I have begun to plan a solar water heater for the spa/hot tub that came with the house I've recently acquired. I am thinking of trying to use a pump that is powered by a 12v/24v DC brushless motor with the following specs: Code: [LIST] [*][COLOR=Red]Power: DC12~24V[/COLOR] [*][COLOR=Red]Current: 3.5A@24V, 1.6A@12V[/COLOR] [*]Output: 40.0L/m (635 GPH) @24V or 380GPH @ 12V [*]Pressure: 9.3psi @24V [*]Motor: DC 3 phase coil, more torque and quiet [*][COLOR=Red]Power: 84Watt/ 19.2Watt[/COLOR] [*]Speed control(3 wires): 0-5V analog [*]Intake: G1/2 (1/2") [*]Outlet: G1/2 (1/2") [*]Vertical lift: 6.5m (21ft) [*]Life span: > [COLOR=orange]20,000hrs[/COLOR] @ 1600rpm~10,00rpm [*]Noise: << 38dB [*]Working Temp: 100'C/ 212'F (non-submersed) [*]Envir Temp: <50'C [*]Size(L*W*D): See "More images for the exact dimension" [*]Weight (net): 21.0oz [/LIST] The amps - wattages for the 12/24v applications seem a bit screwey. I'm wondering if they might have mixed up the amperage requirements, if 3.5A@24V & 1.6A@12V might more accurately be 1.6A@24V & 3.5A@12V. Then, the wattage requirements would change from 84Watts @ 24v & 19.2Watts @ 12v to 42 watts @ 24v and 38 watts @ 12v. Those numbers seem to be a bit more reasonable to me. But then, my electrical knowledge is skimpy to say the least. Anyone out there with enough knowledge to confirm or deny my feeling about this?

I read it as when you put in 12v you get 19w and 380 GPH and less than 9.3 PSI. With 24v you 84w, 635 GPH & 9.3 PSI. The 21 ft head is probably at 24v and at 0 PSI. To crosscheck, hp to lift water = GPM x Head in feet/3956, there are about 2.3' of head for each PSI (33' = 14.7 PSI) and a hp = 746w. This little pump may be 10% efficient ("wires to water") so the denominator should be about 400. My little pond pump is maybe 1% efficient. Ask 'em for the pump curve. Sometimes they put the efficiency curve on the same graph. But if this thing is powered by a switch-mode power supply then I'd expect the 84w to be constant over 12 to 24v. Instead this thing seems to use a DC powered 3 phase oscillator at some AC frequency.

I agree, the amperages seem backwards to me too. I have never heard of a three phase DC motor so you already know more about them than I do. I sell a DC pump that operates on 12 volts DC. There are 6 to choose from, putting out between .85 gpm and 7 gpm. Pressures as high as 60 psi. With or without built in pressure switches. I would recommend using Solar for your energy source. You can see them here: http://www.pumpsandtanks.com/Pumps/delavan_pumps.htm You can use this to compare them to the ones your looking at.

And this link http://www.pumpsandtanks.com/Pumps/delavan_pumps.htm gives a few points on the pump curve.