xw battery charging and temp correction

gruntgrunt Solar Expert Posts: 37 ✭✭
Most of the time when I do my monthly charging of my grid tied battery bank I just turn off my grid support for my XW and let my out back Mx 60 run through a 3 phase charging cycle using the sun. The problem is when I turn on the charging feature on the xw6048 during a power outage or during a charging cycle using grid power. It wants to charge at a higher rate than it should. I have AGM batteries and there bulk rate is 57.6 and it wants to charge at 58.something. Now my basement during the winter is 45-56 degrees most of the time and I know that temperature has something to do with charging voltage (as my temp lead for the XW is hooked up) but how can charging the AGM at a higher then recommend voltage be a good thing when they are supposed to be sensitive to overcharging.
If I switch from the Default AGM setting, in the battery charging men and use the custom menu with the proper number plug in it, to try to remedy the problem it wants to charge at 60 something volts. Why does it not charge at the voltage I programmed in to the custom setting like the MX 60 does? I know it has to do with the ambient temp but I am not sure how it works. Someone please explain.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,705 admin
    Re: xw battery charging and temp correction

    I am certainly no expert... First you are talking about 57.6 volts rather than 58 amps?

    Next the XW displays the "corrected" batter voltage... So, in a cold garage, it may display 58.0 volts but the batteries are at 59.something.

    I am not sure that I would trust the XW volt meter accuracy to better than ~2% or so... Or +/- 1.2 volts at 60 volts. Once you know the "offset" (as measured with a calibrated DMM)--it should repeat very accurately,

    The XW acts like a "shunt" charge controller--So it takes the "excess energy" from the battery bank and ships that off to the grid... One of the things that, I am guessing, is an issue is that the inverter takes a few seconds (at least) to stabilize at a new voltage (change in cloud cover, etc.). So you can see wide voltage swings.

    Normally, you have the solar charge controllers set to some high voltage (like over 60 volts) and the XW set to sell at ~54 volts or so... If the XW determines that the bank needs recharging, it should lite the voltage go upwards to the "programmed" bulk/absorb setting for X hours, then haul it back down to float voltage.

    How many watts of solar panels, what size XW (watts/bank voltage), and how many AH of batteries do you have (at xx bank voltage)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gruntgrunt Solar Expert Posts: 37 ✭✭
    Re: xw battery charging and temp correction

    57.6-.2 volts is sun extender battery requirments for bulk. With the XW you disable the charging feature durring normal operations. You just have the sale back voltage high enough to maintain the proper float voltage and it sales back every thing esle once it has reached that voltage.
    Solar guppie recomonded setting it up that way it it seems to work. Durring sale back of energy my battery bank stays at 53.6 wich is the proper float for that type of battery
    http://www.sunxtender.com/solarbattery.php?id=18
    the system is a 2.7k
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: xw battery charging and temp correction

    also note that although agms are touchy on the voltage they most likely won't go haywire from a ramped voltage due to temperature compensation as agms are after all still batteries and are prone to the same effects of temperature as fla types are.
    it is good to see that caution in you though.:D
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