Voltage drop to inverter

Plucka
Plucka Registered Users Posts: 130 ✭✭
in General Solar Power Topics #1
What sort of voltage drop should I expect from the mppt controller  through lithium management system to the inverter. I getting  .6 of a volt [13.3 to 12.7 ] but I know I need to improve my cables which I'll do tomorrow .
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Not sure I know what a Lithium Management System is.   Sounds like Snake Oil.     If it's a BMS, it should be called a BMS.
      Your solar charge controller should manage all the power going to the battery, if you have properly selected your components.

      But any voltage drop is precious solar power wasted.    We need to know the amps in the wire at the time of the measured drop.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Plucka
    Plucka Registered Users Posts: 130 ✭✭
    #3
    Improved my earthing and loss has gone from .6 volt to .4 volt
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Just to be clear on terms... In US English, "earthing" tends to mean the green wire safety ground. Generally no current should flow through the safety ground unless there is a short circuit.

    With battery systems, we have the + (hot) and - (return) cables. Typically (not always), the ground of the battery bank is tied to earth/safety/green wire/chassis/cold water pipe grounding.

    With "automotive systems", the frame of the car is both the - return power connection and the safey ground too (you only have one power cable, the + wire, and the return is the frame ground connection).

    In "high power" DC systems, generally we have both a + and - cable and all current should flow through these cables. None should flow through the earthing cable/frame connection--Earthing is for safety and frame/body panels generally do not have a very good electrical connection for the upwards of 100 amps or more that flow to the AC inverter DC input connectors... That is why we focus on the maximum current (for your needs/inverter) and the length of the cables--To make sure that you don't have much drop from cable resistance.

    For a 12 volt system, having a 0.5 volt drop is about the maximum we would design for. Typically, a short/heavy set of cables is needed to supply this current. And jumper cables with alligator clips will not work (reliably).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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