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Thread: 2 Speed Motor

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    2 Speed Motor

    I just installed a 2 speed motor for my pump.

    Since low runs at 1/2 speed of full could I expect the GPM would be pretty much exactly 1/2?

    Full speed the pressure at the filter is 18 psi compared to 2 psi at low.

    Since the pressure is not proportional could I say that at high speed the pump is pumping much more that the filter can most efficiently filter. Would this be the bell curve that motor manufacturers have with their pumps. Reading into this more my question above could I be getting more that half the flow at low speed.

    Everything is working great but I'm a techy and am curios, and you guys on this forum seem to know everything?
    16,000 Plaster/Gunite - Pentair FNS Plus Fiberglass D.E. Filter
    Heat Siphon Heat Pump Z375HP- Hayward Pro Logic PL-P4 Automation
    Hayward Chlorinator Cell T-CELL-9 - Waterway SVL5 Pump
    A.O. Smith Two Speed Motor B983 - Solar Blanket - Polaris 380
    Test Kit K-2006c

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    JasonLion's Avatar
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    Re: 2 Speed Motor

    Low speed does indeed move half as much water (GPM) as high speed. The dramatic reduction in filter pressure is normal. Filter pressure comes from resistance to flow, essentially friction, which increases far more rapidly than the flow rate increases. I've forgotten the exact formula, I think resistance to flow increases by the square or the cube of the flow rate.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    svenpup's Avatar
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    Re: 2 Speed Motor

    That is why the motor runs at half speed (and has half the flow rate), but uses ~1/6 the power.
    TFP Method Advanced Intermediate
    • 17,500 gallons - In Ground - Plaster - Hayward Swimclear 3020 Cartridge Filter - Sta-Rite Max-E-Glas Main Pump upgraded with A.O. Smith B2980 E-Plus New Centurion Two-Speed Motor - Polaris 280 Cleaner with Polaris PB4-60 Booster Pump - TightWatt2 Timer - Taylor K-2006 Test Kit - Pool Pilot Digital Nano SWCG

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  4. Back To Top    #4

    Re: 2 Speed Motor

    Wow 1/6 the power.

    Is there any reason why I would need to use the high speed? My Polaris with separate pump seems happy at the low speed. I measured the rotation according to the Polaris manual and its even on the high end. I know the Skimmers will not be the greatest but I am experimenting with shutting off the bottom drain to increase the flow at the skimmers.
    16,000 Plaster/Gunite - Pentair FNS Plus Fiberglass D.E. Filter
    Heat Siphon Heat Pump Z375HP- Hayward Pro Logic PL-P4 Automation
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    A.O. Smith Two Speed Motor B983 - Solar Blanket - Polaris 380
    Test Kit K-2006c

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    Melt In The Sun's Avatar
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    Re: 2 Speed Motor

    If your skimmers work well at low speed, then you probably will only need high speed for backwashing/recoating, vacuuming, and things like that.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    svenpup's Avatar
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    Re: 2 Speed Motor

    I run mine on high while the polaris booster is running. I am not sure if this is strictly necessary (I also noticed the booster seems OK with main at low), but I think it may help get the suspended particles that the cleaner stirs up into the filter.
    TFP Method Advanced Intermediate
    • 17,500 gallons - In Ground - Plaster - Hayward Swimclear 3020 Cartridge Filter - Sta-Rite Max-E-Glas Main Pump upgraded with A.O. Smith B2980 E-Plus New Centurion Two-Speed Motor - Polaris 280 Cleaner with Polaris PB4-60 Booster Pump - TightWatt2 Timer - Taylor K-2006 Test Kit - Pool Pilot Digital Nano SWCG

    Helpful Links: Pool School, BBB for Beginners, How to Shock (hint...it's a process not a product), Chlorine/CYA Chart, Jason's Pool Calculator

