Batteries only charging to 70%?

robynrobyn Registered Users Posts: 1
Hope someone can help me with this:

Am 100% off-grid for 3 yrs now. Past several very sunny days here in southern Ca, my batteries are only charging to about 70%. I have checked everything I can think of, and yes, batteries have water. I am NOT a tech expert, by any means...just a gal trying to figure this out...

My system is thus: 14 NINGBO Solar panels, model TPB125X125-96-P @ 230 WP

(3X) 8x6 volt=48 volt system so, 24 batteries total T105 RE Trojan

Using Xantrex: controller: XW-MPPT 60-150
inverter: XW 6048 120/240 60

ANY assistance is greatly appreciated...I need my batteries to charge 100% !!!!




  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batteries only charging to 70%?

    welcome to the forum.
    not sure how old your batteries are, but i suspect there may be a bad battery or 2 or 3. to start this may be an inconvenience to you, but i would allow all of the batteries to rest for 3-4 hours. that means no charging or loads to the batteries. after that isolate each battery electrically by disconnecting appropriate wires and measure each battery's voltage. mark this down and paste the result to each battery tested and recheck your readings afterward too to be sure you got it right. this may prove if bad cells are present or if there are other imbalances going on here. it may also be good to measure the specific gravity of each cell and put that info also attached to each battery. don't have a hydrometer to measure it then you need to buy one if the voltages don't show problems, but you will want to report all your findings here too for interpretation.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Batteries only charging to 70%?

    Welcome to the forum Robyn.

    The logical first question is: how do you judge them to be 70% charged? Are you taking SG readings? Do you have a battery monitor? Are you going by Voltage?

    Next issue: you have three parallel strings of eight Trojan T105's @ 225 Amp hours for a grand total of 675 Amp hours @ 48 Volts. That brings up two issues: three parallel strings may not be wired ideally for current sharing, meaning some may have been doing most of the work all this time while the others haven't contributed (thus killing all of them faster); 675 Amps hours could require more charge current than the 60 Amp controller can handle. If I read your array correctly you have fourteen 230 Watt panels which would theoretically supply 67 Amps maximum if everything is good.

    Now, do you ever use the XW's built-in AC charger (powered from a generator) to supplement?

    And then there is the whole question of what the Bulk/Absorb Voltage and Absorb time are set for. Yes, it's a lot of details but they are all necessary.
  • BB.BB. Super Moderators, Administrators Posts: 30,740 admin
    Re: Batteries only charging to 70%?

    Welcome to the forum Robyn!

    I will give it a shot... you have 14*230 Watt panels.

    The rough typical maximum current I would expect to see from your solar array through a MPPT charge controller on a very nice day with batteries that need charging would be:

    14*230 Watts * 0.77 panel+controller derating * 1/58 volts = 42.7 amps

    Do you see this level of current from your solar array?

    Next, how do you know your battery bank's state of charge?

    If it is a flooded cell bank (sounds like it is), a hydrometer to log the temperature corrected specific gravity of each cell... What are you seeing at the end of a sunny day for each cell (yea--72 cells).

    Bad cells (shorted or open) and bad cabling can cause strings to be "out of balance".

    Do you have a DC Current Clamp DMM (digital multi-meter)? If not, I would suggest this one from Sears is pretty cheap and "good enough" for our needs here.

    With an accurate DMM (and good batteries in meter), can you measure the voltage across each battery and record it (and tell us when the voltage was taken, morning before sun up, middle of day, night just as sun went down).

    Next--using the DMM, can you measure the voltage at the 48 volt battery bus at different times of the day (i.e., 49 volts in the morning, 58-59 volts during mid-day, towards 52 volts float charging later in afternoon, etc.)? Ideally, we should see the battery voltage rise to ~58-59 volts and be held there for ~2-4+ hours per day, then reduced to 51 volts (or below 50.4 volts as the charging falls off).

    When the sun is up in the mid-morning (and your batteries need charging, or you can even turn on some AC loads to get a power drain), you can use the DC current clamp meter to measure the current in each solar panel string. You are looking for "differences"--It all is well, each string should have about the same current flowing--If one is very low, or they are all over the place, there may be some wiring/panel issues (note: the Sears DC Current Clamp meter has a strange "zero" function--Read the instructions carefully, and try it on your car battery first to make sure you understand how it works--or ask here--It is not difficult, just different than you would expect).

    You can also use the DC Current Clamp meter to measure current through each parallel battery string (ideally under heavy charging and discharging currents)--You are looking that the strings a sharing the current--If you see one string with 50% more or 50% less current than its neighbors, need to investigate.

    Is this an On-Grid System? Do you have a backup genset? etc...

    In general, we try to understand the condition of the battery bank and get it recharged--Batteries sitting round at less than ~75% state of charge for days/weeks/etc. is not good for them.

    Did anything change recently--Have you confirmed that the system is not charging correctly, etc.?

    How I would start.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Batteries only charging to 70%?

    Welcome to the forum,

    I don't have much to add to what the moderators have offered... they (and I) seem to be thinking that there may be a bad cell in one or more batteries... but we do indeed need to know WHY you think your batteries are only 70% charged, and what your charge settings are on your Xantrex equipment.

    If you would like to read a bit about parallel batteries and some of the issues with them, try this thread:

    One of the things you can do without meters is disconnect two of the three battery strings and see how the remaining string behaves. Make sure there is no charging or discharging when you do this, and don't do this without protective clothing and an insulated wrench. Using meters is a safer and more informative approach.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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