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Solar Well Pump

Posted: Mar 25 2019 3:55pm
by TPA
I need to see if you guys know if a product exists.

What I would like to do is add a fail safe mechanism to a water well PV system.

It will be a basic dedicated off grid system:
Grundfos well pump 230V (the pump is the only load at 1400-1500W except maybe a light in the well house).
3 200W solar panels
4 golf cart batteries (24V system)
MPPT controller (currently looking at VICTRON SMARTSOLAR 75/15 MPPT CHARGE CONTROLLER)
Still looking at inverter options. This one is challenging since the pump is 230V. I have a 2000W transformer, but I'm afraid it will be too parasitic.

Charge controllers and Inverters have the ability to protect batteries with a low voltage cutoff. I hope to have this ability with both components, but I would like to add another layer.

If there happened to be a break in the water line, it would gush water until one of the components tripped the LVC.

Is there a timer device that can disconnect either the inverter or the batteries if the current has been flowing for more than a few minutes (adjustable)?

I do not use prolonged watering of any kind, so there should not be any constant operation of the well pump. The pump only takes about 15-30 seconds to fill the tank and shut off. I would like a device that will interrupt the system if it is drawing current for more than a few minutes, and require a manual reset to resume operation to protect batteries, save water, and prevent water damage.

Know of any such device?

Re: Solar Well Pump

Posted: Mar 25 2019 10:14pm
by amberwolf
I am pretty sure I've seen someone on ES using such a timer, but I can't remember where.

You could make such a timer fairly easily with a 555 timer chip and a current sensing shunt that simply triggers a comparator. The comparator detecting current flow then enables the timer chip in one-shot mode, so that it will eventually trigger (and disable the inverter, or shutdown the BMS, or whatever), at whatever time you've chosen by the resistor and capacitor values (or use a potentiometer so you can vary it).

Can add a reset button to the 555 timer if you need one.

Re: Solar Well Pump

Posted: Mar 30 2019 12:19pm
by cricketo
While a timer would work, it's always easier for non-EE types to go with software implementations. There are many examples on interfacing Arduino boards with Hall effect sensors and / or Water flow sensors. Then the only other component needed is a latching relay to control the power. I think it would be better to step up the battery configuration to 48v, to cut the input current in half, so relay component would be less beefy and less likely to get its contacts welded together.

Re: Solar Well Pump

Posted: Mar 30 2019 12:35pm
by cricketo
Here is an example relay that may work (50A rated) : ... 7223!US!-1

50A at 48v nominal is 2400W. Now if the voltage is 24v, it's obviously only half that, at 1200W, which may be insufficient given the requirements. Also this relay has 12v coil, which shouldn't be a major show stopper - a smaller 5v relay can be used directly from Arduino output pins to drive the 12v supply to power relay.

Re: Solar Well Pump

Posted: Mar 30 2019 9:04pm
by major

I live out in the sticks. Need a back-up for my well pump. Don't like gas engine generators. I have plenty of batteries. So I have a number of UPS units which I can use for different appliances. The well pump was a challenge due to inrush or start-up current. It is a single phase induction motor on 110V. Rated at 1/2hp (might be 1/3). 3.1KVA inverter would trip out. Had to go to 4.3KVA. Good news was cheap UPS on eBay. Sold off due to dead batteries. Replace with external battery pack (48V in this case) and it runs good as new.


Re: Solar Well Pump

Posted: Apr 14 2019 11:50am
by jhaz6471
In order to smooth out starting loads use oil filled capacitors . they will take the shock of the starting load off the inverter.
You can use one out of a house air conditioner , it stays on line with the inverter. You need to put it in a metal box if it should ever fail with a 20amp circuit breaker for safety and almost zero power usage.


Re: Solar Well Pump

Posted: Apr 16 2019 12:34pm
by TPA
I think I am very close with this device. If I could get one at 15A, it would be just right. ... B007ID7OXI