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landyacht318's avatar
landyacht318
Explorer
Nov 07, 2015

0.0 amps at 15.1v on an AGM

I've been using the 0.5% of capacity at 14.46v as an indicator as to when to stop charging my Northstar group 27 AGM.

But I have also let voltage to stay at 14.46 overnight, and the Ammeter reads 0.0 amps at 14.46v in the morning. Obviously some current is required to hold it at 14.46v but my tools cannot read it.

The other night after 4 deep cycles with a low and slow solar only recharge, voltage under load for the AH removed was not impressive, and I decided to let the Meanwell do its 40 amp thing until amps taper to 0.42amps at 14.7v.

When it got there I lowered voltage to 14.0v and let amps taper to 0.0a.

For grins I bumped voltage upto 15.1v, and it only took 0.1amps to get it there, and then it dropped back to 0.0amps quickly. I bumped it upto 15.5v, and the same thing. 0.1 amps tapered to 0.0 amps.

I guess there is little danger of popping the vents at these high voltages when the battery is already brimming full, and needs so little current to be held at these voltages.

The next discharge, the performance( judged by voltage held for AH removed under a certain load) was back. I love a battery which loves high amp recharging, I just wish it was also happy with the 200 watts of low and slow solar taking all day to get to 0.42amps at 14.46v.

But it is so Obviously unhappy with the low and slow recharge treatment. I watch performance drop every night until it gets its high amp recharge.
It really seems the higher the amp are, applied from its most depleted State, the happier this battery is.

I think I am going to add my Schumacher's ~29 amps to my Meanwell's 40 the next time I blast it from 50%. The Schumacher should not drop out for a while. It depends on if it is in its 16.4v masochistic mode or not

9 Replies

  • landyacht318's avatar
    landyacht318
    Explorer
    Nov 08, 2015
    Yeah, I'm keeping to specs mostly.

    My Vehicle's engine computer is the wild factor allowing 14.9v, soon to be remedied.

    But it has seen extended periods at 14.9v too, even when depleted and taking 30+ amps, and does not appear any worse for wear from it.

    When I take 45AH from its claimed 90AH capacity in 7 hours then remove loads, voltage rebounds above 12.2.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Nov 08, 2015
    Don't wanna get carried away. The positive plate grain refining alloys will leach and migrate to the surface. Sort of like what antimony does in a flooded battery. Chemistry blended with metallurgy. This should serve to caution deviation too far from OEM guidelines.
  • landyacht318's avatar
    landyacht318
    Explorer
    Nov 08, 2015
    A higher absorption voltage would likely extend the time needed between high amp recharges.

    Northstar says nothing about EQ voltages on their AGM. This is currently my only battery, for engine and house so NOT having to do 16v EQ's every 14 days, like the screwy31 required, is nice.

    This time of year there 200 watts is not really enough on its own to even return my AH counter to zero, it depends on the laptop usage, so the meanwell or alternator are required anyway, and they fulfill that high amp recharge requirement.

    This thread was more an observation than a complaint. Bringing an AGM to a dead stop at absorption voltage is just interesting. Was thinking I could bump up voltage to 16v and it might require only 0.0x amps to be held that high too.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Nov 08, 2015
    Hi Landy,

    Does the solar controller have an equalize setting? If so try bumping the voltage to 16 (careful of the rv computer boards), and see if that will do the same as the high rate charging?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Nov 08, 2015
    Senor pianotuna's insistance on solar for boondocking has total merit. Years ago I would generator charge to 90% very early in the morning while multi-tasking the AC. then around 10AM I minimized DC loads and let the solar speed-bag the batteries the rest of the day. Worked like a charm.
  • RoyB's avatar
    RoyB
    Explorer II
    Nov 08, 2015
    Since 2009 I have been running my wet cells down to their 50% charge and recharging back up to the 90% charge state for about 12 days or so before I start seeing the daily performance start dropping off.

    I base the bad performance on draining around 20AMPS continuous for about 5 hours each day along with the usual parasitic drain all day long. Doing this I make it until 8AM each morning before re-charging for three hours using 14.4VDC. If I do this 50%-90% charge state routine more than 12 or so times without doing a full 100% charge state using 14.4VDC I can only last until around 10PM each night before the batteries drop down to their 50% charge state (Around 12.0VDC).

    After recharging to a full 100% which takes around 11-12 hours using 14.4VDC I can do this same routine all over again and make it thru the whole night for another 12 days or so.

    My Battery bank was installed in late 2008. I am just now starting to see the overall performance being harder to maintain doing the 50%-90% charge state recharge each day meaning I need to do the full 100% charge state recharge more frequent...

    Time for new batteries I suspect...

    Roy Ken
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Nov 07, 2015
    Batteries got personalities!

    Try feeding liver & onions to a hundred people and see a perfect example of personality.

    It's the CHEMISTRY. Something no sensor or 29 cent chip can ever hope to satisfy. Chow Hall diet makes some folks fat and others skinny. Me? I haven't got the bankroll to let a 29 cent chip think for me.
  • landyacht318's avatar
    landyacht318
    Explorer
    Nov 07, 2015
    I do notice after a bunch of low and slow recharges, that it takes forever for amps to taper to 0.42, much longer than normal.

    And when I do plug in the meanwell to hold it at 14.4v long enough to taper to 0.5% of capacity, it still behaves badly, well, not as well as it does after a High amp recharge.

    So Sometimes absorption stage lasts 3 hours, sometimes it takes 8 to 10 hours after a bunch of low and slow 50 to 97% recharges.

    How is any automatic charger today supposed to account for every battery's characteristics when there is no programmable amperage threshold?

    Time for nailing that chicken to the front door I guess.
  • BFL13's avatar
    BFL13
    Explorer II
    Nov 07, 2015
    Can't say about AGMs, but after a 50-90 it is much harder to get a Wet to "true full" than if you had only gone down to 80%. A few 50-90s in a row then trying for 100 is a real struggle.

    Low and slow might work from 80-100 but it doesn't work from 50-100 at least in my case.

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