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    Re: 2 Speed Motor

    I run mine on low speed 24/7 and only toggle over to high speed for 1-2 min. backwash. My skimmer functions well on low speed if the skimmer valve is fully open and the main drain valve is 3/4 to 1/2 open. I manual vacuum to the filter via skimmer plate using low speed with the main drain valve only 1/4 open (or less). This works great because at low speed there is almost none of the "blow back" of fine sediment into the pool that normally occurs at high speed while vacuuming. I have been amazed at how much better my sand filter works on a day to day basis using the low speed...the water moves so gently that filtration is greatly increased over my previous set-up of a single speed one (1) hp motor where some of the fines were passing through the filter due to the force of the water.

    And yes, low speed moves 1/2 as much water (it takes twice as long to move the same amount of water), but with the new high efficiency 2 speed motors with capacitor start/capacitor run low speed, it only takes 1/8 the power to move 1/2 the water! These new motors offer 20% energy savings over previous 2-speed motors. On low speed, my 3/4 hp full rated motor is only 0.10 hp and pulls 2.2 amps @ 115V...barely noticeable on the monthly electric bill though running 24/7 in summer.
    Vintage 1963 20' x 40' elliptical, 27,000 gal. painted concrete, diving board, Sta-Rite Dura-Glas pump DIY upgrade 2009 with A.O. Smith B2981 E-Plus New Centurion High Efficiency Two-Speed Motor, full rated-1.67 SF 115V, 3/4 hp-12.4 amps high speed, 0.10 hp-2.2 amps low speed running 24/7 low speed, Hayward 225T sand filter

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    JasonLion's Avatar
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    Re: 2 Speed Motor

    The electrical usage on low speed for a standard two speed motor is in theory 1/4th of the usage on high speed, but no motor is perfect enough to actually achieve that. The real world usage is typically more like 1/3rd of the usage on high speed. To make a fair comparison, you then need to multiply that by two, so you are moving the same total amount of water. The overall electrical usage ends up being around 2/3rds of what it would be on high speed to move the same total amount of water.
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    mas985's Avatar
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    Re: 2 Speed Motor

    The CEC measurement data actually shows that most two speed pumps use about 1/4 the power on low speed than high. Some are better some are worse but on average about 25%.

    However, I think there is some confusion from the previous posts on the application of pump affinity laws. These are stated as follows:

    GPM Low Speed = GPM High Speed * (RPM Low Speed / RPM Hi Speed)
    Head Low Speed = Head High Speed * (RPM Low Speed / RPM Hi Speed)^2
    HHP Low Speed = HHP High Speed * (RPM Low Speed / RPM Hi Speed)^3

    HHP, the hydraulic HP, is what goes down by a factor of 8 but the pump affinity equations do not account for efficiency in the pump and motor so adjustments are required to calculate the change in input power. 1/2 speed on a typical pump tends to be about 50% less efficient than high speed because twice the windings and fields are involved. So the actual power draw of low speed is about a 1/4 of high speed for most pumps. Some pumps are better some are worse but again, you can see this in the CEC measurement data.

    Also, you can explain the difference in pressure by using the head loss formula so the pressure should decrease by a factor of four. However, you need to take into account the height of the filter gauge so the adjustment needs to be:

    (18 PSI + 3'/2.31) / 4 - 3'/2.31) = 3.5 PSI

    Gauge accuracy is no better than +- 1 PSI and some even worse so it is pretty close to what is observed.
    Mark
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  10. Back To Top    #10

    Re: 2 Speed Motor

    Wow, incredible analysis.

