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Cable size for pump

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  • Cable size for pump

    Hi, I have bought a Chinese submersible pump and controller which is being shipped now. Its a 3FLS2.3/140-D48/750. The pump is 48 volt and 3 phase I think. It is 750 watt.
    It comes with an MPPT controller.
    I have 4 X 260 watt. Vmp 31.91v, Imp 8.15Amps
    I would like to mount the panels about 50 meters away from the pump where is is an easy accessed flat area and much more sun.
    The sales person says I can use 2.5mm cable up to 60 meters but this sounds quite small for that distance. I'm not sure if the MPPT controller will help with the voltage drop or not.
    The sales person says the pump will just run a bit slower but doesn't say by how much. I'm pumping water to 90 meters height.
    Would be be best to keep the controller close to the pump and extend the solar panel cables?
    I think the controller has a maximum input voltage of either 50 or 100 volts.
    Thanks,
    Last edited by asdex; 12-02-2017, 06:13 PM.

  • #2
    Originally posted by asdex View Post
    Hi, I have bought a Chinese submersible pump and controller which is being shipped now. Its a 3FLS2.3/140-D48/750. The pump is 48 volt and 3 phase I think. It is 750 watt.
    48 volt DC is not 3-phase AC power. 48 volt DC is just 48 volt DC period.

    Originally posted by asdex View Post
    I have 4 X 260 watt. Vmp 31.91v, Imp 8.15Amps
    I would like to mount the panels about 50 meters away......
    I think the controller has a maximum input voltage of either 50 or 100 volts.
    Thanks,
    Well then how in the hell is this suppose to work? If max input is 50 volts you are screwed because it takes at least 2 panels in series which gives you 62 volts. Ideally you want to wire all the panels in series which you cannot do.

    Anyway assuming 750 watts at 64 volts = 16amps. Depends on how much power loss you are willing to take. At 10% power loss, you could go with as small as 4 mm (6 AWG) copper. At 3% would require 12 mm (4/0 AWG).

    FWIW the minimum gauge to just handle 16 amps is 2 mm (12 AWG) but you would loose 40% of your power at 50 meters one-way.

    So how much are you willing to loose? You have to choose loosing money or power. You cannot have both.
    • If you want to cut power loss to 3% requires 4/0 aka 12 mm, you will spend $5/ft x 330 ft = $1650 USD.
    • 10% works out to 6 AWG aka 4 mm $0.60/ft x 330 ft = $200 USD
    • 40% works out to 12 AWG aka 2 mm $0.10/ft x 330 feet = $33

    So your answer is $33 to $1650. You figure it out.

    Now if this were say a 120 volt DC pump @ 750 watts at 50 meters would only require 6 amps of #14 AWG aka 1.5 mm. That works out to roughly 4% loss and 330 feet orr 50 meters cost less than $25 USD. Going low voltage is expensive and waste a lot of resources like copper, fuel, and nasty stinking money which you must have a lot of to go off-grid.
    Last edited by Sunking; 12-03-2017, 01:12 PM.
    MSEE, PE

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