Batteries not charging

South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭

What am I missing?

I have:
1) 3 x 310w Tenesol panels, connected parallel. Per panel the specs are:
  • Max Power: 315w
  • V at Max Power: 36.3v
  • Current at Max Power: 8.6a
  • Open Circuit: 45.35v
  • Short Circuit: 9a
2) 2 x 200ah batteries, connected for 24v.
3) Morningstar Tristar 45a PWM Controller. Absorb set to 28.70v, float at 26.80 and EQ at 28.80v
4) Victron BMV600 battery monitor.
5) Victron 1600va Inverter, not the Multiplus, just the inverter.

After 14h00 today, the controllers green LED was flashing indicating PWM absorption status, Victron battery monitor showed SOC as 100%. Actually, it has been showing 100% SOC that since 11ish.

I then tested the batteries with a hydrometer, and they are no-where full.

Also to note is that I have a automated switch that once the SOC is 98%, utilities is disconnected and computers are powered by the inverter.
Once SOC is 95%, inverter power is disconnected from powering the computers, they are back onto utilities power, in order to have enough battery power at night for lights and a small fridge (158kwh per annum load).
Batteries are seldom below 80% SOC, for they can only go max 50% DOD.

What am I missing re. the batteries not being fully recharged with the above equipment?


  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    When the charge controller is charging... What is the battery bus voltage--Is is near 28.7 volts?

    Also, if these are standard deep cycle flooded cell batteries--You could probably charge them near 29.6 volts and see how they do?

    What you need is for them to be held at ~29 to 29.6 volts for ~2-6 hours (the deeper they are discharged, the longer the absorb time).

    Also, are you getting the current you expected from the array when the battery bank is low/charging (perhaps add some loads to "help" get the controller to produce maximum current).

    You could also jumper around the charge controller and make sure the panels/wiring/connections are all passing the proper current without too much voltage drop anywhere.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    Out of interest. Trying these batteries out to see a) also be able to say I can read a hydrometer :-) and b) to see how they preform for use in UPS'es.
    Two 200ah batteries are +-R1000.00 cheaper than 4 x 105ah, and they weight 14kg more than 4 x 105ah batteries. The more lead, the better it is I am told.
    Why? from 2 hours load shedding to 2.5 hours, most 105ah batteries are either drained or close to 50% DOD, so now we are doubling up, at 50% of the cost.

    Battery Bus voltage: Yes, I get see 28.7 on the battery monitor.
    Type of battery: Yes, standard low maintenance lead acid battery.
    Charging Voltage: Changed charging voltage to 29.6v as the new standard.
    Load: During the day, once SOC is 98%, the load of about 300-400watts are powerred till about +-17h30.
    Cables: Checked. The are 25mm2 and short.

    Will now only charge batteries for the day, and the check with the hydrometer again ... please cANCer, no load shedding today for it will be rather inconvenient if I must switch on the inverter.
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