making a final battery decision...

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So I've mulled all the specs I can handle, and I figure I had better just lay down the cash for some batteries before the price of lead skyrockets anyfurther. I have narrowed my search down to two options: 2 deka 6v 220AH AGMs or 2 deka 12v 228AH AGMs. I could save a fair bit of money if I ordered the 6volts, or I could support a local business and spend quite a bit more with the 12volts. I guess I wanted to run it by some pros to see if I am going to be complicating or shortchanging my primarily 12VDC system by going with two 6v in series, as opposed to 2 12v in parallel. either way I see it, I will have about the same capacity at 12v.

The other thing I am still not totally clear on is why gel batteries are not superior to AGMs. When comparing total number of cycles of this group size of battery at 10% DOD, the AGM only has 3200 cycles vs. the gel, which had 5000 at the same DOD. Is the sensitivity of a gel battery what prevents one from reaching this optimum life?

Your comments are very much appreciated.
Itchin for spring, Sol

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: making a final battery decision...

    My 2 cents--I would recommend 2x 6 volt batteries in series rather than 2x 12 volt batteries in parallel... Easier to fine a bad battery with volt meter and no issues with trying to ensure that both batteries are charged in parallel (poor connection, bad wire, unbalanced resistance between the two parallel connections, etc. preventing identical charge and discharge currents)...

    However, Wind-Sun (adm for this site) sells batteries in both Series and Parallel configuration and sees similar life for both...

    Regarding Gel batteries, from the Wind-Sun site battery FAQ:
    Gelled batteries, or "Gel Cells" contain acid that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill acid even if they are broken. However, there are several disadvantages. One is that they must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturers specifications. Most better inverters commonly used in solar electric systems can be set to limit charging current to the batteries.

    Some other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th's less) than flooded or AGM batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. In hot climates, water loss can be enough over 2-4 years to cause premature battery death. It is for this and other reasons that we no longer sell any of the gelled cells except for replacement use. The newer AGM (absorbed glass mat) batteries have all the advantages (and then some) of gelled, with none of the disadvantages.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
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    Re: making a final battery decision...
    solsauce wrote: »
    I have narrowed my search down to two options: 2 deka 6v 220AH AGMs or 2 deka 12v 228AH AGMs. I could save a fair bit of money if I ordered the 6volts, or I could support a local business and spend quite a bit more with the 12volts. I guess I wanted to run it by some pros to see if I am going to be complicating or shortchanging my primarily 12VDC system by going with two 6v in series, as opposed to 2 12v in parallel. either way I see it, I will have about the same capacity at 12v.


    Well, I am certainly no pro here... but... The above statements are a bit confusing to me. Just to be clear: two 6V batteries in serries would give you 220AH at 12V, two 12V batteries in parallel would add up to 456AH at 12V, or double the capacity. Maybe there's a typo in there? Just wanted to clarify that if you were unsure... good luck, those thingy's are getting $$$$$ :(
  • System2
    System2 Posts: 6,290 admin
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    Re: making a final battery decision...
    hillbilly wrote: »
    solsauce wrote: »
    Just to be clear: two 6V batteries in series would give you 220AH at 12V, the two 12V batteries in parallel would add up to 456AH at 12V, or double the capacity.
    =================================
    My thoughts exactly.
    Wayne