Battery Dilemma

Hello all and greetings from Heron, Montana

As we approach the black hole of pv production this time of year in our neck of the woods it becomes challenging to keep our battery banks charged and in good health. My dilemma was a challenge from the beginning when we bought this place 2 years ago. The previous owner was a scrounger(an admirable quality) and the system he put together is most likely a classic example of too large a battery bank and not enough charging capacity. It consisted of a hodgepodge mix of 400 watts of roof mounted panels, a 12v charge controller( a Steve Willey special from Backwoods Solar), a Napa battery charger, and a Kubota 15kw diesel generator. The battery bank consists of 15, 4volt 2-PDQ-17 batteries that are rated at 5580 watts each and 835 AH each at the C8 rate. So go figure. It's like filling a dumptruck with a spoon.

The good news is I've recently upgraded the system. I have 6 Solar World 245 mono panels, an Outback Flexmax 80 amp cc, and a Trace SW 4024 24v inverter. I've taken 3 of the batteries off line and rewired the other 12 for 24v. I'm hoping for the best to bring new life to the batteries but I'm afraid of the worst. The batteries will not hold the charge overnight. So here I am thinking the batteries have served their useful life. Please bring your questions and suggestions.



  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Battery Dilemma

    it indeed sounds like time to shop for new batteries. Actually, a good time to rework all those parallel batteries into a series string for 48V, and avoid the parallel issues. Resell the 24v inverter, and use 48, one with a good power factor charger in it.
    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: ,

  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Battery Dilemma

    Check to see if all the batteries are losing charge, or only 1 or 2. If you only have a couple that are totally bad, that might get you through the winter.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Battery Dilemma

    When working with parallel battery banks (and large DC current systems), I would humbly suggest that you get a DC Current Clamp Meter (such as this $60 version)... It will allow to to see which string is carrying current, or not. Plus it is a much safer way of measuring current in different parts of your system (meter also has an AC current mode too; as well as a full Digital Multi Meter function).

    And, the usual recommendations for a hydrometer and a Battery Monitor (or Victron Battery Monitor).

    The above links are just starting points--There are lots of other products out there too.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Battery Dilemma

    For now it's gotta be 24v. I've been looking for new batteries and it seems like the Trojan T105 is the best value at $2.85 per AH.
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