Inverter AMP Draw

Blackcherry04
Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
in Off Grid Solar & Battery Systems #1
If I take a 2500 Watt Inverter and on the inputs I parallel a 55 amp charger and the Battery Bank. If I drop a 1500 Watt load on the Inverter it take the total output of the 55 amp charger and will pull 2.5 amps from the battery bank. If I drop the 1500 watt load the power the Inverter the 55 amps reverse and go to the battery bank. As has been stated electrons do not care, they take the path of least resistance. If I reduce the load to 100 watts then the output of the chargers 55 amps minus the amps necessary for the 100 watts goes to the Battery bank ( 49 amps ).

Why would this not be a better to connect to the Outputs of the Charge Controller directly on inverter inputs in parallel with the battery instead of on a buss or directly to the Battery Bank ? Is satisfying the load a priority or Is delivering current to the battery and having double conversion losses. Is there any difference ??

Tell me where I am wrong in my thinking.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Inverter AMP Draw

    Voltage drop under load.
    When the inverter is drawing current the Voltage at the inverter is not the same as the Voltage at the battery. The greater the load, the bigger the Voltage difference.
    The charge controller reads Voltage to judge SOC. If it is reading it at the inverter it may be reading it wrong. It could try to increase Voltage when not necessary or incorrectly compensate for temperature of battery. This can be a problem even when the controller is wired to the battery, and is why some companies like Morningstar includes separate "battery sense" terminals on their controllers; to read the Voltage without the 'interference' of the current through the wires.

    On some systems wiring the controller to the inverter terminals wouldn't make any difference at all. On others it would "self-correct" when the load is removed. But there will be those where such wiring would make the charge controller operate inaccurately.

    Another thing to consider is the fusing: if the inverter's CP trips or it is disconnected, will the charge controller still be supplying to the battery?

    For over-all system performance it's best to keep the circuits separate even though they interact electrically.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Inverter AMP Draw

    Several reasons I would not...

    First--Fusing/breakers and safety. The Inverter is a high current device and the battery chargers are fairly high current too... Adding multiple power sources (battery, charge controller, possilbly inverter/charger) creates more of mess of trying to figure out the optimum way to wire and fuse the multiple power source "bus connections". Terminating loads and sources at the battery bus common point is usually much easier to understand and install protection devices. Also--If an inverter fuse blows, you still have charging and other load connections available (does not throw the whole system into electrcal darkness and/or kill your charging sources, which can kill the battery bank).

    Another issue is electrical noise... Inverters have 120 Hz of I2 current and possible other noise profiles too (such as a MSW inverter with sharp edged square wave creating lots of high frequency noise). The bit of wiring from the inverter back to the battery bank does give a bit of LC (inductive/capacitive) filtering--And will not as likely cause confusion at the charger (we had one poster here report that Desulfators--which make lots of high frequency hash--actually reduce the output of several Outback MPPT charge controllers--everything worked, just not nearly as well when the desulfator was turned off).

    lastly, you want the charge controller to measure the battery voltage "exactly"--And not add the votlage drop from the inverter into the confusion. If you keep the battery voltages "correct"--Then the current will flow where needed (battery, inverter, or to both--as the battery bus voltage and charge controller settings require).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #4
    Re: Inverter AMP Draw

    Both points taken. I have more than adequate safety in place. I have a double Bussman fuse block with a fuse for each source ( Charger & Battery Bank ) mounted on the Inverter input block with a lever switch. As I just did it this morning, I wanted to test it some and see the results, I'll post back. I wanted to see if I saw a difference with a Honda EU 2000 and how it reacts to the charger in this set up. I want to know, If I am burning gas, how do I get the best bang for the Buck. Also I wondered how the Outback GFX with Generator input makes it's decisions how to draw power from the Generator or the Battery Bank.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Inverter AMP Draw

    I always suggest using a Kill-a-Watt type meter on the generator output--And keep track of fuel used. Tracking kWH per Gallon (or what ever make sense to you)--Can help guide your optimum generator use (50% minimum loading for optimal fuel usage, 25% minimum for the Honda and other(?) type inverter generators will still be fairly fuel efficient).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Inverter AMP Draw

    this is almost like opportunity loads from solar would be except you are going with the utility as the power source. the main priority is at the batteries, always, as the side benefit to the loads are secondary.
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