Strange readings with Xantrex Link 20 monitor

Westsailor
Westsailor Registered Users Posts: 5 ✭
in Advanced Solar Electric Technical Forum #1
I have a Link 20 monitoring 2 banks of two T-105's (wired in series to provide 12v). I always use both banks together, i.e. I do not use one bank at a time, switching between one bank to another.

What is interesting is my Link 20 is beginning to think bank one is supplying more amp hours than bank two. As a result, over time I am accumulating more negative amp hours in bank one than in bank two. Yet the battery voltage of the two banks is the same (well, within .05v) and both banks charge at the same rate.

For example, last night I started with -27 amp hours in bank one, -10 amp hours in bank two. This morning the link 20 displayed -41 amp hours used in bank one and -20 amp hours in bank two.

So according to the Link 20, Bank one supplied 14 amp hours while bank 2 supplied 10.

If I am using both banks in parallel (i.e. the load is equal on both banks) how is this possible?
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Comments

  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #2
    Re: Strange readings with Xantrex Link 20 monitor

    I do not believe there is a shunt for this system. If there was you would need 2 to monitor 2 banks. Maybe the second AH reading is meaningless because bank 2 is not being sensed as your battery switch is in parallel? I wish I could remember the marine stuff....... I do remember the Westsail sailboats, which model?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
    Re: Strange readings with Xantrex Link 20 monitor

    If you do have two (identical) shunts in your two parallel battery banks... A couple of possibilities that I can think of:
    1. It is possible that one bank has a bad connection. It take only a little bit of dirt/corrosion to make enough resistance that one bank will see substantially less current than the other (charging and discharging). check/clean all of the connections. Also, put a heavy load (or charge) current on the bank, and use an accurate DVM to check the voltage drop across each cable/connection point. If you have a higher drop across one point--you will find your bad connection and/or cable.
    2. You may have a longer cable path to one bank vs the other. Longer cables add enough resistance that will unbalance the banks (actually, quite a common problem). Change the bank so the + cable connects to the positive battery terminal on one bank, and the negative cable to the negative terminal on the other bank ("kitty corner"). Or make sure you have the same cable lengths on both banks. See page 7/8 of this user guide (PDF) for an example drawing.
    3. Lastly, are you properly/fully charging your battery bank? I believe most battery monitors will "reset" to battery bank capacity once they have been fully charged and equalized (to allow for minor measurement errors to be "reset" back to full capacity).
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    #4
    Re: Strange readings with Xantrex Link 20 monitor

    Also take a hydrometer reading of both banks for a second opinon
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  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    #5
    Re: Strange readings with Xantrex Link 20 monitor

    I have 2 indentical meters in my system, in different locations, both on the same shunt, monitoring 1 battery bank. Not the same as your system but, when I first installed the second meter I noticed a large difference on the AH readings. After a few days I found a connection at the shunt that was loose. I reset the meters and now they agree pretty closely, but not exactly, probably a 10% difference between the 2, but close enough for me. so if I had to guess I would say you probably have a loose, corroded, or bad connection like Bill suggested above.
    Good luck,
    Larry
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