Battery bank discharges, no loads applied

I have a weird problem, battery bank of eight 6 volt deep cycles, wired for 24 volts (two banks of four each). New TS-60 charge controller, and four BP-185 panels, 24 volts. When the sun starts to go down, the state of charge indicated on the controller starts to drop, and after dark, it is showing discharge, but there is nothing turned on and no load applied to the battery bank. Today, I soldered new blocking diodes in the positive leads at the panels, suspecting a bad diode in a panel (and of course, the BP panels are made so one cannot replace the diode). No difference. The sun is going down and I'm losing battery voltage. Also, the controller will not go into the equalization mode. Can anybody offer any tips or advice? I'm at my wit's end. Thanks !!


  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    Re: Battery bank discharges, no loads applied

    Give specifics on battery voltage drop. You should see if there is actually current backwash.

    It is normal for battery to go to equilibrium state which will drop in voltage from what it was when non-equilibrium charging current is applied.

    If it drops to 25.4 vdc this is normal equilibrium fully charged state.

    There is kinetic polarization voltage necessary whenever there is current movement in or out of battery. This is to convert lead to lead sulfate on discharge and lead sulfate to lead on recharge, along with movement of ions and electrolyte mixing.

    This is why the battery voltage drop immediately when loaded and rises immediately when put on charge.

    You could have battery leakage causing self discharge. This is usually result of overcharging or a normal aging battery.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery bank discharges, no loads applied

    could you elaborate on the ah capacity and age of the 6v batteries you are using?
    if you have a voltmeter please check each battery's voltage and if you have taken specific gravity measurements as to what they are too.
    assuming the meter is good and wired correctly the way i see it is either the batteries have a problem or you have a load on you may not be aware of. there is another possibility too of the batteries being wired wrong, but i am giving the benefit of the doubt there.
  • mtnmankevmtnmankev Registered Users Posts: 7
    Re: Battery bank discharges, no loads applied

    When it's light out tomorrow, I shall do voltage readings and hydrometer readings, then do again about midday and again at sundown. The batteries are 2 years old, and I triple checked the wiring on them. 6 volt 100ah golf cart batteries.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery bank discharges, no loads applied

    do not do this while charging. you must check the batteries while they've had no charge or load on them within about 3 hours or so.
  • mtnmankevmtnmankev Registered Users Posts: 7
    Re: Battery bank discharges, no loads applied

    Thank you for that advice, I shall disconnect the ground lead from the charge controller at the battery bank before bedtime tonight, and I'm using a gen for power tonight, so won't be drawing any power from the battery bank.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery bank discharges, no loads applied

    Remove the diodes you soldered in, as they will reduce voltages in the system. Your charge controller will/should prevent night time loss.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

Sign In or Register to comment.