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12volt solar power cables

Discussion in 'Power Electronics' started by Bearlike, Apr 7, 2020.

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  1. Bearlike


    Mar 26, 2020
    I want to run 12volt back up power to my UK house, from two (I might add two more) 6v Platinum PLA-T105 225ah batteries in my shed 6 meters away.
    I may want to keep my 240volt 150watt freezer running (maybe not), and defiantly one or two laptops 4amp each, monitor & satellite tv box 8amp, lighting 3amp. So around 19amps and what ever the freezer uses through a 2000watt peek pure sign wave inverter.

    What cables do I need to run? I have a 240volt 1.5mm and 2.5mm drum (twin and earth) house cabling (I'm guessing 2.5mm). Will I need to conduit the cable, or do I need armored, or something completely different?
  2. Bluejets


    Oct 5, 2014
    Freezer has a motor and motors draw up to 6 times full load at startup.
    If the capacity to drive this is not present, the motor simply will create a voltage drop that will hold in the start winding until the motor burns out.
    Exception to this is inverter style drives which freezers don't have.
    I would tend to allow around 900 watts and that should cover inefficiency in the power inverter.
    So somewhere in the vicinity of 75 amp at 12v for the freezer.
    19 amp for the rest. Total 94 amps.
    As per calculator link below [email protected] 6 metre run gives a voltage drop on 16 sq mm cable at 1.2v if you can live with that. (12-1.2=10.8V)!

    Remove the freezer from the equation.....
    19 Amp @ 6 metres = 1.55v on 2.5 sq mm and 0.97v drop on 4 sq mm.

    Inverter operation is an unknown as no link or detail so no comment....
  3. Bearlike


    Mar 26, 2020
    Thank you for your time explaining this to me.
    Here's the link to the inverter:
    Although I think I'll not bother with the freezer after seeing how much energy it will need. I can see myself spending £1000 on batteries etc to get the job done, and then find a few weeks of bad weather and then I'm back to square one.
    I think I'd have better luck with an old style pantry; a thick slate box in my drafty garage should do it. :)

    I'm now thinking a double run of 6mm cooker cable, or building a battery shed at the back of my house.

    Well it's been an education, thank you.
    bob.steel likes this.
  4. bob.steel


    Feb 27, 2020
    Before you go I saw one system on Instructables here that ran a small freezer and a TV and a computer . Not cheap to set up and running on 48V but definitely doable for under probably USD $3000.
    Another cheaper one here running on 24V probably USD $500
    Those types of inverters don't seem to last long. If you have to replace them every 12 months it mounts up quickly.
    I would go straight to MPP inverters that many of the off grid guys use and don't waste your money learning . About a Grand but they will last better and you can boost up your system in batteries as LFP gets cheaper.
    In my opinion lead acid is dead , at least it certainly is for me!
    Learn about LFP here.
    And use Victron solar controllers ,they just work.
    Last edited: Apr 8, 2020
  5. Bluejets


    Oct 5, 2014
    What a load of rubbish.
  6. dpuklicz


    Apr 11, 2020
    Battery loading realities:
    At fully charged your batteries will offer you 450a/hr @ 6v (in parrallel) or 225a /hr @ 12v (in series).

    Power(w) = Volt(v) X Current(a) so then Current(a) = Power(w) / Voltage(v)

    At 12v the current draw for a 200w device is 200/12 = 16.66 amps. At 6v the current draw for a 200w device is 200/6 = 33.33 amps.

    My point here is that as the battery voltage drops (which it does whenever under load and no charging) the current to run any given device goes UP. Your fully charged (12v) batteries running your (intended) 12v inverter will never let you draw 25amps for 9 hours. Typically planners use 70% of the full charge rated capacity of a battery system to extract more realistic run times (reserve capacity). So, assuming you have a way to regularly charge the batteries to 100% (daily), you have roughly 158amp/hr (225 x 70%) full charge capacity. So you know then that you could run a 1kw load total (83.33amps @ 12v) for about 113 minutes maximum. That calculation BTW, is a based on a constant, non-varying load.

    If you have devices that have start-up surges (like freezers and refrigerators, which can be 3 or 4 times run consumption) total support (reserve) time goes down significantly more.
    hevans1944 likes this.
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