[RE-wrenches] off-grid pump controls

[Mendocino Solar Service]

Hello Wrenchers,

I'm sure some of you guys and gals are familiar with this one: We  
have a customer with an off-grid studio building that gets little  
use, but has a nice 1.5 kw Unisolar array going unused most days. The  
owner wants to use the excess capacity to pump water from a well into  
his pond. We set up a 12 volt coil relay controlled by the MX-60 to  
run the Grundfos AC pump, but the question is what is the best  
control strategy? This is open pumping with no float or pressure  
switches, from a 20 gpm well.

We used the Diversion Mode first, but it only makes the AUX active  
during Absorb, Float, or EQ. As soon as those timers run out the AUX  
goes inactive so no pumping. Low Batt Disconnect is another option,  
but if that were set at around float, the load may not allow for a  
normal Absorb charge.

Some thoughts are to pump into a large pressure tank with a slower  
bleed into the pond to allow for better cycling, though this would  
limit the total pumping possible from the gusher well; or put in a  
timer so the relay couldn't activate until late enough in the morning  
for the Absorb to finish.

The parameters of the problem include:
1) allow for normal absorb charges
2) not cycling on and off excessively
3) let the battery be at or near float

I'll bet I'm trying to reinvent the wheel here, so do some of you  
wheel-inventors have any thoughts?
Thanks,

Bruce Erickson
Mendocino Solar Service
PO Box 1252
Mendocino, CA 95460
707-937-1701



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