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Thread: New 2 Speed Pump Motor Installed

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    New 2 Speed Pump Motor Installed

    Hi All,

    I just installed a new (Century A.O. Smith B975) 2 speed motor on my 1hp Hayward Super pump (SP2607X10).

    Here are some readings I have taken to date.

    High speed- filter pressure- 8.5psi. Seems to run the same as the older single speed motor did.
    amps- 5.75 Didn't check older single speed motor amps but seems low for high speed.

    Low speed- filter pressure- 1psi Barely moves the gauge
    amps- 2.25

    1-1/2" piping both inlet and outlet of pump.
    27000 gallon pool

    It seems to me that I'm not saving that much on low speed by having to run twice as long. I know the amp readings aren't true power indicators in wattage, but should still give me some indication of power usage. Do these amp readings seem normal?

    I'm not sure what the flow is from the pump, I'm guessing around 55 GPM using the pump curve and total head (45ft)estimates. I need to get a gauge for the suction side to figure out actual head loss. The flow on low speed seems to be a bit lower than half of the high speed if that's possible. The strainer basket is pretty full when on low speed and even primes the pump from being off all night.

    Without a power meter and flow gauge I'm not sure the system is working properly or as efficient as I expected.

    So should I be concerned?

    Thanks, Jim

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: New 2 Speed Pump Motor Installed

    The water flow on low speed has to be exactly half of the flow on high speed, unless you have a spring style check valve somewhere in the main plumbing path.

    The electrical usage on low speed is typically 1/4 (for same run time), but that varies somewhat. When comparing electrical usage, it is important to measure watts (easiest to do by watching the electrical meter) rather than measuring amps, as the amps reading can be a little bit deceptive for inductive loads.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. Back To Top    #3

    Re: New 2 Speed Pump Motor Installed

    Thanks Jason,

    Well, it's a Hayward Perflex DE filter and I believe it has a swing type check valve. If I get a flow meter it would need to be able to be installed in a close proximity to 90 deg. elbows due to the short runs at the pump/filter. But those are expensive.

    I can't really use my electrical meter because I have solar panels tied to the grid. Unless I check it in the dark. I'll keep looking for a cheap 220v watt meter and try that route.

    I just thought the amp readings were a bit too close for half the speed. For all the examples I see, the high speed amps are low on my pump but the low speed seems about right. I still don't think the power reading would show a significant difference from amperage reading.

  4. Back To Top    #4
    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: New 2 Speed Pump Motor Installed

    On low speed, the power factor drops dramatically and wouldn't surprise me if it is around 50% so the "real" power is about half of V*A. The other 1/2 is inductive so it isn't actually used but an amp meter still measures it. To confirm, you can use your house power meter to get a true power reading.
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
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    Re: New 2 Speed Pump Motor Installed

    Thanks guys, I'll check the meter tonight.

  6. Back To Top    #6

    Re: New 2 Speed Pump Motor Installed

    Okay, It's cloudy out today so I shut my solar down to check power usage on my pump in both speeds and then without it running.
    Using the Calculator from here using Kh1.0 even though my meter says Kh7.2 here are the results.
    Hi Speed- 10 beats in 27 seconds = 1145 watts
    Low Speed- 10 beats in 86 seconds = 231 watts
    Pump Off- 10 beats in 191 seconds = 188 watts
    So I looks like with these readings my pump running on low speed uses around 20% the power high speed uses...WOW! Correct me if I'm wrong.

    I checked the pressure again with a very accurate gauge and here is what I came up with.

    Return Head Loss= 2.31 * F.P. (9.75) +3 = 25.52
    Suction Head Loss= 1.13 * Inches Mercury (9.5") = 10.74
    Total Head Loss = 25.52 + 10.74 = 36.26ft.
    According to the pump curve the flow rate should be around 70 GPM 35 GPM 1/2 speed

    Thanks again everyone on this site for all the information you have shared.

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