Operating a Grundfos SQFlex 1.2 at reduced flow

[HBB]

Hello,

I have a 1200 liter hour pump operating in a well that is only capable of 950 liter hour.

When used directly with solar panels I limit pump flow by using only the number of panels accordingly to the power needed. That is about 120 watt.

On cloudy days, the problem is that if I run the pump directly from my 48 Volt battery bank, or from 220 VAC generator, the pump logic applies full power to the pump (about 180 watt), the pump runs fine, but dries the well in 15 minutes aprox. Then the pump security switch reacts and stops the pump for five minutes.

I dont want to operate that way, because that means to use the security system as a standard operating system, and I dont like to go that way.

What I am trying to find out is a sort of Dc Dc converter to go from 48 VDC to 120 VDC (voltage in which the pump logic has the maximum efficiency) and limit the power to 120 watt.

I am achieving that scheme, but with poor power efficiency. I work with a PIC controlled converter that drives 2 IGBT, a power transformer with primary winding for 48 + 48 Volt and a secondary of 110 Volt. Then filtering and powering the pump.
I would rather like a switching high frecuency dc - dc converter with power limitation.

Any ideas from similar cases ?

Best Christmas and New Year for all readers !

Horacio

[inetdog]

Hello,

I have a 1200 liter hour pump operating in a well that is only capable of 950 liter hour.

When used directly with solar panels I limit pump flow by using only the number of panels accordingly to the power needed. That is about 120 watt.

On cloudy days, the problem is that if I run the pump directly from my 48 Volt battery bank, or from 220 VAC generator, the pump logic applies full power to the pump (about 180 watt), the pump runs fine, but dries the well in 15 minutes aprox. Then the pump security switch reacts and stops the pump for five minutes.

I dont want to operate that way, because that means to use the security system as a standard operating system, and I dont like to go that way.

What I am trying to find out is a sort of Dc Dc converter to go from 48 VDC to 120 VDC (voltage in which the pump logic has the maximum efficiency) and limit the power to 120 watt.

I am achieving that scheme, but with poor power efficiency. I work with a PIC controlled converter that drives 2 IGBT, a power transformer with primary winding for 48 + 48 Volt and a secondary of 110 Volt. Then filtering and powering the pump.
I would rather like a switching high frecuency dc - dc converter with power limitation.

Any ideas from similar cases ?

Best Christmas and New Year for all readers !

Horacio

If you do not mind running the pump in on-off cycles, but do not want it to run dry every time, with possible damage to bearings, impeller, etc. each time, or are willing to limit the output at all time I have two suggestions for you:

1. Install a flow limiting (constant flow) valve so that the rate at which water is pumped does not ever exceed the recharge rate of the well. If you do this, the pump will draw less current, as it is moving less water (assuming that it is a centrifugal impeller pump rather than a positive displacement pump). The panel voltage will rise closer to Voc, but the pump will not be damaged if you have set up the array to limit Voc to what the pump can tolerate. If it does not use the full output capacity of the panels, no harm will be done.

2. If you want to keep the full flow rate of the pump, set up timer so that the pump turns on and is shut off after, say, 12 minutes, before it runs dry. Then the timer will keep the pump off for what you determine to be the necessary refill period before starting again. This cycle will continue as long as you have power. The disadvantage is that the pump will also cycle on and off even if it is not pumping at full rate because of low power from the panels.