Pumps are bad news for off-grid systems – here is how I solved it.

As I’m putting the second off-grid winter behind me, I’ve learned more about the behaviour of my well pump and septic system and how it effects the batteries.

My Grundfoss SQFlex well pump (1HP) runs for approx. 3 hours using 500W and the Orenco AX20-RT recirculation system runs two 3/4 HP pumps every 30 min for about 30 seconds each and more frequently if there are a lot of people in the house. All pumps are installed with a variable frequency drive (VFD) to ease the impact on the inverter when they start. That part works well.

The bad news however is that the system runs all night and grinds down the batteries before dawn. The voltage in my 48 volt battery bank has dropped below 46V on several occasions which triggers the generator to start (at 5am in the morning!) and recharge the batteries.

To solve this problem – keep my batteries healthy and get some uninterrupted sleep – I’ve programmed my Outback Mate 3 Low Battery Disconnect AUX port. If the voltage drops below 48V It enables a 12v/240v relay and turns off the Orenco system and well pump until the battery voltage raises above 49V.

The relay shuts down the power to the pumps – so they for a few hours become inoperable until the sun rises and the PV panels receive enough daylight to begin charging the batteries.

So far this has kept the battery voltage above 48V and prevented the generator from starting.

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