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Old 02-25-2014, 04:48 AM  
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Default 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?

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Old 02-25-2014, 05:32 AM  
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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.

Last edited by Wuzzat?; 02-25-2014 at 09:06 AM. Reason: I'm lousy at numbers
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Old 02-25-2014, 08:17 AM  
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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.
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Old 02-25-2014, 09:08 AM  
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And this link
gives a few points on the pump curve.
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