Battery bank Blunder..

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rgearhead
rgearhead Solar Expert Posts: 38
I started gathering pieces parts to build a solar - battery back up system and to run a few things on weekends to work the system and have it at the ready in a power outage time..

well last fall i want to Sam's and bought 6 of there deep cycle egc2 battery's with 230ah each and planned to use them in a 12 volt bank so that's 3 parallel in series being 690 ah total

in the bank.. So for starters what are the problems with 3 in parallel ? is it the odd # would it work out if it was 8 battery's 4 in parallel ?? the 6 i do have have never been worked , just sitting, if 8 batterys are the way to go and i can still get same brand and model, will adding 2 work out ??





thanks for any n all help..

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Battery bank Blunder..

    You need to wire the parallel connections according to one of these methods.

    Can you wire more battery strings in parallel (one is ideal, 2-3 is my personal recommendation for a reasonable limit), yes and many people do.

    It is just if you have a choice, limiting parallel battery strings / connections is a good goal.

    Generally, if you wanted a larger bank, then I would suggest looking at a 24 volt bank (4x 6 volt batteries in series, parallel 1-3 strings).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Battery bank Blunder..
    rgearhead wrote: »
    I started gathering pieces parts to build a solar - battery back up system and to run a few things on weekends to work the system and have it at the ready in a power outage time..

    well last fall i want to Sam's and bought 6 of there deep cycle egc2 battery's with 230ah each and planned to use them in a 12 volt bank so that's 3 parallel in series being 690 ah total

    in the bank.. So for starters what are the problems with 3 in parallel ? is it the odd # would it work out if it was 8 battery's 4 in parallel ?? the 6 i do have have never been worked , just sitting, if 8 batterys are the way to go and i can still get same brand and model, will adding 2 work out ??





    thanks for any n all help..

    It isn't the odd number, it's the number. The more parallel batteries the greater the chance for uneven current between them. That means one string gets discharged/charged most and one gets discharged/charged least so they do not share the burden evenly. It shortens battery life.

    Usually the way to go if you need that amount of stored capacity is to up the Voltage. Some explanation about different system Voltages: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    The trouble is your batteries are already several months old and not in use, neither of which is good for them. Adding a couple more now so you could have two parallel strings of four (for 24 Volts) may not be such a good idea. At this point you should be checking the specific gravity (SG) of every cell and charging/equalizing if necessary to prevent further decline.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
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    Re: Battery bank Blunder..
    rgearhead wrote: »
    I started gathering pieces parts to build a solar - battery back up system and to run a few things on weekends to work the system and have it at the ready in a power outage time..

    well last fall i want to Sam's and bought 6 of there deep cycle egc2 battery's with 230ah each and planned to use them in a 12 volt bank so that's 3 parallel in series being 690 ah total

    in the bank.. So for starters what are the problems with 3 in parallel ? is it the odd # would it work out if it was 8 battery's 4 in parallel ?? the 6 i do have have never been worked , just sitting, if 8 batterys are the way to go and i can still get same brand and model, will adding 2 work out ??





    thanks for any n all help..

    hopefully you have been at least floating them.
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
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    Re: Battery bank Blunder..

    And unless something changed at Sams since I bought mine a year ago, the ones they sell are 215ah each. So your bank would be 645ah, usable = 320ish.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html