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Running a 900w poolpump


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2 hours ago, Majoor Doppies said:

run a 900w pool pump from 20:00 till 04:00 the next morning (8 hours) ?

Why not run it during the day?

8 hours at around 1kw constant, thumbsuck, means 8kwh to make the math easy. For 8kwh storage you're talking a big bank of Trojan L16RE-B (to remain above 40% DoD), or 4 Pylontech racks. You need to recharge them with the average 5 hours of solar day we have in SA, so around 2kwp of PV, probably more to account for days that are a little less sunny. For the inverter... well... that's the easy part. Something that can handle the startup of a 900W motor, so probably something around the 2kva range. I know a 1600VA Victron Phoenix will handle that easy.

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One has to size the inverter to accommodate the spike that occurs at start up which can be up to 2½-3  times the normal draw. To give you an example I have a client with a  cold room which draws about 26-27A but has a start up draw of 72A. That is why single phase motor often have a capacitor to help with that spike and 3 phase motors have star-delta starter to slowly get things going.

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Over and above the answers above, I have a question: Why run such a load at night?

The cost in batteries will be substantial.

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I have a 5KVA Mecer-Axpert with 8 x 200Ah Narada batteries and 6x265W + 6x260W panels. I have a 1.5HP (rated 1,500W max) booster pump we use to run pop-up sprinklers, 1HP pump which pumps utility water to a 5m stand tank (feeds the house by gravity, no need to have a wasteful booster which runs each time a tap is opened) from a collecting ground tank. I also have a 0.5HP sump pump which circulates water in our backyard aquaponics DIY system. The 1.5HP starting surge puts the Axpert in overload for a sec but steady run is lower than the rated 1.5kW. As the overhead tank water level activates the float switch the ground pump starts with no problem and the combined load is easily handled by the inverter and more importantly by the solar panels. I actually have to run the fish pond sump pump to make use of the available solar.

In short, run your pool pump during the day and it should be operated by solar energy free of charge with 4x320W panels mated with a 4x 200Ah battery bank and a 5KVA inverter. I would connect the inverter to some household loads to optimise the investment.

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13 hours ago, The Terrible Triplett said:

Over and above the answers above, I have a question: Why run such a load at night?

The cost in batteries will be substantial.

You can also get pool pumps that run directly from solar, not cheap I believe, but you won't need batteries. : Like this : https://www.sustainable.co.za/bundu-power-sp-jp13-13-370w-solar-pool-pump.html

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14 hours ago, Chris Hobson said:

That is why single phase motor often have a capacitor to help with that spike and 3 phase motors have star-delta starter to slowly get things going.

It gets a bit more interesting than that :-)

With a single phase motor, that capacitor isn't there so much to limit inrush current, it is there because without it the motor would not be able to start at all. A capacitor is what one might call a "frequency dependent resistor". When used in an AC circuit it passes current proportional to the frequency, and it also shifts the waveform. By applying this shifted waveform to an auxiliary winding on the motor, you can generate a rotating magnetic field that sends the motor running in a particular direction.

(That's why, on a motor with a broken starter cap, you can sometimes start it by spinning it in the right direction by hand).

With three phase starters the goal is to either limit inrush current or to reduce mechanical stress on whatever that motor is driving. What that does is wire the motor in delta at the start (so the voltage across any winding is lower), and then when the speed increases you reconfigure it to delta placing the full voltage across each winding.

These videos explain it rather nicely:

 

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5 hours ago, DeepBass9 said:

You can also get pool pumps that run directly from solar, not cheap I believe ...

Jip, they are. Farmers can benefit though.

I once looked at, cannot find it now, where someone made a box that you connect your stock standard pool pump to.

This box is then connected to a solar inverter / solar panels, no batteries.

The box sorts the startup current, ensures the pump only runs when there is enough power from panels somehow.

And it was inexpensive compared to a solar pump.

Plus, stock standard off the shelf pool pumps are easy to get, maintain and replace and WAY cheaper than solar pumps..

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4 hours ago, The Terrible Triplett said:

Jip, they are. Farmers can benefit though.

I once looked at, cannot find it now, where someone made a box that you connect your stock standard pool pump to.

This box is then connected to a solar inverter / solar panels, no batteries.

The box sorts the startup current, ensures the pump only runs when there is enough power from panels somehow.

And it was inexpensive compared to a solar pump.

Plus, stock standard off the shelf pool pumps are easy to get, maintain and replace and WAY cheaper than solar pumps..

Pump inverters - INVT make a very nice one that I recently installed.

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