it) and the one that was on the charger would hook up to the inverter.

I'm not even sure if this is a feasable way to do, and allso i do not know how to solve it ina way that the pump never stops.

and i have no clue why that pump has to run 24/7...


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MacFromOK
Posted: August 07, 2017 08:15 pm
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Always run the pump from the battery. If both the solar and grid are off for a while, you still have battery power.

Use the grid and solar only for charging the battery.

Use a relay on the solar output to turn on when solar voltage is high enough, and release the grid power. When solar voltage drops, the relay would turn off the solar and turn the grid power back on.

You could build a window comparator to trigger the relay, but it would be simpler to adjust the relay coil with a pot IMO.

Pretty simple, but it should make the most of the solar power. Would be even better if he could get a DC pump and avoid the inverter altogether.

My two cents. beer.gif


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dmg
Posted: August 07, 2017 10:36 pm
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hmm good point on the inverter.

what if the solar panel makes enough volts, but not enough amps ?
thent he pump will stall, but it will not change back to grid power charging the battery, right ?
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MacFromOK
Posted: August 08, 2017 02:49 am
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QUOTE (dmg @ August 07, 2017 04:36 pm)
what if the solar panel makes enough volts, but not enough amps ?
thent he pump will stall, but it will not change back to grid power charging the battery, right ?

I don't think so. As amp requirement increases, voltage will drop and the grid will kick in.

There might be a good bit of switching back and forth though. If so, then a window comparator might be a good idea to provide some hysteresis.


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dmg
Posted: August 08, 2017 07:56 pm
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i'd probabyl need a diode too to allow the relay to switch, and not be fooled by the battery voltage, right ?
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MacFromOK
Posted: August 08, 2017 09:45 pm
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Probably so. Just remember to allow for the voltage drop (usually 0.7V or so).


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dmg
Posted: August 09, 2017 11:15 am
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allso i might be better with an solid state relay, one rated for 5 volts, and probably a potmeter to set switching on and off.

i should sortha put this thing before a charge controller, supposedly those have boost converter inside to help increase the voltage i think.
i gona look around maybe i can source a charge controller that has cut in/cut out functionality. probably one that is supposed to be used for wind has something like that.
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