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Thread: New 1HP well pump: Do I need a Control Box with both RUN and START capacitors ?

  1. #1

    Default New 1HP well pump: Do I need a Control Box with both RUN and START capacitors ?

    I'm replacing my 2HP submersible pump/motor/control box with a 1HP for a geothermal HVAC system, in order to reduce power consumption (1/2 the HP, but also 1/2 the pressure - I'll have to use a booster pump for irrigation now...)

    Anyway, the Grundfos motor / pump-end only has a corresponding 1HP control box with a start capacitor - They (Grundfos) don't make a box that has start and run caps until 1.5 HP. I've been told that start / run boxes are more efficient.

    Since the entire point of changing out my pump is to reduce energy use, should I use a Franklin control box with the Grundfos motor (Franklin does make a 1HP 2-capacitor control box, but I don't know if it would be wise to "mix and match" motors and control boxes) or should I just go with the simple start-capacitor-only Grundfos 1HP control box?

    My pump motor use averages over 350 hours / month over the last 2 years, so run time is pretty significant.

    Thanks for any help with this.

  2. #2
    In the Trades Texas Wellman's Avatar
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    The "big" control box uses slightly less electricity because it engages the start winding with the run winding on a Franklin. I can't speak about the Grundfos, I really don't see too many.

    I do know from experience that you can use a Franklin box on a Grundfos pump. I would put in a 1-HP Franklin "big box" (they make one that will fit either 1 or 1.5 HP). It should work. The amps difference is only slight so I'm not sure if you're really gaining anything. Might be best to measure before/after wattage to see the difference.

    Best of luck.

  3. #3

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    Thanks for the info - with the cost of the motor/pump, I just want to use the best box period - the difference in cost between boxes is minimal. I also don't want to possibly shorten the motor's life or anything - Maybe it would be best to just use the basic Grundfos "1HP" box, I just don't know what the power useage difference would be.

  4. #4
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by iamjcl View Post
    Thanks for the info - with the cost of the motor/pump, I just want to use the best box period - the difference in cost between boxes is minimal. I also don't want to possibly shorten the motor's life or anything - Maybe it would be best to just use the basic Grundfos "1HP" box, I just don't know what the power useage difference would be.
    You may want to check the pump manufactures website to get an idea about pump performance.
    A lot of variables come into play with pumping systems.

    In my experience better efficiency is not as important as reliability.


    Good luck on your project.


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  5. #5
    General Engineering Contractor ballvalve's Avatar
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    You really want a run capacitor box. Or better yet, a three phase motor which runs like a 1940 singer sewing machine next to a single phase rig. The run cap brings you a bit closer to the smooth sine waves of 3 phase. Thus reliability increases, with a bit of efficiency. Once you have a shop with 3 phase, you get sick looking at a 120 volt split phase piece of junk.

    Still, I would try and get that HP down on the pump WAY lower, at the bare minimum for the sys. - even if you have to trickle feed off water to a large tank and use another submersible in there.

    I just bought a 2500 gallon tank for 500$ -prices are down now.

    If you run your cost numbers with even a 1 HP pump running that many hours, you will find that your investment in "geothermal", and its component lifespan and complexity, will never pay back over burning natural gas or pallets in a wood stove.

    I think valveman has a geothermal, and uses a 1/3 hp pump. But unless you live next to a volcano, or hot spring, I would have never installed it.
    Last edited by ballvalve; 12-20-2011 at 10:58 AM.

  6. #6

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    I would like to get the Run cap box - but is it fine to use a Franklin Run-cap 1hp box with a Grundfos 1hp motor ? That's what I'm not clear on. Grundfos doesn't make a 2 capacitor box for 1hp - only 1.5 and up.

  7. #7
    In the Trades Texas Wellman's Avatar
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    I have used the Franklin box with the Grundfos so I can say for a fact that it will work. Does the manufacturer agree with me? Maybe not. But it works.

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