posted 10 years ago
"NO YOU CANNOT RUN YOUR HOME WATER PUMP OFF OF A BATTERY BANK !!!"
I have seen actual systems that do this. It is not uncommon in off grid situations. It's just expensive. There are ways to optimize the system so that it's not so crazy expensive as well.
My pump runs, on average, about 12 starts a day, and runs for less than two minutes. While the draw IS high (1,100 watts running, almost 4 kw starting) it doesn't run very long. It's a 1.5 hp pump.
My battery bank had 8 t105 batteries, and could supply 1.5 kwh per battery if you go to 100% dod. So the max would be 8 x 1.5 kwh = 12 wkh
Conservatively, I can discharge to 50% DOD, that gives me 6 kw hours.
In 24 hours, the pump uses 1,100 watts x .4 hours = 0.44 kwh
My battery bank could operate my well pump for 6 kwh/.44 kwh = 2 weeks if I ran nothing else and had no means of charging the batteries. Realistically, in a grid down scenario, I'd be careful about water use and get a month out of it, and have a generator to charge the battery bank as needed.
There are also soft start systems that would reduce the strain on a marginal inverter.
There are also 1/2 horsepower deep well 120 volt pumps that make this more do-able as well. They draw ~450 watts running, and ~1,500 watts starting.
I can't run my well pump on my battery bank because the inverter was too danged expensive. As in thousands of dollars. But I'm not optimized for this application.
It is technically possible.
If optimised for this, you can get 4 kw full sine wave inverters for around a thousand bucks.
8 t105 batteries will also run you about a thousand bucks.
I lay out the math just for illustrative purposes. After all the math and the hand waving, Steve is right for all practical purposes unless you're willing to spend a big chunk of cash.