Xantrex MPPT 60 ReCharge voltage question.

lesnoy
lesnoy Registered Users Posts: 8 ✭✭
As of right now I have Xantrex 6048 connected to 48v battery bank in grid tie configuration. It is being recharged by Xantrex solar charge controller set to 2 stage charging (no float) and internal XW charger is disabled. Based on info I have I set grid support to 52V and enabled Sell to grid option.

When looking at advanced setting on solar charge controller I see that default value to start recharging batteries is set to 50 V. Way I understand once battery bank will drop below 50v for over one min SCC will start processing input from PV modules and if bank voltage remain above 50V SCC will not send anything from PV to bank/6048.

My question is should I raise SCC recharge voltage to say 52-53V in order it to stay in constant Bulk/Absorbtion mode since once battery bank is full whatever is coming from PV will be used to support house loads and leftovers sold to grid? Because as of now it seems once bank is 51.9-50V range, grid support will not function (grid support set to 52V) and new charge cycle will not start until bank drops to 50V. Also as I mention it is grid tie setup and batteries will be used only on rare occasions when grid power is lost so I do not expect many charge recharge cycles, ideally I just want to have constantly charged bank ready to go if grid power is lost.

Would greatly appreciate any advice or tip on this matter.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Xantrex MPPT 60 ReCharge voltage question.

    It may depend on what firmware version you have in your XW (inverter/chargers?) system. There is a new mode (Automatic?) that (last I have heard) is not document in the current user manual.

    Basically, the way "it should work"--The Solar panels + charge controllers should be using MPPT to output the maximum amount of solar energy to the battery bank. And the "bulk/absorb" charging set point should be something like 59 volts (and float should not be enabled).

    The XW Inverter in Grid Tie mode acts like a dump controller... It tries its best to hold the battery around 52-54 volts or so by taking enough current (and converting that into 240 VAC utility power) and shipping the power off to the house wiring/utility grid.

    If the XW inverter detects that the batteries have been used sufficiently (below XX volts?) as during a power failure, then the XW will go into Absorb Mode charging--and let the batteries rise to ~59 volts until they meet the requirements for current/time to be 100% charged (whether charging charging from the solar panels or from the XW AC charger itself). At that point, the it will go back to "float mode" and start skimming off enough current to keep the battery bank around your "sell voltage" (I believe the set point is ~0.5 - 1.0 volt accurate--so if you have 52 volts as your set point, you may need to set it to 53.x volts).

    Also, some of the DC battery voltage readings of the XW hardware are actually temperature corrected voltage... I.e., the battery bank may be Hot or Cold (with respect to 77 degrees Fahrenheit)... So if you have a "hot bank" you may read 52.0 volts with your meter, but the XW will adjust the voltage to 54.0 because the bank is much hotter than 77F.

    The devil is in the details... The GT specifications (I guess) prevent the inverter from changing its output quickly--so shadows from clouds can affect the battery bank voltage and cause the voltage to wonder out of the "assigned" range (especially with small capacity battery banks).

    So--That is my understanding. The solar chargers are always outputting as much energy as possible and the XW Inverter is skimming off power to keep the batteries floating (or the higher set point voltage if recharging the battery bank after a power outage).

    The solar charge controllers should not be "regulating" during normal operations.

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