Some Battery Questions...

Busby573 Registered Users Posts: 11
Ok, so in my original thread I was able to fix the wiring of my batteries to something more proper, at this point I'm trying to figure out some problems I'm having with battery life, (not because of the new wiring).

I have a bank of 3 strings of 105 AH batteries, four 12V batteries per string on a 48V system. At this point I know these batteries are probably rather sulfated because they haven't been maintained at optimal charging periods or percentages.

(A.K.A we had someone move in with us who used way to much electricity for a year causing them to be charged way too many times, too low, probably ruining them.)

My first question is for 12V AGM Batteries:
- What should be the cut in voltage, (low voltage)
- What should be the cut out voltage, (high voltage)
- What should be the Maximum Bulk Charge voltage
- What should be the Float voltage, and how long should the float period last

I think some of these voltages monitored by the inverter are set wrong, causing the batteries to be drained too much and not be charged to full capacity.

Second question is, do appliances/power tools that draw large amounts of Amps, (6-16Amp load) adversely effect battery life since they cause the batteries to drop really low in voltage in order to provide that much electricity for a very short period of time? The reason is because my dad does every construction trade, and we are often using lots of short-time-use power tools on the system. For things like the table-saw and compressor that run for a long time, we use a separate small backup generator.

Ultimately we want to replace all these batteries with one or two much higher capacity battery banks, but we need to make the ones we have work for this winter at least. I want to see if changing some setting will help get them back on track.


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Some Battery Questions...

    Your battery mfg will have chart/table for voltage settings for charging.

    I don't think high draw power tool usage is damaging to a good battery bank.
    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: ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Some Battery Questions...

    "I don't think high draw power tool usage is damaging to a good battery bank."

    to add to the above- unless it is drawing too much from the battery and too deeply as this shortens battery life. 15a at 120v is 1800w and that translates roughly to at least 37.5a at 48v.