    I measured the draw at both speeds and at high speed I get 8.1A and low speed I get 3.00A
    16,000 Plaster/Gunite - Pentair FNS Plus Fiberglass D.E. Filter
    Heat Siphon Heat Pump Z375HP- Hayward Pro Logic PL-P4 Automation
    Hayward Chlorinator Cell T-CELL-9 - Waterway SVL5 Pump
    A.O. Smith Two Speed Motor B983 - Solar Blanket - Polaris 380
    Test Kit K-2006c

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    mas985's Avatar
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    Re: 2 Speed Motor

    Keep in mind though that the power factor decreases with low speed so your actual power consumption is less than what the 3A would indicate.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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    Re: 2 Speed Motor

    So then 8*220=1760 watts at high
    and 3*220=660 at low

    Is this what you mean?
    16,000 Plaster/Gunite - Pentair FNS Plus Fiberglass D.E. Filter
    Heat Siphon Heat Pump Z375HP- Hayward Pro Logic PL-P4 Automation
    Hayward Chlorinator Cell T-CELL-9 - Waterway SVL5 Pump
    A.O. Smith Two Speed Motor B983 - Solar Blanket - Polaris 380
    Test Kit K-2006c

  13. Back To Top    #13
    mas985's Avatar
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    Re: 2 Speed Motor

    With AC waveforms, the voltage and current can become out of phase in the inductive load of a motor. This creates a situation where there is both real and imaginary power but the power company only charges for the real power since the imaginary power is sent back on the line and is not consumed. To account for this effect, the true formula for real input power is:

    Real Power = V * A * PF

    where PF is the power factor and is between 0 and 100%. At high speed, the power factor is usually over 90% but on low speed it will go down some because effectively the motor in underloaded. So my guess is that the input power is closer to 440 watts instead of 660 watts. The other 220 watts is imaginary power.

    The best way to measure pump power is via the electric company's power meter. This will measure only real power. If you take a reading with and without the pump running, you can find out just the pump power.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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    Re: 2 Speed Motor

    I used the Kill A Watt Ez to measure the PF as well as amps and wattage for my pumps. This is a cool tool even will calculate cost per hr/day/week/month/year for you via the menu!

    http://www.homedepot.com/h_d1/N-5yc1vZ1 ... ogId=10053

    unlike some amp meters or using my Fluke meter, this thing takes PF into account. It also allows fractional cost per/Kwatt hr input, example we pay 11.2 cents a kwatt hr.
    20,000 gal. 32' x 17' freeform custom pool, 3ft. shallow - 8ft. deep end, Pentair Whisper flow 2.2 HP WF-6, Purex/Triton Nautilus FNS48 DE filter, 2 Intex Chlorine Generators (retired) SR Smith Rouge Rapids curved slide, The Pool Cleaner 4-wheel model w/Hayward large leaf canister. Tightwatt pool timer Spa: Beachport 5 person/350gal. Wishlist: move Neiko Tools pump to slide, solar system, Fountain, Automation. http://www.poolcalculator.com/

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    mas985's Avatar
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    Re: 2 Speed Motor

    I believe that unit is only rated for 125v maximum and should only really be used for plug in pumps. Are you using it to measure 240v power? While it may work, for safety reasons, I don't think I would recommend that anyone should do this.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: 2 Speed Motor

    I run this pump: neiko-tools-usa-1-hp-water-pump-with-strainer-review-109-99-t20674.html

    The draw is weel below the 15 amp rating of the Kill A Watt. I have tested my Pentair 240v pump with it but thats trickier. I had to cut a 14ga. extention cord in half and down to 3 feet. then run just one of the phases thru the Kill A Watt. I then double our rate of 11.2 cents/kwatt hr. to get a accurate Dollor readout as the Kill A Watt can only see half the draw.
    20,000 gal. 32' x 17' freeform custom pool, 3ft. shallow - 8ft. deep end, Pentair Whisper flow 2.2 HP WF-6, Purex/Triton Nautilus FNS48 DE filter, 2 Intex Chlorine Generators (retired) SR Smith Rouge Rapids curved slide, The Pool Cleaner 4-wheel model w/Hayward large leaf canister. Tightwatt pool timer Spa: Beachport 5 person/350gal. Wishlist: move Neiko Tools pump to slide, solar system, Fountain, Automation. http://www.poolcalculator.com/

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