quoting the nemo website:
2. OVERHEATING of FLOJET MOTOR: The Flojet motors used in Nemo Pumps are designed for intermittant duty service, which means they will overheat during extended run times or if overloaded.
/quote
personally, I don't think I'd depend on a "submersable diaphram pump" in a well, especially one that is a modification of an intermittant duty pump that is NOT normally submersable. of course, your milage may vary.
If i HAD to depend on one, I'd think long and hard about how to protect it from voltage swings and stalls; replacing worn diaphrams and brushes is one thing, but to pull the thing out of the well and discover that it had burnt a commutator or the windings . . . let's just say I get really crabby when I'm dehydrated.
Nemo are claiming 2000 hours TTMO (total time between major overhauls) in optimal conditions. I'd be skeptical of that number; if you run the brushes out, you'll tear up the commutator, and that's a machine-shop job to fix. (or buy an new motor) 1000 hours MTBF is my guess; so I'd be overhauling the thing at 500 hours. (see comment on dehydration) guessing that the pump is going to run 3 hours a day, (200 gal/day for irrigation? pretty small patch you're cultivating) I see a lot of pump-pulling in your future. . . .
That said, and bearing in mind that you will not see the full "nameplate voltage" out of your panels with a load on them. . . . certainly not in the mornings and afternoons and with dust, etc. on the panel faces:
you can run a DC brush motor over-voltage. (the Electric Car folks do it all the time with wound-field motors, but not in a continuous duty full power scenario.) the problem you have is that you will be running the pump either full blast or off, and if you're supplying irrigation water with it, it will run for extended periods at full load. That means that the brushes, bushings/bearings and (cheap) permanent magnets will take a pounding, especially with a reciprocating load on the output. That adds up to significantly less reliability on a style of pump that isn't renowned for its durability. (nothing against FloJet- all recip pumps tend to shake themselves to pieces) this is probably the route I would take if forced to choose a brush motor recip pump. . . and there's that 500 hours again.
Running a brush-type DC motor on lower than nameplate volts will not hurt it as long as you don't allow it to stall. A stalled motor will burn out its windings in surprisingly short order, even when supplied with lower-than-nominal voltage. If you run the motor directly off solar panels, you're partially protected by the source impedance of the panels (ie you won't get big current into a short circuit like a stalled motor) BUT, with a diaphram pump like the one nemosolar is offering, you stand a real danger of stalling (or failing to start) the motor when trying to start under full head without the big amps a battery can supply. Maybe 10% real-world undervoltage (measured at the motor) would be acceptable, but I wouldn't try much more than that. If you go this route, make sure that your down-hole wire is good and thick to minimize transmission voltage drop. There are time-delay relays and other semismart electronics dodges that can use your batteries to supply starting current, then cut them out to run on solar alone, but system reliability and parts count are usually inversely related.
a brushless motor is a little more complicated as you need to supply the control electronics with a certain minimum voltage before they'll do their thing, and the same electronics will fry if you supply too MUCH volts. the good news is that as long as your voltage stays in a reasonable range, the electronics will go a long way toward keeping your windings happy despite voltage swings, etc. AND, the electronics can live somewhere you can get at them without pulling the pump. . . . and by definition, there are no brushes to overhaul. Brushless DC motors are about the only exception I can think of to the parts-count rule.
Save your coffee money and buy a brushless centrifugal pump for your well. you'll probably get more water for less power, too.
-Dan
