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Thread: Charge controller, battery & inverter connections

  1. #1
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    Default Charge controller, battery & inverter connections

    Question on charge controller, battery & inverter connections.

    From the off-grid basic setup scheme :
    Array >> Charge Controller >> Battery / Inverter >> AC load

    1 - Where is the inverter drawing power from?
    2 - Are the battery & inverter connected in parallel to the charge controller or are they
    connected in series?

    If the battery & inverter are connected in parallel (that is, battery & inverter positive terminals connected together & their negative terminals similarly connected together) and then connected to the charge controller, is the inverter drawing power from the battery or from the charge controller ?

    Is it possible for the inverter to draw power directly from the array instead of getting power from the battery during DAYTIME to lessen the charge/discharge cycles of the battery? And then at the same time charge the battery to be used during NIGHTTIME.

    Is this possible at all? Can anyone help, please?

    Thanks.

  2. #2
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    First, connect the inverter cables to the battery posts. This places the high current wire next to the battery terminal, less loss.

    Then, either on top of inverter cable, or on the other side of the battery post, your charge controller connections, and the Battery Temperature Sensor goes on top of that.

    If you have more than one battery, read up on connecting on the "diagonal"

    Inverter and Charger connect to the same terminals.

    Here's a great article about connecting batteries in parallel (on the diagonal)
    http://www.smartgauge.co.uk/batt_con.html (connect batteries on diagonal )

    and some other battery stuff:

    http://www.windsun.com/Batteries/Battery_FAQ.htm (short & sweet)
    http://www.batteryfaq.org/ (very large)

    Generally, much easier to manage 2, 6V in series, than 2, 12V in parallel. Same wattage.



    Don't forget a fuse on your battery, I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse)

    Get the fuse & holder.

  3. #3
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    Quote Originally Posted by nayubis View Post
    1 - Where is the inverter drawing power from?
    2 - Are the battery & inverter connected in parallel to the charge controller or are they
    connected in series?
    1., From the batteries mainly, sometimes from both batteries and solar panels, and at rare times just the panels. Depends. Battery acts as a buffer..
    2. Neither really. The batteries are connected to the output of the CC


    Quote Originally Posted by nayubis View Post
    If the battery & inverter are connected in parallel (that is, battery & inverter positive terminals connected together & their negative terminals similarly connected together) and then connected to the charge controller, is the inverter drawing power from the battery or from the charge controller ?
    It depends on the state of charge of the batteries, how much load you are demanding, and how much power the panels are producing. It is all a balancing act that has to equal.

    For example lets say it is solar noon, batteries are fully charge, and power demand is less than the maximum input power to the CC from the panels. In that case provide the power.

    However if demand exceeds the input power from the panels it comes from both panels and batteries making up for the short fall If it is dark, all batteries.




    Quote Originally Posted by nayubis View Post
    Is it possible for the inverter to draw power directly from the array instead of getting power from the battery during DAYTIME to lessen the charge/discharge cycles of the battery? And then at the same time charge the battery to be used during NIGHTTIME.
    Think I just covered that. However if you asking can you connect panels directly to a battery inverter the answer is NO.

    Battery inverters have vary narrow input voltage requirements that have to be met, and solar panels are not voltage sources they are current sources with willy large voltage variations the inverter cannot tolerate. Therefor you must have a battery acting as a buffer, or some kind of voltage regulation.
    MSEE, PE

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    Thank you for the quick response.

  5. #5
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    Default Similar question

    My question is very similar to the one posted here but I just want to be sure I understand.

    Mine is a very small system designed to add minimal LED lighting to an out-building. One 50W x 12v panel with a single 12v x 50 Amp Hour AGM battery and an 1100 Watt inverter.

    My charge controller has a set of terminals each for the panel(s), the battery, and the "load". The connections to the solar panel and the battery are obvious and if I understand correctly I can use regular 12-14 gauge household wire for those connections as they are only carrying a small charge from the panel and no run is more than 20 feet.

    However I'm not sure if I should connect the inverter to the "load" terminals on the charge controller or directly to the battery. It seems the charge controller should be able to kill the load on the battery if the charge drops below a set level... assuming the inverter is connected to it. Or should that be the inverter's job? Are the "load" terminals only for DC powered devices?

    Also I believe the inverter needs to connect to the battery with heavier gauge wire than what comes from the panels since the current depends on what you are trying to power. I think something I read said to use 6 Gauge battery cables. But I'm not sure what gauge wire is safe to use with my small 10 Amp charge controller if it is between the battery and the inverter.

    I'm just figuring this all out and still waiting on some parts so any advice is appreciated.

    - Mickey

  6. #6
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    Charge controller load terminals are only for small, low amp loads. Connecting an inverter will blow the controllers fuse, or the controller. It should state the limits in your paperwork.

    inverters generally have their own Low Voltage Disconnect.

    14 ga wire is generally safe for 15Amps Be sure you use a fuse near the battery, in case the + wire develops a short, the fuse blows, life is fine. No fuse, and something happens, you get a fire.

    Use what the inverter suggests for wire.

    Longer wires need to be larger gauge (smaller number, 12ga is larger than 14 ga, just like shotguns ! )
    Last edited by Mike90250; 05-19-2011 at 02:55 PM.
    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

  7. #7
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    Thank you for clearing that up!
    I expect most of my load will be from AC devices through the inverter. So unless I'm going to string some 12v DC xmas lights or something along those lines I probably won't even use the "Load" terminals on the controller... is that right?

    I was also planning to ask about fuses next. You say "... Near the battery...". Can you be more specific? Are we talking a 10Amp fuse between the battery and inverter? Between the controller and the battery? Both? And do I only need to fuse the positive wire(s) or negative as well? If I don't fuse the negative do I need a ground wire?

    I'm pretty comfortable with AC household wiring projects but this off-grid DC stuff is new to me.

    Thanks again!
    - Mickey

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    I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse)

    Get the fuse & holder. Bolts to the battery terminal, and is a very clean install.

  9. #9
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    Quote Originally Posted by Mike90250 View Post
    I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse)

    Get the fuse & holder. Bolts to the battery terminal, and is a very clean install.
    Only problem I have found with that Mike is the terminal bolt size. Works great if you select the right battery terminal post when you buy the batteries, suks otherwise because you have to rig something to make it work. Not too mention a bit pricey of around $16 to $30 for the connector, plus another $12 to $25 for the fuse. But i have used then and they are slick.
    MSEE, PE

  10. #10
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    The battery fuse looks very cool! Never knew such a thing existed.
    My battery has an L2 post so I'll have to see how that works out.

    So it looks like that one fuse will cover everything... and I guess there is no real need for a ground wire on my little system?

    Thanks again guys. It's great to ask a question and actually get an informed answer.

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