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4gnomad's avatar
4gnomad
Explorer
May 23, 2016

I Think I Just Bought Way Too Much Battery

Hi guys, I'm hoping I'm wrong and someone will point something out to me that I haven't considered. I just purchased 2 L-16 batteries from some off-brand (that is supposedly US Battery underneath it all) that cost me $810. They're 6V, 400AH, which, I thought, was going to be awesome for boondocking. I bought them, the seller ordered them and delivered them, and in the meantime I looked up the 'right' way to charge the bank.

From what I can tell from the spec sheet the "charge characteristic curve" (which is here: http://www.vision-batt.com/site/product_files/EVL16-400A-AM.pdf) has the charging current at .25CA. I think that means that these 400AH batteries want to be charged at 100A, which is a TON of amps to be pushing for my little class B RoadTrek (in fact, I think it's a 30A electrical system so I can't). The most I can reasonably expect to push is 33A, and that's with an install of 4 100W 12V solar panels on the roof.

So my question is, if this pair wants 100A and I'm only able to push 33A (max, not including management/wiring losses), and I going to sulfate these things like crazy really quickly? FWIW they're AGM, which I think tolerate lower charging currents a bit better, but I think it's still not a great situation.

Any thoughts or clarifications on what I'm getting wrong here are really appreciated. Or, if I'm understanding the situation correctly, confirmation of that. I'm thinking I need to off-load these brand new L16s and get a more modest 12V bank right now.
Class B
  • 4gnomad's avatar
    4gnomad
    Explorer
    May 23, 2016
    They don't fit in the existing compartment. They're housed in a closet space that is right next to the existing compartment. My understanding is that the charge current varies by manufacturer, and I'm just wondering how bad it will be if I'm only charging them at .0825CA instead of the .25CA that the PDF indicates as a "standard" charge. I don't know how to assess the consequences of that, or whether it's enough to prevent sulfation..
  • pianotuna's avatar
    pianotuna
    Nomad III
    May 23, 2016
    Hi 4g,

    Physical space requirements will almost certainly be different than for the marine battery.

    My 139.2 amp-hour AGM's are limited to 27 amps @ (nominal) 12 volts for recharging.
  • 4gnomad's avatar
    4gnomad
    Explorer
    May 23, 2016
    Uh oh, now I'm a little confused. I did think that dropping in these two L16s would be a drop-in replacement for my much smaller current marine battery. Aren't the components that require upgrade limited to the charge converter + wiring to the terminals (+ the equivalents in solar when I install it)? The loads in the rig won't change substantially.
  • 4gnomad's avatar
    4gnomad
    Explorer
    May 23, 2016
    Wow, that was quick. I'm not sure of the converter yet, but I'm willing to replace it. In terms of the 33A that I can produce on my own (solar) that's 4 100W panels on the roof + a (theoretical as I haven't installed solar yet) MPPT controller.

    Each battery is 100lb - actually more manageable than I expected. We'll see how they perform.

    So it sounds like if I connect to 30A 120V shore power for a full day for a recharge (with a sufficient converter) I'll be fine in terms of preventing sulfation, but if I'm just recharging from solar at 33A, 12V I'll just be at .0825CA which will generally be undercharging the pair, right? That's my main concern, I was planning to go to 25% DOD on these so they would last forever, but if I'm killing them by only charging at .0825CA anyway I might as well not install solar and just rely on hooking up to shore power at a park. Is there some rule of thumb that describes how frequently you need a faster charge to keep things mixed up? Every time, every 5 cycles, every 10? I guess given that there are enough amps coming in with shore power it's the frequency of desulfation I need to figure out. I'll see if that's a phrase Google knows. :)
  • 4gnomad's avatar
    4gnomad
    Explorer
    May 23, 2016
    I think there is a standalone converter directly connected to the battery and I can hook shore power to it, so I can upgrade that whole set of wiring to push the 100A without worrying about the wiring through the whole rig. In terms of where the batteries are they're AGM and I have them in a closet (close to the ventilated compartment the existing marine battery sits in). I was thinking that with a controller + temp monitor I should be fine.

    Trying to respond to the other comments but the post is failing for some reason.
  • GordonThree's avatar
    GordonThree
    Explorer
    May 23, 2016
    Ed_Gee wrote:
    GordonThree wrote:
    Back of the napkin so to speak;

    30 amps at 120vac is 3,600 watts... 3600 watts at 12v is 300 amps. You'll have no problem running a 100amp converter off your 30a electrical system.

    Depending on efficiency you'll need 12-15 amps at 120vac.

    3000 amp dead-short discharge on those bad boy batteries, make sure you use a CLASS T fuse, not a wimpy ANL or dc circuit breaker.


    I doubt his class B has proper DC wiring to carry such high current, even if he does upgrade to a 100A charger. And I am wondering where two L-16 batteries can be safely mounted in such a comparatively small rig.


    You raise several valid points. New batteries are not a "drop in" replacement for existing / old batteries. OP will require significant upgrades to several facets of the DC system.
  • Ed_Gee's avatar
    Ed_Gee
    Explorer II
    May 23, 2016
    GordonThree wrote:
    Back of the napkin so to speak;

    30 amps at 120vac is 3,600 watts... 3600 watts at 12v is 300 amps. You'll have no problem running a 100amp converter off your 30a electrical system.

    Depending on efficiency you'll need 12-15 amps at 120vac.

    3000 amp dead-short discharge on those bad boy batteries, make sure you use a CLASS T fuse, not a wimpy ANL or dc circuit breaker.


    I doubt his class B has proper DC wiring to carry such high current, even if he does upgrade to a 100A charger. And I am wondering where two L-16 batteries can be safely mounted in such a comparatively small rig.
  • GordonThree's avatar
    GordonThree
    Explorer
    May 23, 2016
    Back of the napkin so to speak;

    30 amps at 120vac is 3,600 watts... 3600 watts at 12v is 300 amps. You'll have no problem running a 100amp converter off your 30a electrical system.

    Depending on efficiency you'll need 12-15 amps at 120vac.

    3000 amp dead-short discharge on those bad boy batteries, make sure you use a CLASS T fuse, not a wimpy ANL or dc circuit breaker.
  • 2oldman's avatar
    2oldman
    Explorer II
    May 23, 2016
    That's a whopping amount of battery, and a lot of weight for such a small rig.

    I don't think you'll sulfate them as long as they stay reasonably charged. My 640ahs of 12v AGMs can handle much more than my solar or charger can pump into them, but they're still fine. Just takes longer. My max charge rate is around 50v x 17a= 900w.

    You say 33a charging.. that means you have a 33x13 ~ 400w charger? That might be a bit thin.

    They will be awesome for boondocking.. until you have to recharge them!

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