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Thread: Replacement pump motor. 1 speed or 2?

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    Join Date
    May 2014
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    Houston, TX
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    Replacement pump motor. 1 speed or 2?

    Need a new motor for my super pump 2 it is 1 speed 1.5 hp 220.

    Is there any advantage to going 2 speed $200.00 more? Do you need to rewire?
    TF-100 Test Kit. 25 year old plaster in ground, 16,600 gallons pool & spa, sand filter, the worlds oldest Jet Vac pool cleaner. Pool is surrounded and covered be large live oak trees.

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    Youngsville NC
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    Re: Replacement pump motor. 1 speed or 2?

    rewire - no. - well - depends on what automation you have or want or where it is at.

    advantages - the high speed on the 2 speed is the same as your single speed. The low speed is half the RPM (and 1/4 the power draw), but you would need to run it twice as long to get the same filtering as the high speed, but in the end, you will save on your power bill. If it was me - yes - I will be getting a 2 speed for my next pump.
    16x32 IG 19,000 gallons, Pentair 1.5 hp Energy Efficient Superflo pump (348024),vinyl liner, Chlorine dispenser, Hayward S-244T sand filter

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    Re: Replacement pump motor. 1 speed or 2?

    The pump affinity law shows that at half the speed, the power draw is 1/8th of full speed. However, in reality, the savings are a little bit less.

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    JoyfulNoise's Avatar
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    Re: Replacement pump motor. 1 speed or 2?

    As long as you have the proper 3-wire cable (4 wires actually, two hots, L1 & L2, one common and one ground) running from the your timer/switch, it should be easy. Otherwise, you might have to upgrade your timer/switch and the wiring that runs from it to the new pump. Post more details about your setup and plenty of folks on here with electrical experience can help.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    mas985's Avatar
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    Re: Replacement pump motor. 1 speed or 2?

    Quote Originally Posted by JamesW View Post
    The pump affinity law shows that at half the speed, the power draw is 1/8th of full speed. However, in reality, the savings are a little bit less.
    The pump affinity laws do not take efficiency into account so technically, the law only applies to the power delivered to the water (i.e. hydraulic HP) and not the motor electrical input power. So shaft BHP is about 1/8th the power but the motor electrical power draw (EHP) is only 1/4th because the motor efficiency drops by about 50% on low speed. Low speed winding's are much thinner than the main winding so I2R losses are close to 2x (i.e. resistance) as much.
    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: Replacement pump motor. 1 speed or 2?

    Quote Originally Posted by mas985 View Post
    The pump affinity laws do not take efficiency into account so technically, the law only applies to the power delivered to the water (i.e. hydraulic HP) and not the motor electrical input power. So shaft BHP is about 1/8th the power but the motor electrical power draw (EHP) is only 1/4th because the motor efficiency drops by about 50% on low speed. Low speed winding's are much thinner than the main winding so I2R losses are close to 2x (i.e. resistance) as much.
    Thanks. What is the correct rule for variable speed pumps?

    The windings are thinner for low speed, but the current is much less, so wouldn't the losses be less as well?

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    mas985's Avatar
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    Re: Replacement pump motor. 1 speed or 2?

    Variable speed pump motors hold the efficiency fairly well at lower RPM but the drive electronics affects the efficiency at very low RPM which is why 1000 RPM seems to be the sweet spot for efficiency. After than, the drive electronics start to dominate the energy use so efficiency drops. For example, here are a few operating points and the loss of efficiency from full speed:

    3450 RPM, 2830 Watts
    1725 RPM, 422 Watts, (17% loss of efficiency vs affinity eqs.)
    775 RPM, 87 Watts, (63% loss of efficiency vs affinity eqs.)

    So at half speed it is better than a two speed efficiency drop but at lower speeds, it gets worse.
    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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    Austin
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    Re: Replacement pump motor. 1 speed or 2?

    As part of an overall programme of energy efficiency in my home, I'm trying to figure out if it's worth replacing my single speed pump.
    How long should I be running the pump daily? In Mas985's signature there is a link to a pump run time study done in the late 1980's which makes me think that I am running it for too long (4 hours) and that I don't need to be running it to filter all the water daily in the summer either.

    I have a booster pump for the spa and for the polaris 280. When the polaris is working the booster pump and the regular pump are both working. When the spa water is being filtered, it's just the booster. Is this strange?
    26,390 gallons IG, Centex plaster, Hayward DE 4820 filter, Century Centurion B2859 pool pump motor.
    Booster pump for polaris 280
    Spa
    Built 1997

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