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Thread: Quick Battery Wire Size Question

  1. #1
    Junior Member
    Join Date
    May 2010
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    7

    Default Quick Battery Wire Size Question

    Hello all,

    First time posting in this form, so first off hello and thanks in advance for any assistance provided.

    I have the following so far:
    2 180 watt 24v panels
    Outback mx60 charge controller

    The panels have been installed, and have them in series so it will run via a 10 gauge wire, 15 feet to the battery bank at 48 volts.

    Thats where I am at so far, dont have the batteries or inverter yet.

    Here is the biggest issue im concerned with - I am going to have a 500 watt inverter set up on this, will only be used to run a flatscreen and a 50 watt computer. Will never exceed 500 watts.

    I plan on getting 8 batteries for the bank (would like to do 24 volt setup with 24 volt inverter if I can find a 24 volt for 500 watts).

    Since the charge and inverter load will be so small, can I use smaller gauge wire for the battery bank? Everywhere I have seen it looks like 2 gauge or bigger wire is used, but thats pretty expensive for that many batteries.

    I have no problem buying the larger wires, dont want to "skimp out" BUT I dont want to buy huge battery wire when I dont have to.

    So ya, what size of wire could I get away with, when using 24v and approx 15 amp dc to charge, and then max load of 24v and 20 amps?

    Seems like linking the batteries that same 10 gauge wire should work with such low charge and load. Is my logic correct on this?


    Another couple of side questions:

    If I use two 10 gauge wires to connect one battery to another, that is the same as using a single 5 gauge wire correct?

    Im about to pick up my batteries. I was thinking of using the costco 6 volt 210 AH batteries for the bank. I found that Interstate down the street from me sells deep cycle 12 volt 110 HR batteries for 35 dollars. They are reconditioned though. Would these be fine to use, especially in such a small system? I could get double the bank for the same price as the costco batteries just dont know about the reconditioned part.

    Ok thanks again!

  2. #2
    Moderator
    Join Date
    May 2009
    Location
    off grid retirement in Northern Calif
    Posts
    7,345

    Default

    Exeltech XP-600/24 24 volt 600 Watt Sine Wave Inverter
    but at $535, they are not cheap. Reliable as gold. http://store.solar-electric.com/xp-600-24.html

    If you think you could get by with a 300W inverter (600W for 10 min), the suresine is a great one, as it's very efficient, but only 12V

    Cables.
    500W @ 12V = 41 amps

    the Exeltech manual has a good chart on page 13, with suggested wire sizes.

    If you can keep the distance to less than 5' to the inverter, #4 cable is suggested. Losses in the wires are much more than folks think they are. At 12 or 24 v, 2% voltage drop is not much, and it only takes a few feet of wire to falsely shut down an inverter with low voltage. place the inverter as close to the batteries as you can.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
    Moderator
    Join Date
    May 2009
    Location
    off grid retirement in Northern Calif
    Posts
    7,345

    Default

    Battery interconnections is another big subject. It's best to wire low voltage batteries in series, to get your desired voltage. Batteries in parallel don't share as well, and tend to become imbalanced. Series connections of 2 6V batteries is better than parallel 12V.
    Big article here about battery interconnections
    http://www.smartgauge.co.uk/batt_con.html
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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