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voyager 02-25-2014 03:48 AM

Power requirements for a DC motor >>>
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:

  • Power: DC12~24V

  • Current: 3.5A@24V,  1.6A@12V

  • Output: 40.0L/m (635 GPH) @24V or 380GPH @ 12V

  • Pressure: 9.3psi @24V

  • Motor: DC 3 phase coil, more torque and quiet

  • Power: 84Watt/ 19.2Watt

  • Speed control(3 wires): 0-5V analog

  • Intake: G1/2 (1/2")

  • Outlet: G1/2 (1/2")

  • Vertical lift: 6.5m (21ft)

  • Life span: > 20,000hrs @ 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

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?

Wuzzat? 02-25-2014 04:32 AM

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.

Speedbump 02-25-2014 07:17 AM

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:
You can use this to compare them to the ones your looking at.

Wuzzat? 02-25-2014 08:08 AM

And this link
gives a few points on the pump curve.